|| mesozoic tectonic history and lithospheric structure of the qiangtang terrane: insights from the...

doi:10.1130/2014.2507(04), published online July 22, 2014;Geological Society of America Special Papers

Alex Pullen and Paul Kapp Insights from the Qiangtang metamorphic belt, central TibetMesozoic tectonic history and lithospheric structure of the Qiangtang terrane:

Online FirstGeological Society of America Special Papers

E-mail alerting services

this article

to receive free e-mail alerts when new articles citewww.gsapubs.org/cgi/alertsclick

Subscribe

Special Papers

to subscribe to Geological Society of Americawww.gsapubs.org/subscriptionsclick

Permission request

to contact GSA.www.geosociety.org/pubs/copyrt.htm#gsaclick

viewpoint. Opinions presented in this publication do not reflect official positions of the Society.positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or politicalarticle's full citation. GSA provides this and other forums for the presentation of diverse opinions and articles on their own or their organization's Web site providing the posting includes a reference to thescience. This file may not be posted to any Web site, but authors may post the abstracts only of their unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education andto use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make

GSA,employment. Individual scientists are hereby granted permission, without fees or further requests to Copyright not claimed on content prepared wholly by U.S. government employees within scope of their

Notes

© Geological Society of America

on August 11, 2014specialpapers.gsapubs.orgDownloaded from on August 11, 2014specialpapers.gsapubs.orgDownloaded from

http://www.gsapubs.org/cgi/alerts

http://www.gsapubs.org/subscriptions

http://www.geosociety.org/pubs/copyrt.htm#gsa

http://specialpapers.gsapubs.org/


71

The Geological Society of AmericaSpecial Paper 507

2014

Mesozoic tectonic history and lithospheric structure of the Qiangtang terrane: Insights from

the Qiangtang metamorphic belt, central Tibet

Alex Pullen*Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA

Paul KappDepartment of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

ABSTRACT

The Triassic Qiangtang metamorphic belt in central Tibet consists of eclogite- and blueschist-bearing tectonic mélange exposed in an intracontinental setting. Study of the belt has yielded insight about the tectonic history and crustal architecture of the Qiangtang terrane. Weakly deformed mafi c blocks exhibiting high-pressure, low-temperature metamorphic mineral assemblages are exposed within a greenschist facies sedimentary-matrix mélange over an east-west distance of ~600 km and north-south distance of ~150 km. Everywhere it has been mapped, the Qiangtang mélange is exposed in the footwalls of Late Triassic–Early Jurassic domal, low-angle normal faults. The hanging walls of these normal faults are composed of late Paleozoic to early Mesozoic metasedimentary and crystalline rocks; similar lithologies are exposed in footwall mélange rocks. High-pressure metamorphism occurred during Middle Tri-assic time. Regional geological mapping and provenance of detrital zircon crystals from late Paleozoic to Mesozoic supracrustal rocks of the Qiangtang terrane indicate that Qiangtang crust exposed on the north and south sides of the metamorphic belt are of Gondwanan affi nity. This is at odds with the widely held belief that the Qiang-tang metamorphic belt marks a suture between a Gondwanan affi nity southern and/or western Qiangtang terrane and a Cathayasian affi nity northern and/or eastern Qiangtang terrane. Furthermore, metasedimentary rocks exposed within the meta-morphic belt yield detrital zircon age probability distributions consistent with deri-vation from Qiangtang terrane supracrustal strata and Paleo-Tethys affi nity rocks exposed north of the Qiangtang terrane. These data, along with the signifi cant north-south surface exposure of the metamorphic belt, suggest that a large part of the lower to middle crust is composed of silica-rich metasedimentary-dominated mélange rock that formed during Middle Triassic southward subduction along the Jinsha suture

*Current address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA; e-mail: [email protected].

Pullen, A., and Kapp, P., 2014, Mesozoic tectonic history and lithospheric structure of the Qiangtang terrane: Insights from the Qiangtang metamorphic belt, central Tibet, in Nie, J., Horton, B.K., and Hoke, G.D., eds., Toward an Improved Understanding of Uplift Mechanisms and the Elevation History of the Tibetan Plateau: Geological Society of America Special Paper 507, p. 71–87, doi:10.1130/2014.2507(04). For permission to copy, contact [email protected]. © 2014 The Geological Society of America. All rights reserved.

on August 11, 2014specialpapers.gsapubs.orgDownloaded from


72 Pullen and Kapp

INTRODUCTION

Investigations of high-pressure (HP), low-temperature (LT) metamorphic rocks provide an opportunity to address fundamen-tal questions in global tectonics concerning the timing and geo-dynamics of oceanic subduction, paleogeography, and the assem-bly and structural architecture of continental crust. Blueschists were recognized in the Qiangtang terrane of central Tibet (Fig. 1) nearly a century ago (Hennig, 1915). Despite the importance of these HP metamorphic rocks in the central Qiangtang terrane in unravelling the tectonic history of Tibet and establishing the initial boundary conditions for Cenozoic growth of the Tibetan Plateau, their origin, evolution, and tectonic signifi cance remain widely debated, even with the intense efforts to study these rocks over the past two decades (e.g., Pullen et al., 2011; Zhang et al., 2011). This debate is, in part, the consequence of an inadequate grasp of established geologic relationships within and adjacent to the Qiangtang terrane, and misconceptions about the geological predictions that end-member models make about the formation of the HP-LT metamorphic rocks. We review the geologic frame-work of the Qiangtang HP-LT metamorphic rocks and attempt to distinguish data and observations from misconceptions and assumptions.

The HP-LT metamorphic rocks of the Qiangtang terrane are exposed as a discontinuous belt in the hinge of a crustal-scale antiformal structural culmination (Fig. 1). Rocks exhibiting eclogite, blueschist, and amphibolite facies mineral assemblages are typically exposed as less-deformed blocks within a highly deformed, dominantly metasedimentary matrix exhibiting green-schist facies mineral assemblages (e.g., Kapp et al., 2000, 2003; Li et al., 2006b, 2007; Pullen et al., 2008). The observation of this block-in-matrix structure and the presence of HP rocks led to the interpretation of the Qiangtang metamorphic belt as a tectonic mélange that was deformed and metamorphosed in an oceanic subduction zone (Li et al., 1995; Kapp et al., 2000). The meta-morphic belt was initially interpreted to represent Qiangtang ter-rane basement rocks nonconformably overlain by Devonian and younger strata (e.g., Cheng and Xu, 1986) or as a collapsed early Permian–Late Triassic extensional basin (Deng et al., 1996). Where the metamorphic belt has been mapped in detail, however, it is exposed structurally beneath Carboniferous–Triassic strata in the footwalls of Late Triassic–Early Jurassic domal, low-angle normal faults (Kapp et al., 2000, 2003, 2005; Pullen et al., 2011). The nature of the metamorphic rocks (i.e., HP-LT) and the fact that they are exposed within a tectonic mélange would be dif-fi cult to reconcile within an extensional basin model. In addition,

the mélange is younger than most of the rocks that structurally overlie it (e.g., Kapp et al., 2000; Pullen et al., 2008; Zhai et al., 2011). The geological relations preclude an unconformable rela-tionship between the Qiangtang metamorphic rocks and adjacent lower-grade strata, either initially or currently.

Substantiated alternative hypotheses suggest the metamor-phic belt formed: (1) in situ between a southern and/or western Qiangtang terrane of Gondwanan affi nity and a northern and/or eastern Qiangtang terrane of Cathaysian or Laurasian affi nity during northward subduction of ocean crust beneath the northern block (Li et al., 1995; Bao et al., 1999; Zhang et al., 2006a; Yang et al., 2011); or (2) from southward subduction of a shallow-dipping Paleo-Tethys oceanic slab beneath the Jinsha suture, tec-tonic erosion, and underthrusting of tectonically eroded material followed by exhumation of the mélange belt in an intracontinen-tal setting within the Qiangtang terrane (Fig. 2; Kapp et al., 2000; Pullen et al., 2008). Each of these models makes predictions that have been tested over the past decade. The model favoring an in situ formation of the Qiangtang mélange between a Gondwanan affi nity and Cathaysian affi nity Qiangtang terranes suggests that the crustal fragments north and south of the Qiangtang mélange should show a strikingly different evolution between the Late Devonian and Early Carboniferous following the rifting of the Cathaysian province (i.e., the South China block, Simao ter-rane, Indochina block, and East Malaya block) from Gondwana (Metcalfe, 2006), and the Middle Triassic suturing between north and south Qiangtang, and formation of the Qiangtang mélange. This model postulates that a suture, referred to as the Longmu Co–Shuanghu suture, separates the northern and/or eastern and southern and/or western Qiangtang terranes. Although the suture has been poorly defi ned, the in situ model has been predicated on the idea that late Paleozoic strata south of the Qiangtang meta-morphic belt have cold-water Gondwanan affi nity faunal assem-blages, whereas similar age strata north and east of the Qiangtang metamorphic belt have warm-water Cathayasian affi nity faunal assemblages (Wang and Mu, 1983; Fan, 1985, 1988; Li, 1987; Li and Zheng, 1993; Chen and Xie, 1994). The in situ model predicts an approximately east-west–striking suture in the mid-dle of the Qiangtang terrane. The model favoring southward underthrusting beneath the Jinsha suture predicts that the entire Qiangtang terrane is of Gondwanan affi nity, had a relatively uni-form history throughout Paleozoic time, and that the Qiangtang mélange is composed of Gondwanan affi nity rocks tectonically eroded from the upper plate and Paleo-Tethys affi nity rocks that were accreted from the subducting slab (e.g., Kapp et al., 2000; Pullen et al., 2008).

on the northern edge of the Qiangtang terrane. The implied crustal structure, which is also defi ned by geophysical experiments, provides an explanation for the apparent deviation from Airy isostasy from the Lhasa terrane to the Qiangtang terrane. We suggest that the replacement or partial incorporation of mafi c crystalline middle to lower crust with less dense metasedimentary mélange rock led to a signifi cant contri-bution of Pratt isostasy across central Tibet.



Qiangtang terrane Mesozoic tectonic history and lithospheric structure 73

Figu

re 1

. Ter

rane

map

of

the

Tib

etan

Pla

teau

and

sur

roun

ding

are

as.



74 Pullen and Kapp

We outline the geological framework and data that are consistent with both substantiated models for the formation of the Qiangtang metamorphic belt and show why the fi rst order redictions of the underthrusting model of Kapp et al. (2000) have withstood hypothesis testing. In addition, we highlight the inconsistencies alternative models have with the understand-ing of the paleogeography and geology of the Qiangtang ter-rane and identify misconceptions surrounding the underthrust model. In the process of summarizing the debate about the Qiangtang metamorphic belt, we also discuss implications that the underthrust model has for the lithotectonic structure, distri-bution of Cenozoic magmatism, and the isostatic equilibrium of the Qiangtang terrane.

