tectonic evolution of the india–asia suture zone since middle eocene time, lopukangri area,...

Journal of Asian Earth Sciences 62 (2013) 205–220

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Journal of Asian Earth Sciences

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Tectonic evolution of the India–Asia suture zone since Middle Eocene time,Lopukangri area, south-central Tibet

V.I. Sanchez a,⇑, M.A. Murphy b, A.C. Robinson b, T.J. Lapen b, M.T. Heizler c

a College of the Mainland, Science and Math Department, 1200 Amburn Road, Texas City, TX 77591, USAb University of Houston, Department of Earth and Atmospheric Sciences, 312 Science and Research Bldg. 1, Houston, TX 772004-5007, USAc New Mexico Geochronology Research Laboratory, New Mexico Bureau of Geology and Mineral Resources, Socorro, NM 87801-4796, USA

a r t i c l e i n f o

Article history:Received 5 October 2011Received in revised form 2 September 2012Accepted 17 September 2012Available online 27 September 2012

Keywords:HimalayaIndia–Asia sutureTibetLopukangriGreat Counter thrustGangdese batholith

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⇑ Corresponding author. Fax: +1 409 933 8025.E-mail address: [email protected] (V.I. Sanchez

a b s t r a c t

Suture zones often archive complex geologic histories underscored by episodes of varying style of defor-mation associated with intercontinental collision. In the Lopukangri area of south-central Tibet (29�540N,84�240E) field relationships between tectonic units juxtaposed by the India–Asia suture are well exposed,including Indian passive margin rocks (Tethyan Sedimentary Sequence), forearc deposits (Xigaze Group),magmatic arc rocks (Gangdese batholith and Linzizong Formation) and syncollision deposits (Eocene–Miocene conglomerates). To better understand the structural history of this area, we integrated geologicmapping with biotite 40Ar/39Ar thermochronology and zircon U–Pb geochronology. The first-order struc-ture is a system of north-directed thrusts which are part of the Great Counter thrust (GCT) that placesIndian passive margin rocks and forearc deposits on top of magmatic arc rocks and syn-tectonic conglom-erates. We infer the south-directed Late Oligocene Gangdese Thrust (GT) exists at unexposed structurallevels based on field mapping, cross sections, and regional correlations as it has been documented imme-diately to the east. A granite in the footwall has a U–Pb zircon age of 38.4 ± 0.4 Ma, interpreted to be theage of emplacement of the granite, and a younger 40Ar/39Ar biotite age of 19.7 ± 0.1 Ma. As the granitesample is situated immediately below a nonconformity with low grade greenschist facies rocks, we inter-pret the younger age to reflect Miocene resetting of the biotite Ar system. Syn-tectonic deposits in theLopukangri area consist of three conglomerate units with a total thickness of �1.5 km. The lower twounits consist of cobble gravel pebble conglomerates rich in volcanic and plutonic clasts, transitioningto conglomerates with only sedimentary clasts in the upper unit. We correlate the syncollision depositsto the Eocene–Oligocene Qiuwu Formation based on field relationships, stratigraphy and petrology.Petrology and clast composition suggest the lower two units of the Qiuwu Formation had a northernprovenance (Lhasa block and magmatic arc) and the upper unit had a southern provenance (Tethyan Sed-imentary Sequence). Our observations are consistent with paleocurrent data from other studies whichsuggest a predominant south-directed paleoflow for this formation. We propose a model in which: (1)granites intrude at 38.4 ± 0.4 Ma; (2) are exhumed by erosion; (3) and buried due to regional subsidenceand initial deposition of a conglomerate unit; (4) exposed by the GT at�27–24 Ma to provide detritus; (5)buried a second time by hanging wall-derived sedimentary deposits and the GCT, then (6) exposed from adepth of �12–10 km by a blind thrust at �19 Ma. An alternate model describes: (1) intrusion of the gran-ites at 38.4 ± 0.4 Ma, followed by (2) exhumation of the granites via normal faulting to provide detritus;(3) then burial by the GCT at �24 Ma, followed by (4) exhumation via regional erosional denudation at�19 Ma. Exposure of the GT west of Xigaze has not been confirmed. We suggest that shallower structurallevels of the India-Asia suture zone are exposed to the west of the study area, compared to the east,where the GT has been previously documented. The GCT in the area is short-lived, as it is cut and offsetby a Middle Miocene �N-striking W-dipping oblique normal fault system.

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1. Introduction

Delineating suture zones in orogens is generally problematicdue to poor exposure and structural complexities along the suture

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(e.g. Dewey, 1977). Determining the geologic relationships alongthe India–Asia suture zone has proved difficult because exposureof suture zone components is generally poor, thus hindering corre-lation of geologic units from one end of the suture to the other. Thishas hindered our ability to understand the timing of continent–continent collision between India and Asia, and the evolution ofshortening along the southern edge of the Tibetan Plateau.

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206 V.I. Sanchez et al. / Journal of Asian Earth Sciences 62 (2013) 205–220

Tectonic models of the development of the India–Asia suturezone broadly include those that describe subduction of oceaniclithosphere along the entire southern margin of the Tibetan Pla-teau (Andean-type) (e.g. Searle et al., 1987), and those that de-scribe subduction of trapped volcanic island arcs and continentalterranes (e.g. Aitchison et al., 2000; Ziabrev et al., 2004) alongthe central and eastern portions of the margin, as exemplified inthe Kohistan and Ladakh regions in the west (Schärer et al.,1984; Searle et al., 1987, 1999; Corfield et al., 1999). Stratigraphy(Searle et al., 1987, 1997; Gaetani and Garzanti, 1991; Beck et al.,1995; Rowley, 1996; Zhu et al., 2005), structural field studies andgeochronology (Gnos et al., 1997), and paleomagnetic research(Patriat and Achache, 1984; Klootwijk et al., 1992; van Hinsbergenet al., 2012) support a diachronous closing of the Neotethys Ocean,closing in the early Paleocene in the west (Beck et al., 1995) and inthe mid Eocene in the east (Dewey et al., 1988); however, many as-pects of the evolution of the India–Asia suture remain unclear.

The interpreted history of the India–Asia suture has been built bypiecing together field relationships from key locations along the su-ture. Field mapping and detailed thermochronology work from theRenbu-Zedong area in eastern Tibet (Fig. 1) document two signifi-cant thrust systems that initiated since �30 Ma (Yin et al., 1994;Harrison et al., 2000). One thrust system, the south-directed Gang-dese thrust, is constrained to have been active between 27 and23 Ma, suggesting intracontinental thrusting was active along theIndia–Asia suture during this time (Yin et al., 1994). A younger epi-sode of thrusting associated with the north-directed Renbu Zedong

Fig. 1. (A) Regional map of the India–Asia suture zone. Abbreviations: IYS – Indus Yalu sThrust, GCT – Great Counter thrust system, RZT – Renbu Zedong Thrust, GT – Gangdese ThTibetan Detachment, TF – Tibrikot fault, BG – Bheri Gad fault, DF – Dangardzang fault, GThiede et al., 2006), TG – Thakkhola Graben (Garzione et al., 2000), GG – Gyirong GrabenSundell et al., 2010), DT – Daggyai Tso Graben (Harrison et al., 1994; Williams et al., 20012006), YG – Yadong Gulu Rift (Harrison et al., 1995), KC – Kung Co (Mahéo et al., 2007),et al., 2002). Primary sources for regional geology and large scale structures include Arm(2009), and Styron et al. (2010) (and references therein) and slight modifications basedstudy area in southern Tibet.

thrust (equivalent to the Great Counter thrust in western Tibet) isconstrained to have been active from �23 to 8 Ma in eastern Tibet(Yin et al., 1994; Harrison et al., 2000) during a period of back-thrusting. Studies in western Tibet involving detailed stratigraphycombined with U–Pb detrital zircon geochronology of late Oligo-cene-early Miocene conglomerate deposits have modified our viewof the timing of basin development along the suture (e.g. DeCelleset al., 2011). Therefore, studies suggest basin development occurredduring an extensional tectonic regime along the India–Asia sutureresulting in long narrow basins with a primarily northern prove-nance (Gangdese magmatic arc) (DeCelles et al., 2011). Transpres-sional deformation dominated in the west (near Bangong Co) at�17 Ma, with the development of the Karakoram fault system;however, there are studies that suggest transpression may havebeen active at the end of the Eocene (�35 Ma) (Lacassin et al.,2004; Searle et al., 1998). Strike-slip and extensional deformationis presently ongoing (Ratschbacher et al., 1994; Yin et al., 1999)but early episodes of transtension were active in the west by�13 Ma (Murphy et al., 2000) along the Karakoram fault. Thesetranstensional episodes may have initiated in the Late Oligocene-Early Miocene (Valli et al., 2008).

Forearc basin deposits (Xigaze Group) and magmatic arc rocks(e.g. Gangdese batholith) are discontinuously exposed along the In-dia–Asia suture in southern Tibet (Fig. 1). Expansive exposures ofintrusive batholithic rocks exist along the eastern and western por-tions of the suture zone, whereas the majority of forearc basindeposits are exposed in the central portion (Liu, 1988; TBGMR,

uture zone (India–Asia suture), BNS – Bangong–Nujiang suture, MFT – Main Frontalrust, KF – Karakoram fault, GMH – Gurla Mandhata Humla fault system, STD – SouthCF –Gyaring Co fault, BC – Beng Co fault. LP – Leo Pargil (Hintersberger et al., 2010;, LK-Lopukangri Rift (Murphy et al., 2010), LS – Lunggar Shan Rift (Kapp et al., 2008;), PZ – Pabbai Zong (Williams et al., 2001), TYT – Tangra Yum Tso Rift (Dewane et al.,AD – Ama Drime Massif, XD – Xainza–Dinggye Rift, GM – Gurla Mandhata (Murphyijo et al. (1986), Liu (1988), Yin and Harrison (2000), Hodges (2000), Taylor and Yinon our field and remote-sensing observations. (B) Inset map shows location of the

V.I. Sanchez et al. / Journal of Asian Earth Sciences 62 (2013) 205–220 207

1992; Yin et al., 1994; Murphy et al., 1997; Harrison et al., 2000;Yin and Harrison, 2000) (Fig. 1). However, relatively undeformedlate Paleocene-early Eocene Linzizong volcanic rocks widely ex-posed north of the India–Asia suture throughout southern Tibetare concentrated along the central portions of the suture from�84 to 87�E. This area overlaps with a region in which forearcdeposits are exposed (89.5–84�E). Discontinuous ophiolite sliversare also found along the suture (Yin et al., 1994).

The nature of the outcrop pattern of forearc deposits and mag-matic belt is often attributed to the paleoarc margin morphology.The paleoarc may have trapped portions of oceanic crust of variousdimensions along the subduction zone (e.g. Einsele et al., 1994).Alternatively, the pattern may be attributed to the style of Neo-tethyan subduction along the length of the margin, such as changesin the subduction angle causing variations in the geometry of theforearc basin. Furthermore, the geometry of the deposits may beattributed to a diachronous continent–continent collision (e.g.Rowley, 1996), or perhaps be the result of the geometry of Indiaupon collision (e.g. Treloar and Coward, 1991). The nature of theirregularity of the outcrop pattern may also be a reflection of thepresent-day erosional patterns of forearc deposits and magmaticarc plutonic rocks (e.g. Yin et al., 1994), or may be due to along-strike variations in crustal exhumation. Shortening associated withthe development of two prominent structures along the India–Asiasuture zone, the Gangdese thrust and the Great Counter thrust,modified the relationships between tectonic units juxtaposedalong the suture in the Oligocene–Miocene.

