Corti Riftlink 2008 m
-
Upload
salimaliomar2000 -
Category
Documents
-
view
218 -
download
0
Transcript of Corti Riftlink 2008 m
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 1/36
CONSTANT NUBIA-SOMALIA KINEMATICS CONTROLS A POLYPHASE
VOLCANO-TECTONIC EVOLUTION OF THE M AIN ETHIOPIAN RIFT,
E AST AFRICA
GIACOMO CORTI
ISTITUTO DI GEOSCIENZE E GEORISORSE, CNRFIRENZE, ITALY
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 2/36
Rifting & magmatism
MER ideal place to study:
-the evolution of continental rifting (magmatic rift that records different stages of
rifting from initiation to incipient oceanic spreading)
Main
Ethiopian Rift
East Afr ican
Rift System
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 3/36
Rifting & magmatism
MER ideal place to study:
-the evolution of continental rifting (magmatic rift that records different stages of
rifting from initiation to incipient oceanic spreading)
-the Nubia-Somalia kinematics (southwards the two-plate model for the East
African Rift is too simplistic)
East African
Rift System
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 4/36
1. Evolution of rifting in the Main Ethiopian Rift-patterns of faulting
-volcano-tectonic evolution
-Nubia-Somalia kinematics
2. Analogue modelling of continental rifting
-oblique rifting-results:
• evolution of the MER
• plate kinematics
3. From rifting to break-up in the MER-relations (feedback) deformation/magmatism
-lithospheric weakening and rupture
Outline of the presentation
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 5/36
Afar
(Pre-rift) Flood basalt event
Voluminous flood basalt
activity (
Afar plume activity)
-emplaced at ~30 My
-uplift (?)
-underplating (10km)
Flood
basalts
No significant extension
(rifting started about 20 My
later)
Kenya
Somalian
plateau
Ethiopian
plateau
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 6/36
Afar
Tertiary rift ing: activation of large boundary faults
First rif ting phase
diachronous activation of large
boundary faults in the different rift
segments (e.g., Wolfenden et al., 2004
EPSL; Bonini et al., 2005 Tectonics)
<5My (?)
6 My
11 My
Kenya
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 7/36
Boundary faults characteristics
Trend around NE-SWTrend around NE-SW
Few widely-spaced, en-
echelon, long faults
with large offset
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 8/36
Rift margin, Asela
3 0 0 m
Boundary faults characteristics
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 9/36
Boundary faults characteristics
A
B
Diffuse volcanism withspatial distribution controlled by
a complex network of boundary
faults and pre-existing structures
Trend around NE-SW
Few widely-spaced, long
faults, en-echelon, with
large offset
Asymmetric basins
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 10/36
Oblique faults
(trend NNE-SSW)in the rift
depression
(Wonji fault belt)
Change in
deformation style
at around 2 My
Tertiary rifting: activation of internal (Wonji) faults
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 11/36
Change in
deformation style
at around 2 My
Tertiary rifting: activation of internal (Wonji) faults
En-echelon
(and sigmoidal)
fault segments
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 12/36
Dense swarms of shortfaults with small
displacement
1 0
m
2 0
m
Wonji faults characteristics
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 13/36
Seismicity of the MER from October 2001 to January 2003 (note that
earthquakes mostly occur above mafic intrusions) [after Keir et al,
2006 JGR]
Seismicity and geodetical data
indicate a strongly localised
deformation within Wonji segments
Lithospheric weakening and strain localisation
Velocity profile from geodetical data in theMER (after Billham et al, 1999 Geophys Res
Lett)
NUBIA SOMALIA
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 14/36
Wonji faults and volcanism
En-echelon Wonji segments
strongly localise
Quaternary volcanic
activity
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 15/36
Controlled-source
tomography at 10 km below
the rift valley (after Keranen
et al, 2004 Geology)
Magma intrusion has a segmented
nature and occurs in right-stepping,
en echelon pattern mimicking the
surface segmentation of Wonji
segments
Wonji faults and magma intrusion
Geophysical data (Ethiopia Afar
Geoscientific LithosphericExperiment, EAGLE project; Maguire
et al., 2003EOS) evidence strong
magma intrusion in the lithosphere
below Quaternary volcanic centres
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 16/36
Summary of evolution
2-phase evolution, with activation of different fault systems (with different trend)
Mio-Pliocene
Development of NE-trending
border faults withalternating polarity
and asymmetric basins
Quaternary
Shift of deformation
and volcanismalong NNE-trending
en-echelon
WFB segments
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 17/36
Summary of evolution
Related to a change in Nubia-Somalia kinematics
(e.g., Bonini et al., 1997; Boccaletti et al.,1998; Wolfenden et al., 2004)
Mio-Pliocene
NW-SE extension
(orthogonal rifting)
Quaternary
E-W extension
(oblique rifting)
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 18/36
Current E-W Nubia-Somalia
motion oblique rifting
kinematics (geodetic data, slip
vectors of Late Quaternary-
Holocene faults)
Nubia-Somalia kinematics and MER evolution
Pizzi et al, 2006 Geol Soc Spec Publ
Fernandes et al, 2004 EPSL
Plate kinematic models:
constant (roughly E-W) Nubia-
Somalia motion since 11Ma(e.g., Royer et al., 2006 Geology)
Constant oblique rifting controls
the two-phase evolution in theMER ?