GEOLOGIC SETTING

Central Tibet is composed of the peri-Gondwana–derived Qiangtang and Lhasa terranes (Allégre et al., 1984; Chang et al., 1986; Şengör, 1987). The Jinsha suture separates the Qiangtang

terrane from the Hoh-Xil-Songpan-Ganzi turbidite complex and Yidun arc in the north, whereas the Bangong suture separates the Lhasa terrane from the Qiangtang terrane in the south (Fig. 1). The Jinsha and Bangong sutures are associated with the clo-sure of the Paleo-Tethys and Meso-Tethys (Bangong) Oceans, respectively, between Laurasia in the north and Gondwana in the south (Allégre et al., 1984). The Qiangtang terrane rifted from the margin of Gondwana as an elongate fragment of continen-tal crust, the Cimmerian superterrane, by late Permian time (Fig. 3; Şengör, 1984, Metcalfe, 1996, 1998, 2006). The position of the Qiangtang terrane along the margin of Gondwana prior to rifting is debated in detail; however, most reconstructions put the Qiangtang terrane near the Lhasa terrane along the Arabia–western Australia margin of Gondwana (Fig. 3; Scotese et al., 1999; Metcalfe, 2002; Guynn et al., 2011). In addition, it remains unclear whether the Qiangtang and Lhasa terranes rifted from Gondwana together and later separated forming the Meso-Tethys Ocean (e.g., Yin et al., 1988; Chang et al., 1989; Schneider et al., 2003), or rifted separately, the Qiangtang terrane fi rst followed

Figure 2. Substantiated hypotheses for the formation of the Qiangtang metamorphic belt during early Mesozoic time. (A) In situ model: the Qiangtang metamorphic belt forms as a suprasubduction tectonic mélange between the northern Qiangtang terrane of Cathaysian affi nity and the southern Qiangtang terrane of Gondwana affi nity. (B) Underthrust model: the Qiangtang metamorphic belt forms from southward subduction beneath the Jinsha suture and tectonic underplating.




by the Lhasa terrane (e.g., Allégre et al., 1984; Şengör et al., 1988; Gaetani and Garzanti, 1991; Metcalfe, 2006). The conti-nental terranes of Cimmerian affi nity are exposed from modern Turkey in the west to the Malay Peninsula in the east (Şengör, 1987; Metcalfe, 2002), and compose a large volume of the highly strained fabric of Eurasia resulting from multiple Phanerozoic continent-continent collisions (Kropotkin, 1971; Burrett, 1974; Şengör, 1987).

Bangong Suture

The Bangong suture is defi ned by discontinuous ophiol-itic fragments and associated Jurassic–Cretaceous deep-marine sequences, mélange, and volcanic rocks (Girardeau et al., 1984; Chang et al., 1986; Yin et al., 1988; Baxter et al., 2009). Clo-sure of the Meso-Tethys (Bangong Ocean) has been attributed to subduction of Tethys oceanic lithosphere northward beneath the southern margin of the Qiangtang terrane (Girardeau et al., 1984; Coulon et al., 1986; Smith and Xu, 1988; Leeder et al., 1988; Guynn et al., 2006) and/or southward beneath the Lhasa terrane (Zhu et al., 2011). Ophiolitic rocks defi ning the Bangong suture formed during Late Triassic–Early Jurassic time and were obducted during Middle–Late Jurassic time. (Girardeau et al., 1985; Bao et al., 1996; Matte et al. 1996; Wang et al., 2002; Lu et al., 2003). Deep-marine sedimentation continued to at least mid-dle Cretaceous time (Smith and Xu, 1988; Baxter et al., 2009). Deformation and nonmarine sedimentation constrain suturing of the Qiangtang and Lhasa terranes along the central Bangong suture zone by 118 Ma (Kapp et al., 2007). The nature and size of the Meso-Tethys Ocean are widely debated (e.g., Mattern et al., 1998; Schneider et al., 2003; Baxter et al., 2009). Arc rocks asso-ciated with subduction of oceanic crust are sparse, contributing to this debate. Workers have speculated that the east-west–trending Qiangtang antiformal structural culmination formed as a crustal-

Figure 3. Global paleogeographic reconstruction for the late Permian after Metcalfe (2006).

scale fault-bend fold over the underthrusting leading northern edge of the Lhasa terrane after Lhasa-Qiangtang suturing but prior to ca. 100 Ma (Kapp et al., 2005).

Jinsha Suture

The Jinsha suture is well defi ned in eastern Tibet where ophiolitic fragments and ophiolitic mélange are exposed between the Yidun arc and Qiangang terrane (Fig. 1; Yin and Harrison, 2000; Wang et al., 2000). Triassic volcanic rocks exposed in the eastern Qiangtang terrane are thought to be the manifestation of southwestward subduction of Paleo-Tethys oceanic lithosphere beneath the Qiangtang terrane (Mo et al., 1994; Shen et al., 1995: Wang et al., 1999). However, some have suggested northeastward subduction beneath the Yidun arc terrane based on deformational fabrics within the Yidun complex (Reid et al., 2005). The Jinsha suture is less well defi ned in central Tibet where exposures of ophiolitic fragments are scarce and very widely spaced (Pan et al., 2004). The Yidun arc is widely thought to have sutured to the Qiangtang terrane by Middle Triassic time (Dewey et al., 1988; Yin and Harrison, 2000; Reid et al., 2005). Some have specu-lated that the suturing of the Qiangtang terrane to the Hoh-Xil-Songpan-Ganzi complex was diachronous along strike, younging westward (Yin and Harrison, 2000), but little is known about the Jinsha suture in central and western Tibet, including its location.

Basement Rocks of South-Central Tibet

Geochronologic investigations suggest that most of the autochthonous crystalline basement of the Lhasa and Qiang-tang terranes formed during Cambrian–Ordovician time (Table 1); however, the basement may include some older, recycled, or inherited components of Mesoproterozoic to Neoproterozoic age (Guynn et al., 2011; Z.M. Zhang et al., 2012). An exposure of orthogneiss in the Duguer Range south of the Qiangtang meta-morphic belt (Fig. 1), interpreted as autochthonous crystalline peri-Gondwana basement, yielded 476–474 Ma U-Pb zircon crystallization ages (Pullen et al., 2011), and a discordant age with a lower intercept of 384.4 ± 7.2 Ma and upper intercept of 1221 ± 142 Ma (Li et al., 2000). Crystalline basements rocks have not been reported in the Qiangtang terrane north of the metamorphic belt. Cambrian–Ordovician ages are common for orthogneiss in the Amdo basement microterrane exposed within the Bangong suture zone (Fig. 1). Orthogneiss samples from the Amdo massif yielded U-Pb zircon discordia upper intercept ages in the range of 910–838 Ma, and concordant ages in the range of 532–483 Ma (Xu et al., 1985; Guynn et al., 2006, 2011). Dis-cordant lower intercept and upper intercept ages have also been reported in the range of 487–463 Ma (Guynn et al., 2011). Ages from autochthonous crystalline basement exposures in the Lhasa terrane are similar to the Neoproterozoic and Cambrian–Ordovi-cian ages reported for the Qiangtang terrane and Amdo gneiss. Hu et al. (2004) reported an age of ca. 750 Ma for gneissic rocks exposed in the central Lhasa terrane, whereas a nondeformed



76 Pullen and Kapp

granite yielded a U-Pb zircon age of 510.4 ± 6.5 Ma (Gehrels et al., 2011).

Genesis of the Cambrian–Ordovician basement rocks of the southern Qiangtang and Lhasa terranes is indistinguishable in age with a thermal-tectonic event that resulted in similar age granite body emplacement into the Indian-affi nity Greater Hima-layan rocks (e.g., Stöcklin and Bhattarai, 1977; Stöcklin, 1980; Gehrels et al., 2003, 2006). This event has been attributed to sub-duction of proto-Tethys ocean crust beneath the Gondwana mar-gin, and terrane or microcontinent accretion (Boger and Miller, 2004; Cawood et al., 2007). Perhaps more important, the crust of this age, widely associated with post-Gondwana assembly meta-morphism and magma genesis (Meert, 2003), composes much of the thickened core of the Alpine-Himalayan orogen spatially distributed between the European Alps and the Indochina penin-sula (e.g., Guillot et al., 2002; Gessner et al., 2004; Hassanzadeh et al., 2008; Liu et al., 2009; Ustaömer et al., 2009; Balintoni et al., 2010). This provides indirect evidence for the dependence of crustal rheology on age.

Qiangtang Terrane Supracrustal Rocks

The autochthonous peri-Gondwana basement of the Qiang-tang terrane is inferred to have initially been nonconformably overlain by Carboniferous–Permian shallow-marine strata in most areas. This inference is based on the age of basement rocks, the age of the oldest supracrustal rocks exposed, and the non-conformable relationship between basement rocks and overlying strata in the Lhasa terrane. Devonian strata have been reported in some areas of the Qiangtang terrane (Cheng and Xu, 1986; Leeder et al., 1988). Paleozoic sequences are most widely exposed near the core of the antiformal culmination that exposes the Qiangtang metamorphic belt in the central Qiangtang ter-rane. Outcrops of Devonian strata consist of limestone and marls, minor siltstone, and sandstone (Ding and Wang, 2008), whereas Carboniferous strata consist of quartzite, metasandstone, carbon-ate rocks, widespread glaciogenic diamicites, and are intruded by late Paleozoic basaltic sills (Cheng and Xu, 1986; Li and Zheng, 1993). Late Paleozoic glaciomarine diamicites are considered diagnostic of Gondwana and adjacent terranes because of the extensive polar ice cap centered on Antarctica and southern India during Carboniferous–early Permian time (e.g., Metcalfe, 2006; Blakey, 2008). Permian strata consist of limestone, volcaniclastic sandstone, micrite, and turbiditic sandstone.

A major argument in favor of the in situ formation of the Qiangtang metamorphic belt along the postulated Longmu Co–Shuanghu suture is based on the assumption that Gondwanan affi nity rocks are lacking north of the Qiangtang metamorphic belt. However, glaciomarine diamicite deposits have recently been documented in Carboniferous–lower Permian strata north of the Qiangtang metamorphic belt (e.g., ~34°03′Ν, 84°47′E; Gehrels et al., 2011). This observation suggests that the north-ern part of the Qiangtang was near the Gondwana margin during Carboniferous–early Permian time. Analyses of detrital zircon

TA

BLE

1. S

UM

MA

RY

OF

QIA

NG

TA

NG

TE

RR

AN

E G

EO

LOG

Y

ecnerefeR

noitaterpretnI

T-P ro eg

A noitpircse

D noi ta coL

em a

N Qia

ngta

ng c

ryst

allin

e ba

sem

ent

1 ,2 D

ugue

r R

ange

sou

th

of th

e Q

MB

1 ,2 or

thog

nies

s 1 47

6–47

4 M

a, U

-Pb

Zr

2 384

Ma,

U-P

b Z

r A

utoc

htho

nous

cry

stal

line

base

men

t, so

uth

of th

e Q

MB

1 Pul

len

et a

l. (2

011)

2 Li

et a

l. (2

000)

Q

iang

tang

m

élan

ge

1 Gan

gma,

wes

t 2 G

uoga

njia

nian

, cen

tral

3 G

angm

a C

o, w

est

4 Gom

o C

o, c

entr

al

5 Gem

u, c

entr

al

6 Ron

gma,

cen

tral

7 m

ultip

le

1 gabb

ro o

phio

lite

2 gabb

ro o

phio

lite

3 amph

ibol

ite g

neis

s 4 m

afic

ecl

ogite

5 m

afic

ecl

ogite

6 ep

idot

e bl

uesc

hist

7 m

ica

and

amph

ibol

e

1 467

Ma,

U-P

b Z

r 2 43

8 M

a, U

-Pb

Zr

3 411

Ma,

Lu-

Hf

4 244–

233

Ma,

Lu-

Hf

5 237–

230

Ma,

U-P

b Z

r

6 223

Ma,

Lu-

Hf

7 231–

194

Ma,

40A

r-39

Ar

1,2 op

hiol

ite in

corp

orat

ed in

to m

élan

ge

3 auto

chth

onou

s cr

ysta

lline

bas

emen

t w

ithin

mél

ange

4,

5, 6

timin

g of

HP

met

amor

phis

m

7 timin

g H

P m

etam

orph

ism

of

blue

schi

st b

lock

s an

d ex

hum

atio

n of

mél

ange

to m

id-c

rust

1 Li e

t al.

(200

8)

2 Zha

i et a

l. (2

010)

3 P

ulle

n et

al.

(200

8)

4 Pul

len

et a

l. (2

008)

5 Z

hai e

t al.