The Lopukangri area of south-central Tibet preserves exposuresof passive margin (Tethyan Sedimentary Sequence, TSS), forearcbasin (Xigaze Group), syncollision sedimentary deposits (Qiuwuconglomerates) and magmatic arc rocks (Gangdese batholith).

In this paper, we document the spatial and temporal relation-ships between the Great Counter (GCT) and inferred Gangdesethrust (GT) systems, the passive margin (TSS), forearc (XigazeGroup), syncollision deposits (Qiuwu Formation), and magmaticarc rocks (Gangdese batholith) that have been mapped along thecentral portion of the suture zone, in south-central Tibet. Our geo-chronologic and thermochronologic results document a series ofexhumation and deposition events in the region. Our results alsobracket timing of the GCT in this area at >19–15 Ma. The lower lim-it of this event is constrained by the initiation of the oblique-normal Lopukangri fault at �15–14 Ma (Sanchez et al., 2010).

2. Regional geology and previous work

2.1. The Gangdese arc

The Gangdese arc resulted from the northward subduction ofthe Indian plate beneath the southern margin of Asia (Allègreet al., 1984). The batholith and associated volcanic carapace are ex-posed along a belt subparallel to the Himalayan arc. Although be-tween 84.5�E and �87�E, plutonic rocks associated with themagmatic arc are scarce (Fig. 1), the volcanic cap consisting ofthe Linzizong Formation crops out as >5 km thick sequences (Cou-lon et al., 1986). The composition of the volcanic rocks has beendocumented to change from potassic calc-alkaline to metalumni-ous in the lower units to shoshonitic and peralumninous in themiddle and upper units (Ji et al., 2009; Mo et al., 2008; Dong,2002; Liu, 1993; Song, 1999; Wang et al., 1999). The compositionof the plutonic rocks of the Gangdese batholith generally rangesfrom subalkaline (monzonitic) to calc-alkaline with an averagecomposition of granodiorite (Debon et al., 1986).

The Gangdese batholith is composed of plutonic bodies that wereemplaced over a wide time range. The oldest plutonic rocks that havebeen obtained from the Gangdese batholith include �210 Ma rocks

from the Nyainqentanglha Shan in the east (Kapp et al., 2005) and�120 Ma rocks from the Xungba (Miller et al., 1999) and Kailas areasin south-west Tibet (Miller et al., 2000). The youngest plutonic rockshave been found in eastern Tibet. In Zedong, granites are �30 Ma(Harrison et al., 2000), and in the Nyainqentanglha Shan, some grani-toids span Oligocene–Miocene ages (Kapp et al., 2005). In the area ofWolong, adakites were emplaced �38 Ma (Guan et al., 2012). How-ever, in western Tibet in the Kailas area, Rb–Sr, Sm–Nd and 40Ar/39Ardata suggest magmatism was active until�40 Ma and volcanism per-sisted until �38 Ma (Miller et al., 2000). Recent studies in the XiaoGurla Range in western Tibet provide evidence of �44 Ma granitesintruding the suture zone suggesting late crustal anatexis was activein the late Eocene (Pullen et al., 2011) and perhaps episodic into theMiocene (e.g. Kapp et al., 2005).

40Ar–39Ar data from the Linzhou basin indicate the Linzizongvolcanic rocks erupted from �64 to 43 Ma (Lee et al., 2009; Zhouet al., 2004; He et al., 2007). Two periods of magmatism have beensuggested to have occurred along the Gangdese arc, an older periodfrom �120 to 80 Ma and a younger from 69 to 43 Ma (Wen et al.,2008) with the period from 80 to 69 Ma interpreted as a magmaticquiet period, or magmatic ‘‘gap.’’ The magmatic arc subsequentlyexperienced rapid denudation in response to crustal thickeningduring the late Oligocene-early Miocene, based on fast coolingrates during that time period (Copeland et al., 1987; Harrisonet al., 1992). Ji et al. (2009), argue for four stages of magmatism,�205–152 Ma, 109–80 Ma, 65–41 Ma and 33–13 Ma, based on acompilation of published data and new U–Pb zircon ages and Hfisotopic analyses. The most prominent stage, 65–41 Ma, is coevalwith Linzizong volcanism and is thought to be the result of Indianslab break-off (Ji et al., 2009). Recent 40Ar/39Ar data combined withpublished data suggest volcanism in the Lhasa terrane was wide-spread during the Cretaceous and more intense but restricted tothe south during the Paleogene (Lee et al., 2009).

2.2. The Gangdese thrust

The GT is a late Oligocene-early Miocene south-directed systemthat places Gangdese granitoids in its hanging wall against TethyanSedimentary Sequence in its footwall (Yin et al., 1994; Harrisonet al., 2000) (Fig. 1). The GT system has been mapped as a�200 m wide shear zone in the Zedong area, in southeast Tibet(Harrison et al., 1992; Yin et al., 1994). In southwest Tibet (Kailasarea) the GT does not crop out, but thermal modeling of a granitefrom the Kailas magmatic complex (Gangdese batholith equiva-lent) suggests these rocks experienced a rapid cooling event at30–25 Ma that may be explained by slip on the GT (Yin et al.,1999). Seismic reflection data from the Yanbajain–Damxung(Yadong-Gulu) graben in eastern Tibet show what is interpretedto be duplexes of the GT soling at �19–27 km depth underneaththe Gangdese batholith (Alsdorf et al., 1998). Several studies havequestioned the existence of the GT system (e.g. Aitchison et al.,2003), as it is not exposed along the entire suture zone, and hasnot been mapped in western Tibet. The observation along the su-ture zone of lower Miocene conglomerates resting on Gangdesegranitoids (or Kailas magmatic complex in the west) does not ruleout the existence of the GT (e.g. Aitchison et al., 2003), nor doesthis observation prove its existence where it does not crop out.However, the lack of outcrop can be explained if the south-dippingnorth-directed GCT has overridden the trace of the GT along mostof the suture zone (Yin et al., 1994, 1999; Harrison et al., 2000;Murphy and Yin, 2003).

2.3. The Great Counter thrust system

The GCT is an imbricate thrust system in southern Tibet thatgenerally juxtaposes the TSS in its hanging wall against Gangdese


granitoids in its footwall (Searle et al., 1987; Liu, 1988; Kidd et al.,1988; Ratschbacher et al., 1994; Yin et al., 1994, 1999) (Fig. 1). To-gether with the south-directed GT, the north-directed GCT (alsoknown as South Kailas thrust in southwest Tibet and the Renbu-Ze-dong thrust in southeast Tibet) delineates the surface trace of theIndia–Asia suture zone for over 1000 km in southern Tibet (Heimand Gansser, 1939; Yin et al., 1994; Quidelleur et al., 1997; Murphyet al., 1997, 2009; Harrison et al., 2000). The age of the GCT is con-strained to be �18–10 Ma from geochronologic studies (Yin et al.,1994, 1999; Quidelleur et al., 1997; Zhang et al., 2011).

2.4. The Xigaze Group

The Xigaze Group represents the basin fill that was deposited inthe forearc basin that resulted from northward subduction of theIndian plate during the middle Cretaceous (Allègre et al., 1984;Searle et al., 1987; Dürr, 1996; Yin and Harrison, 2000). This unitis primarily interpreted to be composed of turbidity current anddebris flow deposits intercalated with volcaniclastic rocks (Dürr,1993; Einsele et al., 1994). The Xigaze Group and TSS constitutethe hanging wall of the GCT system which places these units ontoPaleogene-Neogene conglomerates.

2.5. Syncollisional conglomerate formations along the India–Asiasuture: southern Tibet

Syncollisional conglomerate sequences have been describedalong the suture by various workers (e.g. Heim and Gansser,1939; Gansser, 1964; Einsele et al., 1994; Yin et al., 1994; Aitchisonet al., 2002, 2009; DeCelles et al., 2011) and are often referred to bydifferent names based on the type locality, including Kailas, Qiuwu,Dazhuqu, and Luobusa Formations. These have been grouped intothe ‘‘Gangrinboche Conglomerates’’ (Cheng and Xu, 1986; Aitchi-son et al., 2002, 2009; DeCelles et al., 2011) because these forma-tions are interpreted to have similar depositional histories (e.g.Aitchison et al., 2002; DeCelles et al., 2011), and to record the col-lision between India and Asia. At least two other formations, theLiuqu (Davis et al., 1999, 2002) and Yamdrok (Liu and Aitchison,2002) mélanges are also located along the suture but differ in prov-enance from the Gangrinboche Conglomerates (Aitchison et al.,2002) and are only locally preserved. In the west, �81–84�Elongitude, the Kailas Formation has been documented to be lateOligocene-early Miocene in age based on detrital and igneous zir-con U–Pb ages (DeCelles et al., 2011) (e.g., Fig. 1). The Qiuwu For-mation has been mapped from �89�E to �85�E (Zhang and Fu,1982). It is generally thought to be a late Eocene-early Mioceneconglomerate (Aitchison et al., 2002; Wang et al., 1999; Dürr,1996; Einsele et al., 1994). The Dazhuqu conglomerate was re-cently bracketed to be late Oligocene-early Miocene based on int-erbedded tuffs (Aitchison et al., 2009). The Luobusa Formation is anOligocene–Miocene conglomerate (Aitchison et al., 2002; Yin et al.,1994, 1999; Yu and Zhen, 1979). The ages are derived primarilyfrom fossils (e.g. Yu and Zhen, 1979). We limit our discussion tothe Kailas and Qiuwu Formations because previous research byMurphy et al. (2010) of the conglomerate exposed in the Lopukan-gri area had interpreted it to be Kailas. We review these two unitsbelow and make a reassessment in our Discussion section.

2.5.1. The Kailas FormationThe Kailas Formation consists of lacustrine, alluvial fan and flu-

vial units deposited in buttress unconformity against Gangdesemagmatic arc rocks (Heim and Gansser, 1939; Gansser, 1964;Cheng and Xu, 1986; DeCelles et al., 2011). Near Mount Kailas,the formation is �3 km thick with the lower units dominated byfluvial sandstone and conglomerate grading upward into lacustrineshale and sandstone, and capped by upper units consisting of red

beds (DeCelles et al., 2010, 2011). DeCelles et al. (2011) bracketthe age of the Kailas Formation between 26 and 24 Ma based onU–Pb ages of tuffs and detrital zircons. In the lower portion ofthe formation, a northern provenance of magmatic arc clasts pre-dominates. In the upper portion, a southern provenance of Tethyanclasts was noted by Aitchison et al. (2002) and DeCelles et al.(2011). The lower portion of the Kailas Formation is interpretedto have been deposited in a predominantly extensional or trans-tensional environment along the India–Asia suture (DeCelleset al., 2011). The Indus Group exposed in northwest Himalaya iscorrelative to the Kailas Formation. The Indus Group is interpretedto also have been deposited in an extensional tectonic setting, andbased on restorations the uppermost units are thought to haveexperienced �36 km of shortening, thus changing provenancefrom a northern to a southern source (Searle et al., 1990). Oxygenisotope data from the red bed member of the Kailas Formationindicate paleoelevation at the time the Kailas was being depositedwas comparable to modern day elevation, �4500 m (DeCelleset al., 2011).