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 19/36
1. Evolution of rifting in the Main Ethiopian Rift-patterns of faulting
-volcano-tectonic evolution
-Nubia-Somalia kinematics
2. Analogue modelling of continental rifting
-oblique rifting-results:
• evolution of the MER
• plate kinematics
3. From rifting to break-up in the MER-relations (feedback) deformation/magmatism
-lithospheric weakening and rupture
Outline of the presentation
A l ( h i l) d l f ( bli ) ift
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 20/36
Syn-rift sedimentation
Materials: K-Feld powder, Plasti lina-sil icone
mixtures
Analogue (physical) models of (oblique) riftdevelopment: set-up
Strength profiles and set-up based on numericalmodels by Van Wijk, 2005 GRL
Corti, 2008Nature geosc
A l ( h i l) d l f ( bli ) ift
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 21/36
Central
MER
Northern
MER
Analogue (physical) models of (oblique) riftdevelopment: set-up
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 22/36
M od e l e x t 2 8 0 3 2 0 0 7
EX T 0 m m
EXT 0 k m
5 c m
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 23/36
M od e l e x t 2 8 0 3 2 0 0 7
EX T 0 m m
EXT 0 k m
EX T 3 m m
EXT 4 .5 k m
SED IMENTAT ION
5 c m
EX T 6 m m
EXT 9 k m
EX T 9 m m
EXT 1 3 .5 k m
EX T 1 2 m m
EXT 1 8 k m
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 24/36
M od e l e x t 2 8 0 3 2 0 0 7
EX T 0 m m
EXT 0 k m
EX T 3 m m
EXT 4 .5 k m
SED IMENTAT ION SED IMENTAT ION
5 c m
EX T 6 m m
EXT 9 k m
EX T 9 m m
EXT 1 3 .5 k m
EX T 1 2 m m
EXT 1 8 k m
EX T 1 5 m m
EXT 2 2 .5 k m
EX T 1 8 m m
EXT 2 7 k m
EX T 2 1 m m
EXT 3 1 .5 k m
EX T 2 4 m m
EXT 3 6 k m
EX T 2 7 m m
EXT 4 0 .5 k m
A l d lli f bli ifti lt
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 25/36
B O U N
D A R Y F A U L T S
S T A G E
I N T
E R N A L F A U L T S
S T A G E
Constant oblique rifting is responsible for the diachronous development of the two fault different
systems (1st: boundary faults, 2nd: en-echelon oblique faults; Corti, 2008 Nature geosc).
Boundary faults can accommodate only a limited amount of displacement; with progressive
extension deformation shifts in the weakest part of the rift (i.e. in the thinned rift depression)
Analogue modelling of oblique rifting: results
Corti, 2008Nature geosc
Analogue modelling of oblique rifting: application to the MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 26/36
modified from Ebinger, 2005 A&G; see also Corti, 2008 Nature geosc
Border faults(11My-2My)
Localiseddeformation onWonji segments
(2My)
Best-fit of fault patterns in modelsand nature suggests a N100°E
Nubia-Somalia extension in the MER(Corti, 2008 Nature geosc)
No change in
kinematics required
Constant (simple)
Nubia-Somalia
kinematics, two-phase
(complex) evolution of
the MER
Analogue modelling of oblique rifting: application to the MER
Analogue modelling of oblique rifting: application to the MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 27/36
Border faults(11My-2My)
Localiseddeformation onWonji segments
(2My)
Analogue modelling of oblique rifting: application to the MER
Model subsidence Scheme of deformation distribution Lithospheric thinning in numerical models(Van Wijk, 2005 GRL)
Obl ique ri ft ing resul ts in a typical en-echelon arrangement deformat ion segments, with max l ithospheric
thinning and focused magma production (numerical models)
Analogue modelling of oblique rifting: application to the MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 28/36
Border faults(11My-2My)
Localiseddeformation onWonji segments
(2My)
Analogue modelling of oblique rifting: application to the MER
Focusing ofmagmatism on
Wonji segments(2My-present)
D f ti d (Q t ) ti i th MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 29/36
Keranen et al, 2004
Geology
Geophysical data (Ethiopia Afar
Geoscientific LithosphericExperiment, EAGLE project; Maguire
et al., 2003EOS) evidence strong
magma intrusion in the lithosphere
below Wonji segments
Pervasive magma intrusion in the
entire lithosphere (uppermost 75km;
e.g., Kendall et al., 2004 Nature; Keir et al., 2005Geophys Res Lett)
Magmatic processes have
fundamentally modified the crust and
mantle lithosphere beneath the rift
Large mafic intrusions (mid-lower
crust), melt-filled cracks/dykes (crust,
upper mantle), magma chambers
(upper crust)
below Quaternary volcanic centres
Deformation and (Quaternary) magmatism in the MER
O tli f th t ti
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 30/36
1. Evolution of rifting in the Main Ethiopian Rift-patterns of faulting
-volcano-tectonic evolution
-Nubia-Somalia kinematics
2. Analogue modelling of continental rifting
-oblique rifting-results:
• evolution of the MER
• plate kinematics
3. From rifting to break-up in the MER-relations (feedback) deformation/magmatism
-lithospheric weakening and rupture
Outline of the presentation
Deformation and (Quaternary) magmatism in the MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 31/36
(seismically) by a combination of
dyking/faulting in the upper crust
(aseismically) by magma injection
within a narrow zone in the
mid/lower crust and upper mantle
Dyke-induced growth of normal
faults (above mafic intrusions)
Model of fault growth during the 2005 Dabbahu magmatic
rifting episode (after Rowland et al, 2007 GJI)
Image of large mafic intrusion (after Keranen et al,2004 Geology)
Extension accommodated
Deformation and (Quaternary) magmatism in the MER
Wonji faults and magma intrusion: lithospheric weakening
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 32/36
Wonji faults and magma intrusion: lithospheric weakening
(after Buck 2006 Geol Soc Spec Pap) Strength
Increase in strain
localisation (e.g., Corti et
al. 2007 JGeodyn)
Decrease in lith strength up to one
order of magnitude
Lithospheric weakening and strain localisation
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 33/36
Seismicity of the MER from October 2001 to January 2003 (note that
earthquakes mostly occur above mafic intrusions) [after Keir et al,
2006 JGR]
Deformation is localised in a very
narrow region (about 10km-wide in
the Northern MER; Keir et al., 2006 JGR)
within Wonji segments
Lithospheric weakening and strain localisation
Velocity profile from geodetical data in the
MER (after Billham et al, 1999 Geophys Res
Lett)
NUBIA SOMALIA
Lithospheric weakening and strain localisation
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 34/36
Localised deformation
Lithospheric weakening and strain localisation
The self-reinforcing process allows the break-up of the continental lithosphere
Pronounced weakening
Focused magma intrusion
see also Corti et al., 2007 JGeodyn
Feedback deformation-
magmatism
Continental break up
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 35/36
Characteristics of Wonji volcano-
tectonic segments (extensive mafic
addition to the crust within a narrow
zone of localized strain,dyking/faulting, seismic activity, low
elastic thickness, morphology &
segmentation,…) typical of slow-
spreading ridges
Continental break-up
(Northern) MER is in the break-up
stage, Wonji segments act as
incipient mid-ocean spreading
centres (e.g., Ebinger, 2005A&G)
Summary and conclusions: from rifting to break-up in the MER
8/13/2019 Corti Riftlink 2008 m
http://slidepdf.com/reader/full/corti-riftlink-2008-m 36/36
Feedback magmatism-
deformation Lithosphere
strongly modified bymagmatism Weakening &
and strain localisation
Summary and conclusions: from rifting to break up in the MER
Border faults,
diffusemagmatism(11My-2My)
Focusing ofmagmatism on
Wonji segments(2My-present)
Break-up and
incipientspreading on
Wonji segments
Localiseddeformation onWonji segments
(2My)