Physico-chemical processes in seawater-saturated...
Transcript of Physico-chemical processes in seawater-saturated...
Physico-chemical processes
in seawater-saturated
subduction zone sediments -
an experimental approach
Dissertation zur Erlangung des
Doktorgrades der Naturwissenschaften
am Fachbereich Geowissenschaften
der Universität Bremen
vorgelegt von
Andre Hüpers
Bremen, Mai 2009
TABLE OF CONTENTS I
Table of contents
ABSTRACT 1
ZUSAMMENFASSUNG 3
CHAPTER 1: INTRODUCTION 6
1.1 Motivation 6
1.2 Outline of the PhD project 7
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 9
2.1 Sediment subduction 9
2.2 Dewatering of subducted sediments 10
2.3 Water-rock interaction 15
2.4 Synthesis and implications for seismogenesis 17
CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 19
CHAPTER 4: MANUSCRIPT 1 23
The thermal influence on the consolidation state of underthrust sediments from the Nankai margin and its implications for excess pore pressure
CHAPTER 5: MANUSCRIPT 2 48
Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – a case study from the Nankai margin
CHAPTER 6: MANUSCRIPT 3 62
The interaction of underthrust sediments with seawater – an approach by hydrothermal consolidation testing
CHAPTER 7: CONCLUSIONS AND OUTLOOK 97
ACKNOWLEDGEMENTS 99
REFERENCES NOT CITED IN THE MANUSCRIPTS 101
APPENDIX 110
ERKLÄRUNG 166
ABSTRACT 1
AbstractAt convergent margins the plate boundary thrust frequently produces high
magnitude earthquakes. Thermal modelling and direct measurements of heat flow
suggest that the onset of seismogenesis along the plate boundary thrust is associated
with a temperature of approximately 150 °C. The reason for the onset of
seismogenesis is controversially discussed. The sediment on the incoming plate is
initially weak, porous and unable to produce catastrophic slip behaviour. Therefore,
the sediment undergoes substantial changes during the passage from the deep sea
trench down to the updip limit of the seismogenic zone. Several hypotheses have been
proposed based on the importance of increasing effective stress and temperature on
mechanical behaviour and diagenetic processes. Previous laboratory studies focused
mainly on one of these parameters (effective stress or temperature) to shed light on
the fate of subducted sediments. In this thesis, results from a novel experimental
approach are presented, which considers increasing temperature and effective stress,
to study the changes of underthrust sediment.
Lithological end members of the incoming sedimentary sequence at the
Nankai margin were subjected to increasing effective stress and temperature in a
specifically adjusted heated oedometer device. Remoulded aliquots of the same
sediment were loaded to effective stresses of ~70 MPa at temperatures of 20 °C, 100
°C and 150 °C, the latter being equivalent to the updip limit of the seismogenic zone.
Post-hydrothermal research on compacts included SEM investigation, XRD analysis,
direct and ring shear test and geochemical pore water analysis.
The major finding of the heated consolidation tests is the positive correlation
of increasing temperature and pore space reduction under normal consolidation state
and drained conditions. The contraction suggests that the intergranular friction is
reduced and compensated by irreversible strain. This phenomenon reveals that the
consolidation state of subducted sediment is not only dependent of effective stress and
time as previously believed, but also on temperature. With the new findings it is
possible to explain the complex consolidation pattern along the “hot” central portion
of the Nankai prism toe where in-situ temperatures reach up to 110 °C. Inferred
excess pore pressure estimates based on the new data suggest smaller overpressures
than previously believed and are consistent with physical properties of compared
boreholes. A comparison of smectite and illite end member’s consolidation behaviour
ABSTRACT 2
further suggests that during the transition of smectite-to-illite, sediment
compressibility decreases during subduction.
Based on the outcome of the hydrothermal tests available laboratory
consolidation data were compiled and reviewed for the Nankai margin. Large
differences between in-situ and room temperature in the laboratory suggested a severe
implication for the observed overconsolidation. A state-of-the-art up-to-date thermo-
mechanical model was applied to estimate the temperature influence. The results
demonstrate that overconsolidation can be partially explained by the hardening effect
of lower temperatures. In essence, the results remove the discrepancy between
consolidation data and the general perception of a normally consolidated incoming
stratum. The data further imply that decollement formation along the central portion
of the Nankai Trough is governed by excess pore pressure generation and low
intrinsically shear strength of the sediment.
The geochemical analysis of expelled pore water during the heated
consolidation tests suggests that water-rock interaction is largely governed by
desorption-adsorption processes. The increasing temperature is associated with
enrichment of K, Ba and Si and the depletion of Mg. Temperature related release of
solutes may facilitate cementation of underthrust sediments and thus elastic strain
accumulation during seismic slip. Evidence of precipitates is only present in the
compact at the end of the 150 °C test of the smectite-rich sample as sulphates.
Consolidation further affects pore water constituents of the smectite end member. The
smectite-rich sample reveals a depletion of predominantly alkaline and earth alkaline
elements at a threshold of ~10 MPa, which is interpreted by the consecutive release of
free pore water and the residual water from the overlapping double layer of smectite.
XRD data after the experiments attest no significant degree of illitisation despite the
high temperatures and the long duration of the 3-5 month for each run.
In addition to the three first author manuscripts (see the three corresponding
paragraphs above), shear strength and frictional properties were measured of
remoulded end member sediments as well as intact compacts at room temperature.
Both the hydrothermal consolidation experiments and the shear tests were also run
with mineral-end members for calibration purposes. Geochemical analyses on these
materials are underway and will be condensed in additional publications.
ABSTRACT 3
ZusammenfassungAn konvergierenden Plattenrändern entstehen entlang der Plattengrenze
wiederholt große Erdbeben mit hohen Magnituden. Direkte Wäremestrommessungen
und thermische Modellierungen dieser Subduktionszonen deuten darauf hin, dass die
Seismogenese ungefähr bei einer Temperatur von 150 °C einsetzt. Die genauen
Gründe hierfür sind bislang wenig bekannt und werden kontrovers diskutiert. Die
subduzierten Sedimente sind anfangs weich, porös und nicht in der Lage zu instabilem
Reibungsverhalten. Daher müssen die Sedimente grundlegende Veränderungen
erfahren, um seismisches Reibungsgleiten (sog. Stick-slip) zu zeigen. Verschiedene
Hypothesen wurden in der Vergangenheit aufgestellt, die die effektive Spannung und
die Temperatur herausstellen und als Hauptursache des veränderten mechanischen
Verhaltens und diagenetischer Prozesse annehmen. Bisherige Laborversuche
fokussierten entweder auf die effektive Spannung oder die Temperatur. In dieser
Arbeit wird demgegenbüber ein innovativer experimenteller Ansatz durchgeführt, der
beide Parameter separat berücksichtigt, um die Veränderung der Sedimente während
der Subduktion zu charakterisieren.
Für die Laborversuche wurden natürliche Proben der abtauchenden
Sedimentabfolge des Subduktionseintrages aus dem Bereich der Nankai
Subduktionszone (SW Japan) ausgewählt, die die lithologischen Endglieder der
subduzierten Sedimente darstellen. Für die Versuche wurde eine speziell angefertigte,
beheizbare uniaxiale Ödometerapparatur entwickelt und benutzt. Die aufgearbeiteten
Proben wurden bis zu einer effektiven Spannung von ~70 MPa belastet und bei
Temperaturen von 20 °C, 100 °C und 150 °C durchgeführt. Die kompaktierten
Sedimente wurden dann weiterführend durch Elektronenrastermikroskopie,
Röntgendiffraktometrie, Direkt- und Ringscherversuche sowie geochemische
Analysen an den ausgepressten Porenwässern untersucht.
Das wichtigste Ergebnis der beheizten Konsolidierungstests ist die positive
Korrelation von Porenraumreduzierung mit ansteigender Temperatur unter normal
konsolidierten und drainierten Bedingungen. Die Kontraktion weißt darauf hin, dass
die intergranulare Reibung geschwächt ist und durch eine irreversible Verformung
kompensiert wird. Der Konsolidierungszustand der subduzierten Sedimente ist neben
den bekannten Größen Zeit und effektive Spannung deshalb auch abhängig von der
Temperatur. Anhand der Ergebnisse war es möglich den komplexen
ABSTRACT 4
Konsolidierungszustand entlang des zentralen Bereiches des Zehs des Nankai
Akkretionskeils zu erklären, wo die in-situ Temperaturen bis zu 110 °C betragen. Die
aus den Erkenntnissen abgeleiten Porenwasserüberdrücke sind kleiner als bisherige
Abschätzungen und wesentlicher konsistenter mit den beobachteten
petrophysikalischen Eigenschaften. Weiterhin lassen vergleichende Untersuchungen
zwischen den Endgliedern vermuten, dass die subduzierten Sedimente sich mit
fortschreitender diagenetischer Smektit-Illit-Umwandlung in der Subduktionszone
weniger kompressibel verhalten werden.
Basierend auf den Ergebnissen der hydrothermalen Konsolidierungstests
wurden verfügbare Daten zum Konsolidierungsverhalten des Subduktionseintrages
am Nankai Trog zusammengestellt und neu bewertet. Die Anwendung eines
thermoelastischen Models zeigt, dass die bisher bestimmten Überkonsolidierungen
partiell auf eine thermische Verfestigung zurückzuführen sind, die mit
Temperaturunterschieden zwischen in-situ und Laborbedingungen erklärbar sind.
Damit konnte die bisherige Annahme einer moderaten Zementierung der Sedimente
teilweise widerlegt werden, so dass die Entstehung des Decollements am Zeh des
Akkretionskeils in der Nankai Subduktionszone wahrscheinlich auf
Porenwasserüberdrücke und geringer intrinsischer Scherfestigkeit des Sediments
zurückgeht.
Die geochemischen Analysen der auspressten Porenwässer belegen, dass die
Wasser-Sediment Interaktion wesentlich durch Desorption and Adsorption
gekennzeichnet ist. Mit zunehmender Temperatur findet eine Anreichung der
Elemente K, Ba und Si sowie eine Abnahme von Mg statt. Die freigesetzten Elemente
können Zementierung und diagenetische Reaktionen unterstützen. Eine Ausfällung
konnte jedoch nur für den Test des smektitreichen Sediments in Form von Sulfat
nachgewiesen werden. Des Weiteren ließ sich zeigen, dass die Konsolidierung die
Zusammensetzung des Porenwassers bestimmen kann, dergestalt dass das Smektit-
Endglied über einem Grenzwert von ~10 MPa eine Abnahme von Alkali- und
Erdalkalielementen verzeichnet. Diese Beobachtung lässt sich durch das
aufeinanderfolgende Auspressen von freiem und adsorbiertem Porenwasser erklären.
XRD-Analysen der smektitreichen Proben zeigen, dass keine nennenswerte
Illitisierung in den Tests erreicht wurde trotz der über 3-5 Monate andauernden
Versuche.
ABSTRACT 5
Zusätzlich zu den drei Erstautoren-Manuskripten (vgl. die drei vorherigen
Absätze) wurden die Scherfestigkeit und das Reibungsverhalten der Sedimente an
aufgearbeiteten Probenmaterial sowie an den intakten Presslingen aus den
hydrothermalen Konsolidierungstests durchgeführt. Des Weiteren wurden auch Scher-
und Ödometertests mit Mineralstandards durchgeführt. Deren Auswertung und die
geochemischen Analysen sind derzeit in Arbeit und werden in weiteren Publikationen
münden.
CHAPTER 1: INTRODUCTION 6
Chapter 1: Introduction 1.1 Motivation
More than 90 % of world’s seismic moment is released along convergent
margins (Pacheco and Sykes, 1992). The majority of megathrust earthquakes with
magnitudes >8 occur in the realm where the subducting plate is temporarily coupled
to the overriding plate. To this day subduction zone earthquakes are a live and
economic threat to the large human population and their economy in the vicinity of
these tectonic plate boundaries. Such disastrous earthquake events are numerously
documented throughout human history including the recent Sumatra earthquake in
Dec. 2004 with a magnitude of 9.3 (Stein and Okal, 2005). It is supposed to be the
second most powerful earthquake ever recorded in modern history and 230000 lives
have been wiped out by the aftermath of the shaking followed by a devastating
tsunami.
Little is known about controlling factors for the unstable mechanical
behaviour because the depths of seismogenic processes has prevented closer
investigations by sampling and in-situ monitoring in the past. The increasing
temperature (T) and pressure (P) conditions in subduction zones yield interrelated
mechanical, mineralogical and geochemical processes. These processes alter the
incoming sediments, which show initially elastic deformation and stable sliding (e.g.
Kastner et al., 1991; Moore and Saffer, 2001). Enormous cost-intensive efforts to shed
light on these processes are currently established with the new drilling vessel Chikyu,
which is capable of reaching the region of seismogenesis at the Nankai convergent
margin in the near future (Tobin and Kinoshita, 2006). A cost-saving approach is the
application of specifically adjusted laboratory studies to simulate underthrusting and
to identify mechanical, mineralogical and geochemical repercussions on subducted
sediments. However, the study of increasing pressure with uniaxial and triaxial
deformation devices is often restricted to room temperature. Thus, mechanical tests
show a good agreement with physical properties at initial burial at the toe of the prism
(e.g. Saffer, 2003), but the mechanical response to increasing temperature is less
known. On the other hand, elevated temperatures are common to study water-rock
interaction, but the applied methods often neglect the change in burial conditions by
using autoclave devices at constant P values (e.g. You et al., 1996).
CHAPTER 1: INTRODUCTION 7
This study represents an attempt to identify the mechanical, mineralogical and
geochemical repercussions of high PT conditions on subducted sediments and its pore
water by laboratory testing during which P and T vary. An uniaxial deformation
device (oedometer) has been modified to allow testing at elevated temperatures. Thus,
it was possible to separate the effect of increasing P and T on the mechanical response
and water-rock interaction. The unique approach assumes that water-rock interaction
and mechanical processes are closely interrelated at active convergent margins.
Specimens for the Nankai Trough (Japan) representing the three end member
compositions in mineralogy were chosen to gather important rock mechanical data in
the area of the planned penetration of the seismogenic subduction thrust within
NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment).
1.2 Outline of the PhD project The PhD project was integrated in the DFG-funded project “Research on
Ocean Margin Earthquakes”. The PhD work comprised the development and
implementation of a heated uniaxial consolidation apparatus (oedometer) at the
MARUM, University of Bremen, which is capable of PT conditions equivalent to the
updip limit of the seismogenic zone (i.e. ~150 °C; Hyndman et al., 1995).
Simultaneously, a large number of samples from the pilot study conducted at the
SCRIPPS Institution of Oceanography was mechanically, geochemically and
mineralogically analysed and interpreted together with the mechanical consolidation
data.
Hydrothermal testing during the pilot study focused among others on
subduction zone sediments from the Nankai margin (SE Japan). The Nankai margin is
an excellent research area because of the high in-situ temperatures of 110 °C along its
central portion. Thus, it was possible to compare laboratory and in-situ influence of
temperature. Three sediment samples got selected from DSDP Site 297, representing
the mineralogical end member of the incoming sequence: A smectite-rich clay (N13),
an illite-rich silty clay (N14) and a dominantly silty to fine sand-grained
quartz/feldspar-rich sample. The samples have consecutively undergone heated
uniaxial consolidation tests at 20 °C, 100 °C and 150 °C. The results showed that
temperature has a significant effect for consolidation behaviour. Two manuscripts
resulted from this finding. The first manuscript (chapter 3) describes the test results
CHAPTER 1: INTRODUCTION 8
and focuses in the discussion on the explanation of thermo-mechanical behaviour and
its implication for the consolidation state, inferred excess pore pressures and the
change of mechanical response in the subduction zone. In the second manuscript
consolidation data from the Nankai margin was reviewed. A temperature correction
was applied to minimise the effects of temperature differences of high in-situ
temperatures and ambient laboratory testing including a new interpretation of the data
(see Chapter 5).
Geochemical analysis of fluids expelled from heated consolidation tests
allowed the detailed study of water-rock interaction. Major elements and trace
elements were analysed on the fluids, and part of the data set were summarised in a
research article (Chapter 6). Additional analyses on both fluids and the solid phase
before and after the deformation tests were analysed for minor constituents B and
�11B. These data appear in the Appendix and will be published later.
Post-analysis of the hydrothermal experiments also included scanning electron
microscope (SEM) investigation, x-ray diffraction analysis (XRD), direct shear
experiments on intact compacts and large strain ring-shear tests on remoulded sub-
samples (Fig. 1). The data were partially presented on a meeting (see appendix) and
the complete data set (see appendix) is considered for publication in future.
Fig. 1: Flowchart of the applied laboratory methods to identify implications of high PT conditions on mechanical behaviour and water-rock interaction.
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 9
The development and implementation of a heated uniaxial consolidation
apparatus is in the mean time completed. Two system were assembled which are
capable of normal stresses of 100 MPa and 300 MPa, respectively, and temperatures
up to 200 °C. A detailed description of the apparatuses is attached in the appendix.
The focus of these new experiments is on mono-mineral samples of the end member
lithologies at the Nankai margin (smectite, illite, quartz). So far, quartz-seawater and
smectite-seawater slurries have been consolidated at various temperatures. The results
are also included in the appendix. After completion, these samples will undergo the
same experimental post analyses as the natural samples.
Chapter 2: Sediments at convergent margins
The following subchapters outline the concept of sediment subduction and
how the sediment changes during subduction. The literature review encompasses the
increasing stress, its implications for excess pore pressure generation and water-rock
interaction as a matter of increasing temperature.
2.1 Sediment subductionThe concept of sediment subduction was developed shortly after the
establishment of plate tectonics in the late 1960ies. Simple balance calculations
revealed that the incoming sediment volume is greater than the observed volume
scraped off in form of an accretionary prism from the oceanic crust (e.g. Scholl and
Marlow, 1974; Scholl et al., 1977). Since then the analogy to the blade of a bulldozer
is used where variable amounts of a sediment pile are scraped off from the incoming
sediments (Chapple, 1978; Davis and Suppe, 1980, Davis et al., 1983).
The material that is scraped off forms a wedge (or prism) shaped accretionary
complex, which grows by ongoing frontal accretion and underplating of subducted
sediment to the base of the prism (Moore et al., 1982; Cloos and Shreve, 1988).
Accretionary prisms favourable form where the plate convergence rate is <6.7 cm/a
and the sediment supply is sufficient to accumulate a trench thickness >1 km (von
Huene and Scholl, 1991; Clift and Vannucchi, 2004). Although some modern
accretionary prisms exhibit large dimensions with up to 200 km width such as
Makran, SE Japan or the Lesser Antilles (Cloos and Shreve, 1988), only the upper 7-
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 10
37 % of the sediment pile is scraped off in a sequence of imbricate thrust slices in
front of the upper plate’s abutment of resistive rock structure (Clift and Vannucchi,
2004). The larger volume is subducted which has been estimated to be approximately
1.5 km3/a for contemporary convergent margins (von Huene and Scholl, 1991).
Accreted and subducted sediments are separated by a detachment fault, which
is commonly called the decollement and marks the plate boundary between the
subducted and the overriding plate. While the maximum principle stress in the
incoming sedimentary sequence is vertically orientated, it becomes inclined due to the
horizontal compression in the accretionary thrust belt above the decollement (Davis et
al., 1983, Moore, 1989). Below the decollement the underthrust sediment remains
horizontally largely undeformed, while the maximum principal stress is nearly vertical
(Fisher and Byrne, 1987). Beneath the accretionary prism, the decollement may step
down into the underthrust sediment and attach sediment to overriding plate and thus
contributes to the growth of the wedge (e.g. Moore et al., 1982). The remaining
sediment beneath the decollement may be subducted to greater depth and eventually
participate in magma generation and crustal growth, or mantle recycling (Clift and
Vannucchi, 2004).
2.2 Dewatering of subducted sediments 2.2.1 Fluid sources
The incoming sediment pile on the oceanic plate is initially weak, porous and
contains a substantial fraction of interstitial water (Bray and Karig, 1988). The
increasing load of the overlying prism sediments and the fast thickening of the trench
wedge deposits leads to rapid consolidation from 70-85 % to ~15 % porosity of the
sediments (Bray and Karig, 1985, 1988; Moore and Vrolijk, 1992). The term
consolidation refers to the mechanical pore space reduction as a response of the
sediment to an applied load. The process is a function of the compressibility of a
sediment and the time-dependent fluid expulsion, which is limited by the permeability
and thickness of the sediment (Terzaghi and Peck, 1948). Accordingly, consolidation
is faster for permeable coarse-grained sandy material than for less permeable, fine-
grained clayey material. If the water expulsion cannot keep pace with the loading, the
total stress is partially taken up by the pore water until the excess pore pressure has
dissipated and the total stress is completely taken up by the mineral framework. This
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 11
relation is expressed in the law of effective stress where �t is the total stress, �e is the
effective stress which is actually taken up by the mineral framework and P is the pore
water pressure in excess of the hydrostatic pressure:
�t = �e +P [1]
The compaction of a sediment in response to an applied load is material
dependent and may vary from margin to margin (Bekins and Dreiss, 1992). However,
the pore space decreases usually exponentially for all sediments with increasing load
(Athy, 1930). Thus, dewatering by consolidation is thought to be important for fluid
production within the first 5 km. (Moore and Vrolijk, 1992; Fig. 2). This is especially
applicable for a clay-rich sediment which can store much more interstitial water under
low stresses than coarse grained material (Karig and Hou, 1992).
Fig. 2: (A) Sketch of an accretionary prism showing that the underthrust section is rapidly consolidated by the overlying accretionary sediment, the area of mineral dehydration (grey shaded) and high permeable faults. (B) Schematic diagram of fluid generation of the subducted sediment. Fluids are initially expelled by sediment consolidation and later by mineral dehydration. Modified after Moore and Vrolijk (1992).
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 12
Subducted sediments may host additional water in the mineral structure, which
is released during diagenetic reactions or lithostatic load (e.g. Fitts and Brown, 1999).
While consolidation is largely completed within the first 5 km, mineral dehydration is
supposed to be the most important remaining fluid source in the subducted sediments
(Vrolijk, 1990; Moore and Vrolijk, 1992). Clay minerals from the smectite group are
believed to be the most important water bearing minerals in the shallow subduction
zone. Smectites are 2:1 phyllosilicate with sheets composed of an octahedral layer
between two tetrahedral layers. Cation substitution in the crystal lattice yields a
negative charge of the clay mineral surface, which is compensated by hydrated cations
in the interlayer of the phyllosilicate sheets. Thus, a fully hydrated smectite can
contain up to ~25 wt-% of water, which can be freed by lithostatic load, high
temperatures or progressively diagenetical smectite-to-illite transformation (e.g.
Colten-Bradley, 1987; Fitts and Brown, 1999). The illitisation starts at a temperature
of ~60 °C (Freed and Peacor, 1989) and is supposed to be completed by ~150°C in
subduction zone systems (Vrolijk, 1990; Moore et al., 2007).
Because of its abundance in many subduction systems (Vrolijk, 1990),
smectite dehydration is thought to be an important key parameter for mechanical and
hydrological processes (Moore and Vrolijk, 1992). Smectite is brought in as a part of
the terrigenous deposits at convergent margins but can also evolve from volcanic ash
alteration (Vrolijk, 1990). Well known examples for smectite-rich subduction inputs
are the Japan Trench (Aoki and Kohyama, 1992), the Barbados Ridge (Deng and
Underwood, 2001), the Nankai margin (e.g. Underwood and Steurer, 2003), or the
Costa Rica segment of Middle America Trench (Underwood, 2007).
Another water bearing phase is the amorphous opal-A. 23 vol-% water is
released during the conversion to quartz, which is completed at 100 °C (Moore and
Vrolijk, 1992; Behl and Garrison, 1994). Opal-A is formed by siliceous microfossil
skeletons of radiolarions and diatoms, which are less common in many subduction
zones and thus considered to be only regionally important (Moore and Vrolijk, 1992).
2.2.2 Physical hydrology
At subduction zones, it is widely acknowledged that the rapid thickening of
the overlying prism is faster than the pore water expulsion of subducted sediments
(von Huene and Lee, 1982; Le Pichon et al., 1993; Saffer and Bekins, 1998; 2006).
This compaction disequilibrium is expressed as excess pore water pressure that was
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 13
widely documented (e.g. Costa Rican, Nankai and Cascadian subduction zone) in the
shallow parts (<1500 meters below seafloor [mbsf]) by direct measurements (Becker
et al., 1997; Foucher et al., 1997) or indirectly estimated from the maximum past
effective stress, which can be inferred from consolidation tests (Saffer, 2003) and
calculated porosity from inverted p-wave velocity in combination with porosity-depth
profiles (Cochrane et al., 1996). Numerical modelling shows that excess pore pressure
built-up can start seaward of the trench by rapid sedimentation of the trench wedge
deposits onto the approaching sediment pile (e.g. Shi and Wang, 1985; Moore, 1989).
The increase in effective stress is hindered and reflected in a low shear strength which
is supposed to be an important reason for decollement initiation besides low intrinsic
strength of clay-rich sediment (Moore, 1989).
At deeper portions of the subduction zone the release of bound water into the
consolidated and low permeable sediment contributes to excess pore pressures
formation (Moore and Vrolijk, 1992). Numerical modelling, considering fluid sources
from consolidation and mineral dehydration, shows that fluid overpressure reaches
near lithostatic magnitudes (e.g. Saffer and Bekins, 1998; 2006; Fig. 3). Furthermore,
fluid transport-related parameters such as sediment permeability and drainage path
length are governing excess pore pressure (Saffer and Bekins, 2006).
Fig. 3: Modelled excess pore pressure distribution in percent of the total stress for the Nankai margin modified from Saffer and Bekins (1998). Note that the overpressure peaks between ~15-20 km arcward of the deformation front and diminishes afterwards.
Widespread appearance of veins and fractures in exhumed accretionary prisms
also attests that excess pore pressure ranges near lithostatic (e.g. Fisher and Byrne,
1987, Moore et al., 2007). These high pore pressures were postulated to facilitate fault
formation, decrease fault strength (Hubbert and Rubey, 1959, Brown et al., 2003),
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 14
reduce taper angle of accretionary wedges (Davis et al., 1983) and favour down-
cutting of the decollement (e.g. Moore, 1989; Saffer, 2003; 2007; Morgan et al.,
2007). Instead, diminishing excess pore pressure or increasing effective stress are
associated with strain localization and the updip limit for of the seismogenic zone
(Moore and Saffer, 2001).
2.2.3 Fluid flow and fluid pathways
High fluid pressure gradients are the driving force for fluid flow in subduction
zones. Dewatering of subducted sediment occurs as dispersed flow if the rate of pore
fluid flow is sufficiently low and advection can be accommodated by intergranular
permeability (Carson and Screaton, 1998). Although the bulk fluid volume is expelled
as dispersed flow out of the accretionary prism, its significance is supposed to be
diminishing with increasing depth because of the decreasing permeability (Moore and
Vrolijk, 1992; Saffer and Bekins, 1998). Where the dispersive fluid flow is
insufficient, fluid expulsion occurs along permeable fault zones and stratigraphical
layers or is expelled from mud volcanoes (Fig. 2; Moore, 1989; Henry et al., 1992;
Carson et al., 1994).
Field evidence for focused fluid flow along permeable layers comes from
geochemical and thermal anomalies. Low-chlorinity anomalies in fault zones are
widely documented and interpreted by deep-seated sourced fluids which originate
from the seawater freshening by smectite dehydration: e.g. You et al. (1993) for
Nankai margin, Kimura et al. (1997) for Costa Rican margin and Kopf et al. (2003)
for Japan trench. Numerical modelling of low-chloride anomalies along the
decollement suggests that subducted sediments are drained preferably to a permeable
decollement (Saffer and Screaton, 2003) and that fluid flow may occur episodically,
which probably associated to episodic fault displacement of seismic cycling (Moore
and Vrolijk, 1992; Saffer and Bekins, 1998). Localized fluid flow from deep sources
may also be characterized by warmer temperatures compared to the wall-rock, as
attested by subseafloor temperature measurements (Westbrook et al., 1994) and long-
term measurements in a sealed borehole (Davis et al., 1995) at ODP Site 892 at the
Cascadia accretionary margin.
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 15
2.3 Water-rock interaction 2.3.1 Conceptual model of fluid geochemistry evolution during deformation
The lithostratigraphic composition exerts a fundamental role for water-rock
interaction and thus fluid geochemistry. However, sediments at convergent margins
are highly variable due to the diversity of depositional settings. They are ranging from
distal abyssal plains on the incoming oceanic plate to the trench wedge and therefore
subduction inputs can range from pelagic ooze to hemipelagic mud and sandy
turbidites (Underwood, 2007). The result is a complex system, which changes from
margin to margin of which a comprehensive overview surely exceeds the scope of this
thesis. However, Kastner et al. (1991) proposed a conceptual model, which is
applicable to all margins: The interstitial fluid of the entering sediment possesses
initially seawater composition. The rapid burial prevents diffusive communication
with ocean seawater at depths greater than a few tens to hundred meters (Kastner et
al., 1991). Thus, the fluid geochemistry is locally dependent on diagenetical fluid
mineral exchange reactions and mineral-dehydration as well as diffusion-advection.
This local fluid is influenced by fluids from within the subduction system or from an
external source. Internal sources are deeper or overpressured regions in the subduction
system. They are characterized by advanced diagenetic reactions, which are
transported by vertical or lateral advection preferably along high permeable faults and
stratigraphic horizons (Moore and Saffer, 2001). External sources comprise meteoric
water, which may be incorporated by short and long-distance seaward transport or
induced by density inversion (Kastner et al., 1991).
2.3.2 Diagenesis in the shallow subduction zone
In the following enumeration, diagenetic reactions and their implication for
fluid geochemistry are presented with a schematic overview in figure 4. The
compilation is based on significant diagenetic reactions in accretionary complexes
according to Kastner et al. (1991) and Moore et al. (2007).
Volcanic ash alteration: The volcanism along convergent margins may accumulate
volcanic ash and tephra in the sediment. Among others volcanic ash was documented
in subduction inputs of the Peru margin (Clayton and Kemp, 1990), Coast Rican
margin (Kimura et al., 1997) and the Nankai margin (Taira et al., 1991; Moore et al.,
2001a). Low temperature alteration transforms the ash into zeolites and hydrous clay
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 16
minerals (smectite). The reaction is accompanied by water, alkalis and Mg uptake
(Kastner et al., 1991). The residual pore fluid becomes enhanced in chlorinity as
reported for the forearc at the Peru margin (Martin et al., 1995).
Hydrocarbon formation and gas hydrate dissociation: Hydrocarbon formation,
especially CH4, is accommodated by degradation of organic matter through bacterial
activity at shallow depth and thermal decomposition at greater depth with its
maximum at ~100 °C (Hunt, 1990). Fluid inclusion studies in fossil accretionary
prisms prove that hydrocarbon fluids can be present in depths of up to 10 km (Vrolijk
et al., 1988). There, hydrocarbon production may account for some H2O and low
density fluids, which may enhance excess pore pressure. In the shallow region
hydrocarbons are important for gas hydrate formation, which forms under certain PT
condition within the uppermost 1 km of the sediment (Kastner et al., 1991 and
references therein). A prominent example for gas hydrates at convergent margins is
the Cascadia subduction zone. The destabilization of the gas hydrates leads to fluid
freshening and free gas at depth, which migrates along faults to the sediment surface
(Kastner et al., 1990). The vent sites are characterized by fluids with e.g. low-
chlorinity, sulphide and ammonia. The expulsion is also associated with methane and
isotopically light CO2 discharge (Suess et al., 1999).
Mineral dehydration: The release of water during mineral dehydration leads to
dilution of the pore fluid. The fluid freshening is commonly characterized by the inert
chloride species (see above) and is ubiquitous at the whole variety of convergent
margins: At the Peru continental margin dilution is up to 20 %. Strontium isotopic
composition points to mineral dehydration, most probably clay dehydration and gas
hydrate dissociation (Elderfield et al., 1990; Kastner et al., 1990). At the accretionary
Nankai margin high basement temperatures along its central portion lead to advanced
smectite dehydration at the toe of the prism. The in-situ dehydration has been
proposed to be responsible for the observed chloride anomaly in the underthrust
sequence (Henry and Bourlange, 2004). For the non-accreting Costa Rican margin
low-salinity fluids have been detected along numerous seeps along the whole margin.
