Gondwana Research 22 (2012) 615–627

Contents lists available at SciVerse ScienceDirect

Gondwana Research

j ourna l homepage: www.e lsev ie r .com/ locate /gr

Tectonic deformation of the southeastern tip of the Indochina Peninsula during itssouthward displacement in the Cenozoic time

Yo-ichiro Otofuji a,⁎, Van Duc Tung b, Makoto Fujihara a, Masayuki Tanaka a, Masahiko Yokoyama a,Kazuya Kitada c, Haider Zaman d

a Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, Kobe, Japanb Department of Tectonic, Institute of Geological Science, Vietnam Academy Science and Technology, Vietnamc Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japand Department of Geology and Geophysics, College of Science, King Saud University, Riyadh, Saudi Arabia

⁎ Corresponding author.E-mail address: otofuji@kobe-u.ac.jp (Y. Otofuji).

1342-937X/$ – see front matter © 2011 International Adoi:10.1016/j.gr.2011.09.015

a b s t r a c t

a r t i c l e i n f o

Article history:Received 6 January 2011Received in revised form 10 August 2011Accepted 5 September 2011Available online 17 October 2011

Keywords:TectonicsContinentPaleomagnetismCretaceousIndochina

The terminal collision of India with Asia brought about significant tectonic deformation into the Asian Conti-nent. In order to depict these deformational features in the southeastern margin of the Indochina Peninsula,Late Cretaceous red beds of the Dak Rium Formation were sampled from Da Lat area (11.7°N, 108.3°E), theKontum massif, Vietnam. Thermal demagnetization procedure revealed the presence of characteristic rema-nent magnetization (with unblocking temperatures around 680 °C) in most samples. Primary nature of thismagnetization is ascertained through positive fold test. A tilt-corrected mean direction calculated for theDak Rium Formation is Dec/Inc=11.4°/35.4° (ks=331.7 α95=1.7°, N=21), with a corresponding paleopoleat 76.5° N, 161.2° E (A95=1.7°). Compared with the European APWP, a negative inclination flattening(−15.2°±4.9°) is observed, indicating southward displacement of the Kontum massif by 9.2°±4.9° sinceLate Cretaceous. Since, comparable amount of southward displacement has been reported from 16 localitiesof the Indochina and Shan–Thai blocks, it seems a reasonable assumption to predict that the Indochina Pen-insula underwent a southward displacement of 5.1°±2.4° (570 km±270 km) as a composite unit (includingthe Shan–Thai Block, Indochina Block and Kontum massif). On the contrary, 27.0°±9.8° counter-clockwiserotation of the Kontum massif with respect to the Indochina Block indicate a significant amount of internaldeformation along the tip of south moving Indochina Peninsula. This rotation of the Kontum massif is attrib-uted to 32–17 Ma left lateral motion along the East Vietnam Boundary Fault, which makes up the 1000 kmlong seaward continuation of the Ailao Shan–Red River shear zone. Tectonic deformation of the IndochinaPeninsula was, thus, partly accommodated by local block rotation (e. g., counterclockwise rotation of theKontum massif) and to some extent by internal tectonic deformation of the Shan–Thai Block.

© 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction

After an initial model of extrusion tectonics in the Asian continentby Tapponnier et al. (1982) as a result of its collision with India, vari-ety of additional evidences have been accumulated from differentfragments of the Asian Plate. As shown in the Fig. 1, several geophys-ical and geological observations have been used in highlighting extru-sion tectonics of the Indochina Peninsula. The global positioningsystem (GPS) data reported from Asia even indicate the present daycrustal movement in the area, i.e., eastward displacement in the east-ern Tibet and southward displacement in the Yunnan area (Gan et al.,

ssociation for Gondwana Research.

2007). On the other hand, the available paleomagnetic data provide arecord of long term clockwise (CW) rotation of the eastern Himalayasyntaxis together with southward displacement of the Indochina Pen-insula since the Cretaceous (Tanaka et al., 2008; Takemoto et al.,2009; Otofuji et al., 2010). Geological observations from the area pro-vide information about the Red River Fault Zone, along which the In-dochina Peninsula extruded by 700 km (Leloup et al., 1995).Furthermore, the reported geochronological results assigned a periodof 32 to 17 Ma to sinistral slip movement along the Red River Fault asa part of extrusion tectonics (Lacassin et al., 1997; Gilley et al., 2003).

The Indochina Peninsula comprises a collage of continental blocks,including the Shan–Thai and Indochina blocks (Ferrari et al., 2008;Metcalfe, 2011). A process of extrusion in the Indochina peninsulaas a result of Indian Plate indentation have been reconstructed by sev-eral researchers on the basis of their geological and geophysical find-ings (Replumaz and Tapponnier, 2003; Aitchison et al., 2007, 2011;Hall et al., 2008). In addition, about 700 km southeastward extrusion

Published by Elsevier B.V. All rights reserved.

Fig. 1. Structural sketch map of the Indochina Peninsula and neighboring areas (modified from Takemoto et al., 2009). The shaded zones in the map indicate distribution of theJurassic and Cretaceous red beds. Names in the boxes indicate the studied localities. The observed declinations from Late Jurassic to Cretaceous rocks of the Indochina Peninsula(including localities from Shan–Thai and Indochina blocks) are marked by arrows (as listed in Table 2). Closed (open) arrows indicate the Cretaceous (Late Cretaceous). A.R.F.,Ailao Shan–Red River Fault; DNCV Massif, Day Nui Con Voi Massif; E.V.B.F., East Vietnam Boundary Fault; L.S.B, Lanping–Simao Basin, S.C.F., Song Ca Fault; S.F., Sagaing Fault,;T.P.F., Three Pagodas Fault; W.C.F., Wang Chao Fault; X.F., Xianshuihe Fault.

616 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

of the Indochina Block together with Eastern Malaya and SW Borneohas been delineated using seismic tomographic imaging (Replumazet al., 2004). Accompanied with southeastward displacement,these blocks underwent differential tectonic rotation as well. Asper the interpretation of Fuller et al. (1999), the Indochina Peninsu-la experienced a CW rotation since the Cretaceous, whereas theEastern Malaya and SW Borneo received a counterclockwise(CCW) rotation. As a result of these tectonic activities, the openingof South China Sea occurred between the Indochina Peninsula andSW Borneo (Briais et al., 1993), while internal deformation of theShan–Thai Block took place after the Eocene (Laccassin et al.,1998; Morley, 2002; Tanaka et al., 2008; Takemoto et al., 2009).

The Kontum massif, a pre-Paleozoic tectonic block (Nam et al.,2001; Lan et al., 2003), is located on the southeastern margin of theIndochina Block. This block is flanked by the rifted South China Sea(Fig. 1). In such a tectonic setting, deformation of the Kontum massifcould be expected. Paleomagnetic technique has been chosen as atool to examine deformational features of the Kontum massif.

Previously, Chi and Dorobek (2004) have reported Cretaceous paleo-magnetic results from igneous and sedimentary rocks of the area.However, their tectonic corrections/fold tests proved unsuccessfulbecause of no proper bedding attitude of the igneous rocks. In orderto obtain reliable paleomagnetic data from the Kontum massif (withclear fold and tectonic corrections), attention have been focused onthe Cretaceous red beds of Da Lat area, which present very clear andobservable bedding attitudes.

2. Geological setting and sampling

As shown in Fig. 1, the Indochina Block is separated from SouthChina Block by Song Ma suture zone to northeast and from Shan–Thai Block by the Uttaradit–Nan–Sra Kaeo sutures to the west (Lepvrieret al., 2004) (Fig. 1). Main part of the Indochina Block is occupied byKhorat Plateau, which is covered by the Mesozoic continental redbeds. The Kontum massif forms the southeastern rim of the IndochinaBlock and is separated from it by the Po Ko fault zone (Lepvrier et al.,

617Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

2004). According to geological observations (Namet al., 2001; Lan et al.,2003), basement of the Indochina Block is exposed in the Kontummas-sif, which was principally originated during the Paleoproterozoic andMesoproterozoic (1.2 Ga to 2.4 Ga). The high-grade metamorphicrocks of the Kontum massif were mainly formed in the Indosiniantime, ca. 258–243 Ma (Carter et al., 2001; Nagy et al., 2001; Nam et al.,2001; Nakano et al., 2007; Owada et al., 2007). A geologically complexregion of the Truong Son Belt, which mainly consists of 245–272 Maigneous rocks (Hoa et al., 2008), is located to north of the Kontummassif.

The Da Lat region is located in the southern part of the Kontummassif (Fig. 2a). This area is made from the Precambrian basementrocks, Jurassic to Cretaceous sediments, late Mesozoic igneous andCenozoic basaltic rocks. Thick pile of slightly folded middle JurassicBandon Formation is widely distributed in the area overlying thebasement rocks. Based on the remote sensing and geological fielddata (Rangin et al., 1995), it has been established that this region issubdivided into small blocks by numerous NE–SW trending strike–slip faults.