2.5.2. The Qiuwu FormationThe base of the Qiuwu Formation has been interpreted to mark

the change from marine to fluvial deposits in the Xigaze area, whereit has been described as alluvial fan and fluvial sequences of coarsegravel interbedded with silty sandstones and shales (Einsele et al.,1994). The contact between the conglomerate-rich sequence andplutonic rocks from the Gangdese belt is a buttress unconformity,similar to the Kailas Formation-Gangdese granite contact inwestern Tibet (Einsele et al., 1994; Qian, 1985). Three members ofthis formation with a total thickness of �4 km have been describedin detail by Qian (1985), Wang et al. (2000), and Aitchison et al.(2002). The formation has distinct sources that vary up-section.The lower member is rich in volcanic mafic detritus whereas themiddle member is rich in volcanic, granitic, and chert clasts. Theupper member is rich in chert, volcanic, quartzite, and some ser-pentinite detritus (Wang et al., 2000). The provenance is also inter-preted to be predominantly a northern one, as in the KailasFormation, based on S–SE to SW paleoflow (Einsele et al., 1994).Various authors bracket the age of the Qiuwu Formation between�54 and 24 Ma (e.g., Qian, 1985; Einsele et al., 1994; Wang et al.,2000) based on the occurrence of palynofossils at the base of theformation (Li, 2004) and 40Ar/39Ar ages of 18.3 ± 0.5 Ma obtainedfrom felsic dikes cutting it (Yin et al., 1994). Aitchison et al., 2009,obtained similar ages of�20–17 Ma in the Dazhuqu area, but inter-preted the dikes to be interbedded tuffs (Aitchison et al., 2009).

3. Geology of the Lopukangri area

3.1. Plutonic bodies

The granite exposed in the study area is coarse-grained withgeochemical affinities with the calc-alkaline series. It crops outalong the crest of a west-trending range and subparallel in aspectwith the GCT immediately to the south of the body (Fig. 2). Thegranite is truncated in the east by the north-striking Lopukangrifault. In map view, the granite is �12 km wide in the northwestand narrows to the east, where it is �3 km wide, adjacent to theLopukangri fault (Fig. 2).

3.2. The Gangdese thrust

The GT is not exposed in the study area. Previous work in thearea and east of our study area depicts the north-dipping GT tobe exposed �4 km north of where we mapped the GCT system, be-tween the syncollisional late Eocene-early Miocene conglomerates

Fig. 2. (A) Geologic map of the India–Asia suture zone, Lopukangri area, south-central Tibet. Equal area, lower hemisphere stereograms show slip direction (Murphy et al.,2010). Sample locations are shown in yellow circles. U–Pb age is indicated by an asterisks followed by the 40Ar/39Ar age. Cross section A–A0 is shown in figure B. (B) Cross-section A–A0 through the GCT system. For location see figure A.


Fig. 2. (continued)


and Gangdese granite (Ding et al., 2005). According to a geologicmap by Ding et al., 2005, both the GCT and GT are exposed�25 km to the east of the Lopukangri fault system. We present apossible explanation to account for the discrepancy between theseinterpretations in the discussion section. The GT soles at �6 km be-low the surface, however, as this is a thick-skinned thrust, it hasbeen interpreted to sole at a �15 km depth in the Renbu andZedong areas based on the structural level of exposure of the Gang-dese granites, thermobarometry, and thermal modeling (Copelandet al., 1987, 1995; Yin et al., 1994; Harrison et al., 2000).

3.3. The Great Counter thrust system

The GCT strikes WNW across the mapped area. It lies along thesouthern flanks of a WNW-trending mountain range which ends toits east at a N–S trending range that contains the highest peak inthe area (Lopukangri – 7095 m). The GCT crops out as a systemof three south-dipping thrusts exposed in the hanging wall of thenorth-striking oblique-normal Lopukangri fault (Fig. 2). The hang-ing wall of the GCT is comprised of folded meta-sedimentary rocksof the TSS, consisting mostly of green and gray phyllite. The TSS isjuxtaposed structurally above Cretaceous fossiliferous siltstone,sandstone and limestone (Klm) along a south-dipping thrust fault.Kinematic indicators measured on fault slip surfaces indicatetop-north motion directed N to 20–50� to the NE. Another south-dipping thrust fault places Klm over Cretaceous fine-grained sand-stone, siltstone and mudstone (Ksh). Both of these Cretaceous unitshave been correlated to the Xigaze forearc sequence (XigazeGroup) of Liu (1988) based on stratigraphy and structural relation-ships (Murphy et al., 2010). Fault striae along the central fault seg-ment show top to the NNW (�15� NW) and NNE (�20–25�NE) slip.

The northernmost thrust places Cretaceous sandstone and shaleover conglomerate sequences interpreted to be early Eocene-Miocene in age. This thrust is exposed as a system of 2–3 intrafor-mational thrust faults in the conglomerates. In the central portionof the mapped area, the shorter intraformational thrust faults areexposed � 5–6 km along strike and merge to the east and west,forming small imbricate or duplex systems, �0.5–1 km in north–south width. Overall, the thrust system strikes NW, parallels theGangdese batholith, and branch-lines converge to a branch-pointtowards the east resulting in thinner thrust sheets.

Based on map relationships we interpret the GCT as an imbri-cate system placing TSS and Xigaze Group rocks in its hanging wallagainst Gangdese granite in its footwall as has been observed tothe east and west of our study area by other researchers (Liu,1988; Murphy and Yin, 2003). Because the hanging wall consistspredominantly of folded and thrust Paleozoic and Mesozoic phyl-lites and marbles, we interpret the GCT to sole at the base of thissequence based on our map patterns and similar relationshipsand map patterns along strike. We speculate that the systemmay sole at �4 km below the surface based on cross sections(Fig. 2B). The intraformational thrusts in the early Eocene-Mioceneconglomerates are interpreted to merge/branch �2 km below thesurface with the northernmost thrust of the GCT system.

3.4. The Lopukangri fault system

To the east, the approximately N-striking W-dipping MiddleMiocene Lopukangri fault system (Sanchez et al., 2010) (Fig. 2) off-sets the trace of the GCT �15 km to the south (Murphy et al., 2010).The Lopukangri fault system bounds a �100-km-long �NW-trend-ing rift and consists of a 3–4-km-wide shear zone that narrows tothe south, where the system terminates (Murphy et al., 2010; San-chez et al., 2010). The fault system juxtaposes greenschist faciesrocks of the TSS in its hanging wall with an assemblage of amphib-olite facies rocks including garnet-muscovite-biotite schists, inter-bedded marble and quartzite in its footwall (Murphy et al., 2010;Sanchez et al., 2010). Based on U–Pb age distribution peaks (San-chez et al., unpublished data) and comparison to documenteddetrital zircon U–Pb ages for the Himalaya and Tibet (Pullenet al., 2011; Gehrels et al., 2006a,b; Martin et al., 2005; DeCelleset al., 2000, 1998) the footwall rocks of the Lopukangri systemare interpreted to have a Tethyan protolith. Evidence of activefaulting is present in the northern half of the rift and may poten-tially be present in the south, however, moraine deposits adjacentto the mountain front obscure any evidence of offsets (Sanchezet al., 2010; Murphy et al., 2010).

3.5. The Xigaze Group

In the study area, the Xigaze Group crops out as a lower �1 kmthick sequence of limestone and siltstone and an upper �1.5 km


thick sequence of interbedded fine grained sandstone, siltstone,and mudstone (Murphy et al., 2010; Liu, 1988). Liu (1988) showsthe Xigaze Group offset left-laterally across a steeply dipping in-ferred fault; however, the map also shows a massive (�20 kmwide) Cretaceous–Paleogene intrusion that may have producedthis map pattern of an apparent offset, rather than offset resultingfrom slip along the Lopukangri fault.

3.6. Oligocene–Miocene conglomerate correlation

In the study area, we identify three conglomerate units (PG–NQ1,PG–NQ2, and PG–NQ3) that differ in clast composition, and interbed-ded sandstone content (Fig. 3) (see also Murphy et al., 2010). Thelowest units, PG–NQ1 and PG–NQ2, consist of cobble gravel pebbleconglomerate beds rich in volcanic/plutonic and metamorphicclasts and interbeds of coarse-grained sandstone. From field clastcounts, in PG–NQ1 over 30% of the clasts are igneous, predomi-nantly green andesite and granite. Metamorphic clasts (�50%) in-clude white quartzite, vein quartz, epidote-rich amphibolite andhornfels. Sedimentary clasts (�20%) include buff sandstone andgray mudstone. PG–NQ2 contains�45% volcanic and plutonic clasts,including gray andesite and granite. Metamorphic clasts (�45%)

Fig. 3. (A) Clast composition plots for the Qiuwu Formation. (B) Clast composition by pesample (6.17.2) with major pebble clast composition noted. Abbreviations: mbl – marble;volcanic clast of pumice or rhyolite affinity; ch – chert; chl alt – chlorite alteration; v qzquartz; and (D) clast composition plot showing individual clast types and by percentageincluded in the percentage calculation.

consist mostly of gray quartzite, hornfels, vein quartz, and minorepidote-rich amphibolite; sedimentary clasts of buff sandstoneand siltstone make up �10%. PG–NQ3 contains only sedimentaryclasts consisting of siltstone, gray sandstone, red mudstone, graylimestone, white limestone, green chert, and minor gray mudstone.

We conducted a pebble (�4–30 mm) clast count on a sample(sample 6.17.2) from PG–NQ1 to assess the clast composition. Thesample is a well-indurated, clast-supported, pebble conglomeratewith sub-angular to sub-rounded clasts. We sectioned the sampleinto two orthogonal cuts, and counted a total of 94 clasts using a10� magnifying hand lens (Fig. 3). By using the smaller clasts,we increased the sedimentary and metamorphic content and de-creased the igneous content that was initially described in our fieldobservations of large pebble (>30 mm) to cobble size clasts in a�1 m2 area. Additionally, we were able to distinguish some ofthe metamorphic clasts and varieties of chert. The sample consistsof over 64% metamorphic clasts, which consist of vein quartz, epi-dote + chlorite-rich schist, green + white quartzite, marble, micaschist, and hornfels. Quartz sandstone and chert (yellow, white,red, green) make up �25% of the sedimentary clasts. Green andes-tite and other volcanic clasts (pumice or tuff?) comprise over �10%of the igneous clasts. Based on the size range of the clasts described

rcentage of metamorphic, igneous and sedimentary types. (C) Photograph of Qiuwuqtz – quartzite; ep + chl – epidote + chlorite rich amphibolite; hfels – hornfels; volc –

– vein quartz; and – andesite; qz ss – quartz rich sandstone; rxtal – recrystallized(below) of metamorphic, igneous and sedimentary clasts; opaque minerals are not


in the field and in hand-sample, we interpret a proximal basementsource for the igneous and metamorphic clasts. This is consistentwith the observation that the clasts are sub-angular to sub-rounded.

Based on the hand sample and field observations, we interpretthat the lower two members of the conglomerate had a northernprovenance (Lhasa block and magmatic arc), whereas the uppermember had a southern provenance. Our observations are consis-tent with data obtained by Qian (1985) and Einsele et al. (1994)from �40 km west of Xigaze, where a dominant south-directedpaleoflow has been documented.

Detrital zircon U–Pb ages of �38 Ma, �42 Ma, and �55 Ma fromthe youngest grains from three conglomerate samples from thelower sequences of this unit have been reported by Aitchisonet al. (2011). They also report an age of �37 Ma from a volcaniclas-tic unit in the Tso Jiangding area, northwest of our study area(Aitchison et al., 2011). These ages suggest a northerly source forthese conglomerates from the magmatic arc, and imply subductionrelated magmatism was active up to the late Eocene (Aitchisonet al., 2011).

Provenance of the lower members of the Qiuwu Formationcould have been as far north as the Bangong–Nujiang suture zone(Qiangtang anticlinorium?) where high topography and possibly(extensive?) south-flowing drainages dominated the landscapeand ophiolitic mélange material was available. The metamorphicclasts could have sourced from local basement exposure and chertclasts from exposed deep ocean deposits. However, based on thesub-angularity to sub-roundness texture of the clasts, the sourcefor the lower members appears to be local (Gangdese arc).