The source of these fluids is the dehydration of smectite and biogenic opal in the
subducting sediment with subsequent vertical fluid transport through the overriding
plate (Kimura et al., 1997; Spinelli and Underwood, 2004; Ranero et al., 2004). The
argumentation is confirmed by isotopic data, which is typical for clay dehydration at
temperatures up to ~150°C (Hensen et al., 2004). The smectite-to-illite reaction may
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 17
also be accompanied by the release of silicon, sodium, calcium, iron and magnesium
and the consumption of K and Al (Boles and Franks, 1979, Kastner, et al., 1991).
Albitisation: Albitisation is an important diagenetic reaction during the burial of
arkoses and graywackes at a temperature range of 110-120 °C (Fig. 4; Boles, 1982).
The reaction is characterized by the transition of detrital plagioclase to albite. To
accommodate the transition sodium is necessary, which may be either provided by be
surrounding seawater or from smectite-to-illite transformation (Boles and Franks,
1979). The Al and Ca by-products of the albitization foster clay mineral, calcite and
zeolite formation (Boles, 1982).
Carbonate and quartz cementation: Authigenic cements and veins form when the
solubility is sufficient to accommodate precipitation. Carbonate precipitates are
reported for shallow regions of accretionary prism (e.g. Barbados accretionary prism:
Vrolijk and Sheppard, 1991; Cascadia accretionary prism: Kopf et al., 1995).
However, studies of fossil accretionary prisms suggest that they are not common
below ~100°C but appear to be abundant principally above 150 °C (Fig. 4; Ernst,
1990; Moore et al., 2007). Ca but also Mg and Fe are provided by the influx of fluids
from the above mentioned diagenetic reactions (Boles and Franks, 1979; Sample,
1990; Kastner et al., 1991) while carbon can derive from seawater, dissolved
calcareous shells, decomposition of organic matter and methane oxidization (Vrolijk
and Sheppard, 1991; Kopf et al., 1995). Quartz precipitation occurs dominantly
> 200 °C (Fig. 4). Si can be provided by diagenetic reaction (e.g. dissociation of
biogenic opal) but also by pressure solution which begins to work > 150 °C and is
fostered by the presence of illite (Moore et al., 2007 and references therein).
2.4 Synthesis and implications for seismogenesis Earthquake distribution can be differentiated along plate boundaries in an
aseismic updip zone, a seismic zone where 90% of the earthquakes occur, and an
aseismic downdip zone (Fig. 4; Marone and Scholz, 1988; Marone and Saffer, 2007).
The seismic zone is characterized by brittle failure and unstable sliding (stick-slip),
which refers to the accelerating runaway behaviour during slip. This material related
rate dependent frictional behaviour is also called velocity weakening (Scholz, 2002).
Modelling of temperature distribution by Hyndman et al. (1995) and Oleskevich et al.
(1999) suggests that the updip limit is associated with temperature of 100-150 °C and
CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 18
the downdip limit with temperatures of 350-450 °C (Fig. 4). While the aseismic
behaviour downdip is generally assumed to be related to the onset of crystal plasticity
(Scholz, 2002), the updip limit of seismogenesis is still actively discussed (e.g. Dixon
and Moore, 2007 and contributions therein).
Fig. 4: (A) Comparison of porosity versus depth for accretionary prism sediments in combination with the inferred onset of seismogenesis for the Nankai margin (modified after Moore and Saffer, 2001). (B) Compilation of important diagenetic reactions in the shallow subduction zone and their approximate temperature range (modified after Ernst, [1990] and Moore et al., [2007]). The grey shaded area indicates the temperature interval of the seismogenic zone along the subduction thrust.
There is common sense that the initial incoming sediment on the oceanic plate
is deforming elasto-plastically and is hence unable of seismic slip. The weakness of
these sediments lacks the capability to store energy which eventually allows a stress
drop sufficient to produce seismic slip (e.g. Byrne, 1988; Moore and Saffer, 2001).
Several theories try to explain the change in mechanical behaviour with in creasing
PT conditions. Early workers emphasised the enhanced compaction due to the high
loads (cf. Fig. 4A). They suggested that a consolidated backstop marks the onset,
which is in accordance with assumption of Marone and Scholz (1988) who proposed
that seismic behaviour in strike-slip faults occurs in highly consolidated and lithified
gouges. A variation of this hypothesis is the assumption that a highly compacted
sediment is sufficient to accommodate unstable sliding (Scholz, 1988). More recent
studies emphasized that the updip limit reflects diagenetic changes and thus
CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 19
temperature. Vrolijk (1990) argued that the transition of smectite-to-illite
coincidences with the onset of seismogenesis which agreed well with later thermal
modelling (e.g. Hyndman et al., 1995). Laboratory tests showed that illitisation causes
a change in frictional strength, but smectite as well as illite favour stable sliding under
stresses equivalent to the updip limit (Saffer and Marone, 2003; Brown et al., 2003).
The latest hypothesis is given by Moore and Saffer (2001) and Moore et al. (2007)
who emphasise the linkage between mechanical and geochemical processes. They
believe that the updip limit relates to the onset of several diagenetic processes (as
described in Chapter 2.3.2), progressed consolidation and a diminishing excess pore
pressure (cf. chapter 2.2.2). The aim of this PhD thesis is to study how high PT
conditions may change consolidation behaviour, excess pore pressure formation and
water-rock interaction towards seismic behaviour.
Chapter 3: The geology of the Nankai margin The samples for this study derive from DSDP Site 297 (Fig. 5), which is
located seaward of the accretionary prism. A detailed description of this and other
related sites at the prism are provided in the manuscript chapters. Thus, this chapter
gives just a brief geological overview of the Nankai margin.
Fig. 5: Geological map of SW Japan region showing major provenances and transportation ways (modified after Moore et al., 2001b; Pickering et al., 1993). Material derived until 2 Ma ago predominantly from the north-eastern Outer belt (SW Japan; large arrows), when it switched to along axis transportation (short arrows) of material from the Izu collision zone (large arrows). The material is partly transported into the Basin or deflected by the basin slope (light arrows). Black dots show locations of DSDP and ODP sites shown in Fig. 6 and the dotted line indicates the location of the cross section of Fig. 7.
CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 20
The Nankai Margin is located in the southwest of the Japan’s Shikoku Island
and the southwest part of Honshu Island (Fig. 5). Along the 700 km Nankai Trough
the Philippine sea plate is subducted at a rate of 2-4 cm/yr to the northeast under the
Eurasien plate (Karig and Angevine, 1986). The formation of the subducting oceanic
lithosphere began in the Oligocene by rifting of the proto-Izu-Bonin backarc and
consecutive seafloor spreading created the Shikoku Basin. The Shichito-Iwojima
Ridge and the Kyushu-Palau Ridge are relics of the former arc, which were separated
by the spreading until it ceased 15 Ma ago (Okino et al., 1994). The onset of
subduction is believed to be reflected in the 17-12 Ma igneous emplacements located
along the forearc (Fig. 5). The typical volcanic front developed later with deeper
penetration of the subducting slab and is associated with the beginning of volcanic
activity in SW Japan 6 Ma ago (Kamata and Kodama, 1994).
The Shikoku Basin is the north-eastern part of the Philippine sea plate which is
eventually subducted at the Nankai Trough. The Shikoku Basin contains a thick
sedimentary cover, which tapers of to the southeast and fades into a thin pelagic cover
(Karig, 1975). The general stratigraphic architecture of the ~1 km-thick incoming
sediment sequence in the Nankai Trough was penetrated during several DSDP (Deep
Sea Drilling Project), ODP (Ocean Drilling Program) expeditions and can be divided
into four major units (Fig. 6; Karig et al., 1975; Kagami et al., 1986; Taira et al.,
1991; Moore et al., 2001a; Mikada et al., 2002). The oldest is a thin layer of early
Miocene Volcaniclastic facies which is overlain by two dominantly hemipelagic
mudstones, the predominantly Miocene Lower Shikoku Basin facies and the Pliocene
to Quaternary Upper Shikoku Basin facies (Fig. 6). The youngest is the Nankai
Trench-wedge facies, which thickens rapidly to the trench (Moore et al., 2001a).
Evidence from seismic imaging and coring suggests that the decollement lies in a
consistent stratigraphic layer at the top of the Lower Shikoku Basin facies off Shikoku
Island (Moore et al., 2001b). Approximately two thirds of the incoming sediment pile
is currently scraped off including the Trench-wedge facies and the Upper Shikoku
Basin facies while the Lower Shikoku Basin facies comprises the bulk of the
underthrust sequence.
CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 21
Fig. 6: Lithostratigraphic architecture along the south-western corner of the Nankai margin after Moore et al. (2001b).
Major provenance regions for abundant influx of terrigenous and
volcaniclastic material for Shikoku Basin sediments are Kyushu, western Honshu and
the Izu collision zone (Pickering et al., 1993). Further inputs are volcaniclastics from
the active Izu-Bonin island arc and the Kyushu-Palau ridge. At least since middle
Miocene turbidites arrived from the Outer belt (Southwest Japan) and accretion built-
up a prism by 4 Ma in front of the Cretaceous to Tertiary Shimanto belt (cf. Fig. 5).
With the Izu-collision 2 Ma ago at the eastern corner of the Nankai Trough, the
provenance shifted and the trench was filled by turbidites travelling along the axis of
the trench (Moore et al., 2001a). This sedimentation pattern is complicated by the
topographically high remnants of the fossil spreading ridge and the adjacent volcanic
Kinan seamount chain along the central portion of the margin (cf. Fig. 5). Terrigenous
sands are deflected by the basement highs and lead to a monotonous sedimentary
sequence above (Pickering et al., 1993; Underwood, 2007). This central portion of the
Nankai margin is still characterized by elevated heat flow and high in-situ
temperatures of ~110 °C, which lead to advanced thermal alteration of the overlying
sediments (Underwood and Pickering, 1996; Underwood and Steurer, 2003).
CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 22
Based on seismic reflection data Moore et al. (2001a) separated the present
accretionary prism into several structural divisions (Fig. 7). The protothrust zone
(PTZ) marks the region where tectonic deformation begins and includes the formation
of the decollement in the Lower Shikoku Basin facies. Tectonic thickening of accreted
sediments is characterized in this region by small faults and ductile strain (Morgan
and Karig, 1995) while it is followed landward by an area of landward dipping
imbricate thrust packages, the imbricate thrust zone (ITZ). The imbricate thrust zone
is cut by a younger out-of-sequence thrust (OOST). This area, where the OOST cuts
from decollement upward is characterized by increased thickening of the accreted as
well as the underthrust sediments. According to the model of Saffer and Bekins
(1998) this area features the highest excess pore pressure ratios (Fig. 3). This
thickening, which is probably accommodated by duplexing, is followed by the deep
down-cut of the decollement into the subducted sediment (Fig. 7). Several packages
above the decollement can be inferred from seismic reflection data according to
Moore et al. (2001a), which may be related to underplating. Seismic imaging suggests
that the down-cutting is associated with a massive drop in excess pore pressures
(Bangs et al., 2004). Above the packages several OOSTs mark the area as a large
thrust-sliced zone (LTSZ), which cut through the prism and lead to substantial
thickening with landward dipping slope sediments. Landward of the LTSZ follow
presumably more rigid and consolidated sediments which are probably capable of
seismogenesis. They are characterized by landward dipping reflectors (LDR zone) and
represent the oldest material of Miocene to Pleistocene age, which is composed of
turbidites from the Outer belt.
Fig. 7: Cross section of the Nankai accretionary prism showing major structural and stratigraphic sequences modified after Moore et al. (2001b). See text for detailed explanation.
CHAPTER 4: MANUSCRIPT 1 23
Chapter 4: Manuscript 1 The thermal influence on the consolidation state of underthrust
sediments from the Nankai margin and its implications for excess pore pressure
A.Hüpers1 and A.Kopf1
1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany.
Earth Planetary Science Letters (in press)
Abstract
The Nankai Trough convergent margin has been the focus of many multi-methodological surveys including half a dozen scientific deep-sea drilling expeditions. The boreholes focused on the smectite-dominated area off Cape Ashizuri and the thermally altered, illite-dominated region off Cape Muroto. On the basis of these surveys a number of studies addressed to the stress state of the underthrust sediments and its implications for the plate boundary thrust. Although the basement temperature has been found to be up to ~110 °C, none of these studies drew close attention to temperature effects on the consolidation state of the sediments. To overcome this shortcoming, we selected end member sediment lithologies from the incoming oceanic plate in the Shikoku Basin and subjected them to elevated stresses and temperatures.
We here present results from a series of heated (20 °C, 100 °C, 150 °C) uniaxial consolidation experiments up to effective normal stresses of ca. 70 MPa. The main finding is a positive correlation between temperature and pore space reduction. Based on in-situ temperature information from earlier scientific drilling, our study suggests that temperature has an influence on the consolidation state of underthrust sediments along the Nankai Margin. Together with secondary consolidation, thermal consolidation serves to explain steep log-linear consolidation curves of the incoming Lower Shikoku Basin sediments. The onset of diagenesis in this realm led to the transition of smectite-to-illite and to a different consolidation behaviour. Estimated in-situ pore pressures based on in-situ temperature data results in up to ~1 MPa smaller overpressures than those previously estimated from drilling data alone. Those values, which imply underconsolidation at drill sites near the frontal Nankai accretionary complex, are further believed to facilitate frictional sliding along the subduction thrust.
CHAPTER 4: MANUSCRIPT 1 24
4.1 Introduction The Nankai Trough accretionary margin (Fig. 1A), off Southwest Japan, has a
1300 yr long record of large earthquakes, including the M>8 events of 1944 and 1946
(Ando, 1975). The margin has been a high priority location for DSDP (Deep-Sea
Drilling Project), ODP (Ocean Drilling Program) and IODP (Integrated Ocean
Drilling Program) drilling including subduction factory research and several studies
addressing to the stress state of underthrust sediments. The area is currently the focus
of the IODP project NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment;
Tobin and Kinoshita, 2007).
Fig. 1: (A) Map of the Nankai subduction zone showing DSDP and ODP drillsites. Sediments of Site 297 were used for hydrothermal deformation experiments. (B) Interpolated temperature profiles of Site 1177, 1173, 1174 and 808 with reliable measurements marked as dots (modified after Moore et al., 2001; Taira et al., 1991; Kagami et al., 1986). The shaded area marks the temperature across the Lower Shikoku Basin with a dotted line to accentuate the decollement zone (DZ). (C) Cross section along the Muroto transect showing major stratigraphic sequences and structure of the toe of the prism (modified after Morgan and Ask, 2004).
CHAPTER 4: MANUSCRIPT 1 25
The development of earthquakes at accretionary margins is directly linked to
changes in mechanical properties of the incoming sediments with depth. Since
seismogenesis cannot occur in the initially weak sediments, significant consolidation
and lithification have to take place along the plate boundary (e.g. Byrne et al., 1988;
Moore and Saffer, 2001; Saffer and Marone, 2003). While sediments above the plate
boundary undergo vertical and lateral (i.e. tectonic) consolidation with accretion,
underthrust sediments have been proposed to remain largely undeformed laterally
during initial subduction (e.g. Karig and Morgan, 1994). As a result of the applied
load due to the overlying prism, underthrust sediments are subjected to rapid
consolidation. Depending on the pore fluid dissipation as a function of permeability of
the overlying sediments, the progressive consolidation is characterised by pore space
reduction with increasing depth. However, modifications of physical properties and
mechanical strength document that underthrust sediments are not only subjected to the
applied load of the overlying prism, but also to increasing temperature, secondary
consolidation (creep), and counteracting processes such as elevated pore pressures due
to mineral dehydration, hydrocarbon formation, and diagenetic effects such as
cementation and chemical compaction (e.g. Moore and Vrolijk, 1992; Moore and
Saffer, 2001; Karig and Ask, 2003; Morgan and Ask, 2004). Such mechanisms
change the mechanical properties of underthrust sediments that are particularly
important for (1) the location of the main plate boundary fault (i.e. the decollement),
which is situated directly above these sediments and often propagates into them
(Brown et al., 2003), and (2) the onset of unstable sliding behaviour at the updip limit
of the seismogenic zone (Moore and Saffer, 2001; Saffer, 2003). So far, the detailed
influence of the different factors on the consolidation state and strength of underthrust
sediments and its consequences for seismogenesis and decollement localisation is
incompletely understood.
Although uniaxial consolidation testing has been successfully applied to study
effective stress and pore pressure distribution of marine sediments along the Barbados
and Costa Rican convergent margins (e.g. Moore and Tobin, 1997; Saffer et al., 2000;
Saffer, 2003), there are noticeable discrepancies between field consolidation and
laboratory consolidation at the Nankai Trough (Morgan and Ask, 2004). Only few
laboratory consolidation tests investigated the mechanisms influencing the
consolidation state of deep-sea sediments. For instance, Morgan and Ask (2004)
assume from triaxial reconsolidation tests that samples of the Nankai margin are
CHAPTER 4: MANUSCRIPT 1 26
moderately cemented. Results from experiments by Karig and Ask (2003) suggest that
secondary consolidation occurs with burial of marine sediments, presumably also
closely linked to diagenesis.
Although temperature is supposed to be a key parameter for the onset of
seismogenesis (Oleskevich et al., 1999) its implication for consolidation behaviour of
underthrust sediments has so far been largely neglected. The objective of this study is
to contribute to narrow this gap. Isothermal uniaxial consolidation tests up to
pressure-temperature (PT) conditions similar to those at the onset of the seismogenic
zone (so called updip limit) have been conducted to shed light on thermal behaviour.
Tested specimen comprise different lithologies of the Lower Shikoku Basin facies
representing along strike variation as well as thermal alteration downslab of
subduction inputs at the Nankai margin. The results are discussed in comparison with
standard laboratory tests and shipboard measurements from drill sites at the toe of the
prism, and with respect to their implications for pore pressure distribution and
mechanical strength of underthrust sediments at the Nankai margin.
4.2 Geological Context and Sampling Strategy 4.2.1 Geological Context
Along the Nankai Trough, the Phillipine Sea plate is being subducted to the northeast
at a slightly oblique angle to the margin of southwest Japan (Eurasian plate) at a rate
of 2-4 cm/a (Karig and Angevine, 1986). Ongoing convergence led to the build-up of
a wide accretionary prism by offscraping of Shikoku Basin and Nankai trench wedge
facies from the downgoing plate (Fig. 1A). The Shikoku Basin was targeted in the
Nankai Trough area during DSDP and ODP drilling Legs 31, 87, 131, 190 and 196
(Karig et al., 1975; Kagami et al., 1986; Taira et al., 1991; Moore et al., 2001; Mikada
et al., 2002). Our study focuses on the Pliocene to Miocene Lower Shikoku Basin
(LSB) facies, which comprises the bulk of the underthrust sediments and has been
penetrated along two transects perpendicular to the margin: the Ashizuri and the
Muroto transects (Fig. 1A,C).
Off Cape Ashizuri, the LSB facies consists of hemipelagic mudstone with
abundant terrigeneous sandy turbidites and volcanic ash. Smectite content is ~20 wt-
% at the top of the LSB at Site 1177 (~23 km seaward from the deformation front)
and increases dramatically within the strata at 600 mbsf to ~50 wt-% (Underwood,
CHAPTER 4: MANUSCRIPT 1 27
2007). It is assumed that no smectite diagenesis has occurred at this depth which is in
accordance with thermal gradients of ~50-56 °C/km along the Ashizuri transect (Fig.
1B). The projected decollement at Site 1177 is at a depth of ~420 mbsf in a
stratigraphic level equivalent to the Muroto transect. With less confidence, it may be
traced to a level of ca. 550 ± 30 mbsf at Site 297 several tens of km outboard of the
trench. The pore space decreases with increasing depth at Site 1177 but is generally
higher compared to equivalent depths of drill Sites at the Muroto transect (Fig. 2).
Fig. 2: Pore space-depth relationships along the Muroto transect (Sites 1173, 1174 and 808) and the Ashizuri transect (Site 1177) based on Shipboard measurements. (modified after Moore et al., 2001; Taira et al., 1991; Kagami et al., 1986). The pore space is presented as void ratio (volume ratio of pore water and solids). The light shaded area shows the Lower Shikoku Basin facies (LSB) and the dark shadings marks the decollement zone (DZ).
The subducting seafloor off Cape Muroto is situated above a basement high,
formed by a fossil spreading ridge and an adjacent chain of volcanic seamounts. The
LSB was penetrated ~11 km (Site 1173), ~0.25 km (Site 1174) seaward of
deformation front, and 1.5 km landward of the deformation front (Site 808; Fig. 1C).
Although sandy turbidites are common within the LSB they have not been sedimented
on this ridge, leading to a monotonous lithological sequence of hemipelagic
mudstone. Due to its location near the fossil spreading ridge, it is characterised by a
high heat flow of ~129-180 mW/m2 and a projected basement temperature of ~110 °C
for Sites 1173 and 808 (Taira et al., 1991; Moore et al., 2001). At Site 1174 the
projected temperatures are up to ~140 °C but may have been overestimated due to the
CHAPTER 4: MANUSCRIPT 1 28
input of warm fluids and thrust faulting (Moore et al., 2001). Thus, a consistent
basement temperature of 110°C has been assumed for this study (Fig. 1B). Kinetic
reaction models for smectite-to-illite transition found to be highly consistent with
measured illite in I-S clays for these high temperature conditions (Saffer et al., 2008).
At Site 1173, smectite content decreases continuously from ~35 wt-% at the top of the
succession to ~25 wt-% at the bottom (Underwood, 2007). Further landward at Site
808, smectite content is just about <6-7 wt-% and illite is the dominant clay mineral
(Underwood and Pickering, 1996). Hence, it can be assumed that the smectite-rich
layers at the Ashizuri transect will undergo a similar mineralogical change, although
less pronounced owing to lower heat flow values (e.g. Moore et al., 2001).
The pore space decreases continuously with depth within LSB strata at Site
1173 (Fig. 2), but this trend is interrupted in the upper part of the LSB by an abrupt
increase in void ratio (Fig. 2) across the decollement zone at the other holes (808-
840 mbsf at Site 1174; 945-964 mbsf at Site 808). This rapid change has been
interpreted as a change in stress state due to overpressuring of the underthrust
sediments (e.g. Screaton et al., 2002; Saffer, 2003) but also due to excess compressive
strength of these sediments as a matter of cementation (Morgan and Ask, 2004). A
more detailed discussion of this topic can be found in Morgan et al. (2007).
4.2.2 Sampling Strategy
To cover the wealth of lithological differences along the Nankai Trough, end
member lithologies were selected based on semi-quantitative XRD results from
Underwood et al. (1997) and Brown et al. (2003). Samples for this study derive from
the LSB facies of Site 297, which is located SW of Site 1177 (Fig. 1A) along the
Ashizuri transect. The selected samples comprise a smectite-rich clay (N13), an illite-
rich silty clay (N14) and a dominantly silty to fine sand-grained quartz/feldspar-rich
sample with some clay fraction (N18). Sampled depths within the lower part of the
LSB (~330-570 mbsf) are 506.83-506.90 mbsf (N13), 507.12-507.20 mbsf (N14) and
554.47-554.63 mbsf (N18), respectively. The accumulated sample material was
disintegrated and homogenised for the experiments. To provide evidence for
mineralogical composition and integrity, sub-samples underwent semi-quantitative
XRD examination at the University of Bremen (Germany) following the methodology
described in Vogt et al. (2002) after completion of the compaction tests. The results
verify a uniform composition for sub-samples of each end member, which attests that
CHAPTER 4: MANUSCRIPT 1 29
no significant smectite-to-illite transition has occurred in our tests. This is in
accordance with slow kinetic reaction of smectite-to-illite at these temperatures
proposed by Huang et al. (1993). However, the end members are significantly
different in the main components (cf. Tab. 1), representing a variation of a mainly
three component system (smectite [Sm], illite [Il], and quartz [Qtz]). Sample N13 is
rich in clay minerals and smectite-dominated with contents representative for
smectite-rich interlayers between the turbidites in the lower part of the LSB along the
Ashizuri transect. Sample N18 possesses a high granular fraction (containing quartz,
feldspar, and tephra) and reflects the turbiditic, coarse-grained end member lithology.
The fine-grained sample N14 has a high illite content and may be therefore (1)
comparable to the fine-grained hemipelagics along the thermally overprinted Muroto
transect and (2) simulate consolidation behaviour during deeper underthrusting
beneath Cape Ashizuri. Thus, we simulate both, thermal alteration along-strike as well
as down-slab.
Tab. 1: Results from quantitative XRD showing major mineral content (wt-%). Sample N13 is smectite-rich clay, while samples (N14) and (N18) contain both large fractions of illite, quartz and feldspar. Although mineralogically similar, sample (N14) is a silty clay while sample N18 is dominantly silty to fine sand-grained with some clay fraction.
Quartz + Feldspar
Smectite + Montmorillonite
Illite + Muscovite Chlorite Mixed layer
clays other
N13-20 5.7 43.5 0.0 2.0 35.6 13.2 N13-100 9.2 56.3 19.9 0.0 12.9 1.7 N13-150 15.1 43.3 8.4 1.9 18.2 13.1
N14-20 49.1 4.0 29.9 1.6 1.7 13.7 N14-100 44.2 6.6 27.0 2.6 6.6 13.0 N14-150 52.0 2.8 29.3 2.4 5.6 7.9
N18-20 51.1 1.8 24.2 3.1 6.7 13.1 N18-100 48.8 0.6 8.9 2.9 22.7 16.1 N18-150 60.0 2.3 19.8 3.0 6.2 8.7
4.3 Methods 4.3.1 Consolidation Theory
The compaction of sediments is described by the effective stress law and the
one-dimensional consolidation theory (e.g. Terzaghi and Peck, 1948), which will be
recapitulated briefly in the following. When a vertical load is applied suddenly onto
CHAPTER 4: MANUSCRIPT 1 30
an unlithified sediment mass, the total pressure is taken up by the mineral framework
and by the water in the pores. The total stress (�t) is, therefore, defined as the sum of
the effective stress on the mineral framework (�e) and the excess pore water (P) in the
effective stress law
�t = �e + P [1].
Over time the water drains from the sediment pores, which causes a transfer of
the stress on the mineral framework and to a plastic deformation of the sediment until
the pore water overpressure dissipates. This process is known as consolidation.
However, if drainage of the pore fluid is hindered, pore space remains high and the
created excess pore pressure reduces the effective stress (�e). The relationship
between pore space and the effective stress can be described after Terzaghi and Peck
(1948) by
e = e0 - Cc * log(�e) [2]
with e being the void ratio (= volume of voids / volume of solids), e0 the void
ratio at an effective stress unity of 1, and Cc the compression index. Although void
ratio is more common in this context some authors also use the porosity as pore space
characterisation for equation [2]. To compare data with such studies, we calculated
void ratio from porosity � for those studies by using the equation
e = � / (1 - �), [3]
and recalculated equation [2] to maintain comparability to our study.
Since the consolidation is material-related, equation [2] has to be determined
by laboratory consolidation tests. Throughout a consolidation test, remoulded
sediments are characterised by plastic deformation. Test results are plotted in a void
ratio vs. log effective stress (�e) diagram where the relationship presented in [2] gives
ideally a straight line, the primary or virgin consolidation line (Fig. 3). It marks the
consolidation state where pore space and effective stress are in equilibrium when the
excess pore pressures has dissipated (�t = �e). The continuing consolidation at a
constant effective stress after pore pressure dissipation is termed secondary
compression (creep). In-situ consolidation is often the result of primary and secondary
consolidation (Karig and Ask, 2003). A sample, which has undergone primary and
secondary consolidation, responds to increasing stress by tertiary consolidation until
primary consolidation is resumed (Fig. 3). Upon unload or reload of a sample
consolidation occurs in an elastic fashion. To avoid relaxation effects due to core
recovery from depth a rebound value of 0.045 % e/log(�e) [= 0.0199 % �/log(�e)] for
CHAPTER 4: MANUSCRIPT 1 31
all shipboard void ratio data from the Muroto transect has been applied after Morgan
and Ask (2004).
Fig. 3: Schematic view showing the known types of consolidation in the void ratio vs. the logarithm of effective stress (modified after Karig and Ask, 2003). Primary consolidation proceeds along line 1 and marks the equilibrium between pore space and the applied load after the excess pore pressure has dissipated. Further settlement of the sediment at constant stress is termed secondary consolidation (2). Unloading or reloading of a pre-stressed sample results in an elastic behaviour (3). Tertiary consolidation (4) occurs between the maximum consolidation state after secondary consolidation and resuming primary consolidation.
4.3.2 Sample preparation and testing procedure
In preparation of each experiment, the core samples were ground until the
samples were fully disaggregated and re-hydrated in seawater for a period of 1 to 5
days. Thereafter, the samples were placed in a self adjusted high-capacity oedometer
with a diameter of 55 mm. Initial void ratios were 4-5 and sample heights were up to
62 mm. Tests with aliquots of each specimen were carried out at 20 °C, 100 °C and
150 °C, and specimen labelling always provides sample ID – T [in degrees C] (e.g.
N13-20 for a room temperature test at 20°C, N13-100 for a test heated at 100°C, etc.).
For the heated consolidation runs, a band heater was placed on the outside of the
confining chamber. The temperature was monitored in the centre of the sample with a
probe that relayed its reading to the heating and was controlled by a high-precision
heating unit (Omega CN7600). Temperature fluctuations during the tests were smaller
than 2 °C. Heating was conducted at the beginning of the tests in several steps over
two days before loading up to approximately 70 MPa.
Consolidation took place under one-sided drained conditions with rates of
strain of <0.0125 %/min for sample N18 and <0.0042 %/min for sample N14 and
CHAPTER 4: MANUSCRIPT 1 32
N13, which are in the range of successfully tested strain rates for different clays by
Smith and Wahls (1969). A backpressure of ~500 kPa was applied to get entrapped air
into solution and to prevent the pore fluid from evaporating. Pore pressures were
measured using Validyne™ differential pressure transducers (accuracy ± 25 kPa)
attached to the fluid drainage at the top and to the bottom of the cell. Shortening of the
sample was measured with a Burster™ displacement transducer (accuracy ±
0.075 mm).
In order to determine the void ratio for any given stress state, the final void
ratio and the final sample height must be known. For this, final compacts were
recovered from the cell after unloading and cooling over a period of ~6-12 h. This
span of time eliminates dehydration effects of smectite during the tests (Fitts and
Brown, 1999). Sample height was determined by taking the average of the
measurement at three different positions of the compact with a sliding calliper
(accuracy ± 0.1 mm). For void ratio determination, consolidated samples were placed
in an oven at 80 °C and were allowed to dry for several days until no further loss of
fluid was noted. This procedure was necessary because the insulation made the
apparatus inaccessible to determine the absolute location of the piston in the cell.
Thus, void ratio data possibly include rebound and cooling effects. Nonetheless,
rebound effects may be negligible when results of the same mineralogical sample are
compared and maximum stresses have been the same.
4.4 Results
An overview of the results of the consolidation study is shown in Figure 3.
Apart from runs N14-20 and N18-20, all samples show a more or less arcuate
consolidation curve, which is especially pronounced for the smectite-rich clay. Data
are sparse in the beginning of some tests, because of greater logging intervals for
some experiments and logarithmic presentation of the measured values. For the best
fit calculation of e vs. log �e, we hence regarded only data greater than 4 MPa. For
this range the majority of the samples display the typical log-linear e vs. �e
relationships for remoulded sediment. We calculated the best fit of equation [2] for
the individual sample data (Tab. 2) to describe the pore space reduction with
increasing effective stress following Terzaghi and Peck (1948). Coefficients of
determination for best fits are better than R2=0.97 except for run N13-150 (R2=0.93).