(201

1)

6 Pul

len

et a

l. (2

008)

7 K

app

et a

l. (2

000,

200

3); L

i (1

997)

; Pul

len

et a

l. (2

011)

Q

iang

tang

mél

ange

st

ruct

ure

1 Shu

ang

Hu,

eas

t 2 R

ongm

a, c

entr

al

3 Gan

gma,

wes

t 4 G

omo

Co,

cen

tral

5 T

sha

Khu

Chu

, nor

th-

cent

ral

1 FW

mél

ange

–HW

Tria

ssic

str

ata

2 FW

mél

ange

–HW

C

arbo

nife

rous

–Per

mia

n st

rata

3 F

W m

élan

ge–H

W

Car

boni

fero

us

4 FW

mél

ange

–HW

C

arbo

nife

rous

-Per

mia

n st

rata

5 F

W m

élan

ge–H

W P

erm

ian

1 low

-ang

le n

orm

al fa

ultin

g=

post

–ear

liest

Tria

ssic

2,

4, 5

low

-ang

le n

orm

al fa

ultin

g:

Per

mia

n3 lo

w-a

ngle

nor

mal

faul

ting:

C

arbo

nife

rous

1,2,

3,4,

5 Qia

ngta

ng m

etam

orph

ic b

elt

has

bloc

k-in

-mat

rix s

truc

ture

(t

ecto

nic

mél

ange

); e

xpos

ed in

the

foot

wal

l of l

ow-a

ngle

nor

mal

faul

ts

1,2,

3 Kap

p et

al.

(200

3)

4,5 P

ulle

n et

al.

(201

1)

Qia

ngta

ng m

élan

ge

HP

-LT

roc

ks

1 Ron

gma

2 Gem

u, c

entr

al

3 Gem

u, c

entr

al

4 Gan

gma,

wes

t 5 R

ongm

a, c

entr

al

1 eclo

gite

2 eclo

gite

3 eclo

gite

4 blue

schi

st

5 blue

schi

st

1 15.6

–23.

5 kb

ar, 3

45–4

88 °

C

2 20–2

5 kb

ar, 4

82–6

25 °

C

3 20–2

5 kb

ar, 4

10–4

60 °

C

4 ~12

.5 k

bar,

~41

5 °C

5 ~

14 k

bar,

~50

0 °C

1 Li e

t al.

(200

6)

2 Zha

ng e

t al.

(200

6)

3 Zha

i et a

l. (2

012)

4,

5 Kap

p et

al.

(200

3)

Not

e : H

P-L

T—

high

pre

ssur

e, lo

w te

mpe

ratu

re; Q

MB

—Q

iang

tang

met

amor

phi

c be

lt; F

W—

foot

wal

l; H

W—

hang

ing

wal

l; P

-T—

pres

sure

-tem

pera

ture

; Z

r—zi

rcon

. Sup

ersc

ripts

tie

obse

rvat

ions

to r

efer

ence

s.




from Carboniferous–Permian sandstone samples exposed to the south and north of the Qiangtang metamorphic belt yielded strik-ingly similar age probability density functions (e.g., Gehrels et al., 2011; Pullen et al., 2011). Together, the detrital zircon and stratigraphic similarities suggest that the entire Qiangtang terrane was adjacent to the Gondwana margin during Carboniferous time and possibly into early Permian time. However, this evidence does not invalidate the in situ model, but is cause for major refi ne-ment of the model. The possibility of an ocean basin between two Gondwana derived north and south Qiangtang terranes remains valid, although unsupported by the regional geologic observa-tions discussed here.

Mesozoic strata are widely exposed on the limbs of the Qiangtang culmination. Triassic strata unconformably overlie Permian strata. The lower–middle Triassic strata consist mostly of limestone, dolomite, oolitic carbonate, and coarse-grained clastic rocks, whereas the upper Triassic strata consist of thin-bedded limestone, shale, coal, and sandstone (Yin et al., 1988; Zhang et al., 2002; Ding et al., 2013). Lower to middle Jurassic strata consist of thin-bedded limestone and fi ne-grained clastic rocks. Upper Jurassic strata are typifi ed by oolitic limestone and interbedded sandstone (Zhang et al., 2002). Lower Cretaceous strata consist of conglomerate, sandstone, and nonmarine clas-tic rocks associated with growth of the Qiangtang culmination and locally marine limestone along the limbs of the Qiangtang culmination (Pan et al., 2004; Kapp et al., 2005; K.J. Zhang et al., 2012).

Cenozoic rocks in the Qiangtang terrane, west of the Lhasa-Golmud Highway, consist of Eocene–Oligocene volcanic rocks (e.g., Ding et al., 2003; Wang et al., 2008a) and mid-Cenozoic redbeds (Kapp et al., 2005). The volcanic rocks are in most places pristine, gently dipping, and unconformably overlie strongly shortened Jurassic and older strata. The mid-Cenozoic redbeds are exposed in east-west–trending intermontane basins, and are folded in the footwalls of mainly north-dipping thrust faults that exhibit less than a few kilometers of throw. Cenozoic shorten-ing accommodated moderate (~25%) shortening in the central and southern Qiangtang terrane (Kapp et al., 2005), but may be substantially greater in the southern Hoh-Xil thrust belt in the northern Qiangtang terrane (Wang et al., 2008); although most of the structural relief on the Qiangtang antiformal culmination was generated prior to mid-Cretaceous time, minor growth of the culmination continued during Cenozoic time.

Qiangtang Metamorphic Belt

The metamorphic belt consists of a block-in-matrix struc-ture and has been widely interpreted as a tectonic mélange (e.g., Li et al., 1995; Kapp, 2001; Kapp et al., 2000; Wang et al., 2009; Liang et al., 2012). The surface expression of the Qiangtang metamorphic belt is extensive, the same order of magnitude as the Franciscan complex of western North Amer-ica (e.g., Jennings, 1977). Exposure of the Qiangtang meta-morphic belt is >600 km east–west and ~150 km north–south.

Metamorphic exposures have been mapped within 40 km of the Jinsha suture to the north and mélange rocks are inferred to underlie much of the northern Qiangtang terrane based on geophysical observations (Fig. 1; e.g., Haines et al., 2003; Pul-len et al., 2011). Relatively undeformed blocks of metaigneous and metasedimentary rocks in the Qiangtang metamorphic belt exhibit greenschist, blueschist, eclogite, and amphibolite facies mineral assemblages (Cheng and Xu, 1986; Kapp et al., 2000, 2003; Li et al., 2006b; Lu et al., 2006; Wang et al., 2006; Zhang et al., 2006a). A wide range of lithologies has been reported for the Qiangtang metamorphic belt; these include metabasalt (including pillow basalt), peridotite, gabbro, metasedimentary schist (±garnet), mafi c schist, intermediate-mafi c gneiss, gran-itoid (diorite), marble, quartzite, slate, and chert (Cheng and Xu, 1986; Li and Zheng 1993; Kapp et al., 2003; Zhang et al., 2006b). Less-deformed blocks, which are also generally more resistant to weathering, are typically on the scale of 10–100 m. This large spatial scale and the presence of lithologies associ-ated with ophiolite units may be one reason why the mélange was initially thought to have formed in situ (Li, 1987). Com-plete ophiolitic sequences, however, have not been documented in the Qiangtang metamorphic belt (Zhu et al., 2012). The con-tacts between the metamorphic belt and overlying supracrustal rocks are generally low angle, and were initially mapped as unconformities (e.g., Cheng and Xu, 1986). These contacts have since been shown to be major Late Triassic–Early Jurassic domal low-angle normal faults (Kapp et al., 2000, 2003; Pullen et al., 2011). Some have argued that the Qiangtang metamor-phic belt was eroding by Early Triassic time (e.g., Zhang et al., 2006a); however, this postulation is inconsistent with the timing of HP metamorphism, the timing of exhumation to mid-crustal levels inferred from 40Ar/39Ar data, and the age of normal fault-ing (e.g., Kapp et al., 2003; Pullen et al., 2008, 2011).

Petrographic analysis and thermobarometric investigations suggest that the eclogite facies blocks reached pressures in the 13–25 kbar range at temperatures in the range of 480–625 °C (Table 1; Li et al., 2006b; Zhai et al., 2011). Although the pres-sure estimates plot near the coesite stability fi eld, coesite has not been reported in these eclogite facies rocks. Other workers have favored more conservative estimates in the range of 13–16 kbar (e.g., Zhang et al., 2006a).

A garnet-amphibole gneiss block from the metamorphic belt yielded U-Pb zircon ages overlapping with the peri-Gondwana autochthonous crystalline basement of the Lhasa and Qiangtang terranes (Kapp et al., 2003), and is interpreted to be a basement sliver that was tectonically eroded from the upper plate and incor-porated into the mélange. A Lu-Hf isochron dating of garnet-amphibole gneiss from the mélange yielded an Early Devonian (411.1 ± 4.3 Ma) age (Table 1; Pullen et al., 2008). Radiogenic isotopic dating of blocks exhibiting blueschist and eclogite facies mineral assemblages has yielded Middle Triassic ages. Lu-Hf isochron dating of mafi c eclogite yielded ages of 244 ± 11 Ma and 233 ± 13 Ma; the same technique applied to a garnet blue-schist yielded an age of 223.4 ± 4.5 Ma (Pullen et al., 2008). U-Pb



78 Pullen and Kapp

dating of zircon from eclogite facies rocks yielded weighted mean ages of 237 ± 4 Ma and 230 ± 4 Ma (Zhai et al., 2011).

The underthrust model of Kapp et al. (2000) speculated that the Qiangtang mélange is composed of Hoh-Xil (Songpan-Ganzi) turbidites deposited into the Paleo-Tethys Ocean north of the Jinsha suture and tectonically eroded Qiangtang affi nity rocks, before the timing of HP metamorphism of mélange rocks was well constrained. Recent work has asserted that the Qiang-tang mélange could not include Songpan-Ganzi turbidites (e.g., Zhang et al., 2011; Zhu et al., 2012) because the deep-water siliciclastic turbiditic rocks were primarily deposited during the Late Triassic (Zhou and Graham, 1996; Chang, 2000; Weislogel et al., 2010). Zhang et al. (2011) and Zhu et al. (2012) errone-ously interpreted this to mean that the Kapp et al. (2000) under-thrust model is invalid in its entirety. In addition to placing addi-tional constraints on the timing of HP metamorphism, Pullen et al. (2008) used U-Pb geochronology on detrital zircon to show that ages for metasedimentary samples from the mélange are consistent with (1) Carboniferous–Triassic supracrustal rocks of the Qiangtang terrane and (2) Paleo-Tethys affi nity rocks. This fi nding strengthens the underthrust model by showing that the mélange is composed of both Qiangtang affi nity rocks and Paleo-Tethys affi nity rocks deposited north of the Jinsha suture, as pre-dicted in Kapp et al. (2000).

The oldest 40Ar/39Ar ages reported for the Qiangtang mélange are in the range of 282–275 Ma for glaucophane; how-ever, the majority of mica and amphibole ages are in the range of 231–214 Ma and some are as young as 194 Ma (Kapp et al., 2000, 2003; Li, 1987; Li et al., 2006b; Pullen et al., 2011; Zhai et al., 2011). The wide range of 40Ar/39Ar from the mélange raises the possibility of longer term suprasubduction mélange forma-tion beneath the Qiangtang terrane than would be suggested by the more narrowly defi ned Lu-Hf and U-Pb zircon ages from eclogite- and blueschist-bearing rocks. The broad geographic distribution of Middle Triassic eclogite and blueschist facies blocks suggests that HP-LT metamorphism occurred during this more narrowly defi ned time and was followed closely in time by Late Triassic–Early Jurassic exhumation from lower crustal levels by normal faulting.