The conglomerates lie in buttress unconformity on calc-alkalinegranite (Figs. 1 and 2). Rocks from this unit show evidence of lowergreenschist facies metamorphism, including a greenish appearanceof the rocks, thin veins rich in epidote and chlorite, and rims ofchlorite surrounding the clasts (Fig. 3). Minor recrystallized quartzsurrounds some of the clasts, as evidenced by small serrated quartzgrains forming rims around some of the larger clasts. Quartz and cal-cite-filled veins (<1 m wide) cut the conglomerate units, suggestingactive fluid migration and fracturing during metamorphism.

The Qiuwu and Kailas Formations are time equivalent, althoughthe Kailas Formation crops out predominantly in western Tibet. Re-gional descriptions of the Qiuwu deposits have no lacustrine mem-bers (e.g. Einsele et al., 1994; Aitchison et al., 2002), whereas theKailas Formation does (DeCelles et al., 2011). Both also share sim-ilar structural relationships to the Gangdese granite with the con-glomerate in buttress unconformity on granite. Although the totalthickness of the conglomerates in our study area is not constrained,a maximum thickness of �1.5 km was obtained from mappedrelationships.

Previously, Murphy et al. (2010) correlated the early Eocene-Miocene conglomerates exposed in this area to the Kailas Forma-tion based on reconnaissance work. However, based on the ab-sence of lacustrine deposits in the study area, petrology, andclast composition we instead correlate the conglomerate unit tothe Qiuwu Formation, which crops out extensively near the Xigazearea (Wu et al., 1977; Einsele et al., 1994; Wang et al., 2000;Aitchison et al., 2002; Li, 2004).

4. Geochronology – analytical methods

We conducted U–Pb zircon geochronology and 40Ar/39Ar biotitethermochronology on a granite sample (sample 6.17.1, refer toFig. 2 for location) collected from the Gangdese magmatic beltnorth of the India–Asia suture zone. The granite is porphyritic,calc-alkaline (e.g. Harris et al., 1988) and biotite rich, located�1.5 km north of the unconformity, in the footwall of the mainGCT.

4.1. U–Pb zircon geochronology

We separated zircons from the granite by standard mineral sep-aration techniques.

We conducted the analyses using laser-ablation inductively cou-pled plasma-mass spectrometry (LA-ICP-MS) on 176 zircons using a25 lm beam at the University of Houston. Measurements weremade on a Varian 810 quadrupole inductively coupled plasma-massspectrometer in laser mode using a CETAC LSX-213 213 nm wave-length laser ablation system (dataset 1) and a Photon Machines Ana-lyte 193 excimer (dataset 2) in high sensitivity mode (Shaulis et al.,2010). Data was reduced using the data reduction software Wave-metrics Igor Pro™ (v. 6.12A) with the add-in Iolite (v. 2.11)(Hellstrom, 2008). Concordia diagrams and data analysis wereconducted using IsoPlot v.4.1 (Ludwig, 2008). We report weightedmean 206Pb/238U ages with analytical uncertainties at 2r confidencelevel for 145 analyses. Uncertainties in the reported ages includerandom and systematic errors and we follow methods outlined inShaulis et al., 2010. More details on our sample preparation, datareduction methods, and instrumentation are found in Appendix A.

4.2. 40Ar/39Ar biotite thermochronology

We obtained 6 mg of biotite through standard mineral separa-tion techniques. The sample was irradiated for 7 h along with thestandard Fish Canyon Tuff sanidine (FC-2) with an estimated ageof 28.02 Ma (Renne et al., 1998) at the United States GeologicalSurvey (USGS) TRIGA Reactor in Denver, CO. The sample was thenstep-heated with a double vacuum MO resistance furnace for4 min at the New Mexico Geochronology Research Laboratory atNew Mexico Tech. For details on instrumentation and analyticalparameters, see Appendix A.

5. Geochronology results

5.1. U–Pb zircon ages

The 206Pb/238U ages obtained fall in the range of �30–�45 Mawith a weighted average of 38.4 ± 0.4 at 2r confidence level(Fig. 4). In general, most zircons have high U concentrations rang-ing from just below 600 ppm in the older zircons to up to�66,000 ppm in the younger zircons (�30 Ma) (Supplementarymaterial). We interpret the 38.4 ± 0.4 Ma age to represent the ageof crystallization of the magmatic body (Fig. 4).

The age supports the interpretation that the granite is part ofthe Gangdese magmatic arc which initiated in the late Cretaceousand lasted into the Eocene. The age obtained is slightly older thanthose reported from the Zedong area (30.4 ± 0.4 Ma – Harrisonet al., 2000) and represents one of the youngest ages obtained forGangdese batholith rocks within a suite of Eocene granites (e.g.Pullen et al., 2011; He et al., 2007; Miller et al., 2000).

5.2. Biotite age

The biotite age spectrum is saddle-shaped and yields an inte-grated age of 19.7 ± 0.1 Ma (Fig. 5). The first 10% of gas releasedyields an apparent age of �23 Ma that decreases to �18 Ma at�50–60% of the gas released before rising to �22 Ma. Isochronanalysis (Appendix A) does not record a homogenous excess argontrapped component and thus the cause or the spectrum complexityis not certain. The biotite is slightly altered and 39Ar recoil artifactsmay best explain the spectrum complexity. Alternatively, the spec-trum could be the result of incomplete degassing during lowergreenschist facies metamorphism (Lanphere and Dalrymple,1976). We suggest that the integrated age of �19 Ma approximates

Fig. 4. (A) Concordia diagram for sample 6.17.1 (n = 145). (B) Weighted average.


the cooling of the sample through �320 �C after a thermal disrup-tion based on the following observations: (1) the Qiuwu Formationexperienced greenschist facies metamorphism and is located abovethe unconformity and (2) the age is consistent with similar EarlyMiocene ages documenting regional exhumation along the Gandg-ese belt (e.g. Copeland et al., 1987, 1995).

Fig. 5. 40Ar/39Ar apparent age spectra for biotite from sample 6.17.1.

6. Discussion

6.1. Assessing ages

We interpret the U–Pb zircon age of 38.4 ± 0.4 Ma to representthe timing of emplacement of the granite and the younger40Ar/39Ar biotite age of 19.7 ± 0.1 Ma to represent the timing of fi-nal cooling of the granite below the biotite closure temperature(�320 �C, Grove and Harrison, 1996; or �12–10 km depth, assum-ing a geothermal gradient of 30 �C/km), or a thermal resetting ofthe biotite at 19.7 ± 0.1 Ma. Because the sample lies directly belowan unconformity with greenschist facies conglomerates, we inter-pret this age as recording the second time the sample has beencooled below the biotite closure temperature. This is similar tothe interpretation called upon by Yin et al. (1999) to explain mod-eled K-feldspar 40Ar/39Ar data from clasts in the Kailas Formationin the Mt. Kailas area.

6.2. Structural evolution of the India–Asia suture zone in theLopukangri area

Below we present two models for the tectonic evolution of theIndia–Asia suture zone, which satisfy our 40Ar/39Ar and U–Pb agesand field mapping (Fig. 6).

Model 1 describes the deposition of the Qiuwu Formation in anintermontaine basin that developed during south-directed motionon the GT in the Late Oligocene. Provenance changed at �24 Ma,when the GCT became active at which time the lower sections ofthe Qiuwu conglomerate were buried and slightly metamorphosedby the hanging wall of the GCT. In this model, the granite is ex-humed by slip on a blind thrust associated with the GCT systemat 19.7 ± 0.1 Ma. Alternatively, Model 2 describes the Qiuwu For-mation as deposited in an extensional basin along the suture. Inthis model, the GT plays no role in the deposition of the Qiuwu For-mation. The granite in this model cooled at 19.7 ± 0.1 Ma by ero-sional denudation.

We describe the following stages for Model 1 followed by thosefor Model 2 for the evolution of the suture zone according to Fig. 6,stages A–G for Model 1 and stages A–F for Model 2.

6.2.1. Model 1 – intermontane basin6.2.1.1. Late Eocene. Emplacement of the granite in the Lopukangriarea took place 38.4 ± 0.4 Ma based on our U–Pb zircon age. Thisage is comparable to other Middle to Late Eocene ages found alongthe suture zone, suggesting that magmatism associated with thelate stages of closure of the Neotethys was still active along the su-ture until the Late Eocene (Schärer et al., 1984; Copeland et al.,1987 ; Aitchison et al., 2011; van Hinsbergen et al., 2012).

6.2.1.2. Oligocene. After emplacement, the granite was exposed atthe surface via erosional exhumation. Subsequently, the first se-quences of terrestrial conglomerates we correlate to the QiuwuFormation (Pg–NQ1–Q2) were sourced from the north and depositedon the exposed irregular surface creating a buttress unconformity.This is an overall tectonically quiet period and regional subsidencecreated depocenters that probably extended along the suture for100s of kilometers.

6.2.1.3. Late Oligocene. At �27 Ma, the GT initiated (Yin et al., 1994;Harrison et al., 2000) creating a shallow intermontane basin onlap-ping the hanging wall thrust sheet. Alternatively, the basin can bemodeled as a piggy-back-like basin deposit by keeping the samethrust geometry but with the deposits on top of the thrust sheet.Detritus continued to be derived from the exposed magmatic arcand from the Lhasa block based on the clast composition, which

Fig. 6. Tectonic evolution model of the India–Asia suture zone in the Lopukangri area. Initial stages A and B apply to both models. Light gray areas or lines are inactive duringthe stage shown. Sample location is indicated by a small triangle. The 320 �C isotherm is shown for reference. Thick vertical arrows indicate cycles of shortening (arrowheadpointing down) and extension (arrowhead pointing up).


Fig. 6. (continued)


is dominated by altered volcanic/plutonic and metamorphic clastsand chert. The basin continued to be fed from the north as the GTthrust sheet advanced to the south. This period, �27–24 Ma, isassociated with regional north–south shortening.

6.2.1.4. Early Miocene. From �24 to 20 Ma slip on the south-directed GT ceases and initiation of the north-directed GCT systemoccurs, which resulted in a change of provenance detritus consist-ing mostly of meta-sedimentary and sedimentary rocks thatformed the PG–NQ3 unit coming from the hanging wall of theGCT in the south. PG–NQ3 is rich in sedimentary detritus thatinclude siltstone, mudstone and coarse-grained sandstone clasts,suggesting no nearby elevated igneous source was exposed at thetime and what was being eroded were probably exposed localbasins to the south. Sources for PG–NQ3 involved exposed Paleozoicand Mesozoic rocks from the south or the northern Lhasa block.

During this stage, the granite that was exhumed in the hangingwall of the GT during the late Oligocene was reburied along withPG–NQ1, PG–NQ2, PG–NQ3 and the Xigaze Group units (Klm andKsh) to a depth of�12–10 km by the GCT system resulting in green-schist facies metamorphism and Ar loss in the biotite from the gran-ite. The trace of the GT was also buried by the GCT at this time.

The southern oldest thrust placed Tethyan meta-sedimentaryrocks in the hanging wall against Cretaceous deposits of the XigazeGroup. The GCT then cut into the Xigaze Group, carrying both of theunits northward onto the early Eocene-Miocene conglomerates.

6.2.1.5. Middle Miocene (P19–15 Ma). At or slightly before 19 Ma,uplift in the area associated with a north-directed blind thrust ofthe GCT system exhumed the granite and the Qiuwu deposits that

were buried earlier. We attribute the 19.7 ± 0.1 Ma 40Ar/39Ar age tocooling of the upper plate due to uplift and erosional exhumationabove a blind imbricate thrust of the GCT system, as no thrust isobserved north of the unconformity.

In outcrop, the Qiuwu Formation rests in buttress unconformityon Gangdese arc rocks (�38 Ma granite) with no structure exposednorth of the intraformational thrust in the Qiuwu conglomerates.In order to explain the biotite cooling age of 19.7 ± 0.1 Ma, wesuggest that a blind thrust of the GCT is responsible for upliftand erosional exhumation of the �38 million year old graniteand the conglomerate from a depth of �12–10 km to the pres-ent-day surface. This is based on mapped relationships of the sys-tem of thrusts south of the sampling location, the nature of the GCTsystem to the east and west of our study area, and from cross-sections that show it to cut the GT at depth. An overall north–southshortening regime characterizes this period.

Contractional deformation then ceases at �15 Ma when the ob-lique N-striking Lopukangri extensional fault system cuts the su-ture zone rocks and the GCT.

6.2.2. Model 2 – extensional basinThe initial stages for Model 2 are the same as in Model 1, with

emplacement of the granite at �38 Ma and surface exposure viaerosional exhumation during the Oligocene.

6.2.2.1. Late Oligocene. The Qiuwu conglomerate units PG–NQ1 andPG–NQ2 were deposited in an extensional basin bounded to thesouth by a north-dipping fault. The conglomerates were depositedon the hanging wall during extension related subsidence in but-tress unconformity with the previously exposed granites. The

Fig. 7. The geometry of the Great Counter thrust system along the India–Asia suture zone from West (Lopukangri area) to East (Zedong). (A) Cross-sections A–E along thesuture zone, lines of section are shown in Figure B. GT – Gangdese thrust; GCT – Great Counter thrust. (B) Regional digital elevation model showing the location of the GT andGCT along the India Asia suture. Thick black lines show the location of cross-sections from various studies (figure A). Digital elevation model was derived from Shuttle RadarTopography Mission (SRTM) 90 m resolution data.


detritus for the PG–NQ1 and PG–NQ2 units were derived from the ex-posed magmatic arc and Lhasa block. Regionally, this is a period ofextension, as interpreted further to the west in the Kailas area(DeCelles et al., 2011) and Ayi Shan (Zhang et al., 2011). Duringthe waning stages of extension, the provenance likely started to in-volve less granitic material from the north, as attested by the clastcomposition of the youngest PG–NQ units.

6.2.2.2. Early Miocene (�20 Ma). The GCT system initiated duringthis time, making a transition from extension to shortening alongthe suture zone. South-derived detritus accumulated in the basin

that was created in the Late Oligocene. The detritus consists oflow-grade meta-sedimentary and sedimentary clasts of the TSSand forearc deposits, changing the clast composition in the QiuwuFormation from predominantly igneous/metamorphic in the lowerunits to sedimentary in the uppermost units.

The GCT hanging wall subsequently buried/reheated the graniteand the Pg–NQ conglomerate sequence to >320 �C, resulting in low-er greenschist facies metamorphism and resetting of the biotite inthe granite. This is a similar interpretation to Yin et al. (1999) whomodeled K-feldspar age spectra to interpret 19 Ma burial/reheatingof a granite cobble from the Kailas area via the GCT.


6.2.2.3. Middle Miocene (619–15 Ma). At �19 Ma, the granite andconglomerate were exhumed via regional erosional denudation.Thickening resulting from previous folding/thrusting by the GCTcould have produced significant relief and thus enhanced denuda-tion during this period. As in Model 1, at�15 Ma, the suture zone isthen cut by an oblique-normal system and any slip on the GCTwould have been terminated by this time. Because this model doesnot require the GCT to exhume the granite, thrusts exposed to thesouth could have been active up until �15 Ma.

6.3. Lifespan of the GCT in the Lopukangri area, south-central Tibet

Previous studies have interpreted the GCT to have been activefrom 19 to 10 Ma (Ratschbacher et al., 1994; Quidelleur et al.,1997; Yin et al., 1999; Yin and Harrison, 2000). In the Ayi Shanarea, west of Mt. Kailas, Zhang et al. (2011) constrained the GCTto have been active between �18 and 10 Ma in Western Tibet.The GCT in Central Tibet was active at �18 Ma based on 40Ar/39Arages of felsic tuffs found interbedded in syncollisional conglomer-ates that are cut by the thrust system in the Dazhuqu area(Aitchison et al., 2009). In Eastern Tibet, the period of activity iseven broader, at �25–10 Ma (Harrison et al., 2000). Our biotiteage data suggest that the GCT was active before 18–19 Ma, provid-ing a lower bound to the initiation age of the GCT. The GCT becameinactive by �15–14 Ma at this location, based on cooling ages inthe footwall of the Lopukangri fault, which cuts the trace of theGCT (Sanchez et al., 2010).

6.4. Inferences for shortening and extension periodicity

The timing of extension–shortening periods interpreted fromour models correlates to the cycles of shortening and extensiondiscussed by Zhang et al. (2011) including Late Eocene to Early Oli-gocene shortening, Early to Late Oligocene extension, Late Oligo-cene to Late Miocene shortening and Middle Miocene to Presentextension for western Tibet. A cycle does not terminate at a specifictime, rather, waning stages of cycles may overlap in time. The pat-tern of extension–shortening implies a cyclicity in the state ofstress during orogenesis that may have implications for processesat depth, such as periods of mantle delamination leading to exten-sion in the upper plate as the orogenic front migrates southwardand the Indian plate impinges onto the Eurasian plate (e.g. Kappet al., 2007; DeCelles et al., 2009, 2010, 2011).

6.5. Suture zone structure: Shallow versus deep level of exposure

Ding et al. (2005) conducted reconnaissance field work in thearea and interpreted the GT to be exposed north of where wemapped the trace of the GCT system. However, our observationsfailed to document any exposure of the GT in the Lopukangri re-gion. Within the southernmost strands of the GCT there are<2 km wide slivers of ophiolitic material. North of the surface traceof the GCT, we encountered granitic rocks that extended for at least10 km to the north, whereas Ding et al. (2005) show a wider ophi-olite body (�5 km wide in the west) and a conglomerate unitattributed to the 65–62 Ma Quxia Formation. However, the GTmay be present �15 km to the east of the Lopukangri normal-oblique fault, where Ding et al. (2005) have mapped. We speculatethat field relationships and age data imply a shallower structurallevel is exposed such that the GT lies at depth beneath the GCT.

6.6. Along-strike changes in exposure of the GT, GCT, and syncollisionalconglomerates

There are many possibilities for the regional outcrop patternswe see today along the suture. Various maps show the GT cropping

out east of the Lopukangri area along with the Renbu-Zedongthrust, which is the continuation of the GCT in the east (Wanget al., 1983, and observations from Yin et al., 1994). The GT doesnot crop out continuously along the suture, it is found mostly inthe Xigaze and Zedong areas, as shown in Figs. 1 and 7. The ab-sence of the Xigaze Group in the east may be due to differencesin the style and magnitude of slip of the GT (Yin et al., 1994), withincreasing magnitude of slip to the east explaining their absence,the exposure of the fault, and thin syncollisional deposits. The Luo-busa Group conglomerates in this area have narrow outcropwidths ranging from <.5 to �1 km thick (also known as Luobusha,Yin et al., 1999; Harrison et al., 2000). The Xigaze Group is missingwest of Kailas and �40 km east of Xigaze (Yin et al., 1994; Dürr,1996), and in the area of Lopukangri, the outcrop width of syncol-lision conglomerates is far less than the �20 km outcrop widthfound in the Xigaze area, suggesting a thinner section is exposedin the Lopukangri area. The change in width of the Xigaze Group,the exposure of the GCT and westward thinning syncollisionaldeposits in south-central Tibet (�85–89�E) may be explained bywestward increasing magnitude of slip on the GCT (Fig. 7). Thickdeposits of syncollisional conglomerates including the �2.5 km-thick Kailas Formation (Aitchison et al., 2002, 2009; DeCelleset al., 2011) and the �2 km-thick Indus Formation (Searle et al.,1990; Sinclair and Jaffey, 2001) are found further west. Their pres-ence may also be explained by along-strike variations in the mag-nitude of slip of the GCT, so that further west of �83�E, themagnitude of slip then decreases. Another possibility is that theexposure of the GCT, GT and syncollisional deposits may be dueto patterns of differential erosion along the arc, or patterns of dif-ferential unroofing along strike (e.g. Yin et al., 1994; Harrison et al.,2000). The role of these short-lived thrust systems from �27 Mauntil �15 Ma may be far more significant than what the erosionalpatterns presently allow us to see along the suture, as noted in thecurrent variations in along-strike exposure (Fig. 7).

7. Conclusions

The field relationships and analytical data from the Lopukangriregion document the tectonic history of the India–Asia suture zonesince the late Eocene.

(1) A system of north-directed imbricate thrusts that we corre-late to the GCT system crop out in the area of Lopukangri insouth-central Tibet. This fault system is cut by the Lopukan-gri normal fault at �15–14 Ma (Sanchez et al., 2010) result-ing in �15 km (see also Murphy et al., 2010) of right lateralseparation.

(2) The GT does not crop out at this location. We suggest thatthe exposed geology reflects a shallower structural levelalong the suture zone, so that the GT is overthrust by thenorth-directed GCT. The GT is reported to be exposed eastof Lopukangri (Ding et al., 2005). Furthermore, we suggestthrusting along the GT may be responsible for the secondpulse of exhumation of the 38.4 ± 0.4 million-year-old gra-nitic pluton that provided detritus for the late Eocene-earlyMiocene Qiuwu conglomerates in the area. Provenance forthe Qiuwu conglomerates changes in the Late Oligocene-Early Miocene, when the north-directed GCT becomes activeand supplies Tethyan sediments.

(3) By �19 Ma, erosional denudation in the hanging wall of ablind thrust associated with the GCT system exhumed thegranite and Qiuwu Formation from a �12 to 10 km depth.

(4) Our preferred evolution model (Model 1) highlights periodsof crustal shortening. During the first period of shorteningafter granite emplacement, the older GT was active and


was responsible for the first phase of exhumation. Thisthick-skinned thrust system is then cut by the youngerGCT system during a more recent phase of shortening. TheGCT buried the granite and Qiuwu Formation to a �12–10 km depth and a blind thrust associated with the GCT sub-sequently exhumed the granite and conglomerates at�19 Ma. The GCT is short-lived in this area because thereis field evidence that an oblique-normal fault system cutsthe GCT by �15 Ma (Sanchez et al., 2010).

(5) Our age data are consistent with a suite of young ages thathave been reported for the Gangdese belt and that have beenused to suggest prolonged arc magmatism after continent–continent collision. Our age implies that magmatism contin-ued for �17 million years after the onset of collision �55 Main south-central Tibet.

Acknowledgements

This study was supported by a grant from the U.S. National Sci-ence Foundation (Grant EAR 0711527 to Murphy). We thank BarryShaulis for training and assistance with sample preparation andICP analyses. We also thank Dr. Yongjun Gao for technical assis-tance in the ICP lab. The authors thank Alex Pullen and JonathanAitchison for providing detailed reviews and useful suggestions.

Appendix A

A.1. Mineral separation details

We crushed the granite (sample 6.17.1) in a jaw crusher, fol-lowed by a disc mill, to obtain material to sieve for mineral picking.We sieved the crushed material into three size fractions:>.420 mm, .420 > x > .250 mm, and <.250 mm. The .420 > x> .250 mm and the <.250 mm fractions were processed by heavy li-quid (Bromoform, q = 2.84 g/mL followed by Methylene Iodide,q = 3.32 g/mL) and magnetic separation techniques (Frantz mag-netic separator) until a fraction of non-magnetic minerals with adensity of P3.32 g/mL remained. We then immersed a portion ofthe P3.32 g/mL in ethyl alcohol to hand-pick grains for mounting.We picked inclusion- and fracture-free grains under a binocularmicroscope using non-magnetic tweezers. The zircon grains wereprismatic, clear, and ranged from �30 to �50 lm wide and �75to �100 lm long parallel to the C-axis. Over 130 grains weremounted in epoxy along with standards FC5z (age = 1099.1 ± 0.1 -Ma; Paces and Miller, 1993), Peixe (age = 564 ± 4 Ma; Chang et al.,2006), Stettin (age = 1565 ± 8 Ma; van Wyck et al., 1994) and NIST612 glass using a 1-in. diameter cylinder. The epoxy cylindermount was dried overnight and the top surface was polished using2500 and 3000 grade SiC sheets to obtain a clean smooth surface toperform laser ablation analyses.

We conducted the analyses using laser-ablation inductivelycoupled plasma-mass spectrometry (LA-ICP-MS) on 176 zirconsusing a 25 lm beam at the University of Houston. Measurementswere made on a Varian 810 quadrupole inductively coupled plas-ma-mass spectrometer in laser mode using a CETAC LSX-213213 nm wavelength laser ablation system (dataset 1) and a PhotonMachines Analyte 193 excimer (dataset 2) in high sensitivity mode(Shaulis et al., 2010). Each analysis involved �20 s of backgroundmeasurement followed by 20 s of ablation and sample analysisand 20 s of washout to allow the signals to return to backgroundlevels. Data was reduced using the data reduction software Wave-metrics Igor Pro™ (v. 6.12A) with the add-in Iolite (v. 2.11)(Hellstrom, 2008). Concordia diagrams and data analysis were con-ducted using IsoPlot v.4.1 (Ludwig, 2008). We report weighted

mean 206Pb/238U ages with analytical uncertainties at 2r confi-dence level for 145 analyses. We report 13 statistical rejections(outliers). Uncertainties in the reported ages include random andsystematic errors (Shaulis et al., 2010).

For details on instrumentation, calibration, data acquisition,data reduction of the U–Pb zircon analyses, see Shaulis et al., 2010.

A.2. 40Ar/39Ar analytical parameters and instrumentation

Biotite was hand-picked with tweezers from the coarsest frac-tion (>.420 mm) or directly from the uncrushed rock. Approxi-mately 6 mg were placed in a glass vial and sent to New MexicoTech for thermochronological analysis.

The following information on analytical parameters and instru-mentation was provided by the thermochronology lab at NewMexico Tech. The biotite sample was loaded into Al discs and irra-diated along with the standard Fish Canyon Tuff sanidine (FC-2,age = 28.02 Ma) for 7 h at the USGS TRIGA Reactor in Denver, CO.The sample was then step-heated for 4 min with a double vacuumMO resistance furnace. Reactive gases were removed during heat-ing with a SAES GP-50 getter that operated at�450 �C and addition-ally for 2–3 min with 2 SAES getters, 1 operated at�450 �C and 1 at20 �C. The electron multiplier sensitivity was �8.0 � 10�17moles/pA. The total system blank and background was 100, 0.2, 0.2, 1.5,0.7 � 10�17 moles for masses 40, 39, 38, 37, and 36. J-factors weredetermined to a precision of�±0.1% by CO2 laser-fusion. Correctionfactors for interfering nuclear reactions were determinedusing K-glass and CaF2 ((40Ar/39Ar)K = 0.010 ± 0.002; (36Ar/37Ar)Ca = 0.00028 ± 0.00002; and (39Ar/37Ar)Ca = 0.00070 ± 0.00005).

Appendix B. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.jseaes.2012.09.004.

References

Aitchison, J.C., Badengzhu, Davis, A.M., Liu, J., Luo, H., Malpas, J.G., McDermid, I.R.C.,Wu, H., Ziabrev, S.V., Zhou, M., 2000. Remnants of a Cretaceous intra-oceanicsubduction system within the Yarlung-Zangbo suture (southern Tibet). Earthand Planetary Science Letters 183, 231–244.

Aitchison, J.C., Davis, A.M., Badengzhu, Luo, H., 2002. New constraints on the India–Asia collision: the Lower Miocene Gangrinboche conglomerates, YarlungTsangpo suture zone, SE Tibet. Journal of Asian Earth Sciences 21, 253–265.

Aitchison, J.C., Davis, A.M., Badengzhu, H., Luo, H., 2003. The Gangdese thrust: aphantom structure that did not raise Tibet. Terra Nova 15, 155–162.

Aitchison, J.C., Ali, J.R., Chan, A., Davis, A.M., Lo, C.H., 2009. Tectonic implications offelsic tuffs within the Lower Miocene Gangrinboche conglomerates, southernTibet. Earth and Planetary Science Letters 34, 287–297.

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 andcollision between India and Asia. Gondwana Research 20, 691–709.

Allègre, C.J., Courtillot, V., Tapponnier, P., Hirn, A., Mattauer, M., Coulon, C., Jaeger,J.J., Achache, J., Schärer, U., Marcoux, J., Burg, J.P., Girardeau, J., Armijo, R.,Gariépy, C., Göpel, C., Tindong, L., Xuchang, X., Chenfa, C., Guangqin, L., Baoyu, L.,Jiwen, T., Naiwen, W., Guoming, C., Tonglin, H., Xibin, W., Wanming, D., Huaibin,S., Yougong, C., Ji, Z., Hongrong, Q., Peisheng, B., Songchan, W., Bixiang, W.,Yaoxiu, Z., Xu, R., 1984. Structure and evolution of the Himalaya-Tibet orogenicbelt. Nature 307, 17–22.

Alsdorf, D., Brown, L., Nelson, K.D., Makovsky, Y., Klemperer, S., Zhao, W., 1998.Crustal deformation of the Lhasa terrane, Tibet plateau from Project INDEPTHdeep seismic reflection profiles. Tectonics 17, 501–519.

Armijo, R., Tapponnier, P., Mercier, J.L., Tong-Lin, H., 1986. Quaternary extension inSouthern Tibet: field observations and tectonic implications. Journal ofGeophysical Research-Solid Earth 91, 13803–13872.

Beck, R.A., Burbank, D.W., Sercombe, W.J., Riley, G.W., Barndt, J.K., Berry, J.R., Afzal, J.,Khan, A.M., Jurgen, H., Metje, J., Cheema, A., Shafique, N.A., Lawrence, R.D., Khan,M.A., 1995. Stratigraphic evidence for an early collision between NorthwestIndia and Asia. Nature 373, 55–58.

Chang, Z.S., Vervoort, J.D., McClelland, W.C., Knaack, C., 2006. U–Pb dating of zirconby LA-ICP-MS. Geochemistry Geophysics Geosystems 7, Q05009. http://dx.doi.org/10.1029/2005GC001100.



http://dx.doi.org/10.1029/2005GC001100


Cheng, J., Xu, G., 1986. Unpublished geologic map of the Gaize region at a scale of1:1,000,000 and the geologic report. Xizang Bureau of Geology and MineralResources, 369 (in Chinese).

Copeland, P., Harrison, T.M., Kidd, W.S.F., Ronghua, X., Yuquan, Z., 1987. Rapid earlyMiocene acceleration of uplift in the Gangdese Belt, Xizang-southern Tibet, andits beating on accommodation mechanisms of the India–Asia collision. Earthand Planetary Science Letters 86, 240–252.

Copeland, P., Harrison, T.M., Yun, P., Kidd, W.S.F., Roden, M., Zhang, Y.Q., 1995.Thermal evolution of the Gangdese batholith, southern Tibet – a history ofepisodic unroofing. Tectonics 14, 223–236.

Corfield, R.I., Searle, M.P., Green, O.R., 1999. Photang thrust sheet: an accretionarycomplex structurally below the Spontang ophiolite constraining timing andtectonic environment of ophiolite obduction, Ladakh Himalaya, NW India.Journal of the Geological Society, London 156, 1031–1044.

Coulon, C., Maluski, H., Bollinger, C., Wang, S., 1986. Mesozoic and Cenozoic volcanicrocks from central and southern Tibet: 39Ar–40Ar dating, petrologicalcharacteristics and geodynamical significance. Earth and Planetary ScienceLetters 79, 281–302.

Davis, A.M., Aitchison, J.C., Badengzhu, H., Luo, H., Malpas, J., Zyabrev, S., 1999.Eocene oblique-slip basin development, Tibet: terrane tracks on the roof of theworld. In: Evenchick, C.A., Woodsworth, G.J., Jongens, R. (Eds.), Terrane Paths 99Terrane Conference, Okanagan Valley, Canada, September 26–October 1, p. 28.

Davis, A.M., Aitchison, J.C., Badengzhu, H., Luo, H., Zyabrev, S., 2002. Paleogeneisland arc collision-related conglomerates, Yarlung Tsangposuture zone, Tibet.Sedimentary Geology 150, 247–273.

Debon, F., Fort, P.L., Sheppard, S.M.F., Sonet, J., 1986. The four plutonic belts of theTranshimalaya-Himalaya: a chemical, mineralogical, isotopic, and chronologicalsynthesis along a Tibet-Nepal section. Journal of Petrology 27, 219–250.

DeCelles, P.G., Gehrels, G.E., Quade, J., Ojha, T.P., 1998. Eocene early Mioceneforeland basin development and the history of Himalayan thrusting, westernand central Nepal. Tectonics 17, 741–765.

DeCelles, P.G., Gehrels, G.E., Quade, J., LaReau, B., Spurlin, M., 2000. Tectonicimplications of U–Pb zircon ages of the Himalayan orogenic belt in Nepal.Science 288, 497–499.

DeCelles, P., Ducea, M.N., Kapp, P., Zandt, G., 2009. Cyclicity in cordilleran orogenicsystems. Nature Geoscience 2, 251–257.

DeCelles, P.G., Kapp, P., Quade, J., Gehrels, G.E., Murphy, M.A., 2010. Oligo-Miocenebasins in Central Tibet and along the Indus Suture: records of plateau evolutionand dynamics of subducting Indian continental crust. In: Leech, M.L., (Ed.),Proceedings for the 25th Himalaya-Karakoram-Tibet Workshop. US GeologicalSurvey.

DeCelles, P.G., Kapp, P., Quade, J., Gehrels, G.E., 2011. Oligocene–Miocene Kailasbasin, southwestern Tibet: record of postcollisional upper-plate extension inthe Indus-Yarlung suture zone. Geological Society of America Bulletin 123,1337–1362.

Dewane, T.J., Stockli, D.F., Hager, C., Taylor, M.H., Ding, L., Lee, J., Wallis, S., 2006.Timing of Cenozoic E–W extension in the Tangra Yum Co-Kung Co rift, South-Central Tibet, Abstract #T34C-04, American Geophysical Union Fall Meeting,San Francisco.

Dewey, J.F., 1977. Suture zone complexities: a review. Tectonophysics 40, 53–67.Dewey, J.F., Shackleton, R.M., Chang, C.F., Sun, Y.Y., 1988. The tectonic evolution of

the Tibetan Plateau. Philosophical Transactions of the Royal Society A 327, 379–413.

Ding, L., Kapp, P., Wan, X.Q., 2005. Paleocene–Eocene record of ophiolite obductionand initial India–Asia collision, south central Tibet. Tectonics 24, 1–18.

Dong, G., 2002. Linzizong Volcanic Rocks and Implications for Probing India-EurasiaCollision Process in Linzhou Volcanic Basin, Tibet. China University ofGeosciences, PhD Thesis, 150p (in Chinese).

Dürr, S.B., 1993. The Mid to Early Late Cretaceous Xigaze Forearc Basin (southTibet): Sedimentary Evolution and Provenance of Clastic Sediments. TübingerGeowissenschaftliche Arbeiten: Geologie, Paläontologie, Stratigraphie. Institutund Museum für Geologie und Paläontologie der Universität Tübingen, 119p.

Dürr, S.B., 1996. Provenance of Xigaze fore-arc basin clastic rocks (Cretaceous, southTibet). Geological Society of America Bulletin 108, 669–684.

Einsele, G., Liu, B., Dürr, S., Frisch, W., Liu, G., Luterbacher, H.P., Ratschbacher, L.,Ricken, W., Wendt, J., Wetzel, A., Yu, G., Zheng, H., 1994. The Xigaze forearcbasin: evolution and facies architecture (Cretaceous, Tibet). SedimentaryGeology 90, 1–32.

Gaetani, M., Garzanti, E., 1991. Multicyclic history of the northern India continental-margin (Northwestern Himalaya). AAPG Bulletin 75, 1427–1446.

Gansser, A., 1964. The Geology of the Himalayas. Wiley Interscience, New York,289p.

Garzione, C.N., Quade, J., DeCelles, P.G., English, N.B., 2000. Predictingpaleoelevation of Tibet and the Himalaya from delta O-18 vs. altitudegradients in meteoric water across the Nepal Himalaya. Earth and PlanetaryScience Letters 183, 215–229.

Gehrels, G.E., DeCelles, P.G., Ojha, T.P., Upreti, B.N., 2006a. Geologic and U–Th–Pbgeochronologic evidence for early Paleozoic tectonism in the Kathmandu thrustsheet, central Nepal Himalaya. Geological Society of America Bulletin 118, 185–198.

Gehrels, G.E., DeCelles, P.G., Ojha, T.P., Upreti, B.N., 2006b. Geologic and U–Pbgeochronologic evidence for early Paleozoic tectonism in the Dadeldhura thrustsheet far-west Nepal Himalaya. Journal of Asian Earth Sciences 28, 385–408.

Gnos, E., Immenhauser, A., Peters, T., 1997. Late cretaceous early Tertiaryconvergence between the Indian and Arabian plates recorded in ophiolitesand related sediments. Tectonophysics 271, 1–19.

Grove, M., Harrison, T.M., 1996. Ar-40(⁄) diffusion in Fe-rich biotite. AmericanMineralogist 81, 940–951.

Guan, Q., Zhu, D.C., Zhao, Z.D., Dong, G.C., Zhang, L.L., Li, X.W., Liu, M., Mo, X.X., Liu,Y.S., Yuan, H.L., 2012. Crustal thickening prior to 38 Ma in southern Tibet:evidence from lower crust-derived adakitic magmatism in the GangdeseBatholith. Gondwana Research 21, 88–99.

Harris, N.B.W., Xu, R.H., Lewis, C.L., Jin, C.W., 1988. Plutonic rocks of the 1985 TibetGeotraverse, Lhasa to Golmud. Philosophical Transactions of the Royal Society A327, 145–146.

Harrison, T.M., Copeland, P., Kidd, W.S.F., Yin, A., 1992. Raising Tibet. Science 255,1663–1670.

Harrison, T.M., Copeland, P., Kidd, W.S.F., Lovera, O.M., 1994. Activation of theNyainqentanghla shear zone: implications for uplift of the southern Tibetanplateau. Tectonics 14, 575–658.

Harrison, T.M., Copeland, P., Kidd, W.S.F., Lovera, O.M., 1995. Activation of theNyainqentanghla shear zone: implications for uplift of the southern TibetanPlateau. Tectonics 14, 658–676.

Harrison, T.M., Yin, A., Grove, M., Lovera, O.M., Ryerson, F.J., Zhou, X.H., 2000. TheZedong window: a record of superposed Tertiary convergence in southeasternTibet. Journal of Geophysical Research-Solid Earth 105, 19211–19230.

He, S., Kapp, P., DeCelles, P.G., Gehrels, G.E., Heizler, M., 2007. Cretaceous-Tertiarygeology of the Gangdese Arc in the Linzhou area, southern Tibet.Tectonophysics 433, 15–37.

Heim, A., Gansser, A., 1939. Central Himalaya, geological observations of the Swissexpedition 1936. Memoires de la Societe Helvetique des Sciences Naturelles 63,245.

Hellstrom, J., 2008. Iolite: software for spatially resolved LA-(quad and MC) ICPMSanalysis. In: Sylvester, P. (Ed.), Laser Ablation ICPMS in the Earth Sciences:Current Practices and Outstanding Issues. Association of Canada, Vancouver, BC,Canada, pp. 343–348.

Hintersberger, E., Thiede, R.C., Strecker, M.R., Hacker, B.R., 2010. East-westextension in the NW Indian Himalaya. Geological Society of America Bulletin122, 1499–1515.

Hodges, K.V., 2000. Tectonics of the Himalaya and southern Tibet from twoperspectives. Geological Society of America Bulletin 112, 324–350.

Ji, W.Q., Wu, F.Y., Chung, S.L., Li, J.X., Liu, C.Z., 2009. Zircon U–Pb geochronology andHf isotopic constraints on petrogenesis of the Gangdese batholith, southernTibet. Chemical Geology 262, 229–245.

Kapp, J.L.D., Harrison, T.M., Kapp, P., Grove, M., Lovera, O.M., Lin, D., 2005.Nyainqentanglha Shan: a window into the tectonic, thermal, and geochemicalevolution of the Lhasa block, southern Tibet. Journal of Geophysical Research-Solid Earth 110. http://dx.doi.org/10.1029/2004JB003330.

Kapp, P., DeCelles, P.G., Gehrels, G.E., Heizler, M., Ding, L., 2007. Geologic records ofthe Lhasa–Qiangtang and Indo-Asian collisions in the Nima area of central Tibet.Geological Society of America Bulletin 119, 917–932.

Kapp, P., Taylor, M., Stockli, D., Ding, L., 2008. Development of active low-anglenormal fault systems during orogenic collapse: insight from Tibet. Geology 36,7–10.

Kidd, W.S.F., Pan, Y., Chang, C., Coward, M.P., Dewey, J.F., Gansser, A., Molnar, P.,Shackleton, R.M., Sun, Y., 1988. Sequence of thrusting in the Tethyan fold-thrustbelt and Indus-Yalu suture zone. Philosophical Transactions of the Royal Societyof London A327, 287–305.

Klootwijk, C.T., Gee, F.S., Peirce, J.W., Smith, G.M., McFadden, P.L., 1992. An earlyIndia contact: paleomagnetic constraints from Ninety East Ridge, ODP Leg 121.Geology 20, 395–398.

Lacassin, R., Valli, F., Arnaud, N., Leloup, P.H., Paquette, J.L., Haibing, L., Tapponnier,P., Chevalier, M.L., Guillot, S., Maheo, G., Zhiqin, X., 2004. Large scale geometry,offset and kinematic evolution of the Karakorum fault, Tibet. Earth andPlanetary Science Letters 219, 255–269.

Lanphere, M.A., Dalrymple, G.B., 1976. Identification of excess 40Ar by the 40Ar/39Arage spectrum technique. Earth and Planetary Science Letters 32, 141–148.

Lee, H.Y., Chung, S.L., Lo, C.H., Ji, J., Lee, T.Y., Qian, Q., Zhang, Q., 2009. EoceneNeotethyan slab breakoff in southern Tibet inferred from the Linzizong volcanicrecord. Tectonophysics 477, 20–35.

Li, J.G., 2004. Discovery and preliminary study on palynofossils from the CenozoicQiuwu Formation of Xizang (Tibet). Acta Micropalaeontologica Sinica 21, 216–221.

Liu, Z.Q., 1988. Geologic Map of the Qinghai–Xizang Plateau and its NeighboringRegions (scale at 1:1,500,000). Chengdu Institute of Geology and MineralResources, Geologic Publishing House, Beijing.

Liu, H.F., 1993. Division of Linzizong volcanic series and its geochronology in Lhasaarea. Xizang Geology 2, 59–69 (in Chinese with English abstract).

Liu, J.B., Aitchison, J.C., 2002. Upper Paleocene radiolarians from the Yamdrokmélange, south Xizang (Tibet), China. Micropaleontology 48, 145–154.

Ludwig, K.R., 2008. User’s Manual for IsoPlot 4.0: A Geochronological Toolkit forMicrosoft Excel. Berkeley Geochronology Center, Berkeley, California.

Mahéo, G., Leloup, P.H., Valli, F., Lacassin, R., Arnaud, N., Paquette, J.L., Fernandez, A.,Haibing, L., Farley, K.A., Tapponnier, P., 2007. Post 4 Ma initiation of normalfaulting in southern Tibet: constraints from the Kung Co half graben. Earth andPlanetary Science Letters 256, 233–243.

Martin, A.J., DeCelles, P.G., Gehrels, G.E., Patchett, P.J., Isachsen, C., 2005. Isotopicand structural constraints on the location of the main central thrust in theAnnapurna Range, central Nepal Himalaya. Geological Society of AmericaBulletin 117, 926–944.

Miller, C., Schuster, R., Klotzli, U., Frank, W., Purtscheller, F., 1999. Post-collisionalpotassic and ultrapotassic magmatism in SW Tibet: geochemical and Sr-Nd-Pb-

http://dx.doi.org/10.1029/2004JB003330


O isotopic constraints for mantle source characteristics and petrogenesis.Journal of Petrology 40, 1399–1424.

Miller, C., Schuster, R., Klotzli, U., Frank, W., Grasemann, B., 2000. Late Cretaceous-Tertiary magmatic and tectonic events in the Transhimalaya batholith (Kailasarea, SW Tibet). Schweizerische Mineralogische Und PetrographischeMitteilungen 80, 1–20.

Mo, X., Niu, Y., Dong, G., Zhao, Z., Hou, Z., Zhou, S., Ke, S., 2008. Contribution ofsyncollisional felsic magmatism to continental crust growth: a case study of thePaleogene Linzizong volcanic succession in southern Tibet. Chemical Geology250, 49–67.

Murphy, M.A., Yin, A., 2003. Sequence of thrusting in the Tethyan fold-thrust beltand Indus-Yalu suture zone, southwest Tibet. Geological Society of AmericaBulletin 115, 21–34.

Murphy, M.A., Yin, A., Harrison, T.M., Durr, S.B., Chen, Z., Ryerson, F.J., Kidd, W.S.F.,Wang, X., Zhou, X., 1997. Did the Indo-Asian collision alone create the Tibetanplateau? Geology 25, 719–722.

Murphy, M.A., Yin, A., Kapp, P., Harrison, T.M., Ding, L., Guo, J., 2000. Southwardpropagation of the Karakoram fault system, southwest Tibet: Timing andmagnitude of slip. Geology 28, 451–454.

Murphy, M.A., Yin, A., Kapp, P., Harrison, T.M., Manning, C.E., Ryerson, F.J., Ding, L.,Guo, J.H., 2002. Structural evolution of the Gurla Mandhata detachment system,southwest Tibet: Implications for the eastward extent of the Karakoram faultsystem. Geological Society of America Bulletin 114, 428–447.

Murphy, M.A., Saylor, J.E., Ding, L., 2009. Late Miocene topographic inversion insouthwest Tibet based on integrated paleoelevation reconstructions andstructural history. Earth and Planetary Science Letters 282, 1–9.

Murphy, M.A., Sanchez, V., Taylor, M.H., 2010. Syncollisional extension along theIndia–Asia suture zone, south-central Tibet: implications for crustaldeformation of Tibet. Earth and Planetary Science Letters 290, 233–243.

Paces, J.B., Miller, J.D., 1993. Precise U–Pb Ages of Duluth Complex and related maficintrusions, Northeastern Minnesota: geochronological insights to physical,petrogenetic, paleomagnetic, and tectonomagmatic processes associated withthe 1.1 Ga midcontinent rift system. Journal of Geophysical Research-SolidEarth 98, 13997–14013.

Patriat, P., Achache, J., 1984. India-Eurasia collision chronology has implications forcrustal shortening and driving mechanism of plates. Nature 311, 615–621.

Pullen, A.P., Kapp, P., DeCelles, P.G., Gehrels, G.E., Ding, L., 2011. Cenozoic anatexisand exhumation of Tethyan Sequence rocks in the Xiao Gurla Range, SouthwestTibet. Tectonophysics 501, 28–40.

Qian, D., 1985. Discussion on the age of Qiuwu coal measures and the preliminarycorrelation of the molasse formation at the Ladakh-Gangdise marginalmountain chain. In: Committee, C.E. (Ed.), Contribution to the Geology of theQinghai–Xizang (Tibet) Plateau Stratigraphy and Paleontology. Ministry ofGeology and Mineral Resources Geological Publishing House, Beijing, p. 264.

Quidelleur, X., Grove, M., Lovera, O.M., Harrison, T.M., Yin, A., 1997. Thermalevolution and slip history of the Renbu Zedong Thrust, southeastern Tibet.Journal of Geophysical Research 102, 2659–2679.

Ratschbacher, L., Frisch, W., Liu, G., 1994. Distributed deformation in southern andwestern Tibet during and after the India–Asia collision. Journal of GeophysicalResearch 99, 19917–19945.

Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, T.L., DePaolo, D.J., 1998.Intercalibration of standards, absolute ages and uncertainties in 40Ar/39Ardating. Chemical Geology 145, 117–152.

Rowley, D.B., 1996. Age of initiation of collision between India and Asia: a review ofstratigraphic data. Earth and Planetary Science Letters 145, 1–13.

Sanchez, V.I., Murphy, M.A.R., Robinson, A.C., Lapen, T.J., Heizler, M.T., Taylor, M.H.,2010. Onset of Oblique Extension in South-Central Tibet by 15 Ma: implicationsfor Diachronous Extension of the Tibetan Plateau Abstract #T43B-2185American Geophysical Union, San Francisco, 13–17 December.

Schärer, U., Xu, H.R., Allègre, C.J., 1984. U–Pb geochronology of Gangdese(Transhimalaya) plutonism in the Lhasa–Xigaze region, Tibet. Earth andPlanetary Science Letters 69, 311–320.

Searle, M.P., 1997. Structure of the North Indian continental margin in the Ladakh –Zanskar Himalayas: implications for the timing of obduction of the Spontangophiolite, India –Asia collision and deformation events in the Himalaya.Geological Magazine 134, 297–316.

Searle, M.P., Windley, B.F., Coward, M.P., Cooper, D.J.W., Rex, A.J., Rex, D., Tingdong,L., Xuchang, X., Jan, M.Q., Thakur, V.C., Kumar, S., 1987. The closing of Tethys andthe tectonics of the Himalayas. Geological Society of America Bulletin 98, 678–701.

Searle, M.P., Searle, M.P., Pickering, K.T., Cooper, D.J.W., 1990. Restoration andevolution of the intermontane Indus molasse basin, Ladakh Himalaya, India.Tectonophysics 174, 301–314.

Searle, M.P., Weinberg, R.F., Dunlap, W.J., 1998. Transpressional tectonics along theKarakoram fault zone, northern Ladakh: constraints on Tibetan extrusion.Geological Society, London, Special Publications, 135. Geological Society,London, pp. 307–326.

Searle, M.P., Waters, D.J., Dransfield, M.W., Stephenson, B.J., Walker, C.B., Walker,J.D., Rex, D.C., 1999. Thermal and mechanical models for the structuralevolution of Zanskar High Himalaya. In: Mac Niocaill, C., Ryan, P.D. (Eds.),Continental Tectonics, vol. 164. Geological Society, London Special Publications,pp. 139–156.

Shaulis, B., Lapen, T.J., Toms, A., 2010. Signal linearity of an extended range pulsecounting detector: Applications to accurate and precise U–Pb dating of zircon

by laser ablation quadrupole ICP-MS. Geochemistry Geophysics Geosystems 11,Q0AA11. http://dx.doi.org/10.1029/2010GC003198.

Sinclair, H.D., Jaffey, N., 2001. Sedimentology of the Indus Group, Ladakh, northernIndia: implications for the timing of initiation of the paleo-Indus River. Journalof the Geological Society of London 158, 151–162.

Song, Q.Y., 1999. Geochemical features of the volcanic rocks of Linzizong group inCoqen Basin. Journal of Geomechanics 5, 65–70 (in Chinese).

Styron, R., Taylor, M.H., Okoronkwo, K., 2010. Database of active structures from theIndo-Asian collision. EOS, Transactions American Geophysical Union 91, 181.

Sundell, K.E., Taylor, M.H., Stockli, D.F., Kapp, P.A., Styron, R.H., Liu, D., Ding, L., 2010.Late Miocene – Pliocene rifting in West-Central Tibet: Evidence from (U–Th)/HeThermochronology of the North Lunggar Rift, Abstract #T43B-2202, AmericanGeophysical Union Fall Meeting, San Francisco, 13–17 December.

Taylor, M., Yin, A., 2009. Active structures of the Himalayan–Tibetan orogen andtheir relationships to earthquake distribution, contemporary strain field, andCenozoic volcanism. Geosphere 5, 199–214.

TBGMR (Tibetan Bureau of Geology and Mineral Resources), 1992. Geologic Map ofXizang Autonomous Region: Beijing, Geological Publishing House, scale 1:500000.

Thiede, R.C., Arrowsmith, J.R., Bookhagen, B., McWilliams, M., Sobel, E.R., Strecker,M.R., 2006. Dome formation and extension in the Tethyan Himalaya, Leo Pargil,northwest India. Geological Society of America Bulletin 118, 635–650.

Treloar, P.J., Coward, M.P., 1991. Indian plate motion and shape – constraints on thegeometry of the Himalayan orogen. Tectonophysics 191, 189–198.

Valli, F., Leloup, P.H., Paquette, J.L., Arnaud, N., Li, H.B., Tapponnier, P., Lacassin, R.,Guillot, S., Liu, D.Y., Deloule, E., Xu, Z.Q., Maheo, G., 2008. New U–Th/Pbconstraints on timing of shearing and long-term slip-rate on the Karakorumfault. Tectonics 27.

van Hinsbergen, D.J.J., Lipert, P.C., Dupont-Nivet, G., McQuarrie, N., Doubrovine, P.V.,Spakman, W., Torsvik, T.H., 2012. Greater India basin hypothesis and a two-stage Cenozoic collision between India and Asia. Proceedings of the NationalAcademy of Sciences 109 (20), 7659–7664.

van Wyck, N., Medaris, L.G., Johnson, C.M., 1994. The Wolf River A-type magmaticevent in Wisconsin: U/Pb and Sm/Nd constraints on timing and petrogenesis.In: 40th Annual Meeting Institute on Lake Superior Geology MichiganTechnological University, Houghton, MI, p. 77.

Wang, X., Li, Z.M., Xiyiao, Q., 1983. Geologic Map of the Xigaze–Zedong Region,Scale, 1:100,000, Xizang (Tibet) with Report, Xizang Bureau of Geology, Lhasa, p.568 (in Chinese).

Wang, T.W., Li, C., Yang, D.M., 1999. Geochemical features and genesis of theLinzizong group volcanic rocks of the early Tertiary in Gangdese. Tibet.Geological Review 45, 966–971 (in Chinese).

Wang, C., Liu, Z., Hébert, R., 2000. The Yarlung-Zangbo paleo-ophiolite, southernTibet: implications for the dynamic evolution of the Yarlung-Zangbo SutureZone. Journal of Asian Earth Sciences 18, 651–661.

Wen, D.R., Liu, D.Y., Chung, S.L., Chu, M.F., Ji, J.Q., Zhang, Q., Song, B., Lee, T.Y., Yeh,M.W., Lo, C.H., 2008. Zircon SHRIMP U–Pb ages of the Gangdese Batholith andimplications for Neotethyan subduction in southern Tibet. Chemical Geology252, 191–201.

Williams, H., Turner, S., Kelley, S., Harris, N., 2001. Age and composition of dikes inSouthern Tibet: new constraints on the timing of east-west extension and itsrelationship to postcollisional volcanism. Geology 29, 339–342.

Wu, H.R., Wang, D.G., Wand, L.C., 1977. The Cretaceous of Lhaze, Jiangze district,southern Xizang. Scientia Geologica Sinica 3, 250–262.

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan–Tibetan orogen.Annual Review of Earth and Planetary Sciences 28, 211–280.

Yin, A., Harrison, T.M., Ryerson, F.J., Chen, W.J., Kidd, W.S.F., Copeland, P., 1994.Tertiary Structural Evolution of the Gangdese Thrust System, SoutheasternTibet. Journal of Geophysical Research-Solid Earth 99, 18175–18201.

Yin, A., Harrison, T.M., Murphy, M.A., Grove, M., Nie, S., Ryerson, F.J., Feng, W.X., Le,C.Z., 1999. Tertiary deformation history of southeastern and southwestern Tibetduring the Indo-Asian collision. Geological Society of America Bulletin 111,1644–1664.

Yu Zheng-Xin, Zhen An-Zhu, 1979. GEOLOGIC map of the Lhasa Region at a Scale of1:1,000,000. Geologic Publishing House, Beijing.

Zhang, S.M., Fu, X.L., 1982. (Compilers) Xizang Autonomous Region Xigaze-SagaGeological Traverse Map 1:200,000. Xizang Geological Survey Geological Team#2, Lhasa.

Zhang, R., Murphy, M.A., Lapen, T.J., Sanchez, V., Heizler, M., 2011. Late Eocenecrustal thickening followed by early-late Oligocene extension along the India–Asia suture zone: evidence for cyclicity in the Himalayan orogen. Geosphere.http://dx.doi.org/10.1130/GES00643.1.

Zhou, S., Mo, X., Dong, G., Zhao, Z., Qiu, R., Guo, T., Wang, L., 2004. 40Ar–39Argeochronology of Cenozoic Linzizong volcanic rocks from Linzhou Basin, Tibet,China, and their geological implications. Chinese Science Bulletin 49 (18), 1970–1979.

Zhu, B., Kidd, W.S.F., Rowley, D.B., Currie, B.S., Shafique, N., 2005. Age of initiation ofthe India–Asia collision in the east-central Himalaya. Journal of Geology 113,265–285.

Ziabrev, S.V., Aitchison, J.C., Abrajevitch, A.V., Badengzhu, Davis, A.M., Luo, H., 2004.Bainang Terrane, Yarlung-Tsangpo suture, southern Tibet (Xizang, China):Bainang Terrane, Yarlung-Tsangpo suture, southern Tibet (Xizang, China).Journal of the Geological Society 161, 523–539.

http://dx.doi.org/10.1029/2010GC003198

http://dx.doi.org/10.1130/GES00643.1

tectonic evolution of the india–asia suture zone since middle eocene time, lopukangri area,...

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