In the area around Da Lat city, the Late Cretaceous rocks are char-acterized by acidic volcanogenic–sedimentary formation that consistsof dacites, rhyolites, tuffs and inter-beds of red continental sediments(Nguyen et al., 1994). The Late Cretaceous Dak Rium Formation, whichoverlies the Jurassic Bandon Formation in the study area, consists ofconglomerate, breccias, purple color coarse-grained sandstones andpurple siltstones. These slightly folded red beds have west-southwest trending strike with variable degree (3° to 30°) of dippingattitude.

As shown in the Fig. 2b, the Dak Rium Formation has been sam-pled at 21 sites in the Da Lat depression, west side of the Da Lat City(12.1°N, 108.5°E). In order to perform fold test in a reliable manner,12 sites have been collected from east-dipping strata, 4 from west-

(a)

Fig. 2. (a) Structural sketch map of South Vietnam (modified from Rangin et al., 1995; LepvStrike and dip of strata at each sampling site are shown at respective location.

dipping strata and the remaining 5 sites from north-dipping strata.Location of each sampling site was determined by portable naviga-tional system, while orientation of the paleomagnetic samples wasmade by magnetic compass. The present day declination value ateach sampling site was evaluated from International GeomagneticReference Field (Macmillan and Maus, 2005).

3. Rock magnetism

Progressive acquisition of the isothermal remanent magnetization(IRM) was performed up to a maximum field of 2.7 T using 2G-pulsemagnetizer. Thermal demagnetization of the composite IRMs (2.7 T,0.4 T and 0.12 T along z, y and x axes, respectively) was carried outto detect the unblocking temperature spectra in the selected samples(Lowrie, 1990).

Rock magnetic investigations generally revealed hematite as adominant magnetic carrier (Fig. 3a and b). The IRM acquisition curvesfor most samples indicate that no saturation is achieved up to a max-imum field of 2.7 T, revealing the presence of high-coercivity magnet-ic minerals, such as hematite or goethite. The presence of hematite isfurther confirmed by an unblocking temperature zone of 660 °C–690 °C in the hard and medium components during thermal demag-netization of the composite IRMs.

The presence of magnetite is suspected in samples from severalsites, e.g., DL02, DL03, DL19, and DL20 (Fig. 3b). Thermal demagneti-zation of the composite IRMs indicates an unblocking temperature ofabout 580 °C in the soft component.

Trace amount of goethite is indicated in some samples (Fig. 3a), asunblocking temperature of about 150 °C is observed in the intermedi-ate components during thermal demagnetization of the compositeIRMs,

(b)

rier et al., 2004) and (b) Geological map of the study area (after Nguyen et al., 1994).

(a) DL 61 (b) DL 192

Fig. 3. IRM acquisition and thermal demagnetization of the composite IRMs (imparted with DC fields of 2.7 T, 0.4 T and 0.12 T along three perpendicular axes) are shown (a) spec-imen DL 61 is from site DL 6 and (b) specimen DL 192 is from site DL 19. Although, the IRM saturation is not achieved up to a maximum field of 1 T, it could have reached at anypoint between 1 T and 2.7 T. Thermal demagnetization of the acquired IRM indicates the unblocking temperatures between 660 °C and 690 °C.

618 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

4. Paleomagnetic results

Individual specimens of 25 mm in diameter and 23 mm in lengthhave been prepared from each sample in the laboratory. Natural rem-anent magnetizations (NRMs) were measured by 2-G Enterprisescryogenic magnetometer. One specimen from each sample was sub-jected to stepwise thermal demagnetization up to 690 °C using Nat-suhara TDS-1 thermal demagnetizer with a residual field of lessthan 5 nT. Demagnetization results for each specimen were plottedon orthogonal vector diagrams (Zijderveld, 1967) to assess compo-nent structure as well as on equal-area projections to evaluate direc-tional stability. Principal component analysis (Kirschvink, 1980) wasused to estimate components directions. Site-mean directions werecalculated using Fisherian statistics (Fisher, 1953). For paleomagneticfold test, a program package of Cogné (2003) has been used.

Remanent magnetizations of 122 samples from 21 sites have beenmeasured. Initial NRM intensities of the studied samples (before de-magnetization) are in a range between 9.2×10−3 and 15.7×10−2 A/m.

Thermal demagnetization procedure generally reveals two com-ponents behavior in NRM directions in almost all samples (Fig. 4).After the isolation of low-temperature component (LTC) around250 °C–350 °C, the high-temperature component (HTC) appears andis eventually unblocked between 650 °C and 690 °C. This indicates he-matite is the main remanence carrier. In addition to this high temper-ature component, an unblocking temperature of about 590 °C is alsoindentified in decay nature of NRM intensity for samples from 9sites (DL01, DL02, DL03, DL07, DL08, DL13, DL17, DL19, and DL20)(Fig. 4), suggesting the presence of magnetite as a sub-ordinate mag-netic carrier (as observed by rock magnetic analysis).

Magnetization related to LTC is identified in 34 samples. With theexception of samples from site DL02, mean direction of D=356.4°,I=23.8°, α95=9.8° (N=26) is obtained for this component, which

is almost parallel to axial geocentric dipole (D=0°, I=22.3°). Al-though, directional behavior of this component shows planar distri-bution rather than Fisherian, its parallelism with geocentric dipolefield implies that the LTC was acquired as a secondary magnetizationduring the Bruhnes Chron. An unblocking temperature range of250 °C to 350 °C for this component suggests the presence of mag-netite or hematite as a carrier of VRM. In the blocking diagrams ofPullaiah et al. (1975), this range of temperature correspond to a re-laxation time of about 1 My, during which the axial geocentric di-pole field was recorded by magnetite or hematite grains in roomtemperature. An enigmatic LTC direction (D~210°, I=15°) is ob-served in the samples of site DL02.

Magnetization related to HTC is identified in all 21 sites. The NRMdirections above 350 °C have been considered as HTC (Table 1). Since,the co-presence of magnetite and hematite is determined in 9 out of21 sites by rock magnetic investigations, remanent directions forboth these components (i. e., magnetite related component from350 °C to 580 °C and hematite related component from 580 °C to690 °C) are calculated by principal component analysis (Table 1). In8 out of 9 sites, the hematite related component shows shallower in-clination than the magnetite related component, whereas samplesfrom the remaining site (DL03) reveal almost opposite behavior.

Site-mean directions of the HTC are tightly clustered. Site-meandirections calculated from components related to hematite and mag-netite also show tight concentration, where precision parameter islarger than 26.5. Directions obtained from all 21 sites give normal po-larity behavior.

Formation mean directions of the studied 21 sites have been cal-culated by three different ways: (1) the NRM directions above350 °C from all 21 sites, (2) the NRM directions above 350 °C from12 sites and those related to magnetite component from 9 sites, and(3) the NRM directions above 350 °C from 12 sites and those of

690oC

590oC

350oC

680oC

530oC

350oC

Jo =69.7 mA/m

DL21 DL37

680oC

300oC

Jo =58.1 mA/m Jo =38.2 mA/m

DL61 DL71DL192 DL127

DL166

DL148560oC

680oC

350oC

560oC

690oC

350oC

560oC

690oC

350oC

560oC

690oC

350oC

560oC

690oC

350oC

560oC

Fig. 4. Representative thermal demagnetization plots of 8 red beds sites from Dak Rium Formation in geographic coordinates. The associated intensity plots, showing normalized intensity versus temperature (in degrees Celsius) are givennearby. In the demagnetization plots, closed (open) symbols represent vector end-points on the horizontal (vertical) plane.

619Y.O

tofujietal./

Gondw

anaResearch

22(2012)

615–627

Table 1Paleomagnetic results of the Upper Cretaceous red bed samples (Dak Rium Formation) from Da Lat area.