Permian-Jurassic Igneous Rocks of the Qiangtang Terrane

Igneous intrusions within Phanerozoic strata of the Qiang-tang terrane are widespread, albeit volumetrically small com-pared to the Gangdese batholith of the Lhasa terrane (Coulon et al., 1986; Harris et al., 1988; Pan et al., 2004). Diabase exposed <70 km northwest of Qiangtang metamorphic rock exposures yielded U-Pb zircon ages of 234 ± 4 Ma and 223 ± 3 Ma (Zhang et al., 2011). Triassic intermediate to felsic composition gran-itoids, including leucogranites, are exposed within the hang-ing walls of the Qiangtang metamorphic belt exposures; these range in age from 220 to 204 Ma (Kapp et al., 2003; Pullen et al., 2011). Crystalline rocks of Early–Middle Jurassic age have not been widely reported in the central Qiangtang terrane; however,

several plutons of felsic composition in the range of 155–118 Ma have been reported here and to the south, including along the Bangong suture (Kapp et al., 2005, 2007; Pullen et al., 2011). Granitoids in the range of 155–147 Ma have been attributed to northward subduction of oceanic lithosphere beneath the south-ern Qiangtang terrane during closure of the Meso-Tethys (Pullen at al., 2011).

Triassic volcanic rocks with wide-ranging compositions have been reported within, adjacent to, and north of the Qiangtang met-amorphic belt near the Jinsha suture. Adakitic, high-magnesium andesitic, and Nb-enriched basaltic rocks in the range of 236–219 Ma have been reported in the eastern Qiangtang terrane, >200 km east of the most eastern exposure of the Qiangtang meta-morphic belt, near Tuotuohe along the Jinsha suture (Fig. 1; Wang et al., 2008b). These rocks have been attributed to southward subduction of young (i.e., late Permian–Early Triassic) oceanic crust beneath the Jinsha suture. Workers have argued that the Nb-enriched basaltic rocks are inconsistent with underthrust model for the Qiangtang metamorphic belt (e.g., Wang et al., 2008b). How-ever, regardless of chemical composition and plausible modes of formation, the locations of these basaltic rocks with respect to the Qiangtang metamorphic belt do not provide evidence sup-porting or refuting either end-member model describing the for-mation of the metamorphic belt. Variable dips in the southward-subducting oceanic lithosphere along the Jinsha suture beneath the Qiangtang terrane could explain the differences in timing and composition of Triassic–Jurassic magmatism in the Qiangtang terrane, and why the Qiangtang metamorphic belt is limited to the central Qiangtang terrane. The magmatic history and position of the Qiangtang metamorphic belt favor low-angle subduction beneath the central Qiangtang terrane and more steeply dipping subduction beneath the Tuotuohe area of the eastern Qiangtang terrane. Another suite of Late Triassic–Early Jurassic volcanic rocks trending east-west in the central Qiangtang terrane are consistent with basaltic to rhyolitic bimodal volcanism (Fu et al., 2010). These rocks range in age from 236 to 177 Ma, based on U-Pb zircon and 40Ar/39Ar geochronologic studies (e.g., Bai et al., 2005; Wang et al., 2008b; Zhang et al., 2011). Mafi c rocks typically yield positive ε

Nd(t) values (-1.08–3.88) and high La/Nb

values, suggesting little contamination by the central Qiangtang crust, whereas the felsic rocks typically yielded negative Nb and Eu anomalies, and typically negative ε

Nd(t) values (0.87–−11.57;

Fu et al., 2010; Zhang et al., 2011). Geochemical results for the basaltic rocks favor an intraplate setting with a component of continental crustal contamination; these rocks have been inter-preted to be consistent with ocean island basalt–like signatures. Rocks with ocean island basalt–like geochemical signatures have also been reported as blocks within the Qiangtang mélange (Zhang et al., 2006b). This geochemistry, the spatial distribution around the Qiangtang metamorphic belt, and the largely younger crystallization ages suggest that a much different geodynamic process generated this suite of volcanic rocks compared with the Tuotuohe suite. Workers have attributed magma genesis of the Late Triassic–Early Jurassic central Qiangtang volcanic suite to




(1) break-off of the oceanic lithosphere subducting northward beneath the hypothetical Longmu Co–Shuanghu suture (Zhang et al., 2011); or (2) an intracontinental rift (Fu et al., 2010). Although rift-related sequences have not been widely documented in the upper Triassic–lower Triassic strata of the Qiangtang terrane, the latter hypothesis is conceptually consistent with the model put forth in Pullen et al. (2011) favoring tectonic erosion and underplat-ing of the Qiangtang mélange by southward subduction beneath the Jinsha suture. This model argues for rollback of Paleo-Tethys oceanic lithosphere during the Late Triassic beneath the central Qiangtang terrane, tectonic thinning of the Qiangtang terrane crust by detachment faulting, and magma genesis. Such a sce-nario may have occurred during Basin and Range extension in western North America (e.g., Bradshaw et al., 1993; Dickinson, 2002; Schellart et al., 2010).

Geophysical and Xenolith Studies

The Qiangtang metamorphic belt exposed at the surface is inferred to extend to depth and be voluminous in the subsur-face of the central and northern Qiangtang terrane (Fig. 1; Kapp et al., 2000, 2003; Haines et al., 2003). Geophysical data show that the dominantly pre–mid-Cretaceous antiformal structural culmination cored by the Qiangtang metamorphic extends to >40 km depth in the Qiangtang crust and is characterized by high conductivity and low seismic velocity zones (Wei et al., 2001; Shi et al., 2004; Klemperer, 2006). Regardless of how the Qiangtang mélange formed, we infer that much of the middle and lower crust of the central and northern Qiangtang is com-posed of silica-rich metasedimentary matrix tectonic mélange rock, which locally may be undergoing partial melting or being intruded by melts. If valid, this implies most of the Cambrian–Ordovician peri-Gondwana autochthonous crystalline basement is restricted to south of the surface exposure of the Qiangtang metamorphic belt (Pullen et al., 2011). If this high-conductivity zone is in fact molten silica and fl uid-rich rocks of the Qiangtang mélange, as suggested, this crustal structure would be diffi cult to reconcile within the framework of the in situ model for the forma-tion mélange (i.e., Li et al., 1995) without signifi cant (>250 km) southward horizontal translation of Qiangtang mélange rocks in the middle and lower crust relative to the upper crust. If the antiformal culmination accurately represents the subsurface distribution of Qiangtang mélange, then more than one-third of the inferred crystalline lower crust of the Qiangtang terrane was tectonically eroded and possibly incorporated into a tectonic mélange, and underplated along with quartz-rich metasedimen-tary rocks. The presence of this silica-rich lower crust has major implications for the rheological structure of the central Tibetan crust (e.g., Ranalli and Murphy, 1987; Rudnick and Fountain, 1995; Clark and Royden, 2000).

Geochemical analysis of Cenozoic volcanic rocks and included xenoliths provides valuable petrogenetic information about the middle and lower crust of the Qiangtang terrane. Most Cenozoic volcanic rocks exposed in the Qiangtang terrane are

shoshonitic in composition, ranging from 51 to 0 Ma with some Paleocene–Oligocene alkaline–calc-alkaline rocks with adakite geochemical signatures (Roger et al., 2000; Ding et al., 2003; Wang et al., 2008a, and references therein). The most volumi-nous eruptions of shoshonitic lavas are in the central and east Qiangtang terrane and most occurred during the past ~15 m.y. (Turner et al., 1996; Williams et al., 2004; Chung et al., 2005); however, some shoshonitic rocks predate this, and are in the range of 31–29 Ma (Ding et al., 2003). Eocene peraluminous rocks from the adakitic suite have been attributed to partial melt-ing of a metasedimentary-rich lower crust of the Qiangtang (e.g., Wang et al., 2008a); this hypothesis is consistent with the presence of metasedimentary xenoliths in Cenozoic volcanic rocks exposed in the northern Qiangtang and substantiated end- member models for the formation of the Qiangtang metamorphic belt (e.g., Li et al., 1995; Hacker et al., 2000; Kapp et al., 2000; Ding et al., 2007). However, the affi nity of these metasedimen-tary xenoliths and the time when the sedimentary protolith was incorporated into the Qiangtang lower crust are uncertain, and may refl ect Cenozoic underthrusting of the Hoh-Xil-Songpan-Ganzi complex beneath the Qiangtang terrane along the Jinsha suture (Hacker et al., 2000).

DISCUSSION

Underthrust Model

Within the framework of the underthrust model the Qiang-tang metamorphic belt consists of tectonic mélange underplated through low-angle southward subduction beneath the Qiang-tang terrane during the Middle Triassic (Kapp et al., 2000). The mélange consists of rock tectonically eroded from the upper plate of the Gondwanan affi nity Qiangtang terrane, Paleo-Tethys oce-anic crust, and sediment deposited on the Paleo-Tethys oceanic crust, and possibly continental crust associated with a Paleo-Tethys arc terrane (Pullen et al., 2008). Southward subduction of Paleo-Tethys oceanic lithosphere along the Jinsha suture beneath the Qiangtang terrane had initiated by Middle Triassic time. Sub-duction at a shallow angle beneath the central Qiangtang terrane is inferred to explain subduction erosion of the upper plate and underplating of the Qiangtang mélange in an intercontinental set-ting (Kapp et al., 2000; Pullen et al., 2011). This shallow subduc-tion angle may have been the manifestation of the partial sub-duction of a Paleo-Tethys arc terrane beneath the north-central Qiangtang terrane, a nonsubducted remnant of which may be the Yidun arc complex exposed along the Jinsha suture in eastern Tibet (Fig. 1; Pullen et al., 2008). The mélange was exhumed in an intercontinental setting by normal faulting within the cen-tral Qiangtang terrane following the closure of the Jinsha suture (Kapp et al., 2000). Rollback of the southward-subducting Paleo-Tethys oceanic lithosphere occurred following the arc-continent collision between the Yidun arc and Qiantang terrane, and pos-sible partial subduction of Yidun along the Jinsha suture. This rollback scenario explains the extensional exhumation of the



80 Pullen and Kapp

Qiangtang metamorphic belt and structural relationship between the Qiangtang mélange rocks and supracrustal rocks of the Qiangtang terrane (Pullen et al., 2008, 2011).

End-Member Models: Questions, Contradictions, and Misconceptions

Lacking a clearly defi ned throughgoing suture in the cen-tral Qiangtang terrane (Fig. 4A), one of the strongest arguments in favor of the in situ Longmu Co–Shuanghu suture model is the documentation of warm-water faunal assemblages in upper Paleozoic strata exposed north and east of the Qiangtang meta-morphic belt and cold-water fauna in coeval strata to the south (e.g., Li et al., 1995). Kapp (2001) pointed out that the faunal dif-ferences occur at differing stratigraphic levels, with warm-water faunas exposed within lower Carboniferous and upper Permian strata in the northern Qiangtang terrane and cold-water faunas exposed within upper Carboniferous–lower Permian strata (e.g., Li and Zheng, 1993). In Kapp (2001) it was suggested that this difference could refl ect the paleogeographic evolution of a single Qiangtang terrane. We further argue that this change from warm-water to cold-water and back to warm-water assemblages may refl ect a confl uence between global atmospheric circulation and paleogeography. A drawdown in atmospheric CO

2 concentra-

tions that began in Late Devonian time and reached a minimum during middle–late Carboniferous time together with Gond-wana movement toward the south pole are thought to signify the most severe glaciation during the entire Phanerozoic (e.g., Crowell and Frakes, 1970; Crowell, 1978; Veevers and Pow-ell, 1987; Beerling, 2002). Coincidentally the global tempera-ture minimum for this late Paleozoic glacial event, refl ecting a >8 °C decrease in mean global temperatures, overlaps temporally with the documented cold-water faunas exposed in the southern Qiangtang terrane (e.g., Crowley, 1999; Berner and Kothavala, 2001; Came et al., 2007). In addition, this scenario is consistent with cold-water faunas documented elsewhere in Gondwana during late Carboniferous–early Permian time (e.g., Dickins, 1992, 1996). These observations coupled with the recent docu-mentation of glaciomarine diamicite deposits in Carboniferous–lower Permian strata north of the Qiangtang metamorphic belt, and the strikingly similar detrital zircon age probability density functions for upper Paleozoic–Triassic strata across the Qiang-tang terrane, suggest that the entire Qiangtang terrane was along the margin of Gondwana until early Permian time (i.e., Gehrels et al., 2011). The presence of warm-water faunas in upper Perm-ian strata of the Qiangtang terrane, possibly deposited before the end of the major late Paleozoic glacial event, may refl ect the rifting of the Qiangtang terrane from the margin of Gond-wana and its translation to tropical latitudes in the Tethys Ocean by late Permian time. The possible shift to warmer water fauna assemblages prior to the end of the Carboniferous-Permian gla-cial is consistent with intense meridional temperature gradients during recent glacial periods (e.g., Raymo et al., 1992; Calvo et al., 2001).