CHAPTER 4: MANUSCRIPT 1 33
Tab. 2: Best fit of least squares of logarithmic equation [2] describing the virgin consolidation behaviour of each specimen. Only data points >4 MPa have been included in the best fit of e vs. log(�e) because of the bent curve progression. The overall high coefficients of determination (R2) of the best fits indicate a good linear relationship between void ratio and the logarithm of effective stress.
20 °C 100 °C 150 °C
N13 e = 1.51 – 0.52 * log(�e)
R2=0.99 e = 1.17 – 0.43 * log(�e)
R2=1.00 e = 1.64 – 0.70 * log(�e)
R2=0.93
N14 e = 1.71 – 0.41 * log(�e) R2=1.00
e = 0.77 – 0.21 * log(�e)*
R2=0.98 e = 0.86 – 0.32 * log(�e)
R2=0.99
N18 e = 1.11 – 0.33 * log(�e) R2=0.99
e = 0.90 – 0.31 * log(�e) R2=0.99
e = 0.84 – 0.28 * log(�e) R2=0.97
Data for the smectite-rich sample N13 show near-parallel curve progression
for the tests at 20 °C and 100 °C at stresses greater than 10 MPa, where compression
indices reached 0.52 and 0.43, respectively (Fig. 4A). The downshift of the 100 °C
run may be given by the difference in e0 and accounts for a shift of 0.34 between the
curves. Both experiments, at 20 °C and 100 °C, were aborted at effective stresses of
45.3 MPa and 53.8 MPa, respectively, because the fluid pressure approached the
maximum range of the pressure transducers. Sample N13-150 shows a good
agreement with the sample N13-100 at effective stresses greater than 30 MPa. At
lower stresses this sample shows steeper void ratio reduction with depth. Hence, the
best fit reveals a higher Cc and e0 compared to the two other runs. Noticeable is the
halt in void ratio reduction with increasing stress, which is followed by an abrupt
decrease in void ratio over small effective stress ranges (e.g. between 6-7 MPa and
20-30 MPa).
The observed shift in void ratio with increasing temperature can also be seen
for the illite-rich sample N14 (Fig. 4B). The shift in e0 of about 0.93 between sample
N14-20 and N14-100 is significantly bigger than for sample N13. In contrast, the shift
between the heated tests is negligible for effective stresses lower than ~15 MPa. With
increasing stress the N14-150 curve retains the higher rate of void ratio reduction so
that at maximum stresses of ca. 70 MPa the difference in e is only 0.11. The slope of
the three consolidation lines deviates between 0.41 and 0.25 with lower values for the
heated runs. Compared to the smectite-rich sample the compression indices are
noticeable smaller.
The turbiditic specimen N18 shows the lowest variation in compression index
(Fig. 4C). Values range between 0.33 and 0.28 with smaller values for the heated
runs. These compression indices are significantly smaller those of the smectite-rich
CHAPTER 4: MANUSCRIPT 1 34
sample and on the lower end of the measured range for the illitic sample. Based on the
good agreement of the compression indices the shift in the consolidation curves of the
room temperature test and the heated test at 100 °C is 0.21 given by e0. The difference
between the heated runs increases due to the smaller compression index of sample
N18-150 and is negligible at the maximum effective stress of 70 MPa. The mentioned
halt in void ratio reduction for sample N13-150, although less pronounced, can also be
observed for sample N18-150 at 3-4 MPa (Fig. 4C). The delay in consolidation may
be created by transient elevated pore pressures owing to low permeability of the
samples or blocked filters. The latter seems more reasonable because no excess pore
pressures have been measured.
Fig. 4: Results from the isothermal consolidation tests for (A) the smectite-rich (N13), (B) the illite-rich (N14), and (C) the quartz-rich (N18) lithologies. Note the offset with increasing temperature towards lower void ratios.
4.5 Discussion and Implications 4.5.1 Interpretation of laboratory consolidation data
From isothermal oedometer tests carried out on end member lithologies from
the LSB succession along the Nankai margin at three different temperatures, we
present nine different consolidation curves (Fig. 4) from which three major
observations can be deduced:
(1) The consolidation lines do not show the ideal log-linear behaviour but
have an arcuate shape.
(2) The slopes of the consolidation lines are different for each sample.
CHAPTER 4: MANUSCRIPT 1 35
(3) The consolidation curve shifts for each sample with increasing
temperature.
Consolidation below 4 MPa reveals a steeper rate of void ratio reduction with
increasing stress than at higher stresses. However, standard soil mechanical testing is
often restricted to lower effective stresses and variation at higher pressures has not
received comparable attention so far. Karig and Hou (1992) commented that the slope
at low stresses smaller than 5 MPa are steeper and cannot be projected to higher
stresses. This is fairly consistent with our results where we set the threshold at 4 MPa.
Accordingly, the change in the slope of the consolidation line indicates that the rate of
compression decreases with increasing effective stress (Karig and Hou, 1992). In fact,
our room temperature tests give compression indices Cc N13 > Cc N14 > Cc N18,
which is in accordance with the proposed order of Lambe and Whitman (1969) for the
compression index of Cc_clay > Cc_silty_clay > Cc_silt. This order represents particle size
and shape as most influencing parameter for the relationship of void ratio and
effective stress.
The most striking finding of this study is the decrease in void ratio at a
constant effective stress with increasing temperature from 20 °C to 100 °C. At higher
temperatures (i.e. between the 100 °C and 150 °C runs), this effect remains observable
but is less pronounced. If the absolute values in the observed offset of the void ratio is
assumed to be linear between 20 °C and 100 °C, the void ratio reduction is 0.012 e/°C
for the illite-rich sample, 0.004 e/°C for the smectite-rich sample and 0.002 e/°C for
the turbiditic sample. Although these data are higher than those of Campanella and
Mitchell (1968), the observed temperature-dependent consolidation trend is in unison
with several studies of thermal clay compaction tests that under fully drained
conditions heat enables greater deformation until a load is compensated by the
mineral framework (e.g. Campanella and Mitchell, 1968; Cekerevac and Laloui,
2004). According to Paaswell (1967) the heating induces a greater motion of water
molecules, which are bond to the clay particles. Coupled with lower water viscosity,
this motion alleviates a pressure-independent resistance between the clay boundary
layers to shear and causes a parallel shift of the consolidation lines for different
temperatures. The latter observation cannot be fully supported by our study up to
70 MPa, most likely because the earlier work focused mainly on low stresses
(<1 MPa; cf. Campanella and Mitchell, 1968; Cekerevac and Laloui, 2004). Although
only slightly, the offset is more pronounced for low stresses in our testing, leading to
CHAPTER 4: MANUSCRIPT 1 36
lower compression indices for the heated tests, so that we assume that the impact of
temperature on the physico-mechanical factors on intergranular friction decreases
with increasing effective stress.
4.5.2 Application to the consolidation state of underthrust sediments
Along the Ashizuri transect where our samples originate from, in-situ
measurements and also physical properties data such as void ratio and temperature
with depth for LSB sediments are very limited from DSDP drillings, and only one
ODP borehole (Site 1177) provided a comprehensive data set later. For this, we use
data from Sites 1173, 1174 and 808 along the Muroto transect for comparison with
our results. These sites have the added advantages that downhole differences in
lithology are smaller than along the Ashizuri transect (e.g. lack of turbidites) and
temperatures are high (Fig. 1B). Further, these sediments have progressively
undergone illitisation from Site 1173 to 808, which makes them suitable to study
temperature and diagenetic effects otherwise encountered only at depths of several
kilometres. The total stress �t for these Sites can be calculated by integrating the bulk
density downward in the holes and subtracting the hydrostatic pressure owing to the
water column of the respective height. When fluid overpressuring is excluded, as it is
assumed for Site 1173 (e.g. Karig, 1993, Spinelli et al., 2007), the calculated stress
equals the effective stress �e.
4.5.2.1 Influence of temperature
To examine the influence of temperature on in-situ consolidation, Site 1173 is
used as a reference (Fig. 5). Although temperatures are high across the LSB (65 °C to
105 °C, Fig. 1B), the degree of illitisation is small and the strata is believed to be
normally consolidated �t=�e (Screaton et al., 2002; Spinelli et al., 2007). Thus, the
void ratio vs. effective stress relationship should be comparable to laboratory
consolidation.
The best fit of the in-situ data for Site 1173 is e = 1.50-1.38*log(�e) (Fig. 5).
Morgan and Ask (2004) derived from laboratory consolidation a value of Cc�=0.236
from the porosity vs. log (�e) relationship which corresponds to Cc ~0.99. This value
reflects the upper threshold of a variety of consolidation results (cf. Spinelli et al.,
2007). Thus, we examine temperature effects conservatively. Applying the laboratory
CHAPTER 4: MANUSCRIPT 1 37
Cc from the top of the LSB to model the response according to the overlying load, the
void ratio decreases by 0.40 across the effective stress range studied. This leaves 0.17
unaccounted for (Fig. 5), so that in-situ consolidation must be subjected to another
effect that introduces additional strain. Given the thermal void ratio reduction under
normally consolidated conditions, the increasing temperature across the LSB strata
may explain the residual amount of void ratio reduction (Fig. 5). To estimate the
expected maximum void ratio reduction of thermal consolidation across the LSB
strata, the approximated thermal consolidation rate of 0.004 e/°C (N13) results in an
additional void ratio reduction of 0.16 for a temperature interval of 40 °C. Secondary
consolidation (creep) may additionally affect consolidation behaviour, reducing pore
space with time. Karig and Ask (2003) suggest that at geological time scales
sediments consolidate slowly enough that primary and secondary consolidation
proceed simultaneously. This may be facilitated by the slow sedimentation rate of 27-
37 m/Ma for the LSB facies (Moore et al., 2001). This suggests that the observed
discrepancy is the combined result of thermal and secondary consolidation, with
secondary consolidation known to be more advanced at higher temperatures (Mitchell
and Soga, 2005).
Fig. 5: Void ratio vs effective stress data (circles) for Lower Shikoku Basin facies at Site 1173 (Moore et al., 2001) with best fit given as dashed line [e = 1.50-1.38*log(�e)]. The solid line marks the estimated void ratio reduction due to mechanical loading (weight symbol) from the top of the LSB strata. The residual of 0.17 (thermometer) is explained by thermal consolidation and creep.
CHAPTER 4: MANUSCRIPT 1 38
Finally, it can be speculated that the observed temperature-dependent
consolidation behaviour may have implications for frictional strength and stability of
underthrust sediments in the seismogenic zone. Our study reveals that thermal
consolidation is a result of decreasing interparticle friction, which suggests a
weakening in sediment strength. Contrariwise, the lower void ratio may compensate
the interparticle weakening by increased compressive strengthening under fully
drained conditions. Under natural conditions pore pressure estimates for accretionary
prisms are generally predicted to be near lithostatic at seismogenic depth, suggesting
that the drainage is hindered (e.g. Saffer and Bekins, 1998). This implies that no
compressive strengthening takes place and that the decrease in interparticle friction
cannot be compensated by thermal consolidation. The greater volume increase of pore
water with increasing temperature may also lead to substantial pore water
overpressure that further weakens the sediment. However, friction experiments under
elevated temperatures have to be conducted to scrutinise these phenomena and their
effect on sliding behaviour.
4.5.2.2 Influence of diagenesis
Once underthrust, sediments are subjected to thermal alteration downslab.
Ongoing illitisation leads to a change in mineralogical composition, fluid release and
thus to different consolidation behaviour. Maximum compression indices reported for
Sites 1173, 1174 and 808 indicate a decrease in the compression index Cc from 0.99 >
0.7 > 0.43, which correspond to the compression indices of 0.236 > 0.186 > 0.160
determined by Morgan and Ask (2004) and Karig and Ask (2003) from the porosity
vs. log (�e) relationship. Similar results on various clays at up to 50 MPa were derived
by Djeran-Maigre et al. (1998) where a decreasing smectite content is also linked with
a decrease compression indices.
The change in consolidation behaviour of the subduction inputs may be
additionally affected by other diagenetic processes and finally by lithification.
Depending on the primary mineralogy, clastic sediments are supposed to be modified
during burial diagenesis by the gradual replacement of smectite, detrital biotite, K-
feldspar and calcic plagioclase by chlorite, illite and albite (Kisch, 1983). Frey (1987)
assumes that more than 95 % of very low-grade metaclastites are a mixture of
muscovite (or illite), chlorite and quartz. Especially quartz formation would foster
earthquake generation because it exhibits unstable frictional sliding behaviour in the
CHAPTER 4: MANUSCRIPT 1 39
range of 150-300 °C. Quartz cementation occurs due to silica dissolution (e.g.
pressure solution), which precipitates at temperature >150 °C (Moore et al., 2007).
Although the contention that smectite-to-illite transition plays a major role in
seismogenic faulting (Vroljik, 1990; Hyndman et al., 1995) has been questioned based
on shear experiments of seawater-saturated sediment at room temperature (Brown et
al., 2003; Ikari et al., 2007) illitisation may facilitate quartz cementation because the
reaction produces silicon as by-product (Curtis, 1985). These finding may be in
favour of the hypothesis that a threshold in consolidation state (Marone and Scholz,
1988; Marone and Saffer, 2007) or the combination of lithification/consolidation and
diagenesis (Moore and Saffer, 2001) are held responsible for the onset of unstable
sliding behaviour.
4.5.3 Implications for pore pressure estimates
The knowledge of the magnitude of pore fluid pressure fluctuations is
important because excess pressures lower the sediment strength and make it prone for
failure (Hubbert and Rubey, 1959; Moore, 1989; LePichon et al., 1993). Regions with
elevated pore pressures are important for the formation of the decollement near the toe
of the forearc, and also for the onset of seismogenesis (e.g. LePichon et al., 1993;
Moore and Saffer, 2001). High pore pressure transients were measured or inferred in
underthrust sediments for several convergent margins (e.g. Foucher et al., 1997;
Becker et al., 1997; Screaton et al., 2002; Saffer, 2003, 2007).
Previous studies used the void ratio vs. log (�e) relationship inferred from
shipboard data from Site 1173 as a reference to estimate excess pore pressure for the
Nankai margin along the Muroto transect (Fig. 6A, Saffer, 2003, 2007). Estimated
pore pressure suggest a landward increase of 2.5-4.6 MPa for Site 1174 and 4-
5.5 MPa for Site 808 (Saffer, 2007). The determined overpressures have been
assumed from rapid sedimentation and thickening of the prism toe and poor drainage
of the sediments. From numerical simulations that take into account the thermal state,
Gamage and Screaton (2006) conclude that rapid trench sedimentation and prism
thickening may be insufficient to explain the high pore pressures reported from
previous studies. Sedimentation of trench wedge facies and thickening of the prism
toe lead to an increase in sediment thickness above the basin hemipelagites to 483 m
at Site 1174 and 620 m at Site 808 (Taira et al., 1991; Moore et al., 2001), which
correspond to a load of ~4 MPa and ~5.5 MPa respectively. This suggests that in the
CHAPTER 4: MANUSCRIPT 1 40
deeper parts of the LSB the additional load is either to small to create the excess pore
pressure or totally taken up by the pore water. In the latter case no reduction in void
ratio can occur under these circumstances and void ratios of all Sites should be the
same. However, comparing the top and the bottom of the underthrust section of LSB
shows that void ratio is smaller for Sites 1174 and 808. Thus, the LSB has undergone
consolidation and partial drainage must have reduced the excess pore pressure. We
revisit the problem using the considerations from our thermal experiments.
Consolidation for Site 1173 is governed by low sedimentation rates and high
temperatures for the projected underthrust sequence (~75–105 °C, Fig 1B). Its
downhole void ratio reduction is the result of mechanical, thermal and secondary
consolidation. With beginning underthrusting at Site 1174 and 808 loading rates
increase dramatically, which makes the sediment less prone for time dependent
secondary consolidation (creep). Further, temperature does not increase with depth
when compared to Sites 1174 and 808 (~87-107 °C) and accordingly, no thermal
consolidation takes place here. Without the additional strain of thermal and secondary
consolidation, we assume that consolidation does not follow the steep trend from Site
1173, but a less steep primary consolidation. Following these assumptions, the
consolidation state between Site 1173 and 1174 and 808 are compared at the top and
the base of the LSB (Fig. 6 B,C) where temperatures are similar, using our primary
consolidation data (Cc=0.99).
The primary consolidation results in lower excess pore pressures of 2.2 -
3.9 MPa for Sites 1174 and 3.0 - 4.9 MPa for Site 808 (Fig. 6 B,C). Although the
differences to the previous study are smaller than 1 MPa the new estimates are in
accordance with the general void ratio reduction. Lower pore pressures remain at the
top of the underthrust section, which points to an upward drainage (Fig. 6), probably
to a free drainage boundary along the decollement (Saffer, 2007). The pore water
expulsion at the top is also reflected in the greater void ratio. Between Sites 1174 and
808 excess pore pressure increases uniformly by ~1 MPa, suggesting that the
additional load of 1.5 MPa is largely taken up by the pore water. This is supported by
the fact that void ratio reduction is almost negligible at these Sites. Although these
excess pore pressure estimates are consistent with the observed void ratio reduction,
in-situ pore pressure data from A-CORK observations may be needed to bring
certainty into these estimates (e.g. Davis et al., 2006). The determined increase in
excess pore pressure is nonetheless in agreement with the assumption that pore
CHAPTER 4: MANUSCRIPT 1 41
pressures increase along the subduction thrust and, together with low basal friction,
are responsible for the small taper angle at the Muroto transect (Saffer and Bekins,
1998; Brown et al., 2003).
Fig. 6: (A) Schematic diagram illustrating our pore pressure estimates. When a load is applied (weight symbol) and no drainage occurs, the additional stress is taken up by the pore water without any reduction in void ratio (1�2). The total stress of (2) is �t=�e+P, and can be inferred from integrating the bulk density down hole. Thus, the excess pore pressure can be directly predicted from the shift relative to the reference line, where �t=�e. Depending on the drainage, the excess pore pressure may partially dissipate and hence cause a reduction in void ratio (3). (B) Previous studies reported the excess pore pressures P (shaded area) directly to the shift of Site 1173 data which is supposed to be normally consolidated (�t=�e). Our approach considers that no thermal or secondary consolidation takes place between the sites. Instead it resumes primary consolidation, which is modelled here exemplarily for the top and the base with a Cc of 0.99. Temperature corrected estimates are presented in (C,D) for Sites 1174 and 808, respectively, showing that excess pore pressures (shaded areas) are smaller. These pore pressures are consistent with the observed void ratio reduction between the sites.
CHAPTER 4: MANUSCRIPT 1 42
4.6 Conclusions Taken together our results, temperature has a veritable impact on the consolidation
behaviour of underthrust sediments from the Nankai margin, with increasing
temperature leading to an enhanced pore space reduction. This change seems to be
more pronounced for temperatures lower than 100 °C. By combining the observed
trends from consolidation tests with field-based data, we explain the consolidation of
the incoming Lower Shikoku Basin sediments as a complex combination of primary,
secondary and thermal consolidation. Besides the direct influence on consolidation,
temperature is the driving factor for the smectite-to-illite reaction, connected with a
change in consolidation behaviour and possibly facilitated by lithification downslab.
Based on our findings, estimated excess pore pressure for the Nankai Trough are
found significant lower than previously believed, so that overall our results have
profound mechanical implications for IODP NanTroSEIZE (Nankai Trough
Seismogenic Zone Experiment) drilling project to the seismogenic zone.
Acknowledgments
We thank Jill Weinberger for her assistance with some of the experiments and
Kevin Brown for providing laboratory space. Christoph Vogt is thanked for XRD
analyses. Samples and data used in this study have been provided by the Ocean
Drilling Program (ODP). ODP was sponsored by the U.S. National Science
Foundation (NSF) and participating countries under management of Joint
Oceanographic Institutions (JOI). This paper benefited from the discussion with
Demian Saffer and numerous other colleagues working off Japan. Funding was
provided to AK by the German science foundation (project KO2108/4-1).
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CHAPTER 4: MANUSCRIPT 1 46
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CHAPTER 5: MANUSCRIPT 2 48
Chapter 5: Manuscript 2
Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – a case study
from the Nankai margin
A.Hüpers1, S.Kreiter1 and A.Kopf1
1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany.
Marine and Petroleum Geology (submitted)
Abstract
The recovery of drilling cores involves changes in pressure and temperature conditions, which alter the mechanical properties of unlithified sediments. In particular, high in-situ temperatures have to be regarded for the interpretation of geotechnical tests conducted at standard ambient temperature conditions and especially for the inferred consolidation state. So far, the interpretation of the consolidation state of the Lower Shikoku Basin facies (LSB) entering the accretionary Nankai margin is ambiguous. Laboratory consolidation test results show a high stiffness, which was interpreted as hardening caused by cementation, while the field-based depth trend of porosity points towards normal consolidation. As an explanation for this discrepancy, the change of the mechanical properties by cooling from in-situ to laboratory conditions is proposed. The results of a thermo-mechanical model are compared to published field data. This comparison suggests that the observed hardening is at least partially an artefact from temperature change during core recovery, and that the strata can be considered normally to only slightly cemented. This normal consolidation state, together with other recent geotechnical studies on the incoming sediments, reveals that the LSB is the primary candidate for decollement development at the Nankai margin.
CHAPTER 5: MANUSCRIPT 2 49
5.1 Introduction Physical properties can serve as proxies for composition, formation and stress
state of the sediment (Casagrande, 1936; Blum, 1997). While some physical
properties can be determined by logging-while-drilling others have to be determined
from core samples. Unfortunately, the sampling leads to changes in pressure and
temperature conditions and thus to sampling artefacts in unlithified sediments. The
pressure release during sampling causes an expansion due to elastic recovery, gas
expansion and mechanical stretching. These effects are widely documented and can
be estimated from laboratory consolidation tests (e.g. Karig and Hou, 1992; Blum,
1997). However, temperature induced artefacts are often ignored although
temperature induced changes may have a severe impact on geotechnical testing
(Campanella and Mitchell, 1968, Sultan et al., 2002).
At the Nankai margin southeast of Japan (Fig. 1), the incoming sediments are
subjected to high in situ temperatures with basement temperatures up to ~110 °C
along its central portion off Cape Muroto (Taira et al., 1991; Moore et al., 2001a). The
consolidation state of these sediments is important for the development of the
decollement zone, which separates frontally accreted from underthrust sediments. The
decollement zone forms along intrinsically weak layers in the incoming sequence such
as clay-rich sediments or underconsolidated layers with excess pore pressure (Moore,
1989). Rapid sedimentation of well-drained turbidites in the trench may cause such
excess pore pressure within the less drained underlying hemipelagic sequence and
make especially its uppermost part prone to decollement formation (Le Pichon et al.,
1993). In contrast, the decollement formation within the incoming Lower Shikoku
Basin facies (LSB), is neither associated with the intrinsically weakest layer
(Underwood, 2007) nor do samples from the LSB exhibit underconsolidation during
laboratory reconsolidation (Morgan and Ask, 2004; Bellew, 2004). Instead, tested
samples show a high stiffness, which was interpreted to be caused by matrix
cementation (Morgan and Ask, 2004; Morgan et al., 2007).
Instead of cementation, thermal hardening is another explanation to cause high
stiffness’s at standard conditions. This possibility has not been tested for subduction
zone settings, so far. Thermal hardening occurs during cooling (Sultan et al., 2002)
and may influence samples from “hot” in-situ conditions such as the Nankai Trough.
Here, we test if the observed stiffness of samples from the LSB succession off the
CHAPTER 5: MANUSCRIPT 2 50
Nankai margin can be explained by thermal hardening. We apply an up-to-date
thermo-plastic model to estimate the shift in pre-consolidation stress due to
temperature differences between in-situ and laboratory conditions. The results are
compared with published consolidation data, and their implications for stress state of
underthrust sediments as well as decollement location are being discussed.
Fig. 1: (A) Map of the Nankai Trough subduction zone and ODP (Ocean Drilling Program) drill site locations off SW Japan. Grey corridor indicates location of interpreted seismic reflection profile shown in Fig. 2.
5.2 Geology of Nankai margin The Nankai margin is located off SE Japan where the oceanic Philippine Sea
plate is subducted to the northeast beneath the Eurasian plate at a rate of ~4 cm/a
(Karig and Angevine, 1986; Fig. 1). Most of the incoming sedimentary sequence is
scraped off, which has led to a wide accretionary prism (Fig. 2). This study focuses on
Site 1173 located 11 km seaward of the deformation front, which was drilled during
Ocean Drilling Program (ODP) Leg 190 as a tectonically undisturbed reference site of
the incoming sequence (Moore et al., 2001b; Fig. 2). The temperature at Site 1173
increases rapidly with depth towards a basement temperature of ~110 °C (Fig. 2),
because of an ancient spreading ridge and the recently active volcanic Kinan
seamount chain nearby (Taira et al., 1991; Moore et al., 2001b).
At ODP Site 1173, the uppermost sandy trench-wedge facies follows a normal
consolidation curve of decreasing pore space (Fig. 2B). Across the underlying Upper
Shikoku Basin facies (USB), the porosity remains nearly constant. p-wave velocity for
the USB suggests a normally consolidated trend down to 230 mbsf, while from 203 to
343 mbsf p-wave velocity is abnormally high (Spinelli et al., 2007). A laboratory
CHAPTER 5: MANUSCRIPT 2 51
reconsolidation test showed a typical consolidation curve for cementation which has
been confirmed by the detection of opal-CT cements identified by SEM (Spinelli et
al., 2007).
Underneath, the Lower Shikoku Basin facies (LSB) resumes a normal, uncemented
trend of porosity (Fig. 2). The reconsolidation of undisturbed specimens from this
section exhibits high pre-consolidation stress, which has been interpreted as matrix
strengthening by authigenic clay cementation (Morgan and Ask, 2004). In contrast,
the decrease in porosity with depth as well as with p-wave velocity has been assumed
to be a normal consolidation pattern without cementation (Moore et al., 2001b;
Screaton et al., 2002; Saffer, 2003; Spinelli et al., 2007).
Fig. 2: (A) Cross section after Morgan and Ask (2004) through the Shikoku Basin and Nankai forearc off the Shikoku Island, Japan and (B) porosity depth (diamonds) and temperature profile (dashed line) for ODP Site 1173 after Moore et al. (2001a).
5.3 Methods 5.3.1 Consolidation and pre-consolidation stress determination
During burial the overburden stress (�t) from an overlying sediment pile is
taken up by the vertical effective stress (�e) acting on the mineral framework and the
pore water pressure in excess of the hydrostatic pressure (P).
�t = �e+P [1]
CHAPTER 5: MANUSCRIPT 2 52
The maximum effective stress �e a sediment has experienced in the past is
termed pre-consolidation stress p’c. It can be determined in laboratory reconsolidation
tests by determining the transition of elastic to plastic deformation (Casagrande, 1936;
Fig. 3A). If the maximum effective stress is p’c = �t, the in-situ stress state is termed
normal consolidated. High loading rates and low permeability often lead to
considerable pore water pressure over geologic timescales and reduce the effective
stress. In this case the determined pre-consolidation stress is smaller than the total
stress. This consolidation state is referred to underconsolidated, which implies that
P>0. For the case that the maximum effective stress p’c is greater than the total stress,
erosion of the overlying sediment can be responsible for the enhanced stiffness. Other
possibilities for a high stiffness of sediments can also be cementation and thermal
hardening (Fig. 3; Burland, 1990; Sultan et al., 2002).
Fig. 3: Schematic consolidation test results of strain measurements vs effective stress. (A) Pre-consolidation stress (white arrow) determination after Casagrande (1936) with minimum and maximum range (dark arrows). Also indicated are the elastic portion and the plastic portion of mechanical behaviour, which are described by the slope Ce and Cc, respectively. (B) Results from Sultan et al. (2002) showing the increasing pre-consolidation stress with decreasing testing temperatures of Boom clay, which was loaded to 4 MPA (dashed line) and 100 °C before reloading. (C) Consolidation is described in the Cam Clay model as specific volume vs mean effective stress with primary consolidation given by � and the elastic value by �.
5.3.2 Temperature sensitivity of pre-consolidation stress and model
To describe soil (or unlithified sediment) consolidation and deformation in
civil engineering an elastoplastic constitutive model, the modified Cam-Clay model,
has been developed (e.g. Schofield and Wroth, 1968). However, this model does not
take the soil’s response to temperature into account which is exemplarily shown in
CHAPTER 5: MANUSCRIPT 2 53
figure 3B. For a normally consolidated soil the grain skeleton is in equilibrium with
the applied load. During heating the interparticle shear resistance decreases and the
sediment is compressed until enough interparticle bonds are formed to carry the stress
at the increased temperature (Mitchell and Soga, 2005). During cooling the
interparticle shear resistance recovers and the additional bonds formed during heating
increase the stiffness of the sediment (cf. Fig. 3). This hardening factor model was
first incorporated into the modified Cam-Clay model by Hueckel and Baldi (1990).
Based on their work, Picard (1994) introduced a simpler modification for the
hardening which provides very satisfactory predictions concerning the hardening
behaviour of boom clay (Sultan et al., 2002):
�T���
e+p'=p' p
0labcsituinc �
��
���
13exp__ [2]
Where p’c_in-situ is the pre-consolidation stress at in-situ temperatures and p’c_lab
is the pre-consolidation stress at standard conditions; e0 is the initial void ratio (void
ratio = volume ratio of pore space and solids), � is the slope of the plastic
consolidation curve and � is the slope of the elastic rebound curve (cf. Fig. 3C) in the
in the cam clay model (Schofield and Wroth, 1968). �T refers to the temperature
difference between in-situ and standard conditions and ap is a positive scalar
coefficient.
5.3.3 Model inputs
We took in-situ data to determine the expected thermal hardening caused by
temperature differences between in-situ and ambient laboratory conditions. Thus, we
calculated the expected pre-consolidation stress at room temperature p’c_lab. For the
model we assume that the in-situ LSB is normal consolidated as proposed by various
authors (Moore at al., 2001b; Screaton et al., 2002; Saffer, 2003; Spinelli et al., 2007).
Thus, the pre-consolidation stress at in-situ temperatures p’c_in-situ is equal to the total
stress �t and can be calculated from the density-depth trend of Site 1173 shipboard
measurements. To get the best in-situ estimates for e0, standard shipboard data (Moore
et al., 2001a) has been corrected for rebound (4.5% e/MPa from Morgan and Ask) and
CHAPTER 5: MANUSCRIPT 2 54
temperature dependent volume change of pore water and soil grains (Campanella and
Mitchell, 1968; Sun et al., 2008).
The reconsolidation data of LSB sediments show a great variability for elastic
(Ce) and plastic (Cc) compression indices (Tab. 1; Bellew, 2004; Morgan and Ask,
2004). Cc and Ce are defined for the change of void ratio e in the vertical stress
regimes (�v), while � and � in the model are defined as the change of the specific
volume (�=1+e) with the mean effective stress �’m=1/3(�’1+2*�’3) (�’1 = maximum
effective stress; �’3 = minimum effective stress; (cf. Fig. 3C; e.g. Azizi, 2000).
Vertical and mean effective stresses in a compression test are directly related by earth
pressure at rest K0 = �’3/�’1, which has been determined for Site 1173 LSB by
Morgan and Ask (2004). The ratio is constant with a value of Kop=0.79 for the plastic
deformation and Koe=0.49 for the elastic deformation. The resulting � and � data are
given in Tab.1. We consider the variability of the consolidation data by taking the
data from the tests with the lowest and the highest values of compression indices (cf.
Tab. 1). The value for p=1.10-4K-1 has been taken from Boom clay (Sultan et al.,
2000), because of the similar mineralogy. Both sediments are composed of smectite,
illite and quartz in similar proportions (cf. Underwood, 2007; Baldi et al., 1988).
Therefore the Boom clay value may be considered as a suitable approximation. To
determine �T a linear temperature increase with depth between 65 °C for the top of
the LSB and 105 °C for the bottom is assumed (cp. Fig.2B).
Tab.1: Consolidation data of LSB sediments at site 1173 and calculated slopes of primary consolidation � and elastic values �. All pre-consolidation stresses are determined after Casagrande (1936). Asteriks marks the considered threshold model inputs for the study. See text for explanations.
Data source Depth (mbsf) p’c (MPa) Cc Ce � � Bellew (2004) 391.3 3.17 0.27 0.014 0.117 0.006 Bellew (2004) 443.7 5.69 0.27 0.032 0.117 0.014 Morgan and Ask (2004)* 476 6.10 0.99 0.045 0.423 0.020
Bellew (2004)* 529.6 6.21 0.18 0.023 0.078 0.010
CHAPTER 5: MANUSCRIPT 2 55
5.4 Results In the following the results of the modelling of the thermal hardening for the
LSB at Site 1173 is presented as pre-consolidation stress p’c_lab and compared to (1)
laboratory derived pre-consolidation stresses p’c by Bellew (2004) and Morgan and
Ask (2004) and (2) the effective stress at normal consolidation state and at in-situ
temperatures.
When fluid overpressuring can be neglected, as we assume it for Site 1173, the
calculated stress equals the effective stress (�t=�e). The total stress �t can be
calculated by integrating the bulk density downward in the hole and subtracting the
hydrostatic pressure produced by the water column of the respective height. The
effective stress determined in this way for the LSB at Site 1173 is shown in figure 4A
plotted against increasing depth and ranges from 2.01 to 5.3 MPa. All laboratory pre-
consolidation stresses p’c determined by Bellew (2004) and Morgan and Ask (2004) at
room temperature plot right of the line showing the above stated high stiffness of the
samples.
Fig. 4: (A) Depth vs. effective stress at in-situ temperature (diamonds) for the LSB at Site 1173 and laboratory pre-consolidation stress (triangles) determined by Bellew (2004) and Morgan and Ask (2004) with range of error; (B) modelled pre-consolidation stresses at room temperature due to thermal hardening for Site 1173 based on model inputs from the sample with the highest � (squares) and (C) the sample with the lowest � (circles). See text for further explanations. The shaded area marks the projected decollement.
CHAPTER 5: MANUSCRIPT 2 56
The results of the modelled thermal hardening are shown in figures 4B and 4C
as pre-consolidation stress p’c_lab. The model with the high � and � are derived from
Morgan and Ask (2004) (cf. Tab. 1) show lower pre-consolidation stresses than the
laboratory determined pre-consolidation stresses (Fig. 4B). After this model the
deeper samples show a higher stiffness with an excess compressive strength of 2.2 to
2.6 MPa and the sample from 391 mbsf is slightly stiffer.
The modelled thermal hardening using lowest � and � (cf. Tab. 1), are shifted
further to higher stresses (2.9 to 7.58 MPa; Fig. 4C). After this model the laboratory
derived pre-consolidation stresses of Bellew (2004) and Morgan and Ask (2004) show
rather good accordance with the predicted thermal hardening. The deviations are
rather small and in a range of -0.2 MPa and +1.4 MPa. The uppermost sample appears
even slightly underconsolidated in this model, while the other samples can be
considered slightly stiffer than expected for normal consolidation.
5.5 DiscussionThe two considered models yield very different thermal hardening because of
the underlying consolidation data. The model with the higher plastic compression
index expects only slight thermal hardening compared to the normal consolidation
state inferred from the shipboard data (Fig. 4B). Although a high compression index
can also be inferred from shipboard measurements (Saffer, 2003), the majority of the
consolidation data show low compression indices (cp. Tab.1). Because of the varying
compression indices with depth the average values of both models may be the best
possible representative. Regarding an average deviation of 0.2 MPa to +2 MPa and
the uncertainty of laboratory pre-consolidation stress determination (Fig. 4; Saffer,
2003), these average values imply that the LSB sequence is normally consolidated in
the upper part and while the observed stiffness for the deeper part is smaller than
previously believed. The slightly higher stiffness may be explained by a minor
cementation in contrast to the previously proposed moderate cementation of Morgan
and Ask (2004). Thus, thermal hardening due to cooling during recovery explains the
observed stiffness response of the specimen at room temperature.
The stratum being normally consolidated to slightly cemented indicates that,
despite the high sedimentation rate of the overlying trench turbidites (450-650 m/Ma.
[Moore et al., 2001a]), there is no excess pore pressure to hinder or delay
CHAPTER 5: MANUSCRIPT 2 57
consolidation. On the other hand, strengthening due to cementation seems to be
negligible or very weak. Although, the large secondary porosity and enhanced
stacking of clay minerals points to cementation (Morgan and Ask, 2004; Ujiie et al.,
2003), only a minor amount of cement may be present, because of the lack of direct
evidence from SEM analysis (Spinelli et al., 2007). An additional argument against a
moderate cementation is the lack of a typical cementation trend in the reconsolidation
curve of LSB samples; for typical cementation curves see Burland (1990). Thus, the
consolidation state of underthrust sediments at ODP Site 1173 can be explained by
loading and the ambient temperature. Elevated temperature may also facilitate
secondary consolidation (creep), which may explain differences between laboratory
and field consolidation curves and may be in this case responsible for the slightly
overconsolidation (Karig and Ask, 2003; Mitchell and Sago, 2005). Previously
contradictory results based on seismic velocity data (Spinelli et al., 2007) and
laboratory tests (Morgan and Ask, 2004) have here been mated for the first time by
incorporating temperature effects on consolidation.
5.6 Implications In the past, the different perceptions of the cementation and consolidation state
led to different interpretations of the stress state of the underthrust sequence and thus
decollement location. Screaton et al. (2002) and Saffer (2003) observed a lack in
consolidation of the underthrust sequence (LSB) for drill sites at the toe of the prism
(ODP Sites 1174 and 808; Fig. 2) compared to Site 1173. They concluded that this is
the result of excess pore pressure created by rapid loading of overlying prism and
poor drainage because of low sediment permeability. High pore pressures hinder
compressive strengthening of the sediment and may control the development and
downstepping of subduction thrust faults (Moore, 1989; Saffer, 2007).
Based on previous interpretation of laboratory consolidation data, the
proposed excess strength due to cementation of the underthrust section by Morgan
and Ask (2004) may also explain the position of the fault. In this case, the
decollement forms preferably in the overlying sediments, which are not hardened by
cementation. Downstepping of the decollement may occur in this scenario when the
enhanced strength due to the cementation is overcome by mechanical load (Morgan
CHAPTER 5: MANUSCRIPT 2 58
and Ask, 2004). However, our data do not support the hypothesis for the decollement
location above a moderately cemented section.
In the following arguments will be discussed for evolution of the decollement
zone in the uppermost part of the LSB at the Nankai margin. It is generally agreed that
the decollement zone forms preferably in a layer with low intrinsically shear strength
or high excess pore pressure (Moore, 1989; Brown et al., 2003). According to the high
average sedimentation rate of the trench turbidites, up to ~1100 m/Ma between Sites
1173 and 1174 (Screaton et al., 2002), the excess pore pressure in the underlying low
permeable hemipelagites should be increased (Moore, 1989). Modelling of this
scenario by Le Pichon et al. (1993) showed that the lowest effective stress is in the
uppermost part of the less drained hemipelagites. For that reason the subduction thrust
fault along the Nankai Trough should be located rather in the Upper Shikoku Basin
facies (USB) than in the LSB (Fig. 2). Instead, opal cementation processes strengthen
the USB sediments and preserve high porosity of >55 % (Spinelli et al., 2007).
Because of this, the formation of excess pore pressure occurs more likely in the
underlying LSB. In addition with the predominant clayey lithology and a rather weak
cementation, LSB sediments may be considered as the weakest portion of the
incoming sequence (Brown et al., 2003). The low effective stresses and low friction
coefficient of clays (Brown et al., 2003) makes them the primary candidate for the
generation of the decollement zone at the Nankai Trough. This is indicated by the
dashed line for the outward-migrating proto-thrust in figure 2A. Progressive
underthrusting may cause the pore pressure to increase, and may hinder further
compressive strengthening of the sediment. This interpretation is in accordance with
previous studies of Saffer (2003) and Screaton (2002) that pore pressures increase in
the underthrust sediments from Site 1174 to Site 808. This would eventually allow
downstepping of the subduction fault deeper into the underthrust sequence, a
phenomenon observed in other subduction systems (Saffer, 2003) and inferred for the
deeper portion of the Nankai plate boundary megathrust off the Kii Peninsula (Moore
et al., 2007).
Acknowledgements
Data used in this study have been provided by the Ocean Drilling Program
(ODP). ODP was sponsored by the U.S. National Science Foundation (NSF) and
CHAPTER 5: MANUSCRIPT 2 59
participating countries under management of Joint Oceanographic Institutions (JOI).
Funding was provided by the German Science Foundation (project KO2108/4-1).
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CHAPTER 5: MANUSCRIPT 2 61
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Columbia University Press, New York, pp. 42-85.
CHAPTER 6: MANUSCRIPT 3 62
Chapter 6: Manuscript 3
The interaction of underthrust sediments with seawater – an approach by hydrothermal consolidation testing
A.Hüpers1, A.Kopf1, W.Bach2 and M. Zabel1
1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany. 2Department of Geosciences, University of Bremen, P.O. Box 330440, 28334 Bremen, Germany.
Geochimica et Cosmochimica Acta (submitted)
Abstract
Geochemical, thermal and mechanical processes are closely interrelated at active convergent margins. To shed light on this linkage hydrothermal water-rock interaction has been studied by means of heated consolidation tests. Sediment samples representing end member mineralogical compositions at the Western Nankai subduction zone have been loaded to effective stresses of up to 70 MPa at temperatures of 20 °C, 100 °C and 150 °C and expelled fluids were analyzed for pore water geochemistry. We show that consolidation directly influences pore water constituents in our experiments. The onset of expulsion generally leads to a transient increase of solutes and with ongoing consolidation the smectite-rich sample shows a depletion of predominantly alkaline and earth alkaline elements. This process is governed by the consecutive release of free pore water and the residual water from the overlapping double layer of smectite. Increasing temperature generally leads to the enrichment of K, Ba and Si and to the depletion of Mg. The review of the literature indicates that the majority of investigators agree that this can be inferred from a changing ion exchange capacity of the sediment. Only the test at 150 °C shows hints for precipitation of sulphates. We suggest that stress depended observations have little geological relevance due to the necessary smectite abundance at depth but temperature related release of solutes may facilitate cementation of underthrust sediments and thus elastic strain accumulation for seismic slip.
CHAPTER 6: MANUSCRIPT 3 63
6.1 Introduction At convergent margins water enters as pore fluid trapped between the particles
or bound in hydrous minerals as an integral part of the subduction inputs. To a greater
extent, the interstitial water will be expelled from the compacting sedimentary
sequence within 3-4 km of burial depth and may impact ocean geochemistry (Bray
and Karig, 1988, Moore and Vrolijk, 1992). Fluid expulsion occurs in this realm as
dispersed flow if the rate of pore fluid flow is sufficiently low and advection can be
accommodated by intergranular permeability (Carson and Screaton, 1998) or as
focused fluid flow along permeable layers such as fault zones (Moore and Vrolijk,
1992; Carson et al., 1994). However, a small fraction of the fluid will be buried with
the sediment to greater depth and thus subjected to the crust and mantle.
The geochemistry of interstitial water at convergent margins is initially close
to seawater and is subsequently affected by mineral dehydration, fluid-mineral
exchange reactions, diffusion-advection and the style of feeding from internal and
external fluid reservoirs (Kastner et al., 1991; Moore and Saffer, 2001). Mineral
transformation causes dehydration processes and has been used to explain the
omnipresent fluid freshening reflected by low-Cl anomalies at convergent margins
(Kastner et al., 1991; Silver et al., 2000; Kopf et al., 2003). This may derive especially
by smectite-to-illite and opal-A-to-quartz transition (e.g. Kastner et al., 1991, Moore
et al., 2001). Dehydration leads to eminent pore pressure generation which has been
postulated to influence fault strength and strain localization of the decollement (e.g.
Moore, 1989), as well as taper angle of accretionary wedges (e.g., Hubbert and
Rubey, 1959; Davis et al., 1983; Saffer and Bekins, 2002). At temperatures of 75–
175 °C carbonate, clay and zeolite cementation may occur (Moore and Saffer, 2001
and references therein) fostering the lithification of the sediments and eventually
allowing accumulation of elastic strain for seismic slip (Moore and Saffer, 2001).
Thus, a detailed insight on water-rock interaction may shed light on the linkage
between mechanical, thermal and geochemical processes within the shallow
subduction zone.
Studying alteration of marine sediment and its interstitial water towards
diagenesis may be complicated when past temperatures and pressures conditions are
unknown or complicated (Rosenbaum, 1976). To overcome this problem controlled
laboratory methods have been applied to study the alteration of marine sediments and
CHAPTER 6: MANUSCRIPT 3 64
its pore waters in the last decades. Fluid-rock interaction has been most notably
studied in rocking autoclaves at constant isotropic pressures of several hundreds bars
and constant water-rock ratios (r>1) at temperatures of T>>200 °C (e.g. Thornton and
Seyfried, 1985; You et al., 1996; You and Gieskes, 2001). Sampled fluids from these
experiments reveal uniform depletion of Mg and sulphate whereas K, SiO2, B and Li
are increased. Further, the mobilization of volatiles (B and NH4) and incompatible
elements (As, Be, Cs, Li, Pb, Rb) is determined in hydrothermal experiments at
temperatures of ~ 300 °C. You et al. (1996) suggest a linkage between observed
mobility and deep arc magma generation in subduction zones. The observed
hydrothermal fractionation of Pb/Ce, La/Ba, Rb/Cs, B/Nb, and B/Be during these
experiments might explain the ratios in arc and maybe in hotspot lavas (You et al.,
1996). However, the set-up of rocking autoclaves includes several shortcomings
compared to burial conditions of natural sediments. It neglects that the applied load of
the overlying sediment pile is compensated according to the effective stress law. The
effective stress is the part of the total stress that is directly acting on the mineral
framework. Under undrained conditions such as in a rocking autoclave the applied
pressure is taken up mainly by the pore water suggesting low effective stresses. In
contrast to the autoclave experiments, the water-rock ratio is in nature constantly
changing with burial depth and can be considered smaller than 1.
To overcome the above mentioned shortcoming we chose the set-up of a
backpressured uniaxial consolidation apparatus (hydrothermal oedometer), which may
better simulate burial conditions. We modified a high capacity consolidometer to
facilitate hydrothermal conditions and to provide a larger spectrum of pressure (P) and
temperature (T) conditions than previous studies with similar apparatuses (e.g.
Chiligarian et al., 1973, Rosenbaum, 1976). The hydrothermal consolidation tests
were conducted up to pressure and temperature conditions equivalent to the upper
limit of the seismogenic zone. Specimens used were marine sediments of different
mineralogical end member composition from the Nankai Trough subduction zone,
(Japan). We analyzed fluids expelled from the compaction tests at 20 °C, 100 °C and
150 °C to evaluate potential fluid-rock interaction at low PT conditions in the shallow
subduction zone.
CHAPTER 6: MANUSCRIPT 3 65
6.2 Sampling site and sample description 6.2.1 Sampling site
For the proposed study we focus on natural samples from the Shikoku Basin.
Although more complex to study than defined mixtures of a few standard materials,
results may be more comparable to studies from field measurements. The Shikoku
Basin is part of the Phillipine Sea plate, which is being subducted to the northwest
under the Eurasian plate at a rate of 2-4 cm/yr almost perpendicular to the Nankai
Trough along Southwest Japan (Fig. 1; Karig and Angevine, 1986). The abundant
influx of terrigeneous sediments from the north led to a huge thickness (up to 1.5 km)
of basin sediments which taper of to the SE. A large part of the sediment pile is
scraped off which led to the built-up of a broad accretionary prism.
Fig. 1: (A) Map showing DSDP and ODP drillsites off Shikoku Island, which lie on two transects perpendicular to the trench. (B) Samples for hydrothermal deformation experiments were selected from Lower Shikoku Basin Facies of DSDP Site 297 (modified after Brown et al., 2003). Smectite-rich clay (N13) is has been sampled from 506.83 mbsf and illite-rich silty clay (N14) from 507.12 mbsf
Samples derive from DSDP (Deep Sea Drilling Program) Site 297 (Fig. 1A,B)
where 679.5 m of the 780 m thick sedimentary cover was penetrated during Leg 31
(Karig et al., 1975). It is located ~100 km SE of the Nankai margin and can be
considered as a tectonically undisturbed reference site. Selected samples are taken
from the Lower Shikoku Basin facies (LSB), which comprises the bulk of underthrust
sediments with the projected decollement slightly beneath the lithological boundary of
the Upper Shikoku Basin facies (USB) and the LSB (Fig. 1B). Across the LSB facies
CHAPTER 6: MANUSCRIPT 3 66
the smectite content increases dramatically to the base of the LSB (~50 to 20 wt-%)
whereas the general clay content increases only slightly (~60 to 50 wt-%; Fig. 1B).
This trend is similar to what has been observed at ODP Site 1177, which is 87 km
northwest (i.e. trenchward) of Site 297 (Brown et al., 2003). The mineralogical
variation might be due to variable fluxes of illite and chlorite from SW Japan relative
to volcaniclastics and smectite derived from the Izu-Bonin arc (Underwood and
Pickering, 1996; Underwood and Steurer, 2003). Although heat flow near the seafloor
is elevated (130-200 mW/m2 [Karig et al., 1975; Yamano et al., 1992]) relative to Site
1177, smectite contents in the deeply buried LSB at Site 297 are not significantly
lower than at Site 1177 and thermal alteration seems to be negligible (Brown et al.,
2003).
6.2.2 Selected samples
On the basis of published XRD-results (Underwood et al., 1997; Brown et al.,
2003; Fig. 1) we selected clay-rich end member lithologies of the incoming LSB. The
samples comprise a smectite-rich clay (N13, 506.83 mbsf) and an illite-rich silty clay
(N14, 507.12 mbsf). The smectite-rich clay is abundant in the lower part of the
Shikoku Basin Facies and may present unaltered sediment input. Sample N14 is more
illite rich and thus may shed light on water-rock interaction of a sediment at the updip
limit of the seismogenic, which has already undergone illitisation. This sample
selection enables us to compare water rock interaction of sediment of different
diagenetically stages, since reaction kinetics are to slow to generate abundant
illitisation at the temperatures during our experiments (Huang et al., 1993). Sub-
samples have also undergone quantitative XRD examination after Vogt et al. (2002) at
the University of Bremen to confirm the proposed end member clay mineralogy (Tab.
1). The results indicate variations of mainly smectite [Sm], illite [Il], and a granular
fraction of quartz [Qtz] and feldspar [Fsp]. As expected, sample N13 is a clay with a
high smectite fraction while sample N14 is silty clay with dominantly illite, quartz
and feldspar. However, grain size distribution is significantly different and may
influence water-sediment interaction due to differences in the specific surface area.
CHAPTER 6: MANUSCRIPT 3 67
Tab. 1: Results from quantitative XRD showing major mineral content (Qtz=quartz, Fsp=feldspar, Sm=smectite, Mont=montmorillonite, Il=illite, Musc=muscovite, Chl=Chlorite).
Qz + Fsp Sm + Mont Il + Musc Chl Mixed layer clays otherNan14-20 49.1 4.0 29.9 1.6 1.7 13.7 Nan14-100 44.2 6.6 27.0 2.6 6.6 13.0
Nan13-20 5.7 43.5 0.0 2.0 35.6 13.2 Nan13-100 9.2 56.3 19.9 0.0 12.9 1.7 Nan13-150 15.1 43.3 8.4 1.9 18.2 13.1
6.3 Methods 6.3.1 Mechanical compaction and set-up
The compaction of the sediments was conducted in a custom-built high
capacity oedometer. Compared to the rocking autoclave system (e.g. Seyfried et al.,
1979) the sediment is allowed to consolidate in this device. In this study consolidation
refers to the settlement a sediment experiences as a result of an applied normal load.
Settlement can only occur when pore water is expelled. Thus, consolidation is time
dependent, a function of the permeability, dependent on the length of the drainage
path and the compressibility of the sediment (Terzaghi and Peck, 1948). The total
stress �t applied can be differentiated between the stress that is taken up by the water
(excess pore pressure P) and the mineral framework (effective stress �e).
�t = �e + P [1]
During consolidation the pore volume decreases. Following Terzaghi and Peck
(1948) the pore space reduction (presented as void ratio = volume voids/volume
solids) can be described as a linear function of the logarithm of the effective stress.
Thus, the data of increasing effective stress presented in this study is related to a
reduction in pore space. The specific consolidation is material dependent and
described for the very same samples by Hüpers and Kopf (EPSL, in press).
The setup of the oedometer (Fig. 2) consists of a piston situated within a
cylinder, which prevents the sample from lateral extension. A hydraulic press system
pushes the piston into the cylinder and compresses the sample. The sediment is
allowed to drain via a borehole in the piston. To the borehole at the base of the
cylinder a Validyne differential pressure transducer (accuracy ±25 kPa) is attached to
measure the pore pressure. Stainless steel filter slabs prevent solids to get into the
bores. A backpressure regulator at the drainage outlet ensures a pore fluid pressure of
~500 kPa and suppresses pore water evaporation and degassing of trapped air in case
CHAPTER 6: MANUSCRIPT 3 68
of heated tests. To minimize interaction of the saturated sample with the equipment,
the consolidation cell was made of titanium (grade 2). Other components such as
tubing and fittings also consist of non-corrosive materials like high-grade stainless
steel, PTFE, or PP.
Fig. 2: Schematic setup of the hydrothermal consolidation apparatus. The sample (grey shaded area) is compressed in the cylindrical cell (1) due to the applied load on the upper piston (2) and a spacer (3). A backpressure regulator (4) maintains a fluid pressure of ~ 500 kPa in the system which is measured by a pressure transducer (5). The fluid pressure across the sample is measured by a differential pressure transducer (6). A temperature probe at the bottom of the cell has been used to determine the temperature and to control the bandheater (dark grey shaded).
For each run, a remoulded sample was disintegrated and re-hydrated with
seawater. After 24h the slurry was centrifuged and again re-hydrated. This procedure
was repeated 1-3 times. Thereafter, the sample was placed in the oedometer and
consolidation was started at a constant rate of strain (<0.0042 %/min) over a period of
3-5 months until approximately �e = 70 MPa were reached. Initial water-rock mass
ratios of ~2 were continuously reduced in the course of an experiment until they
approached ~0.1. The applied backpressure, shortening of the sample, applied load
and differential fluid pressure across the sample height was logged continuously
during each experiment. The pore fluid expelled during consolidation was collected in
flasks attached to the upper drainage. Sample height reduction has been measured
with a Burster displacement transducer (accuracy ±0.075 mm). The tests were
CHAPTER 6: MANUSCRIPT 3 69
repeated with aliquots of fresh specimen at constant temperatures if 20 °C, 100 °C and
150 °C. For the heated experiments, a band heater was placed around the
consolidation cell. Through a temperature probe in the base of the cell the heating was
controlled by a heating unit within a fluctuation range of 2 °C.
6.3.2 Chemical analysis
After detaching the flasks (each containing up to 4 ml fluid), the sampled
fluids were sealed, stored at ~4°C without further treatment and measured after
consolidation tests were completed. The collected fluids and the initial seawater were
analyzed for selected major and minor solutes. Cl and SO4 were measured with a
HPLC system with an anion separation column and indirect UV-detection at 288 nm.
Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Si, Sr and Ti had been measured by ICP-OES.
Samples had been diluted with acidified, deionised water for this analytical method at
a ratio of 1:10. Rb, Y, La, Ce, Yb, Lu, Pb, Th and U were analyzed by ICP-MS.
Samples had been diluted with acidified pure water at a ratio of up to 1:20 prior to
analyzing. The precision of is for all instruments <2 %. All data are reported in mg/l
except for ICP-OES and ICP-MS measurements which are given as ppb. The data
were normalized to the reactively conservative chloride, to minimize possible leakage
of the consolidation cell. All data are, nonetheless, included in table 2 for complete
documentation.
Concentrations are presented versus effective stress. The related stress value
corresponds to the average pore space that the sediment sample experienced between
mounting and removing a fluid sampling flask. According to the logarithmic
relationship of void ratio and effective stress, individual flasks recovered from the
early part of the consolidation tests span over a narrower effective stress range than
those later in the experiment. In consideration of the wealth of data and to avoid a
detailed description of the data on an element-to-element basis, we will focus our
discussion on first-order patterns in normalized element concentrations.
CH
APT
ER 6
: MA
NU
SCR
IPT
3
70
Tab.
2: M
easu
red
data
nor
mal
ized
to a
con
stan
t Cl o
f 186
00 m
g/L.
The
orig
inal
chl
orid
e va
lues
and
the
infe
rred
nor
mal
izat
ion
fact
ors
are
liste
d in
the
first
col
umns
. NN
stan
ds fo
r val
ues b
elow
det
ectio
n lim
it an
d N
D fo
r not
det
erm
ined
in th
e sp
ecifi
c an
alys
is.
P
oros
ity
(%/1
00)
Stre
ss
(MP
a)C
l (m
g/L)
no
rm.
Fact
or
Al (
mg/
L)
Ba
(mg/
L)
Ca
(mg/
L)
Fe (m
g/L)
K
(mg/
L)
seaw
ater
18
600
N
D
0.00
3 39
8 0.
08
393
N13
-20-
1 0.
79
5.88
E-0
5 35
986
0.51
69
3.95
0.
110
434
4.48
41
9 N
13-2
0-3
0.78
1.
88E
-04
4846
1 0.
3838
13
.48
0.12
4 56
5 2.
47
422
N13
-20-
5 0.
76
5.42
E-0
4 33
128
0.56
15
0.75
0.
053
544
0.05
35
4 N
13-2
0-7
0.75
1.
35E
-03
6579
8 0.
2827
0.
00
0.06
4 58
9 0.
13
368
N13
-20-
9 0.
74
3.25
E-0
3 37
331
0.49
82
0.20
0.
030
492
0.02
34
1 N
13-2
0-12
0.
71
1.40
E-0
2 45
097
0.41
24
0.13
0.
023
446
0.01
33
8 N
13-2
0-15
0.
68
6.22
E-0
2 40
097
0.46
39
0.09
0.
019
441
0.01
33
6 N
13-2
0-18
0.
65
2.55
E-0
1 40
399
0.46
04
0.06
0.
022
446
0.02
33
7 N
13-2
0-21
0.
60
1.02
E+0
0 62
671
0.29
68
0.09
0.
016
416
0.01
35
7 N
13-2
0-24
0.
56
2.72
E+0
0 45
652
0.40
74
0.09
0.
015
454
0.02
32
9 N
13-2
0-27
0.
52
7.00
E+0
0 43
808
0.42
46
0.11
0.
015
463
0.02
32
8 N
13-2
0-31
0.
43
2.94
E+0
1 33
242
0.55
95
0.16
0.
020
400
0.03
24
1 N
13-2
0-32
0.
40
4.37
E+0
1 74
349
0.25
02
0.09
0.
012
242
0.01
20
2 N
13-1
00-1
0.
77
6.07
E-0
6 40
453
0.45
98
8.66
0.
205
481
9.63
49
6 N
13-1
00-3
0.
77
1.11
E-0
5 53
082
0.35
04
2.45
0.
184
498
5.86
53
8 N
13-1
00-5
0.
76
2.53
E-0
5 65
562
0.28
37
0.03
0.
139
488
0.13
52
9 N
13-1
00-7
0.
78
4.94
E-0
6 68
233
0.27
26
0.13
0.
128
501
0.13
55
8 N
13-1
00-9
0.
74
1.10
E-0
4 37
874
0.49
11
0.22
0.
098
461
0.01
49
8 N
13-1
00-
13
0.72
5.
48E
-04
5624
4 0.
3307
0.
18
0.07
9 40
5 0.
03
492
CH
APT
ER 6
: MA
NU
SCR
IPT
3
71
Tab.
2: c
ontin
ued.
M
g (m
g/L)
Mn
(mg/
L)N
a (m
g/L)
S (m
g/L)
Si (
mg/
L)S
r (m
g/L)
Ti (m
g/L)
SO
4 (m
g/L)
seaw
ater
12
82
0.00
04
1027
3 88
8 2.
9 7.
83
ND
25
00
N13
-20-
1 13
10
NN
11
796
903
6.71
8.
61
0.29
6 54
75
N13
-20-
3 12
48
0.46
3 12
044
815
24.8
2 10
.92
0.01
7 42
55
N13
-20-
5 11
09
0.91
3 10
866
755
17.8
9 10
.80
NN
22
85
N13
-20-
7 12
07
NN
11
665
803
6.05
12
.33
NN
36
89
N13
-20-
9 11
58
NN
10
764
766
5.44
11
.16
NN
23
33
N13
-20-
12
1181
0.
025
1081
5 76
4 6.
18
10.2
3 N
N
2404
N
13-2
0-15
12
20
0.30
9 10
900
809
7.92
9.
18
NN
25
29
N13
-20-
18
1248
0.
325
1093
1 82
4 7.
66
9.41
N
N
2615
N
13-2
0-21
13
30
0.28
4 11
589
879
7.22
9.
65
NN
26
47
N13
-20-
24
1275
0.
482
1091
6 88
0 8.
22
9.80
N
N
2748
N
13-2
0-27
13
37
0.61
8 11
073
892
8.66
9.
80
NN
26
70
N13
-20-
31
1316
0.
745
1081
3 78
1 13
.05
8.36
N
N
2521
N
13-2
0-32
14
10
0.39
4 10
327
583
9.16
5.
57
NN
24
35
N13
-100
-1
1343
N
N
1256
5 89
8 29
.03
9.48
0.
184
5145
N
13-1
00-3
11
68
0.35
4 12
143
840
36.4
7 10
.58
0.06
6 41
36
N13
-100
-5
1098
N
N
1165
6 81
7 10
.22
10.8
3 N
N
3679
N
13-1
00-7
11
57
NN
12
015
852
7.42
11
.38
0.00
8 37
87
N13
-100
-9
1046
0.
134
1119
8 79
4 6.
15
10.4
8 N
N
2414
N
13-1
00-1
3 10
43
0.52
8 11
096
766
7.79
9.
59
NN
24
78
CH
APT
ER 6
: MA
NU
SCR
IPT
3
72
Tab.
2: c
ontin
ued.
Por
osity
(%
/100
)S
tress
(M
Pa)
Cl (
mg/
L)
norm
.Fa
ctor
A
l (m
g/L)
B
a (m
g/L)
C
a (m
g/L)
Fe
(mg/
L)
K (m
g/L)
se
awat
er
1860
0
ND
0.
003
398
0.08
39
3 N
13-1
00-1
7 0.
70
2.49
E-0
3 59
232
0.31
40
0.17
0.
070
409
0.00
50
4 N
13-1
00-2
1 0.
67
1.21
E-0
2 61
000
0.30
49
0.09
0.
070
424
0.53
48
9 N
13-1
00-2
8 0.
58
2.98
E-0
1 39
882
0.46
64
0.13
0.
074
454
0.02
48
9 N
13-1
00-3
0 0.
55
6.94
E-0
1 38
002
0.48
95
0.39
0.
078
463
1.20
49
3 N
13-1
00-3
4 0.
48
3.94
E+0
0 67
877
0.27
40
0.10
0.
084
440
0.04
47
4 N
13-1
00-3
5 0.
46
5.07
E+0
0 38
414
0.48
42
0.19
0.
096
479
0.01
47
7 N
13-1
00-3
6 0.
45
6.83
E+0
0 36
620
0.50
79
0.12
0.
093
507
0.02
48
1 N
13-1
00-3
8 0.
41
1.21
E+0
1 36
196
0.51
39
0.06
0.
109
499
0.02
46
7 N
13-1
00-3
9 0.
39
1.66
E+0
1 64
680
0.28
76
0.11
0.
111
497
0.01
47
1 N
13-1
00-4
1 0.
34
3.26
E+0
1 52
728
0.35
28
0.00
0.
071
476
0.02
38
5 N
13-1
50-5
0.
76
8.14
E-0
3 53
283
0.34
91
0.66
1.
047
613
0.19
62
4 N
13-1
50-7
0.
64
6.71
E-0
1 61
015
0.30
48
0.14
0.
274
610
0.10
59
7 N
13-1
50-9
0.
62
1.08
E+0
0 72
982
0.25
49
NN
0.
319
552
0.16
55
7 N
13-1
50-1
0 0.
60
1.53
E+0
0 66
867
0.27
82
NN
0.
360
515
0.14
55
3 N
13-1
50-1
1 0.
58
2.20
E+0
0 14
879
1.25
01
NN
1.
152
544
0.79
62
5 N
13-1
50-1
3 0.
54
4.43
E+0
0 68
356
0.27
21
NN
0.
438
475
0.11
54
1 N
13-1
50-1
4 0.
50
8.31
E+0
0 75
682
0.24
58
NN
0.
557
478
0.13
52
9 N
13-1
50-1
6 0.
45
1.56
E+0
1 60
609
0.30
69
0.07
0.
869
468
0.19
53
2 N
13-1
50-1
7 0.
42
2.05
E+0
1 12
416
1.49
81
NN
2.
329
374
2.97
63
3 N
13-1
50-1
8 0.
40
2.39
E+0
1 11
05
16.8
309
12.3
6 10
.372
17
9 77
.23
921
N13
-150
-19
0.36
3.
59E
+01
1014
18
.338
9 50
.88
6.03
2 35
2 95
.76
1161
N
13-1
50-2
0 0.
30
5.42
E+0
1 71
9 25
.867
3 20
1.25
7.
962
133
239.
32
1121
CH
APT
ER 6
: MA
NU
SCR
IPT
3
73
Tab.
2: c
ontin
ued.
M
g (m
g/L)
M
n (m
g/L)
N
a (m
g/L)
S
(mg/
L)
Si (
mg/
L)
Sr (
mg/
L)
Ti (m
g/L)
S
O4
(mg/
L)
seaw
ater
12
82
0.00
04
1027
3 88
8 2.
9 7.
83
ND
25
00
N13
-100
-17
1054
0.
492
1117
3 79
7 10
.76
9.01
N
N
2299
N
13-1
00-2
1 10
32
0.70
2 11
163
807
11.4
1 9.
01
NN
25
98
N13
-100
-28
1054
0.
750
1126
3 81
3 14
.12
9.30
N
N
2581
N
13-1
00-3
0 10
67
0.79
6 11
345
827
15.5
8 9.
42
NN
25
76
N13
-100
-34
1031
0.
564
1105
6 77
5 9.
23
9.14
N
N
2475
N
13-1
00-3
5 10
54
0.24
2 11
254
808
10.9
9 9.
75
NN
25
91
N13
-100
-36
1083
0.
586
1143
1 83
4 11
.23
10.2
9 N
N
2345
N
13-1
00-3
8 10
80
0.41
0 11
477
817
15.0
1 9.
89
NN
23
15
N13
-100
-39
1096
0.
074
1207
2 84
5 13
.05
9.79
N
N
2434
N
13-1
00-4
1 10
18
3.08
4 11
272
803
32.9
6 8.
84
NN
22
87
N13
-150
-5
712
1.80
1 11
517
72
39.7
5 11
.92
NN
0
N13
-150
-7
718
1.88
3 11
388
78
28.6
6 11
.91
0.00
6 0
N13
-150
-9
721
2.06
9 11
392
103
26.0
4 11
.07
NN
0
N13
-150
-10
714
2.07
9 11
481
119
27.1
6 10
.46
NN
0
N13
-150
-11
745
0.83
6 12
989
137
41.3
5 11
.22
0.04
5 0
N13
-150
-13
720
2.19
7 11
331
112
27.1
3 9.
83
NN
0
N13
-150
-14
742
2.36
4 11
109
109
26.2
6 9.
95
0.00
8 0
N13
-150
-16
748
2.32
6 11
655
106
35.0
5 9.
87
0.00
4 0
N13
-150
-17
586
NN
13
980
67
82.5
8 8.
06
0.00
7 0
N13
-150
-18
NN
N
N
1929
0 30
39
1.86
6.
48
0.86
1 0
N13
-150
-19
113
NN
19
617
1108
47
0.84
10
.64
NN
0
N13
-150
-20
NN
N
N
1925
9 14
24
126.
28
7.58
1.
416
0
CH
APT
ER 6
: MA
NU
SCR
IPT
3
74
Tab.
2: c
ontin
ued.
R
b (n
g/m
L)
Y (n
g/m
L)
La (n
g/m
L)
Ce
(ng/
mL)
Y
b (n
g/m
L)
Lu (n
g/m
L)
Pb
(ng/
mL)
Th
(ng/
mL)
U
(ng/
mL)
se
awat
er
120.
40
0.41
0.
51
0.61
0.
46
0.34
1 15
.09
0.59
0.
85
N13
-20-
1 87
.12
43.9
4 33
.11
97.6
6 3.
90
0.57
8 66
9.83
5.
66
18.2
0 N
13-2
0-3
95.2
6 10
6.10
51
.28
119.
96
9.03
1.
369
547.
30
11.3
7 7.
67
N13
-20-
5 12
8.40
73
.97
35.1
5 63
.29
4.58
0.
797
100.
84
7.84
0.
67
N13
-20-
7 86
.96
4.60
2.
77
3.06
0.
17
0.02
9 3.
50
0.90
1.
97
N13
-20-
9 74
763.
32
47.3
3 65
.11
74.0
6 0.
51
0.13
1 51
4.76
3.
41
8355
.97
N13
-20-
12
115.
08
1.21
0.
65
0.76
0.
27
0.11
8 2.
54
0.77
60
.27
N13
-20-
15
123.
95
1.20
0.
63
0.73
0.
28
0.12
9 1.
81
0.75
77
.08
N13
-20-
18
129.
97
1.16
0.
62
0.69
0.
27
0.12
5 1.
32
0.72
80
.68
N13
-20-
21
82.4
6 0.
32
0.29
0.
37
0.16
0.
080
0.66
0.
43
25.7
0 N
13-2
0-24
10
8.82
0.
44
0.46
0.
53
0.23
0.
113
1.48
0.
61
46.5
7 N
13-2
0-27
10
3.77
0.
42
0.40
0.
52
0.23
0.
116
0.98
0.
63
37.2
9 N
13-2
0-31
67
.63
0.70
0.
71
0.92
0.
32
0.15
7 2.
88
0.89
41
.94
N13
-20-
32
16.5
8 0.
39
0.26
0.
34
0.15
0.
069
0.89
0.
43
19.3
3 N
13-1
00-1
12
8.69
47
.98
22.4
1 58
.50
4.19
0.
618
464.
37
11.4
1 7.
34
N13
-100
-3
187.
82
20.9
9 9.
84
23.8
3 1.
55
0.24
9 98
0.99
1.
53
2.03
N
13-1
00-5
16
1.67
0.
31
0.30
0.
40
0.16
0.
078
2.30
0.
43
0.45
N
13-1
00-7
20
8.22
0.
19
0.05
0.
13
0.01
0.
002
3.06
0.
02
0.33
N
13-1
00-9
30
9.98
0.
50
0.54
0.
66
0.28
0.
138
4.23
0.
75
1.54
N
13-1
00-1
3 20
6.83
0.
38
0.32
0.
43
0.18
0.
088
2.18
0.
48
2.25
CH
APT
ER 6
: MA
NU
SCR
IPT
3
75
Tab.
2 co
ntin
ued.
R
b (n
g/m
L)
Y (n
g/m
L)La
(ng/
mL)
Ce
(ng/
mL)
Yb
(ng/
mL)
Lu
(ng/
mL)
Pb
(ng/
mL)
Th (n
g/m
L)U
(ng/
mL)
seaw
ater
12
0.40
0.
41
0.51
0.
61
0.46
0.
341
15.0
9 0.
59
0.85
N
13-1
00-1
7 21
0.16
0.
33
0.29
0.
39
0.17
0.
086
0.86
0.
48
3.49
N
13-1
00-2
1 20
2.57
0.
30
0.30
0.
38
0.16
0.
083
1.21
0.
45
3.14
N
13-1
00-2
8 32
7.11
0.
61
0.46
0.
49
0.45
0.
303
1.07
0.
55
4.85
N
13-1
00-3
0 33
8.52
0.
64
1.14
1.
20
0.41
0.
297
4.75
0.
52
5.11
N
13-1
00-3
4 17
7.25
0.
34
0.25
0.
29
0.23
0.
165
5.88
0.
28
2.26
N
13-1
00-3
5 31
7.18
0.
62
0.51
0.
52
0.40
0.
288
20.5
9 0.
49
3.98
N
13-1
00-3
6 32
6.49
0.
62
0.48
0.
53
0.42
0.
301
3.28
0.
50
3.30
N
13-1
00-3
8 29
9.67
0.
66
0.53
0.
57
0.42
0.
302
97.5
3 0.
51
3.01
N
13-1
00-3
9 15
1.27
0.
37
0.41
0.
45
0.24
0.
172
8.71
0.
29
3.07
N
13-1
00-4
1 13
2.46
0.
43
0.39
0.
42
0.30
0.
218
4.12
0.
37
0.52
N
13-1
50-5
27
9.49
2.
92
3.80
8.
49
0.19
0.
025
127.
41
2.25
0.
77
N13
-150
-7
269.
41
0.35
0.
64
1.35
0.
02
0.00
4 43
.66
0.03
0.
05
N13
-150
-9
255.
17
0.22
0.
31
0.71
0.
01
0.00
1 77
.94
0.01
0.
02
N13
-150
-10
248.
25
0.65
0.
74
1.82
0.
04
0.00
5 22
1.36
0.
33
0.12
N
13-1
50-1
1 27
3.00
0.
67
0.64
1.
59
0.04
0.
010
240.
38
0.19
0.
14
N13
-150
-13
239.
57
0.24
0.
25
0.65
0.
02
0.00
2 16
6.44
0.
02
0.03
N
13-1
50-1
4 24
0.20
0.
23
0.25
0.
63
0.01
0.
002
228.
60
0.02
0.
02
N13
-150
-16
224.
19
0.30
0.
25
0.64
0.
03
0.00
3 19
3.59
0.
03
0.04
N
13-1
50-1
7 N
D
ND
N
D
ND
N
D
ND
N
D
ND
N
D
N13
-150
-18
354.
48
1.31
1.
41
2.24
0.
07
0.00
0 10
97.2
6 0.
24
1.76
N
13-1
50-1
9 47
0.52
2.
48
3.15
4.
58
0.15
0.
075
1223
.65
0.11
1.
50
N13
-150
-20
9718
.36
112.
69
137.
87
217.
12
8.92
0.
831
3850
7.86
4.
95
58.1
0
CH
APT
ER 6
: MA
NU
SCR
IPT
3
76
Ta
b.2:
con
tinue
d.
P
oros
ity (%
/100
)st
ress
(MP
a)C
l (m
g/L)
norm
. fac
tor
Al (
mg/
L)B
a (m
g/L)
Ca
(mg/
L)Fe
(mg/
L)K
(mg/
L)se
awat
er
1860
0
ND
0.
003
398
0.08
39
3 N
14-2
0-1
0.73
4.
24E
-03
3358
0.8
0.55
39
NN
0.
085
429
0.17
43
4 N
14-2
0-4
0.61
2.
26E
+00
3838
4.8
0.48
46
0.04
0.
055
396
0.11
40
1 N
14-2
0-6
0.60
3.
37E
+00
1891
4.9
0.98
34
NN
0.
066
414
0.05
41
1 N
14-2
0-8
0.59
4.
84E
+00
1860
0.8
1.00
00
NN
0.
063
408
0.05
40
3 N
14-2
0-10
0.
57
8.42
E+0
0 19
040.
3 0.
9769
N
N
0.06
5 40
6 0.
11
397
N14
-20-
12
0.57
9.
26E
+00
2337
0.1
0.79
59
0.06
0.
061
397
0.06
39
2 N
14-2
0-13
0.
56
1.11
E+0
1 19
204.
2 0.
9685
N
N
0.06
1 41
0 0.
04
395
N14
-20-
14
0.56
1.
30E
+01
1901
7.3
0.97
81
0.02
0.
060
405
0.03
38
3 N
14-2
0-15
0.
55
1.42
E+0
1 18
960.
2 0.
9810
N
N
0.05
8 40
1 0.
04
371
N14
-100
-1
0.74
1.
00E
-06
1052
9.0
1.76
65
0.08
0.
257
521
0.09
59
9 N
14-1
00-2
0.
66
3.91
E-0
6 12
650.
7 1.
4703
0.
16
0.27
9 56
0 0.
68
759
N14
-100
-4
0.59
5.
29E
-04
1855
6.8
1.00
23
NN
0.
181
535
0.04
57
7 N
14-1
00-6
0.
55
7.32
E-0
3 47
955.
5 0.
3879
0.
00
0.19
1 55
4 0.
12
622
N14
-100
-7
0.53
2.
45E
-02
2914
9.2
0.63
81
0.01
0.
145
522
0.02
54
8 N
14-1
00-9
0.
47
2.68
E-0
1 29
170.
0 0.
6376
0.
03
0.14
9 54
1 0.
10
539
N14
-100
-10
0.43
1.
04E
+00
2912
4.6
0.63
86
0.02
0.
149
545
0.04
54
2 N
14-1
00-1
2 0.
36
8.96
E+0
0 39
082.
1 0.
4759
0.
00
0.14
5 50
3 0.
02
518
N14
-100
-13
0.32
2.
93E
+01
3202
0.6
0.58
09
0.04
0.
168
515
0.02
48
4
CH
APT
ER 6
: MA
NU
SCR
IPT
3
77
Tab.
2: c
ontin
ued.
M
g (m
g/L)
Mn
(mg/
L)N
a (m
g/L)
S (m
g/L)
Si (
mg/
L)S
r (m
g/L)
Ti (m
g/L)
SO
4 (m
g/L)
seaw
ater
12
82
0.00
04
1080
0 88
8 2.
9 7.
83
ND
25
00
N14
-20-
1 13
94
0.00
00
1220
8 93
7 1.
10
8.40
0.
02
5698
N
14-2
0-4
1259
0.
4473
11
175
859
6.07
7.
68
NN
22
42
N14
-20-
6 13
05
0.39
20
1116
1 89
6 3.
12
8.09
0.
00
2530
N
14-2
0-8
1278
0.
4094
11
364
876
2.92
7.
93
NN
25
86
N14
-20-
10
1261
0.
4769
11
022
863
3.07
7.
79
0.00
25
20
N14
-20-
12
1250
0.
5665
11
276
856
3.48
7.
63
0.01
24
79
N14
-20-
13
1276
0.
5258
11
291
874
3.51
7.
88
0.00
26
14
N14
-20-
14
1258
0.
6153
11
079
872
3.65
7.
75
0.00
25
53
N14
-20-
15
1258
0.
6915
11
040
856
3.92
7.
69
NN
26
37
N14
-100
-1
1207
1.
0726
11
422
925
47.0
3 8.
91
0.00
30
97
N14
-100
-2
1276
0.
0863
13
972
993
105.
18
9.28
0.
01
0 N
14-1
00-4
10
71
1.43
79
1080
2 80
4 35
.38
9.10
N
N
2498
N
14-1
00-6
12
30
0.15
99
1189
6 85
4 35
.90
8.81
0.
02
4275
N
14-1
00-7
11
70
0.86
77
1093
9 85
0 27
.51
8.24
N
N
2482
N
14-1
00-9
12
01
4.97
03
1074
1 88
0 34
.66
8.40
N
N
2541
N
14-1
00-1
0 12
16
5.53
67
1042
3 88
0 35
.93
8.45
N
N
2616
N
14-1
00-1
2 11
89
4.30
23
1065
9 84
7 29
.79
7.80
N
N
2374
N
14-1
00-1
3 12
09
4.77
03
1073
0 87
4 37
.68
7.73
N
N
2430
CH
APT
ER 6
: MA
NU
SCR
IPT
3
78
Tab.
2: c
ontin
ued.
R
b (n
g/m
L)
Y (n
g/m
L)La
(ng/
mL)
Ce
(ng/
mL)
Yb
(ng/
mL)
Lu
(ng/
mL)
Pb
(ng/
mL)
Th (n
g/m
L)U
(ng/
mL)
seaw
ater
12
0.40
0.
41
0.51
0.
61
0.46
0.
34
15.0
9 0.
59
0.85
N
14-2
0-1
88.3
8 1.
94
3.47
8.
74
0.11
0.
01
6.05
0.
01
4.44
N
14-2
0-4
73.1
4 0.
42
0.51
0.
73
0.26
0.
13
6.01
0.
72
5.57
N
14-2
0-6
151.
29
1.06
1.
01
1.37
0.
55
0.27
4.
48
1.78
12
.68
N14
-20-
8 14
9.18
0.
84
0.91
1.
21
0.54
0.
27
2.27
1.
54
14.5
3 N
14-2
0-10
26
4.64
3.
07
1.31
1.
51
0.61
0.
29
5.34
1.
63
90.5
5 N
14-2
0-12
12
3.54
0.
65
0.95
1.
29
0.42
0.
21
37.4
1 1.
15
14.1
2 N
14-2
0-13
14
8.50
0.
79
0.92
1.
22
0.52
0.
26
6.30
1.
43
18.8
3 N
14-2
0-14
14
3.97
0.
90
1.02
1.
29
0.59
0.
28
6.40
1.
46
20.6
8 N
14-2
0-15
13
5.70
0.
79
1.07
1.
36
0.53
0.
27
8.22
1.
46
23.7
6 N
14-1
00-1
44
1.62
1.
71
2.46
2.
27
1.46
1.
04
15.0
8 1.
81
2.53
N
14-1
00-2
N
M
NM
N
M
NM
N
M
NM
N
M
NM
N
M
N14
-100
-4
451.
98
1.12
1.
16
1.50
0.
85
0.61
18
.60
1.06
1.
96
N14
-100
-6
291.
22
0.20
0.
09
0.23
0.
01
0.00
5.
53
0.08
0.
22
N14
-100
-7
452.
73
0.84
0.
87
0.83
0.
52
0.37
5.
34
0.70
0.
95
N14
-100
-9
460.
76
1.07
0.
73
1.05
0.
55
0.39
6.
12
0.79
0.
82
N14
-100
-10
471.
83
1.04
0.
79
1.08
0.
57
0.40
16
.12
0.75
0.
83
N14
-100
-12
353.
52
0.56
0.
45
0.49
0.
41
0.29
0.
71
0.49
0.
74
N14
-100
-13
389.
34
0.63
0.
51
0.61
0.
47
0.34
2.
38
0.58
1.
10
CHAPTER 6: MANUSCRIPT 3 79
6.4 Results A noticeable increase in element concentration at the very beginning of the
tests is observable for room temperature tests as well as for heated tests between
1*10-5 and 1*10-6 MPa (Fig. 3A,B). After this early peak in solutes, the concentrations
drop down and remain fairly constant until at least �e=10 MPa. This is particularly
obvious for the 100 °C temperature test of the smectite-rich sample N13 (e.g. K, Na,
Ba, Sr, S, Si), because of the larger number of measured samples in the low stress
range. Single elevated concentrations for the illite-rich sample may hint to a similar
trend for these experiments. However, for room temperature tests most solutes return
to seawater composition with increasing stress. Exceptions are enriched
concentrations of Na, Ba and Mn for the illite-rich and Na, Sr, Si and Mn for the
smectite-rich sample with solute concentration higher than the seawater concentration.
The most notable observation is the temperature-related change in solute
concentrations. It is marked by an offset compared to the room temperature tests
which develops immediately after heating started (Fig. 3C-F). Although there are
common elements for both lithologies showing the offset, there are slightly more
affected solutes for the illitic sample. The enrichment of the very same element can be
quite ambiguous with different lithology (e.g. Rb; Fig. 3E,F). However, the observed
offsets towards enrichment with increasing temperature from 20 °C and 100 °C tests
are observable for the smectite-rich sample N13 for K, Ba, Rb and Si. The step
between the 100 °C test and the 150 °C test for these elements is quite ambiguous.
Some elements are further enriched (K, Ba, Si) while Rb shows no difference between
the 100 °C and 150 °C tests (cp. Fig. 3C-F). For the illitic sample it is pronounced for
the elements K, Ba, Ca, Rb, Si and, less explicitly, for Mn due to larger scatter.
Instead, Mg solely decreases with increasing temperature. It is observable for both
lithologies in N13 and N14, with a stronger depletion for the smectite sample (Fig.
3G,H).
The smectite-rich sample N13 reveals some unique characteristics. Most
notable is the decrease in solute concentration beyond a threshold of ~10 MPa (Fig.
3I). For the room temperature test these are Na, K, Ca, Sr and S. The Na depletion
might be also allusively displayed for the illitic sample. The depletion is for the
100 °C run less obvious because fewer fluids have been sampled at stresses higher
than 10 MPa (Fig. 3I). Thus, a similar trend than that of the room temperature tests
CHAPTER 6: MANUSCRIPT 3 80
may also be assumed. The 150 °C test follows this trend clearly for the elements Ca,
Sr and S, but indicates gentle enrichment for Na and K (Fig. 3A,D). Most strikingly,
however, are a strong decrease in sulphur and the total loss of sulphate (Fig. 3J).
Fig. 3: Pore water concentrations for selected elements vs logarithm of
effective stress. (A,B) Note the peaks for the smectite (N13) as well as the illitic (N14) sample at the beginning of consolidation. (C,D) K shows a clear enrichment with temperature which increases for the 150 °C test of the smectite sample at the end of the test. (E,F) Average value for Rb at 20 °C and 100 °C (dotted line) and shaded areas as standard deviation to highlight the temperature dependent offset. (G,H) The depletion is more enhanced for the smectite than for the illite sample and shows a larger offset between the 100 °C and 150 C test. (I) Besides Ca, also Na, K, Ca, Sr and S show a significant depletion beyond an effective stress of 10 MPa. (J) Note the strong depletion in S for the 150 °C test which may hint to the precipitation of sulphate.
CHAPTER 6: MANUSCRIPT 3 81
There are also some less pronounced trends, associated to a small number of
elements or related to a specific lithology. Heavy rare elements (Yb, Lu), for example,
are depleted only for smectite tests (N13). The same can be observed for Pb in all
experiments conducted. U takes the role of an outlier because the room temperature
tests show enrichment for both lithologies (N13, N14). Light rare earth elements (e.g.
La, Ce and Y) do not display a variation between different temperatures, stresses or
lithologies at all and trends remain ambiguous due to large scattering for Al and Fe.
6.5 Discussion In the following the possible processes, which are responsible for the observed
changes in element concentrations during hydrothermal oedometer testing are
discussed. The influence of increasing effective stress and temperature is separately
addressed in subchapters. The identified processes are then examined for their
geological relevance and their significance for pore water sampling.
6.5.1 Primary results from hydrothermal oedometer tests
From the results several major trends can be distinguished for the illite- and
the smectite-rich samples. One is the offset in solute concentration between 20 °C,
100 °C and 150 °C test, which is observable for both lithologies. This observation is
discussed in the light of temperature dependencies since they seem unrelated to
increasing stress.
The observed early peaks in solute concentrations for room temperature and
high-temperature tests appear to be independent of temperature and were observed for
both specimens tested (cf. K, Ba). The significant depletion of solutes beyond
�e=10 MPa is observed only for the smectite-rich sample, but is noticeable at the three
temperatures tested.
6.5.1.1 Temperature
Temperature increase leads to an almost instantaneous increase in K, Ba and
Si as well as to a depletion of Mg for both tested lithologies. This is quite similar to
the observation from hydrothermal tests of marine sediments in rocking autoclaves
(e.g. Thornton and Seyfried, 1985; You et al., 1996). The average concentrations
between 1 and 10 MPa document a total exchange of solutes of 564.1 mg/l (N13) and
CHAPTER 6: MANUSCRIPT 3 82
1015.5 mg/l (N14) between the 20 °C and 100 °C runs with net differences
accounting for a small enrichment of 8.8 mg/l and 40.9 mg/l, respectively. This
residual surplus may be accounted to the depletion of solutes, which have not been
measured yet (e.g. NH4).
Results of rocking autoclave testing have been mainly interpreted in terms of
thermal alteration of the sediment and most of the proposed diagenetic reactions occur
>> 150 °C (cp. You and Gieskes, 2001). The interpretation is supported by the fact
that boron isotope measurements suggest that efficient release of lattice bound B starts
not until T 300 °C in these experiments (You and Gieskes, 2001). The rapid
release/depletion of solutes in our experiments, the lower temperature and the
consistency of released elements despite the different initial compositions argue for
the absence of such a thermally driven diagenetic reaction in our experiments.
Considering that an ion can be found in three sites within the sediment, namely the
interstitial solution, the exchangeable sites and integrated in the lattice (Murthy and
Ferrell, 1972), we propose that the observed change in element concentrations is
merely due to the interaction of the pore water with exchangeable sites at the charged
surface of clay minerals. Additionally, the ion exchange reactions with clay minerals
have been proposed to be rather fast (Masuzawa et al., 1980). Results from Bischoff et
al. (1970) and Masuzawa et al. (1980) corroborate our hypothesis. These authors
analyzed temperature effects while squeezing pore waters from marine sediments.
Although these experiments were conducted at significant lower temperatures (2-
25 °C), these researchers found enrichment in K and Si. Also, the observed depletion
of Mg is strikingly similar to our results. Collectively, these experiments suggest that
the ion exchange capacity of clay minerals is a function of temperature, but also
depends on variables such as the type of clay mineral, crystal size and the clay-water
ratio (Bischoff et al., 1970). These processes may explain the differences in
magnitude of enrichment and depletion of single elements (e.g. Ca). However, we can
conclude that the ion affinity for K decreases with increasing temperature and leads to
its release into the solution whereas the capacity increases for e.g. Mg and causes an
uptake of that element. Thus, the heating changes the replaceability sequence of
cations and generates the early offset of solute concentrations. According to the
enrichment/depletion in the solution (Fig. 4A,B) we propose the following retention
sequence with increasing temperature of Mg>Ca for divalent cations and Na>K for
CHAPTER 6: MANUSCRIPT 3 83
monovalent cations. Unless there is no decomposition of clay minerals, this
phenomenon is reversible (Masuzawa et al., 1980).
Fig. 4: (A,B) Mg/Ca and Na/K concentration ratios in the expelled pore water
at 55% porosity for both lithologies vs temperature. Decreasing ratios indicate that the clay surface attraction is Mg>Ca for divalent ions and Na>K for monovalent ions with increasing temperature.
The 150°C test of the smectite-rich sample (N13) follows the temperature-
dependent trend described above, and shows an immediate depletion of S (Fig. 3J).
The strong deviation from the 100 °C test and the late enrichment suggest another
phenomenon than the above proposed ion exchange reaction. The decrease of SO4 and
S strongly hints to the precipitation of sulphates such as gypsum or anhydrite.
Experimental data by Bischoff and Seyfried (1978) on seawater geochemistry suggest
that anhydrite reaches saturation between 150 and 200 °C. Although the determined
amount is close to the detection limit, XRD analyses show a notable fraction of
anhydrite in the 150 °C test, but not in the 100 °C test. Thus, it may support the
precipitation of small amounts of this mineral. Another possibility for the decreased
sulphate concentration is the formation of kieserite, which forms upon evaporation of
seawater (Matthes, 1987). In addition, the formation of a Mg-hydroxysulphate hydrate
(caminite) may be possible. This phase has been reported to precipitate in laboratory
hydrothermal testing of seawater and marine sediment by Thornton and Seyfried
CHAPTER 6: MANUSCRIPT 3 84
(1985), although at slightly higher temperatures (200 °C) than our tests. Precipitation
of a Mg-sulphate salt may be suggested by the similarity in the development of both
Mg and SO4 concentrations (e.g., sinoidal patterns with a minimum at 0.01 MPa and
similar relative concentration differences between the 100 °C and 150 °C
experiments; Figures 3G and 3J), whereas Ca does not display a close similarity with
SO4, which would be expected if anhydrite was the sole sulphate phase precipitated.
Thus, we propose that the Mg and sulphate depletions are the result of precipitation of
a Mg-sulphate phase.
6.5.1.2 Effective stress
It is well known that the negative charge of the surface of the clay particles
attracts cations from the surrounding solution while anions are repelled. This is
counteracted by diffusion, which tends to balance the unequal charge distribution. A
double layer is formed by the diffusive layer, which is characterized by exponential
increasing cation concentrations and inversely increasing anion concentrations to the
clay surface (Kharaka and Berry, 1973; Meunier, 2005). Thus it can be distinguished
between the free pore water and the water of the diffusive layer (Baldi et al., 1988;
Henry 1997; Fig 5).
With the onset of consolidation the steady state of the resting sediment
seawater slurry is disturbed by the spatial convergence of the sediment particles and
the change of the pore water from a static to a flowing state with the onset of pore
water expulsion. Upon the initiation of fluid flow the water movement deforms the
double-layer (Hanshaw and Coplen, 1973). During the manifestation of this process
weakly associated cations in the vicinity of the double layer may be dragged with the
effluent until a new equilibrium is established. Similar observations have been made
by Tang et al. (2006) for the Pb distribution in expelled fluids during consolidation
tests. These authors propose that the high seepage velocity at the beginning of their
tests may change the adsorption-desorption equilibrium near the drainage surface.
Considering that the deformation of the double layer is a function of the flow velocity
(Kharaka and Berry, 1973) this assumption would be consistent with our
interpretation.
Another likely explanation might be that element exchange between
seawater and clay surfaces was incomplete after re-hydration. Thus, the peak in
concentrations at the beginning of the deformation experiments results from the
CHAPTER 6: MANUSCRIPT 3 85
transitional condition until the exchange is completed, which is than represented by
the constant element concentrations afterwards. However, a definitive answer is not
possible under these circumstances and stresses the importance for a better control of
the re-hydration process by geochemical measurements of fluids sampled during the
procedure.
Fig. 5: (A) Schematic distribution of particles and pore water in a clayey sediment (modified after Kharaka and Berry, 1973; Baldi et al., 1988; Henry, 1997). The total pore water can be distinguished into free pore (dotted) and double layer water (grey shaded) associated to the clay particles. (B) The accentuation in the upper right shows that the anions (as Cl-) are restricted mainly to the free pore water. (C) Where the double layer is overlapping the ion concentration of interstitial water is dominated by cations.
With increasing stress the pore space decreases and the double layers of
opposite clay particles will eventually overlap (Fig. 5). Several authors demonstrated
that such highly compacted clays function as filtration membranes for cations (e.g.
McKelvey and Milne, 1962; Hanshaw and Coplen, 1973; Kharaka and Berry, 1973).
Kharaka and Smalley (1976) propose a retention sequences for monovalent ions of
Cs>Rb>K>Na>Li and Ba>Sr>Ca>Mg for divalent cations where the replacing power
is greater for ions with higher charges and hydrated radii. Comparing the major cation
concentrations before and after the threshold effective pressure of 10 MPa is reached
for the 20°C test of this study we can propose an equivalent retention sequence with
K>Na and Ca>Mg (Fig. 6). These sequences are opposite to the thermally driven
retention, which may explain the observed weakening of filtration at higher
temperatures by Kharaka and Berry (1973). Nonetheless, the assumption of
CHAPTER 6: MANUSCRIPT 3 86
membrane filtration is supported by the fact that the illite-rich sample does not reveal
the depletion effect because of phyllosilicates are less abundant and a considerable
amount of quartz and feldspar is at hand to separate the clay particles.
Fig. 6: A,B) Mg/Ca and Na/K concentration ratios in the pore water vs effective stress for smectite-rich sample (N13) at 20 °C. The linear fit increases at an effective stress > 10 MPa. This indicates that the clay surface attraction is Ca>Mg for divalent ions and K>Na for monovalent ions. The solid line suggests a good linear fit. In general, the filtration efficiency increases with compaction and ion
exchange capacity of the sediment (Kharaka and Berry, 1973). The flow of ions
through the membrane may be further influenced by the concentration of the solute,
the velocity of the flowing pore water, the electrical interaction of the ion with the
negative sites of the clay particle and the interaction with the streaming potential
(Hanshaw and Coplen, 1973; Kharaka and Berry, 1973). The streaming potential is
the electrical potential gradient across the membrane formed by the deformation of
the double layer. The outflow side of the membrane becomes positively charged, this
way accelerating anions relatively to flow of the pore water. This hydraulic drag of
the anions is larger on divalent than on monovalent cations according to the Stokes
equation (Kharaka and Berry, 1973; Sacchi et al., 2001).
Another explanation might be that the free pore water will be pushed out
first and the anions are to a large extent expelled with it (Sacchi et al., 2001 and
CHAPTER 6: MANUSCRIPT 3 87
references therein). Once the free pore water is gone, the solutes from the double layer
will start to be released. Because of electrical neutrality the loss of cations is
dependent on the anions which are depleted in the remaining solution. Thus, the
expelled fluid should have a lower salinity, which is consistently true with our results.
Similar observations were made by von Engelhardt and Gaida (1963) with starting
depletion between 3 and 81 MPa for montmorillonite clay. Although both
explanations are feasible, membrane filtration refers to flow through experiments
while latter one was established by compaction testing (von Engelhardt and Gaida,
1963; Chiligarian et al., 1973) and seems more suitable to explain the observed
depletion for the smectite sample beyond �e=10 MPa (Fig. 4).
6.5.2 Geological relevance of hydrothermal experiments
Our experiments show that temperature and increasing effective stress can
modify the composition of pore fluid that is expelled from the sediment during
consolidation and that these changes are independent of diagenetic processes. The
compaction driven retention is detectable only for the smectite-rich sample above a
threshold of �e=10 MPa. In contrast, the T-induced enrichment/depletion seems less
dependent on the nature of the lithologies tested. For natural conditions it can be
assumed that the thermally driven release/retention increases with depth as a function
of the regional geothermal gradient. Considering the low temperatures along the
subduction thrusts, this process may be rather relevant for deeper portion of the
subduction zone. Accordingly increasing effective stress and temperature may be
important for pore water geochemistry at burial depths >>1 km.
It remains difficult to quantify the significance of the identified processes for
their geologic consequences at convergent margins. Although increasing effective
stress is supposed to be analogous to the natural process of consolidation,
experimental pore water release is rather high because of rapid loading under
laboratory conditions. Accordingly advection has a higher impact than under natural
conditions and diffusion is underestimated.
The influence of membrane filtration at convergent margins was discussed by
Martin et al. (1995). These authors suggested that it is negligible although fluid
pressures are sufficiently high to favour fluid flow through highly compacted clays.
Its significance is supposed to be small because of the complex geochemical effects as
a result of dilution through mineral dehydration, fluid-mineral exchange reactions,
CHAPTER 6: MANUSCRIPT 3 88
diffusion-advection and mixing with external (e.g. meteoric water) or internal sources
(e.g. deep-seated fluids). Further, focused fluid flow along permeable faults at
convergent margins would allow circumventing clay membranes and only sediments
with high smectite contents can produce a significant filtration effect.
On the other hand, it can be argued that highly permeable faults may also act
as drainage for compacting sediments (Carson and Screaton, 1998). In this case the
permeable conduit is at least partially fed by the pore water expulsion from the
surrounding sediment. Depending on the consolidation state, the sediment will
eventually release low salinity pore water after the free pore water is expelled. The
extensive testing of Kharaka and Berry (1973) and results from this study suggest that
high clay contents and especially smectite must be present in the sediment to produce
considerable effects of membrane filtration or consecutive release of free and
adsorbed pore water. Further, high fluid pressures determined for the accretionary
Nankai margin and other subduction zone sediments may delay consolidation and thus
closer packing of clay minerals (Saffer, 2007; Fig. 7). Eventually smectite-rich
sediments will loose their retention efficiency with the transition of smectite-to-illite.
Kharaka and Berry (1973) suggest a low retention capacity for illite of less than 10 %
below of 70 MPa. In summary, it can be suggested that the subsequent release of pore
water constituents due to overlapping double layer is negligible.
Fig. 7: Cross section of the Nankai margin (modified after Morgan et al., 2007). Shaded areas indicate excess pore pressure with 90 %, 80 %, 70 %, and 60 % of the lithostatic stress. The outtake shows fluid flow at toe of the prism with localised fluid flow along faults (solid arrows) and diffusive fluid flow between (dotted arrows) (modified after Yamano et al., 1992).
CHAPTER 6: MANUSCRIPT 3 89
Although the amount and the number of elements changes with sediment
composition, end member lithologies suggest the release of K, Ca and Si and the
removal of Mg from the pore water with increasing temperature at the Nankai margin.
Even if the impact of this process is small the increased availability of released
elements may facilitate diagenetical processes and lithification at depth, making the
sediment prone to unstable failure (Moore et al., 2007). The temperature-related
release of K may facilitate the smectite-illite conversion, which is important for the
hydrology and stress regime at convergent margins (Brown et al., 2003; Saffer et al.,
2008). The transition starts at 60 °C and is virtually completed at 150 °C under natural
conditions (e.g. Colten-Bradley, 1987). The reaction equation is given by:
clay (kaolinite, smectite) + cations (K+) = aluminosilicate (illite) + quartz + water
following Bjorlykke (1998).
The greater desorption of Ca and Si with increasing temperature may facilitate
the precipitation of quartz and carbonate cements and veins. This would be in
accordance with the observation that cementation and veining by carbonates becomes
common above 125 °C and quartz veining by 200 °C (Moore et al., 2007) and can be
associated with enhanced mobility of Si, Na, K, Ca and trace elements (Bebout and
Barton, 1989). This correlation suggests that the observed desorption/adsorption
processes may be more important for water-rock interaction in the shallow subduction
zone than previously believed by other workers (e.g. Kastner et al., 1991).
Heat flow distribution on the Nankai trough seafloor suggests that warm fluids
flow to the ocean along the decollement or fault zones (Yamano et al., 1992, Fig. 8).
Thus, the released elements may also be expelled to the ocean unless they are
consumed by diagenetical reactions. It may be assumed that fixed elements to the clay
surface will be dragged further down-slab. The release of HFSE, REE and volatile
elements during hydrothermal uniaxial deformation testing was suggested to have
implications on HFSE enrichment in magmas as proxy for sediment consumption
(Kopf et al., 2002). You et al. (1996) proposed from hydrothermal rocking autoclave
experiments that the released elements are partially taken up by newly metamorphic
minerals and thus being further dragged down. Observed hydrothermal fractionation
of Pb/Ce, La/Ba, Rb/Cs, B/Nb and B/Be are supposed to explain ratios in arcs.
However, it can only be speculated that the observed retardation and release of
CHAPTER 6: MANUSCRIPT 3 90
elements with increasing temperature and effective stress from our experiments may
foster the enrichment of large-ion-lithophile elements (e.g. Mg, K, Ca, Sr) in arc
magmas relative to high-field-strength elements (e.g. Ti, Th, Hf, Nb, Zr).
6.5.3 Significance of results for laboratory pore water sampling
While the thermal and stress induced impact on pore water geochemistry
under natural conditions may be preliminary and highly variable depending on the
location, its significance for laboratory conditions is important and has been
established before (e.g. McKelvey and Milne, 1962; Bischoff et al., 1970; Hanshaw
and Coplen, 1973; Kharaka and Berry, 1973; Masuzawa et al., 1980; Sacchi et al.,
2001). Especially the pore fluid sampling may suffer from their influence. In the
following we will focus the discussion on pore fluid sampling by squeezing which is
the present standard sampling procedure within the IODP (Integrated Ocean Drilling
Program). A broader overview of pore water sampling artefacts is given by Sacchi et
al. (2001).
Fitts and Brown (1999) have shown that interstitial water studies of marine
sediments may be substantially affected by stress-induced smectite dehydration from
squeezing. Under certain circumstances the observed compactive fluid filtration from
this study may also affect sampled fluids. However, besides smectite content the
effective stress must be >10 MPa to have a significant influence. The study by Fitts
and Brown (1999) demonstrated that under rapid loading rates the effective stress
remains rather low because of the time-dependent dissipation of the pore water.
Considering that sample squeezing is a very fast process we propose that compactive
filtration should be negligible.
The temperature dependence of ion exchange capacity is long known (e.g.
Bischoff et al., 1970; Masuzawa et al., 1980) and its impact can be prevented by
squeezing at in-situ temperatures. While near seafloor surface temperatures (~ 4 °C)
are in most cases slightly lower than at laboratory conditions deep drilling is
occasionally related to areas with high thermal gradients. The central part of Nankai
margin is such an area. Relating to the enrichment found for particular elements, it
can be assumed that the core recovery in areas with high in-situ temperatures leads to
an underestimation of e.g K and Si while Mg will be overestimated because of the
reversibility of ion exchange (Masuzawa et al., 1980). A quantitative correction of the
effect afterwards, however, is difficult because of the complexity owing to various
CHAPTER 6: MANUSCRIPT 3 91
parameters such as type, size and abundance of clay minerals (Bischoff et al., 1970).
Thus, squeezing at in-situ temperatures may be necessary to accurately address pore
water geochemistry for samples with very different in-situ temperatures or from large
subseafloor depth.
6.6 ConclusionsThe pore waters expelled from hydrothermal laboratory consolidation of
sediments from the Nankai margin bear some similarity with data from previous
rocking autoclave testing (e.g. You et al. 1996). However, due to lower temperatures
we found our results especially influenced by ion-exchange behaviour of clays. The
ion-exchange capacity may be a function of parameters such as clay mineralogy,
temperature, fluid content or fluid flow velocity. A significant difference is the
consecutive release of free pore water followed by double layer water which led to a
significant depletion effect. This feature is neglected in rocking autoclaves where
effective stresses remain low due to high fluid pressures. The potential impact of the
observed ion exchange suggests that their relevance might be more important at burial
depth of several kilometres. The observed change in pore water geochemistry may
foster diagenetic processes at convergent margin but their geological relevance
remains rather small because the footprint of diagenetical processes is supposed to be
more evident. Nonetheless, the observed processes are relevant for pore water
sampling by squeezing.
Acknowledgments
We appreciate the assistance of Jill Weinberger for some of these tests and
Kevin Brown for providing laboratory space. Christoph Vogt is thanked for XRD
analyses. Samples and data used in this study have been provided by the Ocean
Drilling Program (ODP). We also thank Silvana Pape, Pat Castillo and Heike Anders
for assisting with pore water analyses.
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CHAPTER 7: CONCLUSIONS AND OUTLOOK 97
Chapter 7: Conclusions and outlook A novel laboratory approach has been conducted to simulate underthrusting of
sediments at convergent margins to understand their response to increasing PT
conditions on their way from aseismic sliding to seismic stick-slip behaviour. The
main conclusions of all three manuscripts as well as the wealth of unpublished results
(see appendices) are highlighted in the following as bullet points with consequences
for future perspectives:
� Tested end member samples reveal contraction behaviour with increasing
temperature regardless of the lithological composition. This observation can be
related to a decrease in intergranular friction. While the induced weakening may be
compensated by compressive strain under normally consolidated, drained
conditions, underthrust sediments are characterized by high excess pore pressures
suggesting that the compressive strain cannot keep pace with thermal weakening.
The test results may have implications for frictional behaviour, which could not
appropriately studied due to large temperature and effective stress differences
between hydrothermal consolidation tests and shear test. Future work by heated
friction experiments has to be conducted to shed light on the two competing
effects.
� Inferred from the hydrothermal consolidation tests the consolidation state of a
specific sediment is dependent on effective stress, time and temperature.
Knowledge of in-situ temperature can provide better description of the
consolidation state as shown for the central portion of the Nankai margin. The
inferred excess pore pressure estimates for the toe of the accretionary prism of the
Nankai margin are found to be smaller than previously believed. Thus, temperature
may have a veritable impact on the consolidation behaviour within deeper parts of
the subduction zone and, therefore, on excess pore pressure generation.
Temperature-controlled permeability tests could help to refine previous estimates.
� The different consolidation behaviour of the smectite and illite end members
suggest that the compositional transition during illitisation decreases the
compressibility with increasing illite. The associated cementation of by-products
such as quartz may facilitate this process and reduce the pore space. The decrease
in permeability may have severe implications for excess pore pressure generation.
Consolidation tests of different smectite-illite mixtures could help to shed light on
CHAPTER 7: CONCLUSIONS AND OUTLOOK 98
the changing consolidation behaviour during the smectite-to-illite transition. Also,
temperature tests at higher temperatures to facilitate smectite-illite transition within
the experimental time would be possible. However, the results of this research
study and of other workers show that mechanical behaviour of underthrust
sediments is subjected to a complex pattern of effective stress, time, temperature
and diagenetic change. All these parameters vary from margin to margin and their
specific impact has to be determined for each margin anew.
� The outlined influence on temperature underlines the importance of temperature
controlled laboratory testing, because major differences between in-situ and
laboratory data exist. The thermal hardening, which happens during cooling of
samples when they are removed from “hot” in-situ conditions may have severe
implications for the interpretation of the data. The application of a thermo-
mechanical model to quantify the thermal hardening enabled the re-interpretation
of available consolidation data of samples from the Nankai margin: The
temperature-corrected data is in better agreement with the general notion of a
normally consolidated stratum seaward of the deformation front of the accretionary
prism. Thus, the effect of cementation to explain overconsolidation may be less
important than previously believed. As a consequence a model was put forward
where decollement formation at the central portion of the Nankai margin is
consistent with additional physical properties data. The study shows that heated
tests are an inevitable tool to avoid thermal artefacts. This may be especially
important for the upcoming deep drilling at the Nankai margin with the riser vessel
Chikyu in the near future, when cores from deep and hot in-situ conditions will be
recovered.
� Geochemical analyses of expelled pore waters suggest that water-rock interaction
occurs mainly as desorption and adsorption processes at the stress and temperature
range regarded. It is astonishing that especially elements such as K and Si are
released from the clay mineral surface, which may directly facilitate smectite-to-
illite transition and quartz cementation. However, the experimental approach has
also shown that studying natural processes is difficult due to slow kinetic reactions
of diagenetic reactions. Experimental temperatures well above 150 °C may
enhance such diagenetic reactions tremendously, resulting eventually in enhanced
progress of diagenesis within the 3-5 month duration of the experiments.
ACKNOWLEDGEMENTS 99
Acknowledgements This PhD thesis was conducted within the framework of the ROME (Research
on Ocean Margins Earthquakes) project. I am very grateful to my supervisor Prof. Dr.
Achim Kopf for providing me with the chance to participate in this exciting
interdisciplinary research at the intersection of soil mechanics, structural geology,
hydrology and geochemistry. I especially valued his insightful input and constructive
criticism during the progress of this work. Particularly his patience during the
development of a heated oedometer, a trying task where I faced many obstacles, was
much appreciated.
I would furthermore like to thank Prof Dr. Tobias Mörz of the engineering
geology group for being co-referee. I am much obliged for the excellent cooperation,
e.g. when it came to sharing standard soil mechanical equipment.
Initial oedometer tests were conducted at SCRIPPS Institution of
Oceanography. Prof. Dr. Kevin Brown and Dr. Jill Weinberger provided laboratory
space and help with these tests, and I am grateful to both of them.
The setup of the heated oedometer devices at the University of Bremen would
have been unimaginable without the help of Matthias Lange. His assistance and
Labview experience definitely proved to be indispensable. The help of Wolfgang
Schunn with assembling electrical equipment of the oedometer device is also much
acknowledged.
I also thank Dr. Stefan Kreiter for his valuable advice concerning soil
mechanical problems. His help was of great benefit. I am also much obliged to Prof.
Dr. Wolfgang Bach and PD Dr. Matthias Zabel who provided helpful comments for
the interpretation of the pore water geochemistry data. Pore water analyses were
conducted by Heike Anders, Pat Castillio and Silvana Pape – I express my gratitude.
I want to give another big ‘Thank you’ to all my co-workers of the marine
geotechnics and the engineering geology group. Their warm welcome made it easy to
start my position at the University of Bremen in the first place, and we shared a
fantastic time in the following years. I very much enjoyed our daily trips to the
canteen and our after work arrangements. Special thanks go to my current and former
roommates Annedore Seifert, Hendrik Hanff and Annika Förster for the occasional
off-topic distraction. Annika needs to be mentioned in particular for babysitting my
ACKNOWLEDGEMENTS 100
oedometer tests at the weekend numerous times, and Katja Zimmerman conducted
some of the direct and ring shear tests.
Last but not least, I want to express my deep gratitude to my parents for their
support during my university studies. They always gave me the freedom to find my
own way. Finally, I want to thank my fiancée Bettina Unger for everything.
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APPENDIX 110
APPENDIXThe PhD project can be separated into two individual parts: (1) Mechanical,
geochemical and mineralogical analysis and interpretation of the large number of
samples from the pilot study conducted at the SCRIPPS Institution of Oceanography
and (2) the development and implementation of a heated uniaxial consolidation
apparatus (oedometer) at the MARUM, University of Bremen. The two thematically
blocks are dived into appendix A and appendix B, respectively.
Outline of Appendix A
There remains a tremendous data set from the post analyses of the pilot study,
which were collected or processed by the PhD candidate and are presented within the
appendix for the sake of completeness.
The focus of the PhD thesis was on samples from the projected underthrust
sequence at DSDP Site 297. However, additional samples were taken around the
future plate boundary thrust, which had also undergone consolidation tests and were
processed by the PhD candidate. Provisional analysis of the data promises a good data
basis for publication. These tests are presented in appendix A1.
In appendix A2 additionally geochemical data is shown. These data could not
be considered for manuscript 3, because of the vast data basis. Thus, it was planned to
split the data into major and trace element geochemistry. The latter is planned for
future publication.
SEM investigations on compacted samples from the oedometer tests were
conducted to shed light on water-rock interaction and textural changes with
deformation. Selected images are presented in appendix A3. They may complement
geochemical data for publication.
The compacted samples from the heated and room temperature tests
underwent mechanical testing at the MARUM soil mechanical laboratory. The
samples were tested for their peak and residual strength as well as rate dependent
friction behaviour. Selected results of direct and ring shear tests are presented in
appendix A4.
APPENDIX 111
Outline of Appendix B
In the appendix B the development and implementation of the heated uniaxial
consolidation apparatuses are described. The general capabilities of the new systems
are shortly outlined and initial results from mono-mineral standards are presented.
Due to the long term tests of 3-5 month, time was too short to accumulate sufficient
data for publication within the PhD project.
APPENDIX 112
APPENDIX A1 As part of the pilot work at SCRIPPS Institution of Oceanography, a number
of room temperature consolidation tests were carried out in addition to the heated
tests, which represent the heart of this PhD thesis. These tests were run on samples
from DSDP Site 297 and sampled the interval in the incoming sedimentary succession
most likely to become the future plate boundary thrust.
At present, the data was reprocessed by the PhD candidate and discussed with the
investigators involved. A publication is planned in the near future focussing on
consolidation behaviour and permeability studies. Owing to the fact that a broad suite
of fine- to coarse-grained specimens was tested, this work expands the understanding
of the overall hydrogeologic behaviour of clay-rich marine sediments during
subduction.
The results of the consolidation studies are shown in Figure 1-7. The majority
of the samples display a similar void ratio vs. effective stress relationship. Typical
values for the compression indices from the log-linear fit line range from 0.43-0.24.
Changes in lithology can alter this relationship and likely account for some of the
variability in the data (cf. Tab. 1). The hydraulic conductivity vs. void ratio
relationship for all the samples is also shown in the figures.
Table 1: XRD results of samples which under went high stress consolidation.
(Sm=Smectite, Qtz=quartz, Plg=plagioclase, Chl=Chlorite, Il=illite,
Musc=muscovite)
Core Name Depth (mbsf) Lithology Sm
(wt-%) Qtz
(wt-%) Plg
(wt-%) Chl
(wt-%) Il
(wt-%)
23-3-102-107 Nan1 594.02 Ash-Rich-silty Claystone 39.37 19.78 10.53 6.69 7.03
26-2-105-108 Nan2 668.55 Volcanic Ash 54.02 36.08 2.81 1.03 39.78 25-3-121-127 Nan3 651.21 Volcanic Ash 33.19 10.78 15.94 6.44 10 24-3-18-26 Nan4 621.68 Silty Claystone 20.2 30.5 17.2 6.6 25.5
23-4-0-6 Nan5 594.5 Ash-Rich-silty Claystone 13.26 18.86 14.18 13.92 43.3
25-6-73-78 Nan9 655.23 Volcanic Ash 51 13 15 4 23.62
APPENDIX 113
Fig 1: Preliminary results of the consolidation test of sample Nan1 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 114
Fig 2: Preliminary results of the consolidation test of sample Nan2 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 115
Fig 3: Preliminary results of the consolidation test of sample Nan3 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 116
Fig 4: Preliminary results of the consolidation test of sample Nan3 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 117
Fig 5: Preliminary results of the consolidation test of sample Nan2 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 118
Fig 6: Preliminary results of the consolidation test of sample Nan6 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 119
Fig 7: Preliminary results of the consolidation test of sample Nan8 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 120
Fig 8: Preliminary results of the consolidation test of sample Nan9 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 121
APPENDIX A2 To understand the transfer of geochemical tracers within the shallow subduction
zone, trace elements (table 1-3) and boron isotopes (Fig. 1) were determined. Trace
elements compositions of sampled fluids from hydrothermal tests were partly measured
at SCRIPPS Institution of Oceanography as well as by the PhD candidate at the
University of Bremen. The latter can be recognized in table 1-3 where the full set of trace
elements is shown. Preliminary results were presented by the PhD candidate at the ICDP-
IODP Kolloquium 2007 in Potsdam, Germany (see next page). Data analyses and
manuscript preparation by the PhD candidate is underway to complete the geochemical
investigation of fluid-rock investigation of the Nankai end member samples.
Fig. 1: Overview of boron systematic in the expelled fluids. (A) Boron enrichment with increasing temperature and effective stress and (B) �11B data plotted against boron content in the fluids. Note that the majority of the data lies between the typical values for seawater and exchangeable boron attached to the clay surface.
APPENDIX 122
Hüpers, A., Kopf, A.J., 2007. Consolidation experiments of marine sediments under hydrothermal conditions: implications for water-rock interaction in the shallow subduction zone, in: IODP-ICDP Kolloquium 2007, Potsdam.
Consolidation experiments of marine sediments under hydrothermal conditions: implications for water-rock interaction in the shallow subduction
zone
A. Hüpers, A.J. Kopf Research Center Ocean Margins, Bremen University, P.O. Box 330440, 28334 Bremen,
Germany ([email protected], [email protected])
Fluids play a critical role to understand key mechanisms in the subduction factory. Hence, it is necessary to reconstruct and quantify the transfer of geochemical tracers from the subducted slab to the overlying lithosphere, hydrosphere and atmosphere. At shallow levels diagenetic and low-grade metamorphic reactions are important processes. They may cause expulsion of large volumes of fluids from hydrous minerals, but also fault seal by precipitation of authigenic phases from interstitial, supersaturated fluids. Both mechanisms can produce pore pressure transients which influence the thermal and rheological development of the accretionary prism. Due to the lack of natural samples from deeper sites, hydrothermal experimental techniques provide the possibility to simulate shallow subduction processes. Previous studies demonstrated the mobilization of large ion lithophile elements relative to high field strength and rare earth elements. Furthermore, they described enrichments in water-soluble elements, as well as on ratios of key trace elements (e.g., B, Ba, Th, Nb).
To characterize the water- rock interaction of marine sediments and seawater, long-term compaction tests were conducted up to PT conditions similar to the upper seismogenic zone. Remoulded samples of the main lithologies (smectite-, illite- and quartz-rich) in the Nankai Trough (Japan) were loaded in an uniaxial apparatus up to 70MPa at 20°C, 100°C and 150°C. Fluids were continuously extracted and analyzed for major and trace elements. As a main result, smectite- and illite-rich samples show a similar distribution of element concentrations with almost constant concentrations of rare earth element during the tests. Fluids of quartz-rich samples show at least twice the threshold for these elements which are already released at low effective normal stresses of < 1MPa. Other elements (e.g. Sr) decrease with increasing pressure towards the end of the tests, while some major elements concentrations (e.g. Mg, Ca) are slightly increasing throughout heated and also room temperature tests. We conclude that some elements may be mobilized throughout our low T hydrothermal experiments (e.g. Rb, K, Ba), although they were previously believed to represent the "slab component" in arc magmas. Thus, such elements are may be less powerful to identify sedimentary input to volcanics than previously assumed. More testing from marine sediments of other convergent margins, possibly at temperatures up to 200-250°C, is necessary to verify these results.
APP
END
IX
12
3
Tab.
1: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of e
xpel
led
fluid
s dur
ing
the
room
tem
pera
ture
con
solid
atio
n te
st o
f the
smec
tite-
rich
sam
ple
(N13
). Th
e as
soci
ated
eff
ectiv
e st
ress
for
the
rele
ased
por
e w
ater
is g
iven
as
aver
age
effe
ctiv
e st
ress
bet
wee
n at
tach
ing
and
rem
ovin
g th
e sa
mpl
ing
flask
.
Sea
- w
ater
N
13-
20_1
N
13-
20_3
N13
-20
_5N
13-
20_7
N13
-20
_9N
13-
20_1
2 N
13-
20_1
5N
13-
20_1
8N
13-
20_2
1N
13-
20_2
4N
13-
20_2
7N
13-
20_2
9 N
13-
20_3
0N
13-
20_3
1N
13-
20_3
2 A
vera
ge
effe
ctiv
e st
ress
(M
Pa)
6.
4011
5E-0
5 0.
0001
9 0.
0005
6 0.
0014
0.
0034
0.
01
0.06
0.
25
0.99
2.
62
6.83
13
.22
18.8
6 27
.85
40.9
7
Ele
men
t
Li
_7(n
g/m
L)
36
1.22
91
4.57
1449
.79
Rb_
85(n
g/m
L)
123.
49
168.
56
248.
20
228.
69
307.
64
27
9.01
26
7.20
28
2.30
27
7.86
26
7.09
24
4.40
20
8.67
16
2.66
12
0.87
66
.27
Y_89
(n
g/m
L)
0.41
37
.29
276.
43
131.
75
16.2
9 94
.99
2.94
2.
60
2.52
1.
07
1.08
0.
99
1.03
1.
26
1.25
1.
55
Zr_9
0(n
g/m
L)
2.
67
31.8
6
5.70
Nb_
93(n
g/m
L)
0.
14
2.59
0.91
Cs_
133
(ng/
mL)
2.85
1.
45
1.
89
La_1
39
(ng/
mL)
0.
54
28.1
1 13
3.60
62
.60
9.79
13
0.67
1.
59
1.35
1.
34
0.97
1.
13
0.95
0.
97
1.19
1.
26
1.05
Ce_
140
(ng/
mL)
0.
63
82.9
0 31
2.55
11
2.72
10
.82
148.
64
1.83
1.
58
1.50
1.
24
1.31
1.
22
1.27
1.
57
1.65
1.
36
Pr_
141
(ng/
mL)
0.
48
6.12
28
.10
10.7
3 0.
87
20.8
7 1.
01
0.95
0.
94
0.92
0.
96
0.94
0.
93
0.92
1.
00
0.95
Nd_
146
(ng/
mL)
0.
43
22.1
7 10
5.43
39
.79
3.26
10
.95
0.94
0.
85
0.84
0.
63
0.65
0.
60
0.63
0.
80
0.86
0.
71
Ta_1
81
(ng/
mL)
0.03
0.
96
0.
20
Pb_2
08
(ng/
mL)
13
.88
568.
56
1425
.97
179.
61
12.3
9
6.15
3.
90
2.87
2.
21
3.62
2.
31
11.3
2 22
.01
5.15
3.
56
Th_2
32
(ng/
mL)
0.
59
4.80
29
.63
13.9
6 3.
17
6.85
1.
88
1.63
1.
57
1.46
1.
51
1.48
1.
49
1.48
1.
60
1.73
U_2
38(n
g/m
L)
0.79
15
.45
19.9
8 1.
20
6.97
146.
13
166.
15
175.
23
86.5
8 11
4.30
87
.84
121.
72
91.4
2 74
.95
77.2
7
Sc_4
5 (n
g/m
L)
0.
26
0.53
0.08
V_51
(n
g/m
L)
24
0.83
13
4.53
20.8
1
Cr_
52(n
g/m
L)
87
50.4
2 22
334.
48
34
0.08
APP
END
IX
12
4
Tab.
1: c
ontin
ued.
Sea
-w
ater
N
13-
20_1
N
13-
20_3
N
13-
20_5
N
13-
20_7
N
13-
20_9
N13
-20
_12
N13
-20
_15
N13
-20
_18
N13
-20
_21
N13
-20
_24
N13
-20
_27
N13
-20
_29
N13
-20
_30
N13
-20
_31
N13
-20
_32
aver
age
effe
ctiv
e st
ress
(M
Pa)
6.
4E-0
5 0.
0001
9 0.
0005
6 0.
0014
0.
0034
0.
01
0.06
0.
25
0.99
2.
62
6.83
13
.22
18.8
6 27
.85
40.9
7
Elem
ent
Co_
59
(ng/
mL)
29.8
4 57
.96
26
.03
Ni_
60
(ng/
mL)
1689
7.8
3560
9.24
1935
0.13
Cu_
63
(ng/
mL)
612.
70
171.
94
16
.92
Zn_6
6 (n
g/m
L)
12
31.3
2 21
65.2
2
350.
85
Ga_
69
(ng/
mL)
0.95
0.
26
0.
02
Sm_1
47
(ng/
mL)
0.
53
6.20
30
.16
9.54
0.
83
27.8
9 0.
98
0.83
0.
85
0.84
0.
90
0.89
0.
84
0.80
0.
76
0.77
Eu_
151
(ng/
mL)
0.
37
0.57
3.
83
1.64
0.
10
11.1
3 0.
46
0.44
0.
43
0.44
0.
44
0.43
0.
42
0.41
0.
45
0.44
Gd_
157
(ng/
mL)
6.25
34
.07
1.
10
Tb_1
59
(ng/
mL)
0.
39
0.97
5.
43
2.30
0.
19
1.27
0.
47
0.45
0.
45
0.45
0.
47
0.46
0.
46
0.44
0.
47
0.46
Dy_
163
(ng/
mL)
0.
28
5.39
31
.99
14.4
3 0.
98
1.07
0.
61
0.57
0.
56
0.48
0.
50
0.48
0.
49
0.51
0.
54
0.53
Ho_
165
(ng/
mL)
0.
49
1.03
6.
71
4.21
0.
26
1.
43
1.33
1.
26
1.40
1.
39
1.41
1.
32
1.22
1.
26
1.24
Er_
166
(ng/
mL)
0.
37
2.94
19
.53
10.4
6 0.
59
10.6
2 1.
00
0.94
0.
89
0.86
0.
88
0.90
0.
84
0.82
0.
90
0.91
Tm_1
69
(ng/
mL)
0.
36
0.36
2.
58
1.66
0.
07
0.82
0.
62
0.60
0.
59
0.60
0.
62
0.61
0.
60
0.57
0.
63
0.62
Yb_1
72
(ng/
mL)
0.
46
3.31
23
.53
8.15
0.
61
1.02
0.
65
0.60
0.
58
0.53
0.
55
0.54
0.
54
0.53
0.
57
0.58
Lu_1
75
(ng/
mL)
0.
34
0.49
3.
57
1.42
0.
10
0.26
0.
29
0.28
0.
27
0.27
0.
28
0.27
0.
27
0.26
0.
28
0.28
Hf_
178
(ng/
mL)
0.09
0.
55
0.
08
APP
END
IX
12
5
Tab.
2: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of
expe
lled
fluid
s du
ring
the
heat
ed c
onso
lidat
ion
test
of
the
smec
tite-
rich
sam
ple
(N13
) at 1
00 °C
. The
ass
ocia
ted
effe
ctiv
e str
ess
for t
he re
leas
ed p
ore
wat
er is
giv
en a
s av
erag
e ef
fect
ive
stre
ss b
etw
een
atta
chin
g an
d re
mov
ing
the
sam
plin
g fla
sk.
S
ea-
wat
er
N13
-100
_1
N13
-100
_3
N13
-100
_5
N13
-100
_5
N13
-100
_7
N13
-100
_9
N13
-10
0_13
N13
-10
0_17
N13
-10
0_21
N13
-10
0_25
av
erag
e ef
fect
ive
stre
ssM
Pa
2.
9E-0
6 6.
02E
-06
4.8E
-06
3.08
E-0
5 4.
7E-0
5 4.
7E-0
5 0.
0003
4 0.
0017
0.
0092
0.
090
Elem
ent
Li
_7(n
g/m
L)
63
1.02
20
61.3
3
3519
.48
4629
.13
Rb_
85
(ng/
mL)
12
3.49
27
9.88
53
6.01
56
9.86
69
6.61
76
3.86
63
1.20
62
5.44
66
9.27
66
4.35
70
7.71
Y_89
(n
g/m
L)
0.41
10
4.35
59
.89
1.11
2.
06
0.71
1.
03
1.14
1.
05
0.99
1.
29
Zr_9
0 (n
g/m
L)
40
.98
7.53
0.52
0.
76
Nb_
93
(ng/
mL)
2.75
2.
14
0.
28
0.17
Cs_
133
(ng/
mL)
3.65
7.
93
10
.18
11.0
8
La_1
39(n
g/m
L)
0.54
48
.74
28.0
8 1.
06
0.83
0.
17
1.10
0.
97
0.94
1.
00
1.45
Ce_
140
(ng/
mL)
0.
63
127.
22
68.0
2 1.
42
1.46
0.
48
1.34
1.
31
1.23
1.
25
1.14
Pr_1
41
(ng/
mL)
0.
48
10.7
6 5.
48
0.95
0.
10
0.04
0.
97
0.90
0.
94
0.93
1.
00
Nd_
146
(ng/
mL)
0.
43
41.4
0 21
.04
0.62
0.
39
0.19
0.
73
0.58
0.
63
0.58
0.
81
Ta_1
81(n
g/m
L)
1.
16
0.46
0.03
0.
02
Pb_
208
(ng/
mL)
13
.88
1009
.96
2799
.63
8.10
48
.67
11.2
4 8.
61
6.59
2.
75
3.96
0.
88
Th_2
32(n
g/m
L)
0.59
24
.81
4.37
1.
51
0.19
0.
07
1.53
1.
45
1.52
1.
47
1.01
U_2
38
(ng/
mL)
0.
79
15.9
7 5.
80
1.60
0.
71
1.20
3.
15
6.81
11
.11
10.3
1 10
.33
Sc_
45(n
g/m
L)
3.
00
1.32
0.08
0.
10
V_5
1(n
g/m
L)
24
9.53
22
6.44
26.9
6 43
.97
Cr_
52(n
g/m
L)
51
245.
09
9877
.75
49
.08
16.4
5
APP
END
IX
12
6
Tab.
2: c
ontin
ued.
Sea-
wat
er
N13
-100
_1
N13
-100
_3
N13
-100
_5
N13
-100
_5
N13
-100
_7
N13
-100
_9
N13
-10
0_13
N13
-10
0_17
N13
-10
0_21
N13
-10
0_25
aver
age
effe
ctiv
e st
ress
M
Pa
2.
9E-0
6 6.
0E-0
6 4.
8E-0
6 3.
0E-0
5 4.
7E-0
5 4.
7E-0
5 0.
0003
4 0.
0017
0.
0092
0.
090
Ele
men
t
Co_
59(n
g/m
L)
11
9.70
55
.51
18
.37
18.3
6
Ni_
60(n
g/m
L)
74
257.
99
3149
8.11
7067
.90
4007
.00
Cu_
63(n
g/m
L)
34
90.4
6 36
08.0
2
3506
.75
4348
.94
Zn_6
6 (n
g/m
L)
21
73.1
5 40
972.
22
11
21.8
5 84
9.08
Ga_
69
(ng/
mL)
0.51
0.
65
0.
03
0.03
Sm
_147
(n
g/m
L)
0.53
11
.97
6.32
0.
87
0.12
0.
10
0.89
0.
63
0.79
0.
92
1.08
Eu_1
51
(ng/
mL)
0.
37
1.39
0.
66
0.51
0.
02
0.01
0.
51
0.46
0.
49
0.48
0.
75
Gd_
157
(ng/
mL)
13.1
5 6.
68
0.
19
0.03
Tb_1
59
(ng/
mL)
0.
39
2.10
1.
05
0.46
0.
01
0.00
0.
47
0.44
0.
46
0.45
0.
34
Dy_
163
(ng/
mL)
0.
28
12.3
7 6.
14
0.50
0.
10
0.07
0.
51
0.47
0.
49
0.48
0.
71
Ho_
165
(ng/
mL)
0.
49
2.60
1.
35
1.33
0.
11
0.11
1.
45
1.04
1.
34
1.39
1.
30
Er_1
66
(ng/
mL)
0.
37
7.43
3.
88
0.88
0.
05
0.01
0.
92
0.81
0.
88
0.87
0.
96
Tm_1
69(n
g/m
L)
0.36
1.
01
0.51
0.
62
0.00
0.
00
0.63
0.
59
0.62
0.
61
0.60
Yb_1
72
(ng/
mL)
0.
46
9.11
4.
43
0.55
0.
11
0.04
0.
56
0.53
0.
55
0.53
0.
84
Lu_1
75
(ng/
mL)
0.
34
1.34
0.
71
0.28
0.
02
0.01
0.
28
0.26
0.
27
0.27
0.
60
Hf_
178
(ng/
mL)
0.88
0.
15
0.
02
0.01
APP
END
IX
12
7
Tab.
2: c
ontin
ued.
Sea-
wat
er
N13
-10
0_28
N13
-10
0_30
N13
-10
0_32
N13
-10
0_34
N13
-10
0_35
N13
-10
0_36
N13
-10
0_37
N
13-
100_
38N
13-
100_
39N
13-
100_
41N
13-
100_
42av
erag
eef
fect
ive
stre
ssM
Pa
0.
27
0.68
1.
24
4.29
5.
65
7.73
10
.33
14.3
0 19
.91
27.
41.3
9
Ele
men
t
C
o_59
(ng/
mL)
Ni_
60
(ng/
mL)
Cu_
63(n
g/m
L)
Zn_6
6 (n
g/m
L)
Ga_
69
(ng/
mL)
Sm
_147
(n
g/m
L)
0.53
0.
96
0.93
1.
03
1.04
1.
01
0.95
1.
13
0.90
1.
04
0.94
1.
77
Eu_1
51
(ng/
mL)
0.
37
0.74
0.
77
0.74
0.
73
0.73
0.
72
0.78
0.
74
0.76
0.
80
0.90
Gd_
157
(ng/
mL)
Tb_1
59
(ng/
mL)
0.
39
0.34
0.
35
0.35
0.
34
0.34
0.
33
0.36
0.
33
0.34
0.
35
0.42
Dy_
163
(ng/
mL)
0.
28
0.71
0.
72
0.73
0.
72
0.70
0.
70
0.85
0.
71
0.72
0.
74
1.34
Ho_
165
(ng/
mL)
0.
49
1.15
1.
24
1.26
1.
30
1.32
1.
37
1.36
1.
30
1.31
1.
31
1.46
Er_
166
(ng/
mL)
0.
37
1.61
0.
96
1.00
0.
94
0.97
0.
95
1.06
0.
96
0.96
0.
97
1.32
Tm_1
69(n
g/m
L)
0.36
0.
81
0.60
0.
61
0.60
0.
59
0.59
0.
62
0.58
0.
59
0.61
0.
64
Yb_1
72
(ng/
mL)
0.
46
0.96
0.
84
0.86
0.
84
0.83
0.
83
0.90
0.
82
0.83
0.
86
1.14
Lu_1
75(n
g/m
L)
0.34
0.
65
0.61
0.
62
0.60
0.
59
0.59
0.
62
0.59
0.
60
0.62
0.
65
Hf_
178
(ng/
mL)
APP
END
IX
12
8
Tab.
3: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of
expe
lled
fluid
s du
ring
the
heat
ed c
onso
lidat
ion
test
of
the
smec
tite-
rich
sam
ple
(N13
) at 1
50 °C
. The
ass
ocia
ted
effe
ctiv
e str
ess
for t
he re
leas
ed p
ore
wat
er is
giv
en a
s av
erag
e ef
fect
ive
stre
ss b
etw
een
atta
chin
g an
d re
mov
ing
the
sam
plin
g fla
sk.
Se
a-w
ater
N
13-
150_
5 N
13-
150_
7 N
13-
150_
9N
13-
150_
10N
13-
150_
11
N13
-15
0_13
N13
-15
0_14
N13
-15
0_15
N
13-
150_
16N
13-
150_
17
N13
-15
0_18
N13
-15
0_19
N13
-15
0_20
aver
age
effe
ctiv
e st
ress
M
Pa
0.
020
0.43
0.
87
1.24
1.
88
3.96
8.
45
12.3
3 15
.87
21.2
4 25
.00
40.6
5 61
.47
Ele
men
t
Li
_7(n
g/m
L)
75
49.9
9 88
70.7
2 11
922.
9 10
974.
31
2529
.87
1156
7.95
13
373.
1 12
741.
25
1088
5.43
19
55.7
23
0.66
21
2.64
28
52.7
6
Rb_
85(n
g/m
L)
123.
49
800.
66
883.
77
1001
.21
892.
45
218.
39
880.
43
977.
34
914.
59
730.
52
145.
25
21.0
6 25
.66
375.
70
Y_89
(n
g/m
L)
0.41
8.
38
1.15
0.
87
2.35
0.
54
0.88
0.
95
1.03
0.
97
0.22
0.
08
0.14
4.
36
Zr_9
0(n
g/m
L)
8.
62
0.38
0.
29
1.74
0.
54
0.33
0.
34
0.38
0.
69
0.27
0.
19
0.20
5.
51
Nb_
93(n
g/m
L)
0.
48
0.02
0.
02
0.10
0.
03
0.02
0.
03
0.03
0.
03
0.02
0.
00
0.00
0.
04
Cs_
133
(ng/
mL)
16.0
3 17
.75
19.4
7 17
.45
4.32
16
.75
18.4
9 16
.91
12.7
9 2.
48
0.46
0.
66
13.5
4
La_1
39
(ng/
mL)
0.
54
10.8
8 2.
10
1.20
2.
65
0.51
0.
93
1.00
0.
97
0.80
0.
22
0.08
0.
17
5.33
Ce_
140
(ng/
mL)
0.
63
24.3
2 4.
43
2.78
6.
53
1.27
2.
40
2.57
2.
55
2.08
0.
47
0.13
0.
25
8.39
Pr_1
41
(ng/
mL)
0.
48
1.93
0.
20
0.12
0.
43
0.08
0.
12
0.12
0.
12
0.11
0.
03
0.01
0.
01
0.39
Nd_
146
(ng/
mL)
0.
43
6.33
0.
63
0.39
1.
37
0.31
0.
40
0.40
0.
40
0.38
0.
10
0.04
0.
04
1.06
Ta_1
81
(ng/
mL)
0.15
0.
02
0.01
0.
02
0.00
0.
01
0.01
0.
01
0.01
0.
00
0.00
0.
00
0.00
Pb_2
08
(ng/
mL)
13
.88
364.
99
143.
23
305.
81
795.
79
192.
30
611.
67
930.
14
922.
61
630.
82
208.
65
65.1
9 66
.72
1488
.67
Th_2
32
(ng/
mL)
0.
59
6.45
0.
11
0.05
1.
18
0.15
0.
07
0.07
0.
07
0.11
0.
05
0.01
0.
01
0.19
U_2
38(n
g/m
L)
0.79
2.
20
0.18
0.
07
0.44
0.
11
0.11
0.
10
0.09
0.
12
0.17
0.
10
0.08
2.
25
Sc_4
5 (n
g/m
L)
0.
93
0.78
0.
36
0.47
0.
18
0.30
0.
34
0.41
0.
84
0.24
0.
07
0.06
2.
34
V_51
(n
g/m
L)
11
.43
0.62
0.
28
9.34
3.
23
0.66
0.
87
0.82
0.
98
0.56
0.
31
0.33
10
.33
Cr_
52(n
g/m
L)
82
.54
21.3
7 27
.44
79.3
9 21
.99
36.8
4 46
.94
52.9
6 64
.64
27.0
5 13
.19
14.6
2 34
5.52
APP
END
IX
12
9
Tab.
3: c
ontin
ued.
Sea
-w
ater
N
13-
150_
5 N
13-
150_
7 N
13-
150_
9 N
13-
150_
10
N13
-15
0_11
N
13-
150_
13
N13
-15
0_14
N
13-
150_
15
N13
-15
0_16
N
13-
150_
17
N13
-15
0_18
N
13-
150_
19
N13
-15
0_20
av
erag
e ef
fect
ive
stre
ss
MP
a
0.
020
0.43
0.
87
1.24
1.
88
3.96
8.
45
12.3
3 15
.87
21.2
4 25
.00
40.6
5 61
.47
Ele
men
t
C
o_59
(n
g/m
L)
4.
28
4.08
5.
55
7.21
3.
70
6.49
5.
65
4.95
5.
73
2.26
1.
51
5.63
98
.74
Ni_
60
(ng/
mL)
554.
05
407.
47
689.
83
1027
.95
479.
32
1505
.94
1352
.7
1141
.0
1348
.55
469.
26
196.
05
531.
59
8484
.87
Cu_
63
(ng/
mL)
456.
70
80.8
5 17
.31
120.
63
47.2
1 31
.06
18.9
9 16
.87
54.2
5 13
1.65
49
.20
96.6
7 22
53.4
9
Zn_6
6 (n
g/m
L)
63
96.4
0 57
5.69
61
5.85
24
449.
13
2910
8.54
73
3.55
65
0.80
99
4.74
24
78.0
9 40
00.0
2 13
245.
42
8657
5.7
1553
849.
57
Ga_
69
(ng/
mL)
7.67
0.
28
0.11
1.
62
0.41
0.
11
0.13
0.
12
0.11
0.
08
0.10
0.
64
11.8
8
Sm
_147
(n
g/m
L)
0.53
1.
51
0.14
0.
06
0.42
0.
06
0.03
0.
09
0.12
0.
09
0.03
0.
01
0.01
0.
31
Eu_1
51
(ng/
mL)
0.
37
0.05
0.
02
0.01
0.
03
0.01
0.
01
0.01
0.
01
0.01
0.
00
0.00
0.
00
0.04
Gd_
157
(ng/
mL)
1.50
0.
20
0.07
0.
35
0.05
0.
10
0.10
0.
08
0.09
0.
04
0.00
0.
03
0.23
Tb_1
59
(ng/
mL)
0.
39
0.20
0.
02
0.01
0.
05
0.01
0.
01
0.01
0.
01
0.02
0.
00
0.00
0.
00
0.05
Dy_
163
(ng/
mL)
0.
28
1.16
0.
09
0.08
0.
20
0.06
0.
07
0.06
0.
06
0.08
0.
02
0.00
0.
01
0.30
Ho_
165
(ng/
mL)
0.
49
0.24
0.
06
0.12
0.
17
0.04
0.
17
0.18
0.
16
0.08
0.
01
0.01
0.
01
0.30
Er_
166
(ng/
mL)
0.
37
0.52
0.
07
0.03
0.
11
0.02
0.
02
0.05
0.
04
0.04
0.
01
0.00
0.
01
0.46
Tm_1
69
(ng/
mL)
0.
36
0.07
0.
01
0.00
0.
01
0.00
0.
01
0.01
0.
01
0.01
0.
00
0.00
0.
00
0.07
Yb_1
72
(ng/
mL)
0.
46
0.54
0.
08
0.05
0.
16
0.03
0.
09
0.05
0.
07
0.09
0.
01
0.00
0.
01
0.34
Lu_1
75
(ng/
mL)
0.
34
0.07
0.
01
0.00
0.
02
0.01
0.
01
0.01
0.
01
0.01
0.
00
0.00
0.
00
0.03
Hf_
178
(ng/
mL)
0.27
0.
00
0.00
0.
03
0.03
0.
02
0.00
0.
01
0.02
0.
02
0.00
0.
01
0.14
APP
END
IX
13
0
Tab.
4: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of e
xpel
led
fluid
s dur
ing
the
room
tem
pera
ture
con
solid
atio
n te
st o
f the
illit
ic sa
mpl
e (N
14).
The
asso
ciat
ed e
ffec
tive
stre
ss fo
r the
rele
ased
por
e w
ater
is g
iven
as
aver
age
effe
ctiv
e st
ress
bet
wee
n at
tach
ing
and
rem
ovin
g th
e sa
mpl
ing
flask
.
Sea-
wat
er
N14
-20
_1N
14-
20_4
N14
-20
_6N
14-
20_8
N14
-20
_10
N14
-20
_12
N14
-20
_13
N14
-20
_14
N14
-20
_15
N14
-20
_16
N14
-20
_17
Ave
rage
ef
fect
ive
stre
ss M
Pa
0.
46
2.29
3.
37
4.89
8.
42
9.27
11
.23
13.0
3 14
.23
26.7
0 56
.15
Ele
men
t
Li
_7(n
g/m
L)
31
7.95
Rb_
85
(ng/
mL)
12
3.4
159.
56
150.
94
153.
85
149.
19
270.
90
155.
22
153.
32
147.
20
138.
33
130.
24
270.
90
Y_89
(n
g/m
L)
0.41
3.
51
0.87
1.
07
0.84
3.
14
0.82
0.
82
0.92
0.
80
0.82
3.
14
Zr_9
0 (n
g/m
L)
0.
04
Nb_
93
(ng/
mL)
0.01
Cs_
133
(ng/
mL)
0.89
La_1
39(n
g/m
L)
0.54
6.
26
1.05
1.
02
0.91
1.
34
1.19
0.
95
1.04
1.
09
1.02
1.
34
Ce_
140
(ng/
mL)
0.
63
15.7
8 1.
52
1.40
1.
21
1.55
1.
62
1.26
1.
32
1.38
1.
27
1.62
Pr_1
41
(ng/
mL)
0.
48
1.27
0.
94
0.97
0.
92
0.97
0.
95
0.92
0.
94
0.95
0.
93
0.97
Nd_
146
(ng/
mL)
0.
43
4.27
0.
66
0.66
0.
57
0.78
0.
67
0.60
0.
59
0.61
0.
61
0.78
Ta_1
81(n
g/m
L)
0.
00
Pb_
208
(ng/
mL)
13
.88
10.9
3 12
.40
4.56
2.
27
5.46
47
.00
6.50
6.
54
8.38
6.
68
47.0
0
Th_2
32(n
g/m
L)
0.59
0.
02
1.48
1.
81
1.54
1.
67
1.45
1.
47
1.49
1.
48
1.48
1.
81
U_2
38
(ng/
mL)
0.
79
8.02
11
.50
12.9
0 14
.53
92.6
9 17
.75
19.4
5 21
.14
24.2
2 27
.77
92.6
9
Sc_
45(n
g/m
L)
0.
03
V_5
1 (n
g/m
L)
9.
32
Cr_
52(n
g/m
L)
83
.45
APP
END
IX
13
1
Tab.
4: c
ontin
ued.
Sea-
wat
er
N14
-20
_1N
14-
20_4
N14
-20
_6N
14-
20_8
N14
-20
_10
N14
-20
_12
N14
-20
_13
N14
-20
_14
N14
-20
_15
N14
-20
_16
N14
-20
_17
aver
age
effe
ctiv
e st
ress
M
Pa
0.
46
2.29
3.
37
4.89
8.
42
9.27
11
.23
13.0
3 14
.23
26.7
0 56
.15
Ele
men
t
C
o_59
(ng/
mL)
5.41
Ni_
60(n
g/m
L)
10
19.6
4
Cu_
63(n
g/m
L)
44
.36
Zn_6
6 (n
g/m
L)
10
94.2
7
Ga_
69
(ng/
mL)
0.01
Sm
_147
(n
g/m
L)
0.53
1.
15
0.78
0.
74
0.67
0.
92
0.61
0.
66
0.64
0.
65
0.67
0.
92
Eu_1
51
(ng/
mL)
0.
37
0.07
0.
43
0.44
0.
44
0.44
0.
43
0.44
0.
44
0.44
0.
44
0.44
Gd_
157
(ng/
mL)
0.87
Tb_1
59
(ng/
mL)
0.
39
0.10
0.
50
0.47
0.
45
0.47
0.
44
0.45
0.
46
0.46
0.
45
0.50
Dy_
163
(ng/
mL)
0.
28
0.55
0.
51
0.50
0.
48
0.56
0.
47
0.48
0.
49
0.49
0.
48
0.56
Ho_
165
(ng/
mL)
0.
49
0.12
1.
13
1.14
1.
05
1.38
1.
00
1.03
1.
06
1.01
1.
02
1.38
Er_
166
(ng/
mL)
0.
37
0.22
0.
84
0.87
0.
82
0.96
0.
82
0.85
0.
86
0.85
0.
84
0.96
Tm_1
69(n
g/m
L)
0.36
0.
02
0.60
0.
62
0.61
0.
62
0.59
0.
60
0.62
0.
61
0.61
0.
62
Yb_1
72
(ng/
mL)
0.
46
0.20
0.
54
0.56
0.
54
0.62
0.
53
0.54
0.
60
0.54
0.
54
0.62
Lu_1
75
(ng/
mL)
0.
34
0.03
0.
27
0.28
0.
27
0.29
0.
27
0.27
0.
29
0.27
0.
27
0.29
Hf_
178
(ng/
mL)
0.00
APP
END
IX
13
2
Tab.
5: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of e
xpel
led
fluid
s du
ring
the
heat
ed c
onso
lidat
ion
test
of t
he il
litic
sam
ple
(N14
) at
100
°C. T
he a
ssoc
iate
d ef
fect
ive
stre
ss fo
r the
rele
ased
por
e w
ater
is g
iven
as a
vera
ge e
ffec
tive
stre
ss b
etw
een
atta
chin
g an
d re
mov
ing
the
sam
plin
g fla
sk.
Se
a-w
ater
N
14-
100_
1 N
14-
100_
4N
14-
100_
6N
14-
100_
7N
14-
100_
8N
14-
100_
9 N
14-
100_
10N
14-
100_
11
N14
-10
0_12
N14
-10
0_13
N14
-10
0_14
av
erag
e ef
fect
ive
stre
ss M
Pa
8.
0E-0
6 0.
0042
0.
035
0.09
0.
26
0.69
2.
37
5.82
12
.89
37.0
9 61
.00
Ele
men
t
Li
_7(n
g/m
L)
39
97.4
3
Rb_
85(n
g/m
L)
123.
49
249.
99
450.
93
750.
83
709.
49
711.
87
722.
61
738.
81
707.
25
742.
82
670.
26
620.
76
Y_89
(n
g/m
L)
0.41
0.
97
1.12
0.
51
1.32
1.
45
1.68
1.
62
1.19
1.
17
1.09
1.
09
Zr_9
0(n
g/m
L)
0.
42
Nb_
93(n
g/m
L)
0.
11
Cs_
133
(ng/
mL)
17.1
6
La_1
39
(ng/
mL)
0.
54
1.40
1.
16
0.22
1.
36
1.09
1.
14
1.24
0.
94
0.94
0.
88
0.99
Ce_
140
(ng/
mL)
0.
63
1.29
1.
50
0.60
1.
31
1.34
1.
65
1.69
1.
14
1.03
1.
04
1.11
Pr_
141
(ng/
mL)
0.
48
1.02
1.
02
0.05
0.
96
0.97
1.
01
1.04
0.
96
0.98
0.
93
0.95
Nd_
146
(ng/
mL)
0.
43
0.88
0.
93
0.16
0.
85
0.89
0.
94
1.03
0.
80
0.85
0.
79
0.79
Ta_1
81
(ng/
mL)
0.01
Pb_2
08
(ng/
mL)
13
.88
8.54
18
.55
14.2
6 8.
38
6.77
9.
60
25.2
3 3.
00
1.50
4.
09
2.68
Th_2
32
(ng/
mL)
0.
59
1.02
1.
06
0.20
1.
10
1.09
1.
23
1.18
1.
01
1.04
1.
00
1.00
U_2
38(n
g/m
L)
0.79
1.
43
1.95
0.
57
1.49
1.
40
1.29
1.
29
1.55
1.
55
1.90
2.
27
Sc_4
5 (n
g/m
L)
0.
08
V_51
(n
g/m
L)
10
.77
Cr_
52(n
g/m
L)
79
.36
APP
END
IX
13
3
Tab.
5: c
ontin
ued.
Sea-
wat
er
N14
-10
0_1
N14
-10
0_4
N14
-10
0_6
N14
-10
0_7
N14
-10
0_8
N14
-10
0_9
N14
-10
0_10
N14
-10
0_11
N
14-
100_
12N
14-
100_
13N
14-
100_
14
aver
age
effe
ctiv
e st
ress
M
Pa
8.
0E-0
6 0.
0042
0.
035
0.09
0.
26
0.69
2.
37
5.82
12
.89
37.0
9 61
.00
Ele
men
t
C
o_59
(ng/
mL)
15.2
0
Ni_
60(n
g/m
L)
14
84.1
1
Cu_
63(n
g/m
L)
61
27.8
9
Zn_6
6 (n
g/m
L)
17
6.09
Ga_
69
(ng/
mL)
0.01
Sm
_147
(n
g/m
L)
0.53
0.
77
0.83
0.
06
0.82
0.
90
0.92
0.
96
0.86
0.
90
0.91
0.
90
Eu_1
51
(ng/
mL)
0.
37
0.73
0.
74
0.01
0.
74
0.73
0.
73
0.79
0.
77
0.80
0.
79
0.81
Gd_
157
(ng/
mL)
0.03
Tb_1
59
(ng/
mL)
0.
39
0.33
0.
34
0.01
0.
32
0.33
0.
34
0.35
0.
33
0.34
0.
32
0.33
Dy_
163
(ng/
mL)
0.
28
0.70
0.
74
0.02
0.
70
0.77
0.
77
0.77
0.
72
0.72
0.
68
0.70
Ho_
165
(ng/
mL)
0.
49
0.67
0.
75
0.04
0.
84
0.92
0.
92
1.04
0.
99
1.06
1.
05
1.13
Er_
166
(ng/
mL)
0.
37
0.87
0.
91
0.03
0.
88
0.95
0.
98
0.97
0.
92
0.96
0.
91
0.94
Tm_1
69(n
g/m
L)
0.36
0.
58
0.60
0.
00
0.58
0.
59
0.60
0.
62
0.59
0.
61
0.57
0.
59
Yb_1
72
(ng/
mL)
0.
46
0.82
0.
85
0.02
0.
82
0.85
0.
87
0.90
0.
83
0.86
0.
80
0.82
Lu_1
75
(ng/
mL)
0.
34
0.59
0.
61
0.00
0.
58
0.60
0.
60
0.63
0.
60
0.61
0.
58
0.59
Hf_
178
(ng/
mL)
0.07
APP
END
IX
13
4
Tab.
6: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of e
xpel
led
fluid
s du
ring
the
heat
ed c
onso
lidat
ion
test
of t
he il
litic
sam
ple
(N14
) at
150
°C. T
he a
ssoc
iate
d ef
fect
ive
stre
ss fo
r the
rele
ased
por
e w
ater
is g
iven
as a
vera
ge e
ffec
tive
stre
ss b
etw
een
atta
chin
g an
d re
mov
ing
the
sam
plin
g fla
sk.
S
ea-
wat
er
N14
-150
_1
N14
-150
_2
N14
-150
_4
N14
-150
_6
N14
-150
_8
N14
-150
_10
N14
-150
_12
aver
age
effe
ctiv
e st
ress
MP
a
2.9E
-10
2.8E
-09
1.2E
-08
1.2E
-08
1.0E
-08
3.9E
-08
11.0
5
Elem
ent
Li_7
(ng/
mL)
14.4
2 3.
59
17.7
9 5.
24
3.34
8.
90
25.2
4
Rb_
85
(ng/
mL)
12
3.49
6.
09
3.20
5.
72
2.29
1.
68
3.03
7.
94
Y_89
(n
g/m
L)
0.41
2.
24
0.76
1.
70
0.62
0.
60
0.88
1.
63
Zr_9
0 (n
g/m
L)
0.
80
0.33
0.
54
0.28
0.
38
0.58
0.
77
Nb_
93
(ng/
mL)
0.15
0.
07
0.16
0.
07
0.09
0.
08
0.19
Cs_
133
(ng/
mL)
0.18
0.
10
0.21
0.
12
0.13
0.
11
0.35
La_1
39(n
g/m
L)
0.54
0.
13
0.05
0.
19
0.07
0.
06
2.77
0.
41
Ce_
140
(ng/
mL)
0.
63
0.53
0.
20
0.68
0.
25
0.23
11
.11
1.28
Pr_1
41
(ng/
mL)
0.
48
0.09
0.
03
0.10
0.
04
0.04
0.
67
0.17
Nd_
146
(ng/
mL)
0.
43
0.52
0.
18
0.51
0.
22
0.21
2.
05
0.82
Ta_1
81(n
g/m
L)
0.
00
0.00
0.
01
0.00
0.
00
0.00
0.
00
Pb_
208
(ng/
mL)
13
.88
36.5
0 17
.36
27.0
2 17
.61
19.5
6 19
.59
33.6
5
Th_2
32(n
g/m
L)
0.59
0.
01
0.02
0.
06
0.04
0.
04
0.09
0.
23
U_2
38
(ng/
mL)
0.
79
7.34
2.
92
3.40
1.
27
1.22
0.
96
1.67
Sc_
45(n
g/m
L)
0.
10
0.11
0.
24
0.12
0.
13
0.18
0.
39
V_5
1(n
g/m
L)
15
.00
8.19
14
.23
9.01
12
.13
22.2
0 13
.69
Cr_
52(n
g/m
L)
30
51.1
8 16
50.5
4 30
69.1
0 13
61.5
9 14
02.8
6 31
78.8
7 52
39.0
8
APP
END
IX
13
5
Tab.
6: c
ontin
ued.
Sea
-w
ater
N
an14
-150
_1
Nan
14-1
50_2
N
an14
-150
_4
Nan
14-1
50_6
N
an14
-150
_8
Nan
14-1
50_1
0 N
an14
-150
_12
aver
age
effe
ctiv
est
ress
MPa
2.
9E-1
0 2.
8E-0
9 1.
2E-0
8 1.
2E-0
8 1.
0E-0
8 3.
9E-0
8 11
.05
Elem
ent
Co_
59(n
g/m
L)
5.
29
2.76
7.
49
3.57
3.
17
5.13
13
.19
Ni_
60(n
g/m
L)
46
17.1
1 37
77.0
2 37
63.8
6 40
58.8
4 38
62.3
5 33
66.9
3 37
18.6
1
Cu_
63(n
g/m
L)
92
2.56
21
4.12
37
69.5
4 54
9.52
75
9.47
20
63.6
7 88
38.5
0
Zn_6
6(n
g/m
L)
45
21.0
0 24
71.4
9 84
59.0
6 39
13.1
7 29
66.7
5 59
60.7
3 17
102.
47
Ga_
69(n
g/m
L)
0.
14
0.07
0.
16
0.06
0.
07
0.12
0.
41
Sm
_147
(n
g/m
L)
0.53
0.
19
0.13
0.
14
0.09
0.
07
0.10
0.
30
Eu_
151
(ng/
mL)
0.
37
0.07
0.
02
0.04
0.
02
0.02
0.
03
0.07
Gd_
157
(ng/
mL)
0.32
0.
11
0.24
0.
12
0.09
0.
21
0.40
Tb_1
59(n
g/m
L)
0.39
0.
06
0.02
0.
04
0.03
0.
01
0.03
0.
05
Dy_
163
(ng/
mL)
0.
28
0.32
0.
12
0.26
0.
14
0.12
0.
17
0.32
Ho_
165
(ng/
mL)
0.
49
0.07
0.
03
0.06
0.
02
0.02
0.
03
0.06
Er_1
66
(ng/
mL)
0.
37
0.17
0.
07
0.12
0.
06
0.06
0.
09
0.15
Tm_1
69
(ng/
mL)
0.
36
0.04
0.
01
0.02
0.
01
0.01
0.
01
0.02
Yb_1
72
(ng/
mL)
0.
46
0.19
0.
09
0.19
0.
06
0.05
0.
11
0.20
Lu_1
75(n
g/m
L)
0.34
0.
03
0.00
0.
02
0.01
0.
01
0.01
0.
02
Hf_
178
(ng/
mL)
0.02
0.
03
0.01
0.
01
0.02
0.
03
0.02
APP
END
IX
13
6
Tab.
7: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of
expe
lled
fluid
s du
ring
the
room
tem
pera
ture
con
solid
atio
n te
st o
f th
e tu
rbid
itic
sam
ple
(N18
). Th
e as
soci
ated
eff
ectiv
e st
ress
for
the
rele
ased
por
e w
ater
is g
iven
as
aver
age
effe
ctiv
e st
ress
bet
wee
n at
tach
ing
and
rem
ovin
g th
e sa
mpl
ing
flask
.
Sea
-w
ater
N
18-2
0_1
N18
-20
_3N
18-
20_5
N18
-20
_7N
18-
20_9
N
18-
20_1
1N
18-
20_1
8N
18-
20_1
4N
18-
20_1
5N
18-
20_1
6N
18-
20_1
8N
18-
20_1
9av
erag
e ef
fect
ive
stre
ss M
Pa
1.33
145E
-05
0.00
237
217
0.03
754
748
0.11
829
973
0.43
860
086
1.38
391
623.
2150
058
95.
9918
579
39.
9063
251
414
.574
038
232
.062
003
51.0
931
485
Elem
ent
Li
_7(n
g/m
L)
4370
.01
4423
.17
43
90.6
7
Rb_
85(n
g/m
L)
123.
49
253.
53
370.
81
388.
46
392.
79
408.
42
404.
27
396.
86
609.
63
556.
55
355.
89
425.
28
218.
90
Y_89
(n
g/m
L)
0.41
16
9.90
49
1.69
70
3.72
75
1.64
80
5.21
80
5.27
80
8.86
10
44.7
6 99
3.87
81
4.70
10
18.8
2 83
6.73
Zr
_90
(ng/
mL)
10
5.03
12
1.95
132.
24
N
b_93
(ng/
mL)
1.
45
1.72
1.92
Cs_
133
(ng/
mL)
8.
43
7.48
5.29
La_1
39(n
g/m
L)
0.54
90
.56
289.
37
413.
84
440.
45
472.
69
477.
14
473.
86
787.
51
757.
07
483.
48
766.
95
490.
88
Ce_
140
(ng/
mL)
0.
63
230.
36
772.
53
1106
.65
1171
.24
1250
.67
1255
.08
1247
.38
1887
.68
1821
.06
1264
.80
1820
.78
1251
.08
Pr_
141
(ng/
mL)
0.
48
25.0
6 87
.45
124.
21
131.
66
140.
92
141.
09
141.
21
183.
97
176.
28
139.
36
172.
01
136.
23
Nd_
146
(ng/
mL)
0.
43
104.
69
373.
08
532.
56
565.
37
602.
78
602.
89
600.
38
670.
28
645.
90
597.
78
624.
65
576.
06
Ta_1
81(n
g/m
L)
1.51
1.
84
2.
27
P
b_20
8 (n
g/m
L)
13.8
8 94
8.79
33
9.92
19
3.38
14
9.87
11
7.55
12
2.40
14
3.15
78
.00
127.
20
138.
56
32.1
0 10
8.98
Th
_232
(ng/
mL)
0.
59
0.82
2.
61
2.93
3.
93
4.82
5.
60
5.96
8.
19
8.82
6.
46
9.27
7.
16
U_2
38(n
g/m
L)
0.79
7.
71
21.2
5 30
.31
31.0
9 32
.67
31.9
4 31
.32
39.2
0 38
.54
29.0
1 34
.82
27.4
9 S
c_45
(ng/
mL)
17
.32
15.3
5
16.7
1
V_5
1(n
g/m
L)
1099
.74
1183
.10
11
73.0
6
Cr_
52
(ng/
mL)
26
94.4
3 28
98.4
3
4658
.82
APP
END
IX
13
7
Tab.
7: c
ontin
ued.
Sea
-w
ater
N
18-2
0_1
N18
-20
_3N
18-
20_5
N18
-20
_7N
18-
20_9
N
18-
20_1
1N
18-
20_1
8N
18-
20_1
4N
18-
20_1
5N
18-
20_1
6N
18-
20_1
8N
18-
20_1
9av
erag
eef
fect
ive
stre
ssM
Pa
1.
33E
-05
0.00
23
0.03
7 0.
11
0.43
1.
38
3.21
5.
99
9.90
14
.57
32.0
6 51
.09
Elem
ent
C
o_59
(ng/
mL)
12
57.5
8 12
12.1
5
1321
.71
N
i_60
(ng/
mL)
79
80.5
5 80
22.7
1
1237
7.5
5C
u_63
(ng/
mL)
64
2.54
47
2.43
349.
73
Zn
_66
(ng/
mL)
73
93.4
1 71
68.9
1
8117
.64
G
a_69
(n
g/m
L)
4.01
4.
22
4.
23
S
m_1
47
(ng/
mL)
0.
53
22.8
1 84
.31
120.
79
129.
12
136.
92
137.
32
136.
52
170.
75
161.
16
133.
25
159.
98
129.
35
Eu_
151
(ng/
mL)
0.
37
4.79
16
.56
23.7
3 24
.95
26.5
9 26
.54
26.5
4 29
.25
27.8
5 25
.71
27.4
0 25
.01
Gd_
157
(ng/
mL)
16
0.99
15
4.55
155.
85
Tb
_159
(ng/
mL)
0.
39
4.83
15
.88
22.7
5 23
.80
25.8
8 25
.70
25.7
5 23
.40
22.7
4 25
.34
22.6
1 24
.73
Dy_
163
(ng/
mL)
0.
28
26.2
4 85
.52
124.
87
132.
33
141.
58
142.
30
140.
67
125.
95
120.
69
139.
24
122.
19
137.
56
Ho_
165
(ng/
mL)
0.
49
5.57
15
.55
21.9
9 23
.05
24.7
3 25
.00
24.7
3 23
.38
22.2
7 24
.22
22.5
0 24
.14
Er_
166
(ng/
mL)
0.
37
15.2
3 44
.43
63.6
1 67
.78
71.4
4 72
.27
71.7
2 63
.00
60.5
8 71
.80
61.1
6 70
.78
Tm_1
69
(ng/
mL)
0.
36
2.48
5.
30
7.24
7.
57
8.09
8.
16
7.97
7.
90
7.62
7.
95
7.58
7.
90
Yb_1
72
(ng/
mL)
0.
46
13.6
3 39
.97
56.1
4 59
.41
63.5
3 63
.72
62.7
0 71
.57
69.9
5 61
.76
67.4
8 61
.55
Lu_1
75(n
g/m
L)
0.34
2.
15
5.09
6.
99
7.42
7.
88
7.81
7.
89
10.4
1 9.
88
7.60
9.
67
7.66
H
f_17
8(n
g/m
L)
1.80
2.
17
2.
51
APP
END
IX
13
8
Tab.
8: R
aw d
ata
of tr
ace
elem
ent m
easu
rem
ents
of e
xpel
led
fluid
s du
ring
the
heat
ed c
onso
lidat
ion
test
s of
the
turb
iditc
sam
ple
(N18
) at
100
°C a
nd 1
50 °C
. The
ass
ocia
ted
effe
ctiv
e st
ress
for t
he re
leas
ed p
ore
wat
er is
giv
en a
s ave
rage
eff
ectiv
e st
ress
bet
wee
n at
tach
ing
and
rem
ovin
g th
e sa
mpl
ing
flask
.
Se
awat
er N
18-1
00_1
N18
-100
_2N
18-1
00_3
N18
-100
_4N
18-1
00_5
N18
-100
_6 N
18-1
00_7
N18
-100
_8N
18-1
00_9
N18
-150
_1N
18-1
50_6
aver
age
effe
ctiv
e st
ress
MPa
0.00
038
0.01
2 1.
47
3.66
7.
10
14.0
4 21
.49
31.8
21
49.7
9 0.
0003
164
0.01
5295
2
Ele
men
t
Li
_7(n
g/m
L)
31
20.0
3
34
8.84
10
.60
Rb_
85(n
g/m
L)
123.
49
664.
91
908.
62
1202
.20
1229
.58
1439
.77
1158
.43
812.
14
551.
80
538.
08
116.
97
5.15
Y_89
(n
g/m
L)
0.41
47
9.68
58
9.03
90
7.27
92
0.86
10
85.0
7 10
31.8
4 85
6.77
88
3.68
73
5.13
72
.18
0.42
Zr_9
0(n
g/m
L)
23
.01
0.69
0.
29
Nb_
93(n
g/m
L)
0.
23
0.02
0.
01
Cs_
133
(ng/
mL)
14.1
8
10
.20
1.17
La_1
39(n
g/m
L)
0.54
36
2.64
36
5.74
52
5.34
48
0.51
47
0.23
38
9.18
31
8.38
24
2.26
18
7.85
31
.62
0.11
Ce_
140
(ng/
mL)
0.
63
863.
99
1043
.01
1500
.71
1440
.47
1574
.93
1434
.87
1195
.39
1057
.98
793.
81
99.3
5 0.
43
Pr_
141
(ng/
mL)
0.
48
84.0
3 12
7.97
19
0.32
18
7.47
21
3.70
19
2.45
16
1.28
15
1.40
11
5.14
12
.60
0.07
Nd_
146
(ng/
mL)
0.
43
307.
60
507.
89
764.
31
764.
57
863.
33
792.
34
664.
52
626.
22
477.
96
53.3
5 0.
37
Ta_1
81
(ng/
mL)
0.15
0.
03
0.00
Pb_2
08
(ng/
mL)
13
.88
2924
.27
2264
.39
2279
.49
1199
8.09
502.
83
226.
95
1187
1.91
401.
31
1096
0.36
590.
89
45.2
9
Th_2
32
(ng/
mL)
0.
59
1.72
11
.30
29.4
0 27
.11
28.6
6 24
.54
21.4
6 16
.72
8.48
0.
03
0.08
U_2
38(n
g/m
L)
0.79
24
.44
85.3
3 13
2.41
12
4.07
13
7.49
12
2.39
94
.99
91.7
2 52
.65
3.28
1.
60
Sc_4
5 (n
g/m
L)
2.
26
0.28
0.
44
V_51
(n
g/m
L)
51
3.25
42
.11
18.6
4
Cr_
52
(ng/
mL)
1063
.79
205.
48
66.9
5
APP
END
IX
13
9
Tab.
8: c
ontin
ued.
S
eaw
ater
N18
-100
_1N
18-1
00_2
N18
-100
_3N
18-1
00_4
N18
-100
_5N
18-1
00_6
N18
-100
_7N
18-1
00_8
N18
-100
_9N
18-1
50_1
N18
-150
_6av
erag
eef
fect
ive
stre
ss M
Pa
0.
0003
8 0.
012
1.47
3.
66
7.10
14
.04
21.4
9 31
.82
49.7
9 0.
0003
1 0.
015
Ele
men
t
C
o_59
(ng/
mL)
627.
54
140.
14
4.37
Ni_
60
(ng/
mL)
5729
.33
2841
.35
257.
82
Cu_
63(n
g/m
L)
13
50.8
4
14
82.2
9 20
.36
Zn_6
6(n
g/m
L)
18
976.
07
22
04.8
8 17
3.86
Ga_
69
(ng/
mL)
0.60
0.
10
0.04
Sm
_147
(n
g/m
L)
0.53
77
.04
117.
87
180.
91
179.
90
204.
29
185.
70
154.
99
146.
55
110.
54
13.8
6 0.
10
Eu_1
51
(ng/
mL)
0.
37
13.3
4 21
.09
31.7
1 32
.08
36.5
9 32
.43
27.1
7 25
.72
19.5
2 2.
60
0.03
Gd_
157
(ng/
mL)
73.1
8
15
.81
0.12
Tb_1
59
(ng/
mL)
0.
39
10.4
6 19
.15
29.1
8 29
.52
34.1
0 31
.61
26.1
5 25
.75
20.6
9 2.
04
0.02
Dy_
163
(ng/
mL)
0.
28
56.4
9 10
2.63
15
4.44
15
5.78
17
8.56
16
4.90
13
8.14
13
5.73
11
0.43
11
.23
0.11
Ho_
165
(ng/
mL)
0.
49
10.6
8 18
.59
27.2
6 27
.69
31.8
3 29
.29
24.8
4 24
.47
20.4
7 1.
97
0.02
Er_
166
(ng/
mL)
0.
37
28.4
4 51
.57
75.1
6 75
.46
87.0
7 80
.52
67.1
5 67
.43
56.4
3 4.
97
0.04
Tm_1
69(n
g/m
L)
0.36
3.
60
7.91
11
.64
11.6
1 13
.43
12.2
1 10
.23
10.4
7 8.
64
0.56
0.
01
Yb_1
72
(ng/
mL)
0.
46
32.9
2 45
.75
64.5
6 64
.60
73.7
2 67
.44
56.4
6 55
.92
47.7
1 3.
65
0.04
Lu_1
75(n
g/m
L)
0.34
4.
74
6.52
9.
14
9.17
10
.33
9.55
8.
03
8.29
6.
88
0.50
0.
01
Hf_
178
(ng/
mL)
0.45
0.
02
0.00
APPENDIX 140
APPENDIX A3The compacted samples underwent SEM investigation to document water-rock
interaction and microstructural features developed during the deformation. As
described in manuscript 1 and 3 no significant mineral alteration took place. Thus, no
mineral surface alteration or new mineral formations were detected. High resolution
pictures of samples after the direct shear tests show distinct slickensides and lineation
on the shear surfaces. Microcracks of coarser grains in samples N14 and N18 suggest
grain crushing either during the consolidation test or the direct shear experiments. All
samples reveal low porosity, which can be related to the high consolidation stresses
the sediment samples experienced. Further, the SEM pictures give evidence for grain
size description outlined in manuscript 1. The selected samples end member samples
are a smectite-rich clay (sample N13; Fig. 1-3), an illite-rich silty clay (N14; Fig. 4-6)
and a clayey silty to fine sand-grained quartz/feldspar-rich sample (N18; Fig. 7-9
Fig. 1: SEM image with diagonal view on a fragment surface of the smectite-rich sample N13-100 after the consolidation. The sample shows an uniform grain size of flaky clay particles.
APPENDIX 141
Fig. 2: SEM overview image with view on a fragment of the sample N13-100 after the consolidation. The view is parallel to the applied load in the consolidation tests. The flaky arrangement of the particles led to a dense surface.
Fig. 3: SEM overview image with vertical view on the shear plane after the compact of N13-100 underwent direct shear testing. The shear surface is characterised by slickensides and lineation.
APPENDIX 142
Fig. 4: SEM image with view on a fragment of the illitic sample N14-100 after the consolidation. The mineral skeleton of the sample shows flaky clay and silty quartz particles. The latter is recognisable by the conchoidal fracture of the grain in the right corner of the picture.
Fig. 5: SEM image with view on a fragment of the illitic sample N14-100 after the consolidation. In the middle of the picture is a silty grained quartz mineral with typical conchoidal fracture. Microcracks of the grain in the lower left corner suggest grain crushing either during the consolidation test or the direct shear experiment.
APPENDIX 143
Fig. 6: SEM overview image with vertical view on the shear plane after the compact of N14-100 underwent direct shear testing. The shear surface is characterised by slickensides and lineation similar to the smectite-rich sample.
Fig. 7: SEM image with view on a fragment of the relative coarser grained turbiditic sample (N18-100). In the middle can be seen a sandy grained quartz mineral and surrounded by silty grains in the lower left and upper left corner and some clayey fraction between.
APPENDIX 144
Fig. 8: SEM image with view on a fragment of the turbiditic sample (N18-100). In the middle can be seen a fractured silty to sandy grained quartz mineral. Microcracks suggest grain crushing either during the consolidation test or the direct shear experiment.
Fig. 9: SEM overview image with vertical view on the shear surface after the compact of N18-20 underwent direct shear testing. The shear surface is characterised by slickensides and lineation similar to the other samples.
APPENDIX 145
APPENDIX A4 Direct shear experiments
The compacted samples from the heated and room temperature tests were
tested for their peak and residual strengths to determine the impact of the alteration on
mechanical behaviour. The residual geometry of the pucks was not feasible to cut an
annular sample for the planned ring shear tests because some material was cut from
the pucks after the oedometer tests to determine the water content. Thus, subsamples
were tested with the direct shear apparatus at the MARUM geotechnical laboratory.
The direct shear device was originally able of 3 MPa given a cell dimension of
100x100 mm and three experiment rigs combined. The PhD candidate modified the
shear apparatus under his own direction to allow a theoretical normal stress of
40 MPa. This corresponds to a force of 30 kN on a sample geometry of 25x30 mm,
which was accomplished by a custom-built spacer (Fig. 1). However, the
experimental setup did not allow shear forces greater 4500N to pull the upper half of
the shear box. This force was found to be not sufficient to shear the samples at the
proposed high stresses. Thus, a normal load of 4 MPa was used for direct shear testing
despite the fact that samples were highly overconsolidated under these conditions.
Further, a re-hydration of the samples for the tests was not possible, because initial
tests showed that the samples disintegrated during the swelling process. The actual
experiments were conducted in collaboration with a master student who was
supervised by the PhD candidate for the tests. The results (Fig. 2-4) were presented in
combination with ring shear data on disintegrated samples during the IODP/ICDP
colloquium 2008 in Hannover. The abstract is attached to the end of this section.
Fig. 1: Photograph of the modified direct shear cell (25 x 30 mm) and spacer.
APPENDIX 146
Fig. 2: Direct shear test results of the smectite-rich sample (N13).
Fig. 3: Direct shear test results of the illitic sample (N14).
Fig. 4: Direct shear test results of the turbiditic sample (N18).
APPENDIX 147
Ring shear experiments
To determine rate-dependence of frictional behaviour and residual shear
strength, ring shear tests were conducted with the heated and non-heated samples
from the oedometer tests. To perform these experiments the samples were remoulded
and placed in the annular sample chamber. The tests were performed at normal
stresses of 0.9, 3.8, 7.6 and 15.2 MPa. Tested velocities were 0.0005, 0.001, 0.01 and
0.1 mm/s. The total duration of an experiment is 2 weeks to test the complete set of
normal stresses and velocities.
The PhD candidate also modified the ring shear apparatus to allow heated ring
shear tests. Heat-sensitive components of the ring shear device were replaced and the
sample chamber was heated by a small heating blanket (McMaster-Carr), capable of
ca. 170 °C maximum temperature. Pilot tests reached ~50 °C within the sample
chamber, which could be enhanced by additional insulation to a maximum
temperature of ~80°C. The majority of the tests were conducted within a period of
24h at a temperature of 80±5°C and a normal stress of 7.6 MPa. Evaporation was
compensated with tempered water. Thus, the fully saturation was ensured throughout
a test. The majority of the tests were conducted by the PhD candidate and some tests
were conducted by a master student. Preliminary results were presented during the
IODP/ICDP Kolloquium 2008 in Hannover and selected plots are presented for room
temperature and heated tests runs at 7.6 MPa in figures 6-16. The abstract is attached
to the end of this section. A publication of the shear test results is planned under the
lead of the PhD candidate.
Fig. 5: Photograph of the ring shear apparatus with the heating unit surrounding the annular sample cell.
APPENDIX 148
Fig. 6: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the smectite-rich sample (N13-20).
Fig. 7: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the smectite-rich sample (N13-20).
APPENDIX 149
Fig. 8: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the smectite-rich sample (N13-150).
APPENDIX 150
Fig. 9: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the illitic sample (N14-20).
Fig. 10: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the illitic sample (N14-20).
APPENDIX 151
Fig. 11: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the illitic sample (N14-150).
Fig. 12: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the heated consolidation test of the illitic sample (N14-150).
APPENDIX 152
Fig. 13: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).
Fig. 14: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).
APPENDIX 153
Fig. 15: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the turbiditic sample (N18-150).
Fig. 16: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).
APPENDIX 154
Zimmermann, K., Hüpers, A. Kopf, A.J., 2008. Physical Properties of Marine Sediments Undergoing Subduction – Results from Heated Shear Experiments at the Nankai Convergent Margin, in: IODP-ICDP Kolloquium, 2008, Hannover.
Physical Properties of Marine Sediments Undergoing Subduction – Results from Heated Shear Experiments at the Nankai Convergent
Margin
K. Zimmermann, A. Hüpers, A. Kopf MARUM, Bremen University, P.O. Box 330440, 28334 Bremen, Germany
Subduction zones produce frequently earthquakes of magnitude M8 or larger.
These events occur along the subduction plate boundary thrust within a temperature range of 100-150°C to 350-450°C, known as the seismogenic zone. The reason for the onset of coseimic behaviour of the sediments is still unknown. Diagenetic and consolidation processes are supposed to alter the mechanical properties of the initially weak sediments, which may lead to the onset of unstable sliding behaviour. However, effects of PT conditions equivalent to the updip limit on mechanical properties of marine sediments are still poorly understood. Since natural samples from these depths are not available, we conducted isothermal compaction test equivalent to the updip limit to overcome this shortcoming. For this, we focused on end member lithologies from underthrust section of the incoming plate at the Nankai margin (Japan), where the Phillippine Plate subducts under the Eurasian Plate with a velocity of ~4cm/yr. Three samples of marine sediments with different grain sizes (clay - silt) were compacted up to 70 MPa at different temperatures (20°C, 100°C, 150°C) in a hydrothermal oedometer apparatus to simulate subduction down the slab. Afterwards these compacted samples were sheared in a direct shear box at a normal load of 3.8 MPa, room temperature conditions up to a displacement of 8 mm with a velocity of 3 x 10-3mm/s. Furthermore, remoulded aliquots of the same samples of compacted clay- (smectite and illite) and quartz-rich sediments were sheared at up to 16 MPa normal stress to high displacement rate using a ring shear device. Those tests were carried out at four shear velocities and both at room temperature under seawater saturated conditions, and were then subsequently heated to >80°C seawater saturated under drained conditions. As a main result from the direct shear experiments, the clay-rich sediments show the most pronounced strain softening with high peak strength and very low residual coefficient of friction. In contrast, the silty samples show little strain softening. Additionally, the discrepancy between peak and residual is largest for the smectite clay compared to the silty specimens. This increase in peak relative to residual strength may be explained by the higher effective surface area in the samples poor in quartz content. Within all tests conducted so far, the samples compacted at 20°C seem slightly stronger than those which got thermally altered. At high displacements during the ring shear experiments, the friction coefficient of clay minerals (�n~2 MPa) show similar values and are much smaller than the quartz rich sample (ca. residual of 0.13-0.23). At higher normal stresses (up to ~16 MPa) and room temperature, the friction coefficients almost double. When the same samples are heated to >80°C, more pore water as well as clay mineral-bound water is released so that the specimens show a strain hardening behaviour and approach friction coefficients of >0.4. The data correlate well with friction values estimated for plat boundary faults with increasing depth.
APPENDIX 155
APPENDIX B To accomplish the proposed goals of the research project ROME, two heated
deformation apparatuses have been developed at the soil mechanical laboratory at
MARUM (Fig. 1). The main objective of the new devices is to study water-saturated
sediment samples of differing compositions over an extensive PT range. The neat
design of the apparatuses allows investigating both, physical and chemical processes,
in long-term experiments. Basically, an apparatus consists of two principal parts: a
hydraulic system and an uniaxial consolidation cell.
A special hydraulic system setup has been adjusted for each apparatus to create
the required vertical forces, consisting of a load frame, a high tonnage cylinder
(HZB), and a power unit. The power units in use are an ISCO 500D and an ISCO
100DX high precision syringe pump. The unique feature of these pumps is the
extremely slow flow rate. The 500D pump is able to generate forces up to 343kN and
flow rates down to 0.001ml/min. Combined with the HZB hydraulic cylinder this
arrangement generates particularly small vertical displacements down to 4.33*10-
2 mm/day, which are needed for long term testing. The 100DX is capable of forces up
to 915 kN and even smaller flow rates down to 0.00001 ml/min creating
displacements down to 4.33*10-4 mm/day. The load frames are also especially
adapted to provide the necessary access to the consolidation cell from all sides.
Fig. 1: Photograph of one (of the two) computer-controlled oedometer frame with titanium sample cell and ISCO high-precision syringe pump.
APPENDIX 156
The actual deformation of the specimen occurs in the uniaxial consolidation
cell. The cell consists of two pistons at either end of the sample. The lower piston is
arrested at the base plate of the load frame, while the upper piston is steadily moving
downward to apply increasing normal loads onto the sample (Fig. 2). This rather
simple design is particularly useful to remove the compacted sediment pucks in a non-
destructional way after the tests by pushing the pistons through the entire length of the
cylinder. The inner diameter of the cell is 63 mm and the cell can be loaded with
initial sample heights of 100 mm. With these sample dimensions we are able to
produce maximum stresses of 110 MPa (equivalent to depths of ~7 km) and strain
rates down to 1.25*10-8 s-1 in case of the 500D-based system. Maximum stresses for
the 100DX system are 293 MPa and strain rates down to 1.25*10-10 s-1. For heated
tests, the consolidation cell is additionally equipped with a band heater which is
wrapped around the cell (Fig. 3). The heater is capable of maximum temperatures of
200 °C with a regulation of the temperature by an external controller that also
measures the temperature in the cell.
Fig. 2: Schematic diagram of the sample cylinder with two pistons, band heater, pore pressure control (bottom), and fluid collection system (left). (B) Photograph of one computer-controlled oedometer frame during a heated test.
APPENDIX 157
For the proposed investigation of the physical and chemical processes in the
specimen, both pistons are equipped with boreholes to get access to the sample.
Stainless steel filter slabs between sample and piston prevent solids to get into the
bores. To get aliquots of pore water throughout the experiment for geochemical
testing, the upper sample access is drained. With increasing stress the pore fluid will
be squeezed out of the system and collected in attached flasks. Thus, we get pore
water samples for different stages of consolidation (i.e. different effective normal
stress ranges). A back-pressure regulator for drainage ensures that the pore water does
not evaporate in case of heated tests, and that accidentally trapped air remains
dissolved in the pore water. The seals in use allow us to increase the back pressure up
to 30 MPa. To minimise interaction of the saturated sample with the equipment, the
consolidation cell was made of titanium (grade 2). Other components such as tubing
and fittings also consist of non-corrosive materials like high-grade stainless steel,
PTFE, or PP.
Fig. 3: Photograph of one computer-controlled oedometer frame during a heated test.
The alteration of mechanical properties such as permeability, void ratio and
porosity can be determined by the change of deformation and pore water pressure
throughout the tests. The deformation is measured by a displacement transducer. Two
pressure transducers, mounted to the bottom and the top of the cell, measure the pore
water pressure gradient in the cell.
APPENDIX 158
Calibration of the heated uniaxial consolidation devices
All data are logged by a self-adjusted computer program (Fig. 4), which also
functions as a control unit for the pump. Therefore, various types of consolidation
tests such as constant-rate of strain (CRS), constant-rate of loading (CRL), or
incremental loading (IL) experiments can be automatically performed. Measured data
of the hydraulic pump, pressure transducers, displacement transducer and temperature
are immediately displayed in a diagram by the graphical user interface of the program.
The system was thoroughly calibrated before the heated consolidation tests.
The calibration included the displacement transducer, the hydraulic pump, pressure
transducers attached to the consolidation cell and the temperature probe (Fig. 5).
Calibration factors can be inserted into the program, which allows the immediate
display of the data (Fig. 4). Further, the systems were loaded to pressures and
temperatures without sample material in the consolidation cell to determine the
compressibility, the heat loss and the thermal expansion of the systems (Fig. 5).
Especially the implications of compressibility and thermal expansion on sample
deformation have to be regarded in the post-processing of the data.
Fig. 4: Screenshot of the user interface of the LabView™ program, which controls the hydraulic system and logs the different parameter. The view shows the logged temperature with time.
APPENDIX 159
Fig. 5: Example of the calibration procedure showing (A) calibration line of the displacement transducer, (B) the hydraulic pump, (C) the temperature transducer, (D) the pressure transducer attached to the bottom of the consolidation cell, (E) pressure transducer attached to the top of the consolidation cell, (F) the compressibility of the load frame, (G) the heat loss between bandheater and consolidation cell, and the thermal expansion of the consolidation cell.
APPENDIX 160
Preliminary results of heated consolidation tests of end member mineral
standards and testing experiences
The first experimental phase of the new heated consolidation apparatuses
focus on pure mono-mineral standards. These mono-mineral standards represent the
pure end members of the tested samples from DSDP Site 297, namely smectite, illite
and quartz. The testing of mono-mineral standards is underway since early 2007 at
MARUM, after setup of the system, extensive calibration of the hydraulic systems
and some preliminary consolidation experiments for testing purposes were finished.
Five tests have been conducted so far with good quality results (Fig. 6-9). The
geochemical analysis will be conducted soon to complete these experiments and to
prepare the data for publication.
Testing began with quartz-seawater slurries at room temperature and 100 °C.
However, high sidewall friction led to severe damage of the cells and some delay
occurred until the consolidation cells were repaired. Thereafter, the consolidation of
the smectite standards at 20 °C and 60 °C went smoothly. After the successful
experiments the consecutive experiments at 100 °C were influenced by severe water
loss along the gap between piston and cell wall. Therefore, the sealing system of the
pistons was re-engineered and the new system prevents the pressing of the sediment
into the gap between cell and piston and thus damaging the sealing. This latest design
seems to satisfy the requirements of temperature of up to 200 °C and 110 MPa
effective stress.
On the strength of the past experiences initial heights of 30 mm or rather
diameter:height ratios of 2:1 are recommended. Thus, sidewall friction is negligible
and does not influence the loading of the specimen in the cell. Starting strain rates of
0.06 % or 0.018 mm/h are adaptable to a wide range of sediments including low
permeable clays. These values are suitable for the proposed testing interval of ~3
month and fulfil ASTM experimental requirements for CRS consolidation tests.
However, despite some initial difficulties, the new systems are ready and provide
several improvements compared to the devices, which were used for the pilot study.
These are amongst others the higher logging resolution, immediate display of logged
parameters and the possibility to apply different methods of consolidation techniques.
APPENDIX 161
Fig 6: Preliminary results of the consolidation test of quartz at room temperature. (A) Settlement of quartz presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 162
Fig 7: Preliminary results of the consolidation test of quartz at 100 °C. (A) Settlement of quartz presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 163
Fig 8: Preliminary results of the consolidation test of smectite at room temperature. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 164
Fig 9: Preliminary results of the consolidation test of smectite at 60 °C. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.
APPENDIX 165
Fig 10: Preliminary results of the consolidation test of smectite at 100 °C. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell. Note that the hydraulic conductivity could be calculated only to a void ratio of 1.1 because of seal breakage.
ERKLÄRUNG 166
Erklärung Hiermit versichere ich, dass ich
1. die Arbeit ohne unerlaubte fremde Hilfe angefertigt habe, 2. keine anderen als die von mir angegebenen Quellen und Hilfsmittel benutzt habe und 3. die den benutzten Werken wörtlich oder inhaltlich entnommenen Stellen als solche kenntlich gemacht habe.
Bremen, den 18.05.2009 ………………………..
(Unterschrift)