Site Location Lithology Attitude n/N Component Dec. (°) Iinc. (°) Dec. (°) Inc. (°) k a95 (°)

Latitude (N°) Longitude (E°) Strike (°) Dip (°) In situ Tilt corrected

DL01 11.622 108.204 S.S. 256.6 17.5 7/7 HTC 12.6 48.8 6.6 32.7 225.9 5.1Magnetite 16.0 50.5 9.0 34.6 486.0 3.0Hematite 7.1 45.2 3.0 28.6 170.5 5.1

DL02 11.622 108.204 Silt 253.6 19.5 8/8 HTC 10.4 52.8 3.0 34.8 539.5 2.98 Magnetite 11.6 60.4 2.1 42.3 581.0 2.38 Hematite 8.8 47.4 2.9 29.3 465.1 2.6

DL03 11.622 108.204 Silt 253.6 15 5/5 HTC 16.4 45.4 10.4 32.4 290.6 4.55 Magnetite 18.2 42.9 12.4 30.1 215.6 5.25 Hematite 15.9 48.5 9.5 35.3 304.0 4.4

DL04 11.622 108.205 Silt 259.6 12 5/5 HTC 13.7 45.0 10.0 33.8 357.2 4.1DL05 11.793 108.235 Silt 207.6 31 6/6 HTC 34.3 34.0 13.6 32.0 580.2 3.8DL06 11.793 108.235 Silt 207.6 28 8/8 HTC 38.5 36.5 17.2 36.7 493.1 3.0DL07 11.794 108.330 Silt 73.6 4 4/5 HTC 7.6 36.5 8.9 40.1 478.9 4.2

4 Magnetite 12.5 41.1 14.3 44.6 621.7 3.74 Hematite 4.6 30.9 5.6 34.6 130.2 8.1

DL08 11.788 108.327 Silt 85.6 4 5/5 HTC 10.5 33.0 11.2 36.9 541.0 3.35 Magnetite 17.0 42.3 18.5 46.1 295.6 4.55 Hematite 9 29.9 9.6 33.8 831.5 2.7

DL09 11.788 108.316 Silt 97.6 3 3/3 HTC 8.3 31.3 8.3 34.3 359.9DL10 11.788 108.327 Silt 86.6 4 5/6 HTC 17.6 35.7 18.7 39.5 26.5 15.1DL11 11.767 108.316 Silt 356.6 11 8/8 HTC 5.4 36.4 13.0 34.0 297.6 3.9DL12 11.766 108.316 Silt 17.6 13 8/8 HTC 9.6 40.1 20.8 40.7 336.0 3.7DL13 11.766 108.317 Silt 11.6 10.5 5/5 HTC 2.8 31.7 9.4 32.7 329.8 6.8

5 Magnetite 9.2 36.3 16.9 36.1 210.1 5.35 Hematite 359.1 26.6 4.4 28.5 390.0 3.9

DL14 11.762 108.315 Silt 22.6 12 5/5 HTC 7.3 32.2 15.1 34.6 425.3 6.0DL15 11.762 108.315 Silt–S.S. 43.6 11 4/4 HTC 6.5 31.2 12.8 37.5 168.0 7.1DL16 11.688 108.268 S.S. 11.6 3 4/4 HTC 6.5 32 8.4 32.2 207.1 6.4DL17 11.687 108.273 Silt 91.6 4 3/3 HTC 11.7 31.3 12.2 35.2 262.6 7.6

3 Magnetite 13.7 32.1 14.3 35.9 195.3 8.83 Hematite 8.6 30.1 8.9 34.1 312.6 7

DL18 11.686 108.272 S.S. 42.6 5 5/5 HTC 6.9 30.4 9.4 33.2 112.3 7.3DL19 11.794 108.237 S.S. 207.6 28 8/8 HTC 27.3 37.4 7.7 32.3 607.4 2.7

8 Magnetite 31.5 37.4 11.0 33.9 681.4 2.18 Hematite 25.3 37 6.4 30.9 521.3 2.4

DL20 11.794 108.237 S.S. 201.6 26 7/7 HTC 36.0 36.1 16.0 38.2 441.3 3.67 Magnetite 39.0 37.7 17.5 40.6 480.0 2.87 Hematite 32.6 33.1 15.0 34 336.9 3.3

DL21 11.619 108.201 S.S. 243.6 15 8/8 HTC 17.7 49.3 8.6 37.7 167.0 5.2121/122

Mean (1) 21/21 HTC 14.5 37.9 55.9 4.3Mean (1) 21/21 11.4 35.4 331.7 1.7Mean (2) 21/21 HTC+magnetite 16.2 39.3 48.9 4.6Mean (2) 12.9 36.8 204.9 2.2Mean (3) 21/21 HTC+hematite 13.4 36.8 50.9 4.5Mean (3) 10.4 34.2 226.7 2.1Mean (magnetite) 9 Magnetite 19.1 42.7 51.2 7.3

12.8 38.2 148.2 4.2Mean (hematite) 9 Hematite 12.2 36.9 45.5 7.7

7.2 32.2 353.3 2.7N Lat. (°N) Long. (°E) A95 (°)

VGP 11.7 108.25 21 76.5 161.2 1.7

Magnetization directions of the high temperature component are listed in this Table. Bedding attitude is marked by strike and dip angle. N and n are number of samples measuredand used for calculation, respectively. Dec. and Inc. are declination and inclination, respectively; k is the Fisherian precision parameter (Fisher, 1953); α95 is the radius of cone at95% confidence level about the mean direction. In order to chose the best results, formation mean direction has been calculated by three ways, (1); the NRM directions above 350 °Cfrom 21 sites have been used, (2); the NRM directions above 350 °C from 12 sites and those of magnetite related component from 9 sites have been used, and (3); the NRMdirections above 350 °C from 12 sites and those of hematite related component from 9 sites have been used. Mean directions of the magnetite and hematite related componentsform 9 sites have also been calculated.

620 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

hematite related component from 9 sites. Because of identical direc-tional behavior from these data sets (Table 1), formation mean direc-tion from the first option has been recognized as a characteristicremanent magnetization (ChRM) for Dak Rium Formation, where direc-tional parameters areDec/Inc=14.5°/37.9° (kg=55.9α95=4.3°) in geo-graphic coordinates and Dec/Inc=11.4°/35.4° (ks=331.7α 95=1.7°) instratigraphic coordinates (Fig. 5).

Taking in to consideration the first option, a fold test has been ap-plied to data from all 21 sites. An application of the DC-tilt test (Enkin,2003) reveals an optimal concentration at 92.7±15.9% unfolding,which is indistinguishable from that at 100% unfolding. Following

the fold test of McFadden's (1990), a value (ξ1) of 17.8511 is obtainedin the geographic coordinates and 4.7887 in the stratigraphic coordi-nates, whilst a critical value (ξc) of 5.3350 (7.4830) is obtained at 95%(99%) confidence level. These results, thus, suggest that the magneti-zation related to HTC is pre-folding in origin.

5. Discussion

The directional behavior obtained from Late Cretaceous Dak RiumFormation (located in the Da Lat area of the Kontum massif) reveals apre-folding origin for the ChRM component. A visible fluctuation in

Fig. 5. Equal-area projections of the site mean directions for high temperature components before and after tilt correction. Formation mean is shown by star with 95% circle of con-fidence (shaded). The asterisk represents the present day axial geomagnetic dipole field. All symbols correspond to projection on lower hemisphere.

621Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

paleomagnetic direction from one site to another is evident from theobtained results, where a declination range of 3.0° to 20.8° and an in-clination range of 32.4° to 40.7° have been observed. This wide rangeof directional fluctuation suggests a long record of secular variation inthe red beds of Dak Rium Formation, which has been sufficiently av-eraged out by formation mean calculations. A tilt-corrected formationmean direction (Dec/Inc=11.4°/35.4°, ks=331.7,α95=1.7°, N=21)is recognized as the Late Cretaceous characteristic paleomagnetic di-rection for the Dak Rium Formation. Appearance of only normal po-larity is probably due to the deposition and compaction of thestudied formation during the Cretaceous long normal-polarity chron(Gradstein et al., 2004).

The previously reported paleomagnetic results (Dec/Inc=14.5°/33.3°, ks=26.7,α95=6.3°, N=21) fromDa Lat area byChi andDorobek(2004) indicate almost similar directional behavior as of the presentstudy. However, 12 out of 21 sites in the previous study were collectedfrom the igneous rocks, where no solid evidence of bedding attitudeand its eventual use in tilt-correction has been reported, which makeit hard to recognize these results as reliable paleomagnetic record.Clear bedding attitude of the Dak Rium Formation can, thus, provide asolid support to accept the present study as a reliable representative ofthe Late Cretaceous characteristic paleomagnetic direction from Da Latarea.

5.1. Southward displacement of the Indochina Peninsula

The Late Cretaceous paleomagnetic direction obtained from Da Latarea is compared with 80 Ma paleomagnetic direction expected fromthe European APWPs (Besse and Courtillot, 2002). Such a comparisonreveal about 15.2° steepness in the observed mean inclination com-pared to that expected from the APWP, indicating a negative flatten-ing (F=Iexp− Iobs) of −15.2°±4.9° in Da Lat area. Evaluation ofinclination values from hematite related 9 sites also reveal negativeflattening (−13.2°±5.3°).

As listed in Table 2, negative flattening in inclinations have fre-quently been reported from the Cretaceous red beds of the Shan–Thai and Indochina blocks (both parts of the Indochina Peninsula).Negative flattening observed in different areas of the Shan–ThaiBlock are λ (the present latitude)=25.8° N; F=−9.5° for Yunlong,λ=24.1° N; F=−11.0° for Zhengyuan, λ=23.0° N; F=−8.4° forPu'ar and λ=21.4° N; F=−11.8° for South Mengla. Negative flatten-ing in the Indochina Block is λ=18.5° N; F=−11.0° for Borikhanxayand λ=16.5° N; F=−9.2° for Nam Nao areas.

Negative flattening in the Indochina Peninsula is attributed to tec-tonically inspire southward displacement. On the other hand, positiveflattening in inclinations is ascribed to bias in sedimentary recordingas a result of syn-sedimentation and compaction related processes(Tauxe and Kent, 2004; Tan et al., 2007). According to a recentclaim by Sato et al. (2011), large positive flattening is the characteris-tic feature of sedimentation in a swiftly developed foreland basin dur-ing the process of orogeny, but only few cases of flattening appearedin the slowly developed basins. Since, the Cretaceous sediments of the

Da Lat area were deposited in a slowly developed basin, negative flat-tening can still be considered as useful indicator to determine paleo-latitude of the studied terrane without any inclination correction (e.g.E/I method; Tauxe et al., 2008).

Southward displacement of the Indochina Peninsula have beenexplained by several numerical and laboratory experiments (Tapponnieret al., 1982; Houseman and England, 1993; Royden et al., 2008). Geolog-ical evidences from the Indochina Peninsula also support its southwarddisplacement through sinistral movement along the Ailao Shan–RedRiver fault zone (Leloup, et al., 1995; Lacassin et al., 1997; Leloup et al.,2001).

Since, negative flattening is a clue to long-term southward dis-placement of the Indochina Peninsula in the post-Cretaceous time,an amount of latitudinal displacement (λobs−λexp) is calculatedfor the studied areas in the Indochina Peninsula (Table 2). As listedin Table 2, twelve paleomagnetic data sets from Shan–Thai Blockand four from Indochina Block passed the fold test (Table 2). Since,the Lai Chau and Yen Chau areas belong to stable South China Block(Takemoto et al., 2005), their respective data sets have been excludedfrom those belong to Indochina Block. The expected paleomagneticdirections (λexp) for the Early Cretaceous (J–K and J3–K1, K1) andLate Cretaceous (K2) have been calculated using the 120 Ma and80 Ma APWPs of Europe (Besse and Courtillot, 2002), respectively.

Thirteen out of 16 reliable data sets, excepting Phong Saly, Kalawand Da Lat data, indicate southward displacement of 5.8° to 8.2° forthe studied areas. Although, data sets from Phong Saly and Kalawshow no sign of southward displacement, their 95% confidence inter-vals join the region of southward displacement. Amount (9.2°±4.9°)of post-Cretaceous southward displacement in the Da Lat area is com-parable with those in the thirteen data sets, suggesting quantitativelysimilar trend of tectonic displacement for Da Lat together with otherlocalities of the Shan–Thai and Indochina blocks.

A contour map has been drawn to examine southward displace-ment of the Da Lat area as a part of the Indochina Peninsula usingan analog view (Fig. 6). The following procedures have been adoptedto depict smooth contouring of the southward displacement: (1) anull value is assigned to several localities along the margin of theShan–Thai and Indochina blocks, and (2) a solution based on tensionparameter TI=0.2 (Smith &Wessel, 1990; Wessel & Smith, 1991) hasbeen applied. Although, only small number of data points has beenused for this purpose, an outline of southward displacement as afirst order approximation is clearly recognized by smooth contouringmap. As evident from this map (Fig. 6), the area with 2° southwarddisplacement covers about 50% of the Indochina Peninsula and ex-tends to Da Lat. Based on these observations, it can be concludedthat the tip of the Indochina Peninsula was subjected to southwarddisplacement as a composite unit.

Variation in the amount of southward displacement can clearly beobserved in the contour map. Undulation in themapmay either be at-tributed to intra-blocks deformation or to uncertainty in data. Recent-ly, internal deformation of the Shan–Thai Block has been reported onthe basis of variation in declinations (Tanaka et al., 2008). However,

Table 2Jurassic to Cretaceous paleomagnetic results from the Indochina Peninsula (the Shan–Thai and Indochina blocks).

Localityname

Age N Rock type Fold test Observeddirection

Reference

Lat.(°N)

Lon.(°E)

Dec. (°) Inc.(°)

a95(°)

Rotation Delta Shallowing Delta Lat. displacement(Northward)

Delta

Shan–Thai BlockYunlong 25.8 99.4 K2 20 Redbeds Positive 40.2 49.9 3.9 31.2 6.2 −9.5 5.7 −7.6 5.9 Sato et al.

(1999)Yunlong 25.8 99.4 K2 29 Redbeds Positive 38.3 50.7 3.4 29.3 5.8 −10.3 5.4 −8.4 5.7 Yang et al.

(2001)Xiaguan 25.6 100.2 K2 9 Redbeds Positive 6.9 47.7 8.6 −2.1 11.0 −7.4 8.3 −5.8 9.3 Huang and

Opdyke(1993)

Weishan* 25.4 100.2 J3 5 Redbeds Inconclusive 7.3 25.3 10.4 −8.0 10.0 26.2 9.9 18.9 9.9 Huang andOpdyke(1993)

Yongping 25.5 99.5 K1 12 Redbeds Positive 42.0 51.1 15.7 28.9 20.8 −8.2 12.7 −6.8 16.6 Funahara etal. (1993)

Jingdong 24.5 100.8 K1–2

13 Redbeds Positive 8.3 48.8 7.7 −0.7 10.2 −9.9 7.8 −7.8 8.5 Tanaka etal. (2008)

Luxi* 24.3 98.4 J2 6 Redbeds Inconclusive 99.7 35.2 11.3 84.3 11.8 14.7 10.5 11.3 11.1 Huang andOpdyke(1993)

Zhengyuan 24.1 101.1 K1–2

7 Redbeds Positive 61.8 46.1 8.1 52.8 10.2 −7.7 8.0 −5.8 8.0 Tanaka etal. (2008)

Zhengyuan 24.1 101.1 K1–2

4 Redbeds Positive 144.2 49.4 6.4 135.2 8.8 −11.0 7.0 −8.6 7.8 Tanaka etal. (2008)

Jinggu* 23.6 100.5 J2 10 Redbeds Inconclusive 83.3 36.8 5.4 68.3 6.7 12.9 6.8 10.0 6.3 Huang andOpdyke(1993)

Jinggu* 23.4 100.4 K1 – Redbeds Inconclusive 84.4 39.6 17.8 71.5 19.1 0.9 0.6 Chen et al.(1995)

Jinggu 23.4 100.5 K2 7 Redbeds Positive 115.8 36.0 6.3 106.9 7.4 1.3 0.9 Chen et al.(1995)

Jinggu* 23.4 100.9 K2 8 Redbeds Inconclusive 79.4 43.3 9.1 70.5 10.8 −5.9 8.7 −4.3 8.5 Huang andOpdyke(1993)

Pu'er 23.0 101.0 K1–2

25 Redbeds Positive 59.9 45.2 5.1 51.0 7.0 −8.4 6.2 −6.2 6.5 Sato et al.(2007)

Mengla* 21.6 101.4 K2 10 Redbeds Inconclusive 60.8 37.8 7.6 51.9 8.6 −3.0 7.7 −2.0 8.1 Huang andOpdyke(1993)

SouthMengla

21.4 101.6 K1–2

14 Redbeds Positive 51.2 46.4 5.6 42.3 7.6 −11.8 6.5 −8.7 6.8 Tanaka etal. (2008)

Phong Saly 21.6 101.9 J3–K1

19 Redbeds Positive 29.8 32.7 9.1 17.1 9.5 5.7 7.5 3.8 6.4 Takemotoet al.(2009)

Kalaw 20.7 96.5 J–K 13 Redbeds Positive 44.7 23.4 6.1 36.2 6.6 9.0 6.8 5.4 6.1 Richter andFuller(1996)

Nan* 19.2 101.0 J1–3 11 Redbeds Positive 32.2 33.3 12.2 17.8 12.3 11.5 11.1 8.2 10.7 Aihara et al.(2007)

Indochina BlockLai Chau* 22.3 103.4 K3 5 Redbeds Positive 12.2 40.1 4.7 3.2 6.3 −3.8 6.0 −2.7 6.2 Takemoto

et al.(2005)

Yen Chau* 21.0 104.4 K3 8 Redbeds Positive 3.2 26.7 12.9 −5.8 12.2 7.9 11.3 4.9 9.8 Takemotoet al.(2005)

Borikhanxay 18.5 103.8 J3–K1

18 Redbeds Positive 41.8 46.6 8.0 29.3 10.1 −12.0 6.7 −8.9 7.2 Takemotoet al.(2009)

AmphoeBungKuan*

18.2 103.9 K2 14 Redbeds Inconclusive 31.8 28.7 3.5 23.0 5.0 1.4 5.5 0.9 5.5 Charusiri etal. (2006)

Nam Nao* 16.5 103.0 K1 10 Redbeds Inconclusive 28.1 40.5 2.4 15.7 4.6 −9.2 2.7 −6.2 2.7 Yang andBesse(1993)

Nam Nao* 16.5 103.0 J3 10 Redbeds Inconclusive 26.6 37.7 2.6 12.8 4.7 4.3 5.7 3.1 5.6 Yang andBesse(1993)

Muan SakonNakhon*

16.5–17.2

102.5–104.1

K2 8 Redbeds Inconclusive 31.4 27.1 9.4 22.7 9.3 1.0 8.9 0.6 8.9 Charusiri etal. (2006)

Muan SakonNakhon

16.5–17.2

102.5–104.1

K1 4 Redbeds Positive 31.8 38.3 5.7 19.4 7.0 −6.1 4.9 −4.1 4.9 Charusiri etal. (2006)

622 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

Table 2 (continued)

Localityname

Age N Rock type Fold test Observeddirection

Reference

Lat.(°N)

Lon.(°E)

Dec. (°) Inc.(°)

a95(°)

Rotation Delta Shallowing Delta Lat. displacement(Northward)

Delta

Muan Phin 16.5 106.0 J(K1)

17 Redbeds Syn-foldingat K1

30.8 39.9 3.0 20.8 5.9 (−8.8) 6.4 (−6.2) 6.2 Takemotoet al.(2009)

Da Lat* 10.4–12.9

105.0–109.4

K 21 Ryolite,Ryolite tuff,granite, silt

None 14.5 33.3 6.3 5.8 7.2 −13.1 6.9 −7.7 6.7 Chi andDorobek(2004)

Da Lat 11.7 108.3 K 21 Redbeds Positive 11.4 35.4 1.7 2.7 4.2 −15.2 4.9 −9.2 4.9

Europe (Besse and Courtillot, 2002)80 Ma (K2)120 Ma (J–K, J3–K1, K1)150 Ma (J, J1–J3)

Abbreviations are: Lon., longitude; Lat., latitude; Age: J, Jurassic; J2, Middle Jurassic; J3, Upper Jurassic; K, Cretaceous; K1, Lower Cretaceous; K2, Upper Cretaceous; E1, Paleocene–Eocene. N (n), number of sites (samples) used for paleomagnetic statistics. Dec. and Inc. are declination and inclination, respectively. α95 is a radii of the cone of 95% confidenceabout the mean direction. Field tests; positive and inconclusive (fold tests). The degree of rotation is evaluated by comparing the observed paleomagnetic declinations withthose expected from the Eurasian APWPs (Besse and Courtillot, 2002). Inclination shallowing (flattening) and northward latitudinal displacement are evaluated by comparingthe observed paleomagnetic inclination (Iobs) and paleolatitude (λobs) with those expected from the Eurasian APWPs. The formulas used for the evaluation ofshallowing=Iexp− Iobs, and that for northward latitudinal displacement=λexp−λobs. Uncertainty in rotational and latitudinal displacement is calculated using the methodof Demarest (1983). Characteristic remanent magnetization from the Jurassic rocks of the Muan Phin (Indochina Block) area is considered as Cretaceous due to its syn-folding ac-quisition during the Cretaceous (Takemoto et al., 2009). Localities with asterisk (*) have not been used for the calculation of southward displacement in the Shan–Thai and Indo-china blocks.

623Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

further paleomagnetic investigations would be required to overcomeuncertainty in data from Indochina Peninsula.

A composite unit model of the Indochina Peninsula for its south-ward displacement is also explained here by digital view points. Com-putational estimation made on 16 reliable data sets, including Da Latdata, reveals 5.1°±2.4° southward displacement of the IndochinaPeninsula. While, an arithmetic mean has been computed using a lat-itudinal difference between these localities (listed in Table 2), its un-certainty with 95% confidence level is estimated through formulat.975·S·n−1/2, where t.975 is the Student's t probability of 0.975, S isthe standard deviation and n is the number of data. These calculationsreveal almost identical amount of latitudinal displacement for Shan–Thai (4.6°±3.2°) and Indochina (7.1°±3.8°) blocks. As evidentfrom the analog view, both the Shan–Thai and Indochina blocksunderwent a southward displacement of 5.1°±2.4° as compositeunits of the Indochina Peninsula since the Cretaceous.

Based on the geological markers from the Ailao Shan–Red RiverFault Zone, an amount of 500–1150 km southward displacement hasbeen advocated for Indochina Peninsula (Leloup et al., 1995). Lateron, this estimate of latitudinal displacement has been brought downto 700±200 km, which is quite compatible with estimate providedby the present paleomagnetic study (5.1°±2.4°). This coincidence ingeological and paleomagnetic interpretations strongly advocates thatsouthward displacement of the Indochina Peninsula was caused by si-nistral motion along the Ailao Shan–Red River Fault Zone (Leloupet al., 1995; Replumaz et al., 2004). An age of 32 to 17 Ma has beenassigned to these tectonic activities by different researchers (Leloupet al., 1995, 2001; Lacassin et al., 1997; Wang and Burchfiel, 2000;Wang et al., 2001; Gilley et al., 2003; Schoenbohm et al., 2005, 2006;Wang et al., 2006; Viola and Anczkiewicz, 2008). Based on these ob-servations, it is concluded that considerable amount of southward dis-placement experienced by the Indochina Peninsula as a compositetectonic block occurred in a period between 32 Ma and 17 Ma.

Uniform displacement of the Indochina Peninsula expected frompaleomagnetic observations is, however, not compatible with thepresent day tectonic movement in the study area, as suggested byGPS measurements (Gan et al., 2007; Simons et al., 2007). Accordingto recent GPS and geodetic observations, the Shan–Thai Block is mov-ing toward S-SE at a rate of 18 mm/yr, while the Indochina Block ismoving toward east at a rate of 8 mm/yr (Calais et al., 2006; Vergnolleet al., 2007). These two tectonic blocks within the Indochina

Peninsula probably began their differential motions after a cease inuniform displacement at 17 Ma.

5.2. Deformation at southeastern tip of the Indochina Peninsula

The Late Cretaceous paleomagnetic direction obtained from Da Latarea through present study is sub-parallel to that expected from theEurasian APWP. An observed mean declination from present studyis 11.4°, whereas the one expected from 80 Ma European pole(Besse and Courtillot, 2002) is 8.7°. Comparison between the ob-served (this study) and expected declinations indicates only smallamount of tectonic rotation (−2.7°±4.2°) in the Da Lat area with re-spect to Eurasia. However, the Cretaceous paleomagnetic results fromcentral part of the Indochina Block (the Khorat basin) reveals morethan 10° CW rotation with respect to Eurasia (Takemoto et al.,2009). In addition, three other reliable data sets from IndochinaBlock (as listed in Table 2) reveal 24.3°±8.9° CW rotation for thisblock since the Cretaceous. This divergence in rotational motion be-tween different areas of the Indochina Block provides a clue for internaltectonic deformation in the eastern part of this extruded block. Com-pared to other areas of the Indochina Block, significantly small degreeof tectonic rotation in Da Lat area can be explained by either of the fol-lowing reasons; (1) no tectonic rotation occurred in Da Lat area sincethe Cretaceous or (2) subsequent to CWrotation of thewhole IndochinaBlock, the Da Lat area underwent a CCW rotation of 27.0°±9.8°.

Keeping in view the tectono-geological characteristics of the studyarea, the second reason can be considered as a plausible interpreta-tion in terms of rotational motion. The eastern margin of the Indochi-na Peninsula consists of two terranes, i.e., the Kontum massif and theTruong Son Belt. These terranes are bounded to the west by the Po Kosuture zone (Lepvrier, et al., 2004) and to the east by the East VietnamBoundary Fault (EVBF). The EVBF makes up about 1000 km long sea-ward continuation of the Ailao Shan–Red River shear zone, whichstraddles through the central and northern shelf of Vietnam beforeterminating at southern part of the Phu Khanh Basin (Fyhn et al.,2009). Sinistral movement along the Ailao Shan–Red River shearzone and the EVBF has been suggested to have occurred between32 Ma and 17 Ma. This was the time when southeastward displace-ment of the Indochina Peninsula was taking place. Since, CCW rota-tion of the crustal material has been anticipated during a sinistralmotion along the fault (e.g. Garfunkel and Ron, 1985; Sonder et al.,

-6000 -4000 -2000 0 2000 4000 6000

100° 110°

10°

20°

30°

Fig. 6. Contours of northward latitudinal displacement are drawn on the topographic map of Indochina Peninsula, where negative values indicate southward displacement. Thesecontours are plotted at 2° interval by inputting the available rotational data from 16 localities (as listed in Table 2) using the General Mapping Tools of Wessel & Smith (1991). Nullvalue is assumed for displacement along the coastline of the Indochina Peninsula. Block boundaries are depicted as shown in Fig. 1. The bathymetry and land topography are derivedfrom ETOPO2 global dataset (National Geophysical Data Center, 2001).

624 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

1986); the Kontum massif could have been subjected to such motionbetween 32 Ma and 17 Ma.

By considering the paleomagnetic parameters together with localgeological features, a bookshelf type of model is proposed for theKontummassif (Fig. 7), indicating a CCW rotation of the Kontummas-sif as a result of sinistral movement along the EVBF. Themodel furtherindicate a dissection in the southern part of the Kontum massif (in-cluding Da Lat area) by a major N50°E trending right lateral strike–slip faults, which remained active during the Paleogene and EarlyNeogene (Fig. 2a). These faults are the expression of E–W trendingshortening in the area, for which a stress field was activated by south-eastward displacement of the Indochina Peninsula. These dissectedblocks could have rotated in CCW sense by right lateral slip motionalong the fault boundaries under the influence of E–W shortening(Ron et al., 1984; Garfunkel and Ron, 1985). This was the timewhen left-lateral movement was occurring across the EVBF.

However, the CCW rotational motion in the study area was haltedprior to extrusions of the Neogene basalts on eastern tip of the Indo-china Peninsula. These basalts, which are distributed in different partsof the Kontum massif, have been dated between10 Ma and 3.3 Ma.Paleomagnetic data reported from these basalts (Dec/Inc=5.2°/24.8°; kg=35.0, α95=7.4°, N=12) indicate no CCW rotation in thesoutheastern tip of the Indochina Peninsula since 10 Ma.

It is therefore stated that more than 10° CW rotations of the Shan–Thai and Indochina blocks during the early stage of India–Asia colli-sion (Otofuji et al., 2007; Tanaka et al., 2008; Takemoto et al., 2009)was followed by CCW rotation in the southeastern part of the Indo-china Peninsula. According to a 4-D evolution model from seismic to-mography (Replumaz et al., 2004), both these blocks experienced aCW rotational motion as a composite unit prior to the commence-ment of southward displacement. The process of CCW rotation be-tween 32 Ma and 17 Ma, which has been linked to southeastwarddisplacement of the Indochina Peninsula, is considered a secondphase of deformation caused by the Indian Plate ongoing penetrationinto Asia. These deformations are ascribed to domino type effects thatoccurred in the Indochina Peninsula subsequently from north tosouth as a result of Indian Plate indentation.

Alternatively, CCW rotation in the Kontum massif can be linked tonorthward extension of the same sense rotation occurred in the SouthSundaland Block (including the Peninsular Malaysia, Borneo, south-ern Sulawesi and Celebes Sea). Richter and Fuller (1996) havereported CCW deflection in declinations from the upper Jurassic toearly Tertiary rocks of the Malaysian territory as well. Same sensedeclinations (D=270°–320°) of the middle Miocene age have alsobeen reported from the Jurassic to Miocene rocks of the SouthSundaland Block (Haile, 1978; Sasajima et al., 1980; Schmidtke

(a) Early stage ofcollision of India

(b) 32 Ma and 17 MaSouthward displacementof Indochina Peninsula

Fig. 7. A model explaining different stages of deformation in the eastern margin of the Indochina Peninsula. (a) In the early stage of India–Asia collision, the Indochina Block ex-perienced clockwise rotation of about 20° together with the Shan–Thai Block and (b) in a period between 32 Ma and 17 Ma, the Indochina and Shan–Thai blocks underwent a co-herent southward displacement along the Red River Fault. Following this, southeastern tip of the south moving Indochina Block experienced a CCW rotation as a result of bookshelftype deformation along the East Vietnam Boundary Fault (E.V.B.F.).

625Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

et al., 1990; Shibuya et al., 1991; Fuller et al., 1999; Hatchison,2010; Yamashita et al., 2011).

6. Conclusions

1. Steep inclination with northerly declination (Dec/Inc=11.4°/35.4°, ks=35.4, α95=1.7°, N=21), which is sub-parallel to LateCretaceous Eurasian paleomagnetic pole, is observed in theUpper Cretaceous red beds of the Dak Rium Formation (Da Latarea of the Kontum massif).

2. An amount of southward displacement in Da Lat area (9.2°±4.9°in latitude) is comparable to previously reported paleomagneticand geological data obtained from other localities of the IndochinaPeninsula, suggesting a southeastward displacement of the Kon-tum massif as a part of the Indochina Peninsula.

3. Prior to its southward displacement, the Indochina Peninsula ex-perienced a CW rotation of 24.3°±8.9° in the early stage ofIndia–Asia collision. Following this, a CCW rotation of 27.0°±9.8°has occurred in the Kontum massif as a result of sinistral move-ment along the East Vietnam Boundary Fault.

Acknowledgments

This research was partly supported by Toyota Foundation. In addi-tion, Grant-in-aid (Nos. 14403010, 18403012, 22403012) fromJapanese Ministry of Education, Culture, Sports, Science andTechnology (MEXT) has been used to accomplish this project. Thisstudy was also supported by a program from Global Centers ofExcellence (GCOE) and Foundation of the International Center forPlanetary Science (MEXT).

References

Aihara, K., Takemoto, K., Zaman, H., Inokuchi, H., Miura, D., Surinkum, A., Paiyarom, A.,Phajuy, B., Chantraprasert, S., Panjasawatwong, Y., Wongpornchai, P., Otofuji, Y.,2007. Internal deformation of the Shan–Thai block inferred from Paleomagnetismof Jurassic sedimentary rocks in Northern Thailand. Journal Asian Earth Sciences30, 530–541.

Aitchison, J.C., Ali, J.R., Davis, A.M., 2007. When and where did India and Asia collide?Journal of Geophysical Research 112, B05423. doi:10.1029/2006JB004706.

Aitchison, J.C., Xia, X., Baxter, A.T., Ali, J.R., 2011. Detrital zircon U–Pb ages along theYarlung–Tsangpo suture zone, Tibet: implications for oblique convergence and col-lision between India and Asia. Gondwana Research 20, 691–709.

Besse, J., Courtillot, V., 2002. Apparent and true polar wander and the geometry of thegeomagnetic field over the last 200 Myr. Journal of Geophysical Research 107,2300. doi:10.1029/2000JB000050.

Briais, A., Patriat, P., Tapponnier, P., 1993. Updated interpretation of magnetic-anomalies in the South China Sea — implications for the Tertiary tectonics ofSoutheast Asia. Journal of Geophysical Research 98, 6299–6328.

Calais, E., Dong, L., Wang, M., Shen, Z., Vergnolle, M., 2006. Continental deformation inAsia from a combined GPS solution. Geophysical Research Letters 33, L24319.doi:10.1029/2006GL028433.

Carter, A., Roques, D., Bristow, C., Kinny, P., 2001. Understanding Mesozoic accretion inSoutheast Asia: significance of Triassic thermotectonism (Indosinian orogeny) inVietnam. Geology 29, 211–214.

Charusiri, P., Imsamut, S., Zhuang, Z., Ampaiwan, T., Xu, X., 2006. Paleomagnetism ofthe earliest Cretaceous to early late Cretaceous sandstones, Khorat Group, North-east Thailand: implications for tectonic plate movement of the Indochina block.Gondwana Research 9, 310–325.

Chen, H., Dobson, J., Heller, F., Hao, J., 1995. Paleomagnetic evidence for clockwise rota-tion of the Simao region since the Cretaceous: a consequence of India–Asia colli-sion. Earth and Planetary Science Letters 134, 203–217.

Chi, C.T., Dorobek, S.L., 2004. Cretaceous palaeomangetism of Indochina and surround-ing regions: Cenozoic tectonic implications. In: Malpas, J., Fletcher, C.J.N., Ali, J.R.,Aitchison, J.C. (Eds.), Aspects of the Tectonic Evolution of China: Geological Society,London, Special Publications, 226, pp. 273–287.

Cogné, J.P., 2003. PaleoMac: a Macintosh™ application for treating paleomagnetic dataand making plate reconstructions. Geochemistry, Geophysics, Geosystems 4, 1007.doi:10.1029/2001GC000227.

Demarest, H.H., 1983. Error analysis of the determination of tectonic rotation from pa-leomagnetic data. Journal of Geophysical Research 88, 4321–4328.

Enkin, R.J., 2003. The direction-correction tilt test: an all-purpose tilt/fold test for pa-leomagnetic studies. Earth and Planetary Science Letters 212, 151–166.

626 Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

Ferrari, O.M., Hochard, C., Stampfli, G.M., 2008. An alternative plate tectonic model forthe Paleozoic–Early Mesozoic Paleothethyan evolution of Southeast Asia (NorthernThailand–Burma). Tectonophysics 451, 346–365.

Fisher, R.A., 1953. Dispersion on a sphere. Proceedings of Royal Society of London Se-ries A 217, 295–305.

Fuller, M., Ali, J.R., Moss, S.J., Frost, G.M., Richter, B., Mahfi, A., 1999. Paleomagnetism ofBorneo. Journal of Asian Earth Sciences 17, 3–24.

Funahara, S., Nishiwaki, N., Murata, F., Otofuji, Y., Wang, Y.Z., 1993. Clockwise rotationof the Red River fault inferred from paleomagnetic study of Cretaceous rocks in theShan–Thai–Malay block of western Yunnan, China. Earth and Planetary ScienceLetters 117, 29–42.

Fyhn, M.B.W., Boldreel, L.O., Nielsen, L.H., 2009. Geological development of the Centraland South Vietnamese margin: implications for the establishment of the SouthChina Sea, Indochinese escape tectonics and Cenozoic volcanism. Tectonophysics478, 184–214.

Gan, W., Zhang, P., Shen, Z., Niu, Z., Wang, M., Wan, Y., Zhou, D., Cheng, J., 2007.Present-day crustal motion within the Tibetan Plateau inferred from GPS measure-ments. Journal of Geophysical Research 112, B08416. doi:10.1029/2005JB004120.

Garfunkel, Z., Ron, H., 1985. Block rotation and deformation by strike–slip faults 2. Theproperties of a type of macroscopic discontinuous deformation. Journal of Geo-physical Research 90, 8589–8602.

Gilley, L.D., Harrison, T.M., Leloup, P.H., Ryerson, F.J., Lovera, O.M., Wang, J.-H., 2003. Di-rect dating of left-lateral deformation along the Red River shear zone, China andVietnam. Journal of Geophysical Research 108, B2. doi:10.1029/2001JB001726.

Gradstein, F., Ogg, J., Smith, A., 2004. A Geologic Time Scale. Cambridge UniversityPress, Cambridge, p. 589.

Haile, N.S., 1978. Reconnaissance palaeomagnetic results from Sulawesi, Indonesia, andtheir bearing on palaeogeographic reconstructions. Tectonophysics 46, 77–85.

Hall, R., Van Hattum, M.W.A., Spakman, W., 2008. Impact of India–Asia collision on SEAsia: the record in Borneo. Tectonophysics 451, 366–389.

Hatchison, C.S., 2010. Oroclines and paleomagnetism in Borneo and South-East Asia.Tectonophysics 496, 53–67.

Hoa, T.T., Anh, T.T., Phuong, N.T., Dung, P.T., Anh, T.V., Izokh, A.E., Borisenko, A.S., Lan,C.Y., Chung, S.L., Lo, C.H., 2008. Permo-Triassic-felsic magmatism of the TrongSon belt, eastern margin of Indochina. Comptes Rendus Geoscience 340, 112–126.

Houseman, G.A., England, P.C., 1993. Crustal thickening versus lateral expulsion in the In-dian–Asian continental collision. Journal of Geophysical Research 98, 12233–12249.

Huang, K., Opdyke, N.D., 1993. Paleomagnetic results from Cretaceous and Jurassicrocks of South and Southwest Yunnan: evidence for large clockwise rotations inthe Indochina and Shan–Thai–Malay terranes. Earth and Planetary Science Letters117, 507–524.

Kirschvink, J.L., 1980. The least-squares line and plane and the analysis of palaeomag-netic data. Geophysical Journal of the Royal Astronomical Society 62, 699–718.

Lacassin, R., Maluski, H., Leloup, P.H., Tapponnier, P., Hinthong, C., Siribhakdi, K.,Chuaviroj, S., Charoenravat, A., 1997. Tertiary diachronic extrusion and defor-mation of western Indochina: structural and 40Ar/39Ar evidence from NWThailand. Journal of Geophysical Research 102, 10013–10037.

Laccassin, R., Replumaz, A., Leloup, P.H., 1998. Hairpin river loops and slip-sense inver-sion on southeast Asian strike–slip faults. Geology 26, 703–706.

Lan, C.Y., Chung, S.L., Long, T.V., Lo, C.H., Lee, T.Y., Mertzman, S.A., Shen, J.S., 2003. Geo-chemical and S-Nd isotopic constraints from the Kontum massif, central Vietnamon the crustal evolution of the Indochina block. Precambrian Research 122, 7–27.

Leloup, P.H., Lacassin, R., Tapponnier, P., Schärer, U., Dalai, Z., Liu, X.H., Zhang, L.S., Ji,S.C., Trinh, P.T., 1995. The Ailao Shan–Red River shear zone (Yunnan, China), Ter-tiary transform boundary of Indochina. Tectonophysics 251, 3–84.

Leloup, P.H., Arnaud, N., Lacassin, R., Kienast, J.R., Harrison, T.M., Phan Trong, T.T.,Replumaz, A., Tapponnier, P., 2001. New constraints on the structure, thermochro-nology, and timing of the Ailao Shan-Red River shear zone, SE Asia. Journal of Geo-physical Research 106, 6683–6732.

Lepvrier, C., Maluski, H., Tich, V.V., Leyreloup, A., Thi, P.T., Vuong, N.V., 2004. The EarlyTriassic Indosinian orogeny in Vietnam (Trong Son Belt and Kontum Massif). Tec-tonophysics 393, 87–118.

Lowrie, W., 1990. Identification of ferromagnetic minerals in a rock by coercivity andunblocking temperature properties. Geophysical Research Letters 17, 159–162.

Macmillan, S., Maus, S., 2005. International geomagnetic reference field — the tenthgeneration. Earth Planets and Space 57, 1135–1140.

McFadden, P.L., 1990. A new fold test for palaeomagnetic studies. Geophysical JournalInternational 103, 163–169.

Metcalfe, I., 2011. Tectonic framework and Phanerozoic evolution of Sundaland. Gond-wana Research 19, 3–21.

Morley, C.K., 2002. A tectonic model of the Tertiary evolution of strike–slip faults andrift in SE Asia. Tectonophysics 347, 189–215.

Nagy, E.A., Maluski, H., Lepvrier, C., Scharer, U., Thi, P.T., Leyreloup, A., Thich, V.V., 2001.Geodynamic significance of the Kontum Massif in central Vietnam; composite 40Ar/39Ar and U–Pb ages from Paleozoic to Triassic. Journal of Geology 109, 755–770.

Nakano, N., Osanai, Y., Owada, M., Nam, T.N., Toyoshima, T., Binh, P., Tsunogae, T.,Kagami, H., 2007. Geologic and metamorphic evolution of the basement complexesin the Kontum Massif, central Vietnam. Gondwana Research 12, 438–453.

Nam, T.N., Sanao, Y., Terada, K., Toriumi, M., Quynh, P.V., Dung, L.T., 2001. First SHRIMPU–Pb zircon dating of granulites from the Kontum massif (Vietnam) and tecto-thermal implications. Journal of Asian Earth Sciences 19, 77–84.

National Geophysical Data Center, 2001. ETOPO2 Global 2' Elevations [CD-ROM]. Na-tional Oceanic and Atmospheric Administration. U.S. Department of Commerce,Boulder, Colorado.

Nguyen, X.B., Tran, D.L., Huynh, T., 1994. Explanatory Note to the Geological Map ofVietnam on 1:500,000 Scale. Geological Survey of Vietnam Press, Hannoi, Vietnam.

Otofuji, Y., Mu, C., Tanaka, K., Miura, D., Inokuchi, H., Kamei, R., Tamai, M., Takemoto, K.,Zaman, H., Yokoyama, Y., 2007. Spatial gap between Lhasa and Qiangtang blocksinferred from Middle Jurassic to Cretaceous paleomagnetic data. Earth and Plane-tary Science Letters 262, 581–593.

Otofuji, Y., Yokoyama, M., Kitada, K., Zaman, H., 2010. Paleomagnetic versus GPS deter-mined tectonic rotation around eastern Himalayan syntaxis in East Asia. JournalAsian Earth Sciences 37, 438–451.

Owada, M., Osanai, Y., Nakano, N., Matsushita, T., Nam, T.N., Tsunogae, T., Toyoshima, T.,Binh, P., Kagami, H., 2007. Crustal anatexis and formation of two types of graniticmagmas in the Kontummassif, central Vietnam: implications for magma processesin collision zones. Gondwana Research 12, 428–438.

Pullaiah, G., Irving, E., Buchan, K.L., Dunlop, D.J., 1975. Magnetization changes causedby burial and uplift. Earth and Planetary Science Letters 28, 133–143.

Rangin, C., Huchon, P., Le Pichon, X., Bellon, H., Lepvrier, C., Roques, D., Hoe, D.N.,Quynh, P.V., 1995. Cenozoic deformation of central and south Vietnam. Tectono-physics 251, 179–196.

Replumaz, A., Tapponnier, P., 2003. Reconstruction of the deformed collision zone be-tween India and Asia by backward motion of lithospheric blocks. Journal of Geo-physical Research 108 (B6), 2285. doi:10.1029/2001JB000661.

Replumaz, A., Kárason, H., van der Hilst, R.D., Besse, J., Tapponnier, P., 2004. 4-D evolu-tion of SE Asia's mantle from geological reconstructions and seismic tomography.Earth and Planetary Science Letters 221, 103–115.

Richter, B., Fuller, M., 1996. Palaeomagnetism of the Sibumasu and Indochina blocks:implications for the extrusion tectonic models. In: Hall, R., Blundell, D. (Eds.), Tec-tonic Evolution of Southeast Asia: Geological Society Special Publication, no. 106,pp. 203–224.

Ron, H., Freund, R., Garfunkel, Z., Nur, A., 1984. Block rotation by strike–slip faulting,structural and paleomagnetic evidence. Journal of Geophysical Research 89,6256–6270.

Royden, L.H., Burchfiel, B.C., van der Hilst, R.D., 2008. The geological evolution of the Ti-betan Plateau. Science 321, 1054–1058.

Sasajima, S., Nishimura, S., Hirooka, K., Otofuji, Y., van Leeuwen, T., Hehuwat, F., 1980.Paleomagnetic studies combined with fission-track dating on the western arc ofSulawersi, east Indonesia. Tectonophysics 64, 163–172.

Sato, K., Liu, Y.Y., Zhu, Z.C., Yang, Z.Y., Otofuji, Y., 1999. Paleomagnetic study of middleCretaceous rocks from Yunlong, western Yunnan, China: evidence of southwarddisplacement of Indochina. Earth and Planetary Science Letters 165, 1–15.

Sato, K., Liu, Y., Wang, Y., Yokoyama, M., Yoshioka, S., Yang, Z., Otofuji, Y., 2007. Paleo-magnetic study of Cretaceous rocks from Pu'er, western Yunnan, China: evidenceof internal deformation of the Indochina block. Earth and Planetary Science Letters258, 1–15.

Sato, S., Yang, Z., Tong, Y., Fujihara, M., Zaman, H., Yokoyama, M., Kitada, K., Otofuji, Y.,2011. Inclination variation in the Late Jurassic to Eocene red beds formations ofSoutheast Asia: lithological to locality scale approach. Geophysical Journal Interna-tional 186, 471–491.

Schmidtke, E.A., Fuller, M.D., Haston, R.B., 1990. Paleomagentic data from Sarawak, Ma-laysian Borneo, and the Late Mesozoic and Cenozoic tectonics of Sundaland. Tec-tonics 9, 123–140.

Schoenbohm, L.M., Burchfiel, B.C., Chen, L., Yin, J., 2005. Exhumation of the Ailao Shanshear zone recorded by Cenozoic sedimentary rocks, Yunnan Province, China. Tec-tonics 24, TC6015. doi:10.1029/2005TC001803.

Schoenbohm, L., Burchfiel, B.C., Chen, L., 2006. Propagation of surface uplift, lower crustflow, and Cenozoic tectonics of the southeast margin of the Tibetan Plateau. Geol-ogy 34, 813–816.

Shibuya, H., Merril, D.L., Hsu, V., ODP Leg 124 Scientists, 1991. Paleogene counter-clockwise rotation of the Celebes Sea - Orientation of the ODP cores utilizing the sec-ondary magnetization. In: Silver, E.A., Rangin, C., von Breymann, M.T. (Eds.), Proc.ODP, Sci. Results, 124, College Station TX (Ocean Drilling Program), pp. 519–523.

Simons, W.J.F., Socquet, A., Vigny, C., Ambrosius, B.A.C., Haji Abu, S., Promthong, C.,Subarya, C., Sarsito, D.A., Matheussen, S., Morgan, P., Spakman, W., 2007. A de-cade of GPS in Southeast Asia: resolving Sundaland motion and boundaries.Journal of Geophysical Research 112, B06420. doi:10.1029/2005JB003868.

Smith, W.H.F., Wessel, P., 1990. Gridding with continuous curvature splines in tension.Geophysics 55, 293–305.

Sonder, L.J., England, P.C., Houseman, G.A., 1986. Continuum calculations of continentaldeformation in transcurrent environments. Journal of Geophysical Research 91,4797–4810.

Takemoto, K., Halim, N., Otofuji, Y., Tran, V.T., Le, V.D., Hada, S., 2005. New paleomag-netic constraints on the extrusion of Indochina: Late Cretaceous results from theSong Da terrane, northern Vietnam. Earth and Planetary Science Letters 229,273–285.

Takemoto, K., Sato, S., Chanthavichith, K., Inthavong, T., Inokuchi, H., Fujihara, M.,Zaman, H., Yang, Z., Yokoyama, M., Iwamoto, H., Otofuji, Y., 2009. Tectonic defor-mation of the Indochina Peninsula recorded in the Mesozoic palaeomagnetic re-sults. Geophysical Journal International 179, 97–111.

Tan, X., Kodama, K.P., Gilder, S., Courtillot, V., 2007. Rock magnetic evidence for inclina-tion shallowing in the Passaic Formation red beds from the Newark basin and asystematic bias of the Late Triassic polar wander path for North America. Earthand Planetary Science Letters 254, 345–357.

Tanaka, K., Mu, C., Sato, K., Takemoto, K., Miura, D., Liu, Y., Zaman, H., Yang, Z.,Yokoyama, M., Iwamoto, H., Uno, K., Otofuji, Y., 2008. Tectonic deformation aroundthe eastern Himalayan syntaxis: constraints from the Cretaceous palaeomagneticdata of the Shan–Thai Block. Geophysical Journal International 175, 713–728.

Tapponnier, P., Peltzer, G., Le Dain, A.Y., Armijo, R., Cobbold, P., 1982. Propagating ex-trusion tectonics in Asia: new insights from simple experiments with plasticine.Geology 10, 611–616.

627Y. Otofuji et al. / Gondwana Research 22 (2012) 615–627

Tauxe, L., Kent, D., 2004. A simplified statistical model for the geomagnetic field and thedetection of shallow bias in paleomagentic inclinations: was the ancient magneticfield dipolar? In: Channell, J.E.T., Kent, D.V., Lowrie, W., Meert, J. (Eds.), Timescaleof paleomagnetic field. Geophysical Monograph Series, vol. 145. American Geo-physical Union, Washington, D.C, pp. 101–116.

Tauxe, L., Kodama, K.P., Kent, D.P., 2008. Testing corrections for paleomagnetic inclina-tion error in sedimentary rocks: a comparative approach. Physics of the Earth andPlanetary Interiors 169, 152–165.

Vergnolle, M., Calais, E., Dong, L., 2007. Dynamics of continental deformation inAsia. Journal of Geophysical Research 112, B11403. doi:10.1029/2006JB004807.

Viola, G., Anczkiewicz, R., 2008. Exhumation history of the Red River shear zone innorthern Vietnam: new insights from zircon and apatite fission-track analysis.Journal of Asian Earth Sciences 33, 78–90.

Wang, E., Burchfiel, B.C., 2000. Late Cenozoic to Holocene deformation in southwest-ern Sichuan and adjacent Yunnan, China, and its role in formation of the south-eastern part of the Tibetan Plateau. Geological Society of America Bulletin 112,413–423.

Wang, J.H., Yin, A., Harrison, T.M., Grove, M., Zhang, Y.-Q., Xie, G.-H., 2001. A. tectonicmodel for Cenozoic igneous activities in the eastern Indo–Asian collision zone.Earth and Planetary Science Letters 188, 123–133.

Wang, Y., Fan, W., Zhang, Y., Peng, T., Chen, X., Xu, Y., 2006. Kinematics and 40Ar/39Ar geo-chronology of the Gaoligong and Chongshan shear systems, western Yunnan, China: im-plications for earlyOligocene tectonic extrusion of SEAsia. Tectonophysics 418, 235–254.

Wessel, P., Smith, W.H.F., 1991. Free software helps map and display data. Eos, Trans-actions of American Geophysical Union 72, 441–446.

Yamashita, I., Surinkum, A., Wada, Y., Fujihara, M., Yokoyama, Zaman, H., Otofuji, Y., 2011.Paleomagnetismof theMiddle-Late Jurassic to Cretaceous red beds from the PeninsularThailand: implications for collision tectonics. Journal of Asian Earth Sciences 40,784–796.

Yang, Z.Y., Besse, J., 1993. Paleomagnetic study of Permian and Mesozoic sedimentaryrocks from Northern Thailand supports the extrusion model for Indochina. Earthand Planetary Science Letters 117, 525–552.

Yang, Z.Y., Yin, J.Y., Sun, Z.M., Otofuji, Y., Sato, K., 2001. Discrepant Cretaceous paleo-magnetic poles between Eastern China and Indochina: a consequence of the extru-sion of Indochina. Tectonophysics 334, 101–113.

Zijderveld, J.D.A., 1967. A.C. demagnetization of rocks: analysis of results. In: Collinson,D.W., Creer, K.M., Runcorn, S.K. (Eds.), Methods in Paleomagnetism. Elsevier,New York, pp. 254–286.