There is little agreement about the location of the hypo-thetical Longmu Co–Shuanghu suture (Fig. 4A). Unlike sutures between other accreted terranes in Tibet, the Longmu Co– Shuanghu suture is not defi ned by ophiolitic belts or by the close spatial juxtaposition of clearly distinct terranes. Rather, the position of the hypothetical suture is imprecisely defi ned by the position of the Qiangtang metamorphic belt (e.g., Li and Zheng, 1993; Li et al., 2006a; Zhang and Tang, 2009; Yang et al., 2011; Zhai et al., 2011; Zhang et al., 2011). The observation that the Qiangtang metamorphic belt is exposed in the footwalls of low-angle normal faults with late Paleozoic–Triassic age hanging-wall strata everywhere the belt has been mapped in detail limits the possible number of scenarios describing the position of the hypothetical suture within the framework of the in situ model (Fig. 4B). For example, if calling upon subduction of oceanic crust northward beneath the hypothetical Longmu Co–Shuanghu suture and the exhumation of the Qiangtang metamorphic belt structurally along normal faults cutting the overriding plate, as detailed structural mapping shows, the hypothetical Longmu Co–Shuanghu suture would be south, not north, of all surface expo-sures of the Qiangtang metamorphic belt, as workers favoring the in situ model show (Fig. 4A). The exception to this would be ero-sion of the entire upper plate above the Qiangtang metamorphic belt; if this occurred starting in Middle Triassic time, then the hypothetical Longmu Co–Shuanghu would be north of the most northern exposures of the Qiangtang metamorphic belt and the metamorphic belt would be exposed as klippen-like structures above the subducting plate (i.e., the southern Qiangtang terrane). This is inconsistent, however, with the geologic observations of the Qiangtang metamorphic belt (Fig. 4B). If wedge extrusion (e.g., Maruyama et al., 1994, 1996) or channel fl ow models (e.g., Cloos, 1982) were applied in this scenario to explain the exhu-mation of the Qiangtang metamorphic belt, the belt would be exposed structurally or stratigraphically above pre–Late Triassic Qiangtang rocks along the southern edge of the metamorphic belt in the hanging walls of Late Triassic thrust faults. However, geo-logic mapping has not identifi ed such relationships (e.g., Kapp et al., 2000, 2003, 2005; Pan et al., 2004, 2012; Pullen et al., 2011).

Whole-rock geochemical analyses of late Paleozoic–early Mesozoic metasiliciclastic and metabasaltic rocks sampled from along the Jinsha suture zone and from the Qiangtang metamor-phic belt have been interpreted to be chemically distinct suites, and these geochemical dissimilarities are thought to invalidate the Kapp et al. (2000) underthrust (Zhang et al., 2006b). Samples from along the Jinsha suture are mapped as Middle and Late Tri-assic age; however, a precise age assignment is fundamentally important here. The vast majority of the siliciclastic rocks depos-ited north of the Jinsha suture in the Hoh-Xil-Songpan-Ganzi basin are Late Triassic and therefore too young to be incorpo-rated into the Qiangtang mélange (e.g., Chang, 2000; Yin, 2003; Weislogel, 2008). In Pullen et al. (2008), it was shown that rocks incorporated in the mélange have detrital zircon age probability density functions similar to the supracrustal rocks of the Qiang-tang terrane and to the ages of pre–Middle Triassic rocks north




Figu

re 4

. (A

) Si

mpl

ifi ed

reg

iona

l geo

logi

c m

ap. P

ropo

sed

posi

tions

of

the

Lon

gmu

Co–

Shua

nghu

sut

ure

are

show

n as

thic

k da

shed

line

s. (

B)

Sche

mat

ic c

ross

sec

tion

desc

ribi

ng th

e in

situ

fo

rmat

ion

of th

e Q

iang

tang

met

amor

phic

bel

t. N

orth

war

d un

dert

hrus

ting

of th

e Q

iang

tang

met

amor

phic

bel

t ben

eath

the

hypo

thet

ical

Lon

gmu

Co–

Shua

nghu

sut

ure

resu

lts in

the

sutu

re to

th

e so

uth

of th

e Q

iang

tang

mél

ange

. Pz—

Pale

ozoi

c; M

z—M

esoz

oic;

K-N

—C

reta

ceou

s–N

eoge

ne.

AB



82 Pullen and Kapp

of the Jinsha suture in the Paleo-Tethys realm; however, these samples are distinguishable from the Hoh-Xil-Songpan-Ganzi turbiditic deposits. Sampling Hoh-Xil-Songpan-Ganzi turbiditic deposits is therefore not a valid test of the Kapp et al. (2000) model as modifi ed by Pullen et al. (2008) after the timing HP metamorphism became better understood. In addition, age prob-ability density functions of detrital zircon samples from the Qiangtang metamorphic belt attributed to the Paleo-Tethys realm have not been recognized in the supracrustal strata of the Qiang-tang north or south of the Qiangtang metamorphic belt, as would be the observation if the Qiangtang terrane is composed of two distinct continental terranes with the Qiangtang metamorphic belt exposed between them (e.g., Pullen et al., 2008, 2011; Geh-rels et al., 2011). We speculate that the geochemical differences interpreted in Zhang et al. (2006b) may better refl ect sampling bias rather than deviation from the geology implicit in the Kapp et al. (2000) model. Analysis of samples along the Jinsha suture that predate formation of the Qiangtang mélange may provide a more legitimate test of the underthrust model.

Implications of the Underthrust Model

The decrease in crustal thickness from the Lhasa terrane (~70 km) to the Qiangtang terrane (~60 km) can be explained by Pratt isostasy, or Airy isostasy with thermal compensation in the mantle. Workers have argued that this south-to-north thinning of the crust refl ects an increasing deviation from Airy isostasy north of the surface expression of the Bangong suture in Tibet (Owens and Zandt, 1997; Nábělek et al., 2009; Tseng et al., 2009). This deviation has been attributed to thermal isostasy with the mantle; however, a simple isostatic equilibrium model with a component of Pratt isostasy could also account for some of the apparent devi-ation (Fig. 5). The implications of silica-rich mélange composing the middle and lower crust of the Qiangtang terrane in lieu of a crystalline basement of mafi c composition suggests that Pratt isostasy may not need to be entirely discounted to explain some of the difference in crustal thickness with the Lhasa terrane. We speculate a combination of thermal isostatic composition, justi-fi ed by the position of Indian lower crust and mantle lithosphere beneath southern Tibet and the anomalously high temperatures inferred for the upper mantle beneath north Tibet, and Pratt isostasy may best explain the elevation, crustal thicknesses, and inferred lithotectonic structure of the Qiangtang terrane.

Melt forming within silica-rich middle and lower crust in the Qiangtang terrane provides one explanation for the postulated zone of low-viscosity crust capable of fl owing eastward to build the high topography in eastern Tibet (e.g., Clark and Royden, 2000; Shen et al., 2001; Clark et al., 2005). However, viscosi-ties of molten crust are typically much lower (104–1015 Pa s; e.g., Nicolas and Ildefonse, 1996; Clemens and Petford, 1999) than the viscosities assigned to the fl owing lower crust of the central Tibetan Plateau (2 × 1018 Pa s). Molten crust, if present in the Tibetan crust as geophysical experiments suggest (e.g., Wei et al., 2001; Klemperer, 2006), would fl ow more easily (i.e., higher

velocities or similar velocities at much lower pressure gradients), with all other parameters being the same, than the modeled solid-state fl ow of the lower crust. Paradoxically, the distribution of geophysical features consistent with melt (Wei et al., 2001; Shi et al., 2004) mimics the antiformal structure of the Qiangtang crust that developed during late Mesozoic time. This implies that the lower Qiangtang crust is not horizontally stratifi ed, as depicted by channel-fl ow model simulations of the lower crust. These observations are not consistent with the channelized solid-state fl ow of viscous lower crust from beneath the central Tibetan Plateau and imply that channel-fl ow models incorrectly assume the width, shape, and viscosity of a low-viscosity zone within the Qiangtang Tibetan crust. These possible inconsistencies pro-vide an opportunity for reexamination and/or refi nement of chan-nel fl ow models to better fi t the geologically and geophysically resolved lithotectonic structure of central Tibet.

The lithosphere beneath the northern Qiangtang terrane may be no older than ca. 230 Ma, the approximate timing of blueschist and eclogite metamorphism within the Qiangtang mélange, a result of earlier fl at-slab subduction and tectonic erosion. This Mesozoic lithospheric removal may explain why this area was a locus of Paleogene shortening of the upper crust following the India-Asia collision (e.g., Fenghou Shan fold and thrust belt; Gangma Co–Shuang Hu thrust system). Older crust may be made

Figure 5. Hypothetical simple isostatic model describing the elevation and crustal thicknesses of the Lhasa and Qiangtang terranes. This mod-el, showing low-density mélange-type rocks composing the lower crust of the central and southern Qiangtang terrane, provides one possible explanation for the 10 km of relief on the Moho between the Lhasa and Qiangtang terranes (e.g., Nábělek et al., 2009; Tseng et al., 2009).




rheologically stronger by processes like mafi c underplating, fl uid depletion, and/or stabilization of cold mantle lithosphere (i.e., Molnar and Tapponnier, 1981; Kusznir and Park, 1987; Burov and Diament, 1995; Neil and Houseman, 1997). The relatively young age of the autochthonous crystalline peri-Gondwana base-ment of the Qiangtang terrane relative to the timing of subduction along the Jinsha suture beneath the Qiangang terrane during the early Mesozoic may have enhanced the processes of subduction erosion postulated in Kapp et al. (2003). In addition to a gen-eral dependence on age, the lithotectonic structure of continental lithosphere profoundly infl uences the distribution of deformation (e.g., Houseman et al., 1981; Hollister and Crawford, 1986). This lithotectonic structure of the Qiangtang terrane is strikingly dif-ferent from the conventional layer-cake structure of continental crust (Fig. 5; e.g., Rudnick and Fountain, 1995; van der Pluijm and Marshak, 2004). The presence of silica-rich mélange rock in the lower and middle crust implies a vast rheologically weak zone within the Tibetan crust. Whether this zone represents chan-nelized fl owing lower crust is debatable, as outlined here. We argue, as have many, that the Tibetan lithosphere was precondi-tioned by its relatively young age and lithotectonic structure to form the largest active orogenic plateau on Earth.

CONCLUSIONS

Studies claiming to challenge the underthrust model are not substantiated. The strongest challenge has been the identifi cation of cold-water faunas in late Paleozoic strata south of the Qiang-tang metamorphic belt and warm-water faunas in late Paleozoic strata north of the Qiangtang terrane (Wang and Mu, 1 983; Fan, 1985, 1988; Li, 1987; Li and Zheng, 1993; Chen and Xie, 1994). However, these disparities are at different stratigraphic levels (Kapp, 2001), overlap with the global Carboniferous– Permian glacial event, and refl ect the paleolatitude of the Qiangtang ter-rane during late Permian time. In addition, the genesis of volcanic suites of adakitic, high-magnesium andesitic, and Nb-enriched basaltic rocks is thought to require the interaction between a subducting ocean slab and sediment package with the astheno-spheric wedge above a subducting slab (Defant and Drummond, 1990; Kepezhinskas et al., 1996; Drummond et al., 1996; Mar-tin et al., 2005). Studies suggesting the presence of a suite of Middle–Late Triassic volcanic rocks with a trinity of composi-tions exposed along the Jinsha suture in order to challenge the underthrust model do not account for the geometry of oceanic lithosphere subducting southward beneath the Qiantang terrane. Slab dips may vary greatly along strike in convergent margin systems. These variations control the timing, composition, and distribution of magmatism throughout the upper plate, as well as controlling subduction erosion and underplating in at the base of the upper plate (von Huene and Scholl, 1991; Kay et al., 2005; Haschke et al., 2006).

We conclude that the underthrust model presented in Kapp et al. (2000), and later modifi ed after the timing of HP meta-morphism and provenance of Qiangtang metasedimentary

strata became more resolved (e.g., Pullen et al., 2008, 2011), best explains our current understanding of the Qiangtang geo-logic record. This model reconciles the following observations: (1) detrital zircon age probability distributions are nearly indis-tinguishable for late Paleozoic–Triassic strata across the Qiang-tang terrane (Gehrels et al., 2011); (2) glaciomarine diamic-tites are exposed in Carboniferous–early Permian strata north and south of the Qiangtang metamorphic belt (Gehrels et al., 2011); (3) lithologies exposed within the mélange are similar to the pre-Jurassic supracrustal rocks of the Qiangtang terrane (Kapp et al., 2003; Pullen et al., 2011); (4) mélange rocks of the Qiangtang metamorphic belt are exposed in the footwalls of low-angle normal faults, structurally beneath Carboniferous–Triassic Qiangtang terrane strata (Kapp et al., 2000, 2003; Pullen et al., 2011); (5) blocks exhibiting blueschist and eclogite facies min-eral assemblages equilibrated at high pressure in Middle Triassic time (Pullen et al., 2008; Zhai et al., 2011); (6) the mélange was exhumed to mid-crustal levels by Late Triassic–Early Jurassic time (Li, 1987; Kapp et al., 2000, 2003; Pullen et al., 2011); and (7) the position of the south- and north-dipping antiformal low-velocity, high-conductivity zone beneath the surface expression of the Qiangtang metamorphic belt (Wei et al., 2001; Shi et al., 2004; Klemperer, 2006).

ACKNOWLEDGMENTS

This material is based upon work supported by U.S. National Science Foundation grants EAR-1118525 and EAR-0438120. We thank our friend and collaborator Ding Lin of the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, for more than a decade of assistance.

REFERENCES CITED

Allégre, C.J., Courtillot, V., Tapponnier, P., Hirn, A., Mattauer, M., Coulon, C., Jaeger, J.J., Achache, J., Scharer, U., Marcoux, J., Burg, J.P., Girardeau, J., Armijo, R., Gariepy, C., Gopel, C., Li, T.D., Xiao, X.C., Chang, C.F., Li, G.Q., Lin, B.Y., Teng, J.W., Wang, N.W., Chen, G.M., Han, T.L., Wang, X.B., Den, W.M., Sheng, H.B., Cao, Y.G., Zhou, J., Qiu, H.R., Bao, P.S., Wang, S.C., Wang, B.X., Zhou, Y.X., and Ronghua, X., 1984, Struc-ture and evolution of the Himalaya–Tibet orogenic belt: Nature, v. 307, p. 17–22, doi:10.1038/307017a0.

Bai, Y.S., Li, L., Niu, Z.J., and Cui, J.L., 2005, Characteristics and tectonic set-ting of Erlongba Formation volcanic rocks in Geladandong area of central Qiangtang: Acta Geoscientica Sinica, v. 26, p. 113–120.

Balintoni, I., Balica, C., Ducea, M.N., Hann, H.P., and Sabliovschi, V., 2010, The anatomy of a Gondwanan terrane: The Neoproterozoic–Ordovician basement of the pre-Alpine Sebeş–Lotru composite terrane (South Car-pathians, Romania): Gondwana Research, v. 17, p. 561–572, doi:10.1016/j.gr.2009.08.003.

Bao, P., Xiao, X., and Wang, J., 1996, Geochemistry and genesis of the Dongcuo ophiolite in Tibet, in Zhang, Q., ed., Study on Ophiolites and Geodynam-ics: Beijing, China, Geological Publishing House, p. 190–194.

Bao, P.S., Xiao, X.C., Wang, J., Li, C., and Hu, K., 1999, The blueschist belt in the Shuanghu region, central-northern Tibet, and its tectonic implications: Acta Geologica Sinica, v. 73, p. 302–314.

Baxter, A.T., Aitchison, J.C., and Zyabrev, S., 2009, Radiolarian age constraints on Mesotethyan ocean evolution, and their implications for development of the Bangong–Nujiang suture, Tibet: Journal of the Geological Society, v. 166, p. 689–694, doi:10.1144/0016-76492008-128.



84 Pullen and Kapp

Beerling, D.J., 2002, Low atmospheric CO2 levels during the Permo- Carboniferous

glaciations inferred from fossil lycopsids: National Academy of Sciences Pro-ceedings, v. 99, p. 12567–12571, doi:10.1073/pnas.202304999.

Berner, R.A., and Kothavala, Z., 2001, GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time: American Journal of Science, v. 301, p. 182–204, doi:10.2475/ajs.301.2.182.

Blakey, R.C., 2008, Gondwana paleogeography from assembly to breakup—A 500 m.y. odyssey, in Fielding, C.R., et al., eds., Resolving the Late Paleo-zoic Ice Age in Time and Space: Geological Society of America Special Paper 441, p. 1–28, doi:10.1130/2008.2441(01).

Boger, S.D., and Miller, J.M., 2004, Terminal suturing of Gondwana and the onset of the Ross-Delamerian orogeny: The cause and effect of an Early Cambrian reconfi guration of plate motions: Earth and Planetary Sciences Letters, v. 219, p. 35–48, doi:10.1016/S0012-821X(03)00692-7.

Bradshaw, T.K., Hawkesworth, C.J., and Gallagher, K., 1993, Basaltic vol-canism in the Southern Basin and Range: No role for a mantle plume: Earth and Planetary Science Letters, v. 116, p. 45–62, doi:10.1016/0012-821X(93)90044-A.

Burov, E.B., and Diament, M., 1995, The effective elastic thickness (Te) of continental lithosphere: What does it really mean?: Journal of Geophysi-cal Research, v. 100, p. 3905–3927, doi:10.1029/94JB02770.

Burrett, C.F., 1974, Plate tectonics and the fusion of Asia: Earth and Planetary Science Letters, v. 21, p. 181–189, doi:10.1016/0012-821X(74)90052-1.

Calvo, E., Villanueva, J., Grimalt, J.O., Boelaert, A., and Labeyrie, L., 2001, New insights into the glacial latitudinal temperature gradients in the North Atlantic. Results from UK’37 sea surface temperatures and terrig-enous inputs: Earth and Planetary Science Letters, v. 188, p. 509–519, doi:10.1016/S0012-821X(01)00316-8.

Came, R.E., Eiler, J.M., Veizer, J., Azmy, K., Brand, W., and Weidman, C.R., 2007, Coupling of surface temperatures and atmospheric CO2 concentra-tions during the Palaeozoic Era: Nature, v. 449, p. 198–201, doi:10.1038/nature06085.

Cawood, P.A., Johnson, M.R.W., and Nemchin, A.A., 2007, Early Palaeozoic orogenesis along the Indian margin of Gondwana: Tectonic response to Gondwana: Earth and Planetary Science Letters, v. 255, p. 70–84, doi:10.1016/j.epsl.2006.12.006.

Chang, C., Chen, N., Coward, M.P., Deng, W., Dewey, J.F., Gansser, A., Har-ris, N.B.W., Jin, C., Kidd, W.S.F., Leeder, M.R., Li, H., Lin, J., Liu, C., Mei, H., Molnar, P., Pan, Y., Pan, Y., Pearce, J.A., Shackleton, R.M., Smith, A.B., Sun, Y., Ward, M., Watts, D.R., Xu, J., Xu, R., Yin, J., and Zhang, Y., 1986, Preliminary conclusions of the Royal Society and Aca-demia Sinica 1985 geotraverse of Tibet: Nature, v. 323, p. 501–507, doi:10.1038/323501a0.

Chang, C.F., Pan, Y.S., and Sun, Y.Y., 1989, The tectonic evolution of Qinghai–Tibet plateau: A review, in Şengör, A.M.C., ed., Tectonic Evolution of the Tethyan Region: NATO ASI Series C259: Dordrecht, Kluwer, p. 415–476.

Chang, E.Z., 2000, Geology and tectonics of the Songpan-Ganzi fold belt, southwestern China: International Geology Review, v. 42, p. 813–831, doi:10.1080/00206810009465113.

Chen, B., and Xie, G., 1994, Evolution of the Tethys in Yunnan and Tibet: Jour-nal of Southeast Asian Earth Sciences, v. 9, p. 349–354, doi:10.1016/0743-9547(94)90046-9.

Cheng, J., and Xu, G., 1986, Geologic map of the Gaize region with report: Tibetan Bureau of Geology and Mineral Resources, 369 p.

Chung, S.L., Chu, M.F., Zhang, Y., Xie, Y., Lo, C.H., Lee, T.Y., Lan, C.Y., Li, X., Zhang, Q., and Wang, Y., 2005, Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism: Earth-Science Reviews, v. 68, p. 173–196, doi:10.1016/j.earscirev.2004.05.001.

Clark, M.K., and Royden, L.H., 2000, Topographic ooze: Building the east-ern margin of Tibet by lower crustal fl ow: Geology, v. 28, p. 703–706, doi:10.1130/0091-7613(2000)28<703:TOBTEM>2.0.CO;2.

Clark, M.K., Bush, J.W.M., and Royden, L.H., 2005, Dynamic topography pro-duced by lower crustal fl ow against rheological strength heterogeneities bordering the Tibetan Plateau: Geophysical Journal International, v. 162, p. 575–590, doi:10.1111/j.1365-246X.2005.02580.x.

Clemens, J.D., and Petford, N., 1999, Granitic melt viscosity and silica magma dynamics in contrasting tectonic settings: Journal ot the Geological Soci-ety, v. 156, p. 1057–1060, doi:10.1144/gsjgs.156.6.1057.

Cloos, M., 1982, Flow melanges: Numerical modelling and geologic constraints on their origin in the Franciscan subduction complex, California: Geo-logical Society of America Bulletin, v. 93, p. 330–345, doi:10.1130/0016-7606(1982)93<330:FMNMAG>2.0.CO;2.

Coulon, C., Maluski, H., Bollinger, C., and Wang, S., 1986, Mesozoic and Cenozoic volcanic rocks from central and southern Tibet: 39Ar-40Ar dat-ing, petrologic characteristics and geodynamical signifi cance: Earth and Planetary Science Letters, v. 79, p. 281–302, doi:10.1016/0012-821X(86)90186-X.

Crowell, J.C., 1978, Gondwana glaciation, cyclothems, continental positioning, and climate change: American Journal of Science, v. 278, p. 1345–1372, doi:10.2475/ajs.278.10.1345.

Crowell, J.C., and Frakes, L.A., 1970, Phanerozoic ice ages and the causes of ice age: American Journal of Science, v. 268, p. 193–224, doi:10.2475/ajs.268.3.193.

Crowley, T.J., 1999, Pre-Mesozoic Ice Ages: Their Bearing on Understanding the Climate System: Geological Society of America Memoir 192, 112 p., doi:10.1130/0-8137-1192-4.1.

Defant, M.J., and Drummond, M.S., 1990, Derivation of some modern arc mag-mas by melting of young subducted lithosphere: Nature, v. 347, p. 662–665, doi:10.1038/347662a0.

Deng, W., Yin, J., and Guo, Z., 1996, Basic-ultrabasic and volcanic rocks in Chagbu-Shuanghu area of northern Xizang (Tibet), China: Science in China, ser. D, v. 39, p. 359–368.

Dewey, J.F., Shackleton, R.M., Chang, C., and Sun, Y., 1988, The tectonic evolution of the Tibetan Plateau: Royal Society of London Philosophi-cal Transactions, ser. A, v. 327, p. 379–413, doi:10.1098/rsta.1988.0135.

Dickins, J.M., 1992, Permian geology of Gondwana countries: An over-view: International Geology Review, v. 34, p. 986–1000, doi:10.1080/00206819209465648.

Dickins, J.M., 1996, Problems of a late Palaeozoic glaciation in Australia and subsequent climate in the Permian: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 125, p. 185–197, doi:10.1016/S0031-0182(96)00030-2.

Dickinson, W.R., 2002, The Basin and Range Province as a composite extensional domain: International Geology Review, v. 44, p. 1–38, doi:10.2747/0020-6814.44.1.1.

Ding, J., and Wang, J., 2008, Report on strategic investigation and evaluation of oil and gas resource in Tibetan Plateau: Chengdu, China, Chengdu Insti-tute of Geology and Mineral Resources, p. 14–18.

Ding, L., Kapp, P., Zhong, D., and Deng, W., 2003, Cenozoic volcanism in Tibet: Evidence for a transition from oceanic to continental subduction: Journal of Petrology, v. 44, p. 1833–1865, doi:10.1093/petrology/egg061.

Ding, L., Kapp, P., Yue, Y., and Lai, Q., 2007, Postcollisional calc-alkaline lavas and xenoliths from the southern Qiangtang terrane, central Tibet: Earth and Planetary Science Letters, v. 254, p. 28–38, doi:10.1016/j.epsl.2006.11.019.

Ding, L., Yang, D., Cai, F.L., Pullen, A., Kapp, P., Gehrels, G.E., Zhang, L.Y., Zhang, Q.H., Lai, Q.Z., Hue, Y.H., and Shi, R.D., 2013, Provenance analysis of the Mesozoic Hoh-Xil-Songpang-Ganzi turbidites in northern Tibet: Implication for the tectonic evolution of the eastern Paleo-Tethys Ocean: Tectonics, v. 32, p. 34–48, doi:10.1002/tect.20013.

Drummond, M.S., Defant, M.J., and Kepezhinskas, P.K., 1996. Petrogenesis of slab-derived trondhjemite–tonalite–dacite/adakite magmas, in Brown, M., et al., eds., Third Hutton Symposium on the Origin of Granites and Related Rocks: Geological Society of America Special Paper 315, p. 205–215, doi:10.1130/0-8137-2315-9.205.

Fan, Y.N., 1985, A Division of Zoogeographical Provinces by Permo- Carboniferous Corals in Xizang, China, in Contributions to the Geology of the Qinghai-Xizang (Tibet) Plateau, Volume 16: Beijing, China, Geo-logical Publishing House, p. 105–112.

Fan, Y.N., 1988, The Carboniferous System in Xizang: Chongqing, China, Chongqing Publishing House, 128 p.

Fu, X., Wang, J., Tan, F., Chen, M., and Chen, W., 2010, The Late Triassic rift-related volcanic rocks from eastern Qiangtang, northern Tibet (China): Age and tectonic implications: Gondwana Research, v. 17, p. 135–144.

Gaetani, M., and Garzanti, E., 1991, Multicyclic history of the northern India continental margin (northwestern Himalaya): American Association of Petroleum Geologists Bulletin, v. 75, p. 1427–1446.

Gehrels, G.E., DeCelles, P.G., Martin, A., Ojha, T.P., Pinhassi, G., and Upreti, B.N., 2003, Initiation of the Himalayan orogen as an early Paleozoic thin-skinned thrust belt: GSA Today, v. 13, no. 9, p. 4–9, doi:10.1130/1052-5173(2003)13<4:IOTHOA>2.0.CO;2.

Gehrels, G.E., DeCelles, P.G., Ojha, T.P., and Upreti, B.N., 2006, Geologic and U-Th-Pb geochronologic evidence for early Paleozoic tectonism in the Kathmandu thrust sheet, central Nepal Himalaya: Geological Society of America Bulletin, v. 118, p. 185–198, doi:10.1130/B25753.1.




Gehrels, G.E., Kapp, P., DeCelles, P.G., Pullen, A., Blakey, R., Weislogel, A., Ding, L., Guynn, J., Martin, A., McQuarrie, N., and Yin, A., 2011, Detrital zircon geochronology of pre-Tertiary strata in Tibetan-Himalaya orogen: Tectonics, v. 30, TC5016 doi:10.1029/2011TC002868.

Gessner, K., Collins, A.S., Ring, U., and Güngör, T., 2004, Structural and ther-mal history of poly-orogenic basement: U-Pb geochronology of granitoid rocks in the southern Menderes Massif, western Turkey: Journal of the Geological Society, v. 161, p. 93–101, doi:10.1144/0016-764902-166.

Girardeau, J., Marcoux, J., Allégre, C.J., Bassoullet, J.P., Tang, Y., Xiao, X., Zao, Y., and Wang, X., 1984, Tectonic environment and geodynamic sig-nifi cance of the Neo-Cimmerian Donqiao ophiolite, Bangong-Nujiang suture zone, Tibet: Nature, v. 307, p. 27–31, doi:10.1038/307027a0.

Girardeau, J., Marcoux, J., Fourcade, E., Bassoulet, J.P., and Tang, Y.K., 1985, Xainxa ultramafi c rocks, central Tibet, China: Tectonic environment and geodynamic signifi cance: Geology, v. 13, p. 330–333, doi:10.1130/0091-7613(1985)13<330:XURCTC>2.0.CO;2.

Guillot, F., Schaltegger, U., Bertand, J.M., Deloule, É., Baudin, T., 2002, Zircon U-Pb geochronology of Ordovician magmatism in the polycyclic Ruitor Massif (Internal W Alps): International Journal of Earth Science, p. 91, p. 964–978, doi:10.1007/s00531-002-0280-0.

Guynn, J.H., Kapp, P., Pullen, A., Heizler, M., Gehrels, G., and Ding, L., 2006, Tibetan basement rocks near Amdo reveal “missing” Mesozoic tectonism along the Bangong suture, central Tibet: Geology, v. 34, p. 505–508, doi:10.1130/G22453.1.

Guynn, J., Kapp, P., Gehrels, G.E., and Ding, L., 2011, U-Pb geochronol-ogy of basement rocks in central Tibet and paleogeographic implica-tions: Journal of Asian Earth Sciences, v. 43, p. 23–50, doi:10.1016/j.jseaes.2011.09.003.

Hacker, B.R., Gnos, E., Ratschbacher, L., Grove, M., McWilliams, M., Sobolev, S.V., and Wu Zhenhan, J., 2000, Hot and dry deep crustal xenoliths from Tibet: Science, v. 287, p. 2463–2466, doi:10.1126/science.287.5462.2463.

Haines, S.S., Klemperer, S.L., Brown, L., Jingru, G., Mechie, J., Meissner, R., Ross, A., and Wenjin, Z., 2003, INDEPTH III seismic data: From sur-face observations to deep crustal processes in Tibet: Tectonics, v. 22, doi:10.1029/2001TC001305.

Harris, N.B.W., Holland, T.J.B., and Tindle, A.G., 1988, Metamorphic rocks of the 1985 Tibet Geotraverse, Lhasa to Golmud: Royal Society of Lon-don Philosophical Transactions, ser. A, v. 327, p. 203–213, doi:10.1098/rsta.1988.0126.

Haschke, M.R., Gunther, A., Melnick, D., Echtler, H., Reutter, K.-J., Scheuber, E., and Oncken, O., 2006, Central and southern Andean tectonic evolution inferred from arc magmatism, in Oncken, O., et al., eds., The Andes—Active Subduction Orogeny: Frontiers in Earth Sciences: Berlin, Springer Verlag, p. 337–353, doi:10.1007/978-3-540-48684-8_16.

Hassanzadeh, J., Stockli, D.F., Horton, B.K., Axen, G.J., Stockli, L.D., Grove, M., Schmitt, A.K., and Walker, J.D., 2008, U-Pb zircon geochronology of late Neoproterozoic–Early Cambrian granitoids in Iran: Implications for paleogeography, magmatism, and exhumation history of Iranian base-ment: Tectonophysics, v. 451, p. 71–96, doi:10.1016/j.tecto.2007.11.062.

Hennig, A., 1915, Zur Petrographie und Geologie von Sudwest Tibet, in Hedin, S., ed., Southern Tibet, Volume 5: Stockholm, Norstedt, 220 p.

Hollister, L.S., and Crawford, M.A., 1986, Melt-enhanced deformation: A major tectonic process: Geology, v. 14, p. 558–561, doi:10.1130/0091-7613(1986)14<558:MDAMTP>2.0.CO;2.

Houseman, G.A., McKenzie, D.P., and Molnar, P., 1981, Convective instability of a thickened boundary layer and its relevance for a thermal evolution of continental convergent belts: Journal of Geophysical Research, v. 86, p. 6115–6132, doi:10.1029/JB086iB07p06115.

Hu, D., Wu, Z., Jiang, W., and Ye, P., 2004, P-T-t path of mafi c granulite meta-morphism in northern Tibet and its geodynamical implications: Acta Geo-logica Sinica, v. 78, p. 155–165.

Jennings, C.W., 1977, Geologic map of California: California Division of Mines and Geology Geologic Data Map 2, scale 1:750,000.

Kapp, P., 2001, Blueschist-bearing metamorphic core complexes in the Qiangtang block reveal deep crustal structure of northern Tibet: Com-ment and Reply: Geology, v. 29, p. 91, doi:10.1130/0091-7613(2001)029<0091:R>2.0.CO;2.

Kapp, P., Yin, A., Manning, C.E., Murphy, M., Harrison, T.M., Spurlin, M., Ding, L., Deng, X.G., and Wu, C.E., 2000, Blueschist-bearing meta-morphic core complexes in the Qiangtang block reveal deep crustal structure of northern Tibet: Geology, v. 28, p. 19–22, doi:10.1130/0091-7613(2000)28<19:BMCCIT>2.0.CO;2.

Kapp, P., Yin, A., Manning, C.E., Harrison, T.M., Taylor, M.H., and Ding, L., 2003, Tectonic evolution of the early Mesozoic blueschist-bearing Qiangtang metamorphic belt, central Tibet: Tectonics, v. 22, 1043, doi:10.1029/2002TC001383.

Kapp, P., Yin, A., Harrison, T.M., and Ding, L., 2005, Cretaceous–Tertiary shortening, basin development, and volcanism in central Tibet: Geological Society of America Bulletin, v. 117, p. 865–878, doi:10.1130/B25595.1.

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

Kay, S.M., Godoy, E., and Kurtz, A., 2005, Episodic arc migration, crustal thick-ening, subduction erosion, and magmatism in the south-central Andes: Geological Society of America Bulletin, v. 117, p. 67–88, doi:10.1130/B25431.1.

Kepezhinskas, P.K., Defant, M.J., and Drummond, M.S., 1996, Progressive enrichment of island arc mantle by melt-peridotite interaction inferred from Kamchatka xenoliths: Geochimica et Cosmochimica Acta, v. 60, p. 1217–1229, doi:10.1016/0016-7037(96)00001-4.

Klemperer, S.L., 2006, Crustal fl ow in Tibet: Geophysical evidence for the physi-cal state of Tibetan lithosphere, and inferred patterns of active fl ow, in Law, R.D., and Searle, M.P., eds., Channel Flow, Ductile Extrusion and Exhuma-tion in Continental Collision Zones: Geological Society of London Special Publication 268, p. 39–70, doi:10.1144/GSL.SP.2006.268.01.03.

Kropotkin, P.N., 1971, Eurasia as a composite continent: Tectonophysics, v. 12, p. 261–266, doi:10.1016/0040-1951(71)90007-2.

Kusznir, N.J., and Park, R.G., 1987, The extensional strength of the continen-tal lithosphere: Its dependence on geothermal gradient and crustal com-position and thickness, in Coward, M.P., et al., eds., Continental Exten-sional Tectonics: Geological Society of London Special Publication 28, p. 35–52, doi:10.1144/GSL.SP.1987.028.01.04.

Leeder, M.R., Smith, A.B., and Jixiang, Y., 1988, Sedimentology and palaeoen-vironmental evolution of the 1985 Lhasa to Golmud geotraverse: Royal Society of London Philosophical Transactions, ser. A., v. 327, p. 107–143, doi:10.1098/rsta.1988.0123.

Li, C., 1987, The Longmu Tso–Shuanghu–Lancang River plate suture and the north boundary of distribution of Gondwana facies Permo-Carboniferous system in northern Xizang, China: Changchun College of Geology Jour-nal, v. 17, p. 155–166.

Li, C., and Zheng, A., 1993, Paleozoic stratigraphy in the Qiangtang region of Tibet: Relations of the Gondwana and Yangtze continents and ocean closure near the end of the Carboniferous: International Geology Review, v. 35, p. 797–804, doi:10.1080/00206819309465558.

Li, C., Liren, C., Ke, H., Zengrong, Y., and Yurong, H., 1995, Study on the paleo-Tethys suture zone of Lungmu Co-Shuanghu, Tibet: Beijing, China, Geological Publishing House, 131 p.

Li, C., Wang, T., Yang, D., He, Z., and Ren, Y., 2000, Study on the isotopic chronology and tectonic signifi cance of Duguer granitic gneiss in central Qiangtang, Tibet: 15th Himalaya-Karakorum-Tibet Workshop: Earth Sci-ence Frontiers, v. 7, p. 182–183.

Li, C., Huang, X.P., Zhai, Q.P., Zhu, T.X., Yu, Y.S., Wang, G.H., and Zeng, Q.G., 2006a, The Longmu Co–Shuanghu–Jitang plate suture and the northern boundary of Gondwanaland in the Qinghai-Tibet plateau: Earth Science Frontiers, v. 13, p. 136–147.

Li, C., Zhai, Q.G., Dong, Y.S., and Huang, X., 2006b, Discovery of eclogite and its geologic signifi cance in Qiangtang area, central Tibet: Chinese Science Bulletin, v. 51, p. 1095–1100, doi:10.1007/s11434-006-1095-3.

Li, C., Zhai, Q.G., Dong, Y.S., Zeng, Q.G., and Huang, X.P., 2007, Longmu Co–Shuanghu plate suture and evolution records of paleo-Tethyan oce-anic in Qiangtang area, Qinghai–Tibet plateau: Frontiers of Earth Science in China, v. 1, p. 257–264, doi:10.1007/s11707-007-0032-3.

Li, C., Dong, Y.S., Zhai, Q.C., Wang, L.Q., Yan, Q.R., Wu, Y.W., and He, T.T., 2008, Discovery of Eopaleozoic ophiolite in the Qiangtang of Tibet Pla-teau: Evidence from SHRIMP U-Pb dating and ins tectonics implications: Acta Petrolei Sinica, v. 24, p. 31–36.

Liang, X., Wang, G., Yuan, G., and Liu, G., 2012, Structural sequence and geo-chronology of the Qomo Ri accretionary complex, Central Qiangtang, Tibet: Implications for the Late Triassic subduction of the Paleo-Tethys Ocean: Gondwana Research, v. 22, p. 470–481.

Liu, S., Hu, R., Gao, S., Feng, C., Huang, Z., Lai, S., Yuan, H., Liu, X., Coulson, I.M., Feng, G., Wang, T., and Qi, Y., 2009, U-Pb zircon, geochemical and Sr-Nd-Hf isotopic constraints on the age and origin of Early Palaeozoic



86 Pullen and Kapp

I-type granite from the Tengchong–Baoshan Block, Western Yunnan Province, SW China: Journal of Asian Earth Sciences, v. 36, p. 168–182, doi:10.1016/j.jseaes.2009.05.004.

Lu, S.W., Den, J.D., Du, F.J., and Liu, P.D., 2003, Tectonic evolution of the Meso-Tethyan ocean: An example from the Nyima region in Xizang: Sedimentary Geology and Tethyan Geology, v. 23, p. 35–39.

Lu, J.P., Zhang, N., Huang, W.H., Tang, Z.H., Li, Y.K., Xu, H., Zhou, Q.E., Lu, G., and Li, Q., 2006, Characteristics and signifi cance of the meta-morphic minerals glaucophane-lawsonite assemblage in the Hongjishan area, north-central Qiangtang, north Tibet, China: Geological Bulletin of China, v. 25, p. 70–75.

Matte, P., Tapponnier, P., Arnaud, N., Bourjot, L., Avouac, J.P., Vidal, P., Qing, L., Yusheng, P., and Yi, W., 1996, Tectonics of western Tibet, between the Tarim and the Indus: Earth and Planetary Science Letters, v. 142, p. 311–330, doi:10.1016/0012-821X(96)00086-6.

Mattern, F., Schneider, W., Wang, P., and Li, C., 1998, Continental strike-slip rifts and their stratigraphic signature: Application to the Bangong/ Nujiang zone (Tibet) and the South Penninic zone (Alps): Geologische Rund-schau, v. 87, p. 206–224, doi:10.1007/s005310050203.

Martin, H., Smithies, R.H., Rapp, R., Moyen, J.F., and Champion, D., 2005, An overview of adakite, tonalite-trondhjemite-granodiorite (TTG), and sanu-kitoid: Relationships and some implications for crustal evolution: Lithos, v. 79, p. 1–24, doi:10.1016/j.lithos.2004.04.048.

Maruyama, S., Liou, J.G., and Zhang, R., 1994, Tectonic evolution of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts from central China: The Island Arc, v. 3, p. 112–121, doi:10.1111/j.1440-1738.1994.tb00099.x.

Maruyama, S., Liuo, J.G., and Terabayashi, M., 1996, Blueschists and eclogites of the world and their exhumation: International Geology Review, v. 38, p. 485–594, doi:10.1080/00206819709465347.

Meert, J.G., 2003, A synopsis of events related to the assembly of eastern Gondwana: Tectonophysics, v. 362, p. 1–40, doi:10.1016/S0040-1951(02)00629-7.

Metcalfe, I., 1996, Gondwanaland dispersion, Asian accretion and evolution of Eastern Tethys: Australian Journal of Earth Sciences, v. 43, p. 605–623, doi:10.1080/08120099608728282.

Metcalfe, I., 1998, Palaeozoic and Mesozoic geological evolution of the SE Asian region: Multidisciplinary constraints and implications for biogeog-raphy, in Hall, R., and Holloway, J.D., eds., Biogeography and Geological Evolution of SE Asia: Amsterdam, Backhuys, p. 25–41.

Metcalfe, I., 2002, Permian tectonic framework and palaeogeography of SE Asia: Journal of Asian Earth Sciences, v. 20, p. 551–566, doi:10.1016/S1367-9120(02)00022-6.

Metcalfe, I., 2006, Palaeozoic and Mesozoic tectonic evolution and palaeo-geography of East Asian crustal fragments: The Korean Peninsula in con-text: Gondwana Research, v. 9, p. 24–46, doi:10.1016/j.gr.2005.04.002.

Mo, X., Deng, J., and Lu, F., 1994: Volcanism and the evolution of Tethys in Sanjiang area, southwestern China, in Metcalfe, I., ed., Gondwana Disper-sion and Asian Accretion: Proceedings of the First International Sympo-sium, IGCP Project 321: Journal of Southeast Asian Earth Sciences, v. 9, p. 325–333.

Molnar, P., and Tapponnier, P., 1981, A possible dependence of tectonics strength on the age of the crust in Asia: Earth and Planetary Science Let-ters, v. 52, p. 107–114, doi:10.1016/0012-821X(81)90213-2.

Nábělek, J., Hetényi, G., Vergne, J., Sapkota, S., Kafl e, B., Jiang, M., Su., H., Chen, J., Huang, B.S., and the Hi-CLIMB Team, 2009, Underplating in the Himalaya-Tibet collision zone revealed by the Hi-CLIMB Experi-ment: Science, v. 325, p. 1371–1374, doi:10.1126/science.1167719.

Neil, E.A., and Houseman, G.A., 1997, Geodynamics of the Tarim Basin and the Tian Shan in central Asia: Tectonics, v. 16, p. 571–584, doi:10.1029/97TC01413.

Nicolas, A., and Ildefonse, B., 1996, Flow mechanism and viscosity in basaltic magma chambers: Geophysical Research Letters, v. 23, p. 2013–2016, doi:10.1029/96GL02073.

Owens, T.J., and Zandt, G., 1997, Implications of crustal property varia-tions for models of Tibetan plateau evolution: Nature, v. 387, p. 37–43, doi:10.1038/387037a0.

Pan, G., Ding, J., Yao, D., and Wang, L., eds., 2004, Geologic map of Qinghai-Xizang (Tibet) Plateau and adjacent areas: Chengdu Institute of Geology and Mineral Resources, China Geological Survey, scale 1:1,500,000.

Pan, G., Wang, L., Li, R., Yuan, S., Ji, W., Yin, F., Zhang, W., and Wang, B., 2012, Tectonic evolution of the Qinhai-Tibet Plateau: Journal of Asian Earth Sciences, v. 53, p. 3–14, doi:10.1016/j.jseaes.2011.12.018.

Pullen, A., Kapp, P., Gehrels, G.E., Vervoort, J.D., and Ding, L., 2008, Triassic continental subduction in central Tibet and Mediterranean-style closure of the Paleo-Tethys Ocean: Geology, v. 36, p. 351–354, doi:10.1130/G24435A.1.

Pullen, A., Kapp, P., Gehrels, G.E., Ding, L., and Zhang, Q., 2011, Metamor-phic rocks in central Tibet: Lateral variations and implications for crustal structure: Geological Society of America Bulletin, v. 123, p. 585–600, doi:10.1130/B30154.1.

Ranalli, G., and Murphy, D.C., 1987, Rheological stratifi cation of the litho-sphere: Tectonophysics, v. 132, p. F281–F295, doi:10.1016/0040-1951(87)90348-9.

Raymo, M.E., Hodell, D., and Jansen, E., 1992, Response of deep ocean cir-culation to initiation of Northern Hemisphere glaciations (3–2 Ma): Pale-oceanography, v. 7, p. 645–672, doi:10.1029/92PA01609.

Reid, A.J., Wilson, C.J.L., and Shun, L., 2005, Structural evidence for the Permo-Triassic tectonic evolution of the Yidun Arc, eastern Tibetan Pla-teau: Journal of Structural Geology, v. 27, p. 119–137, doi:10.1016/j.jsg.2004.06.011.

Roger, F., Tapponnier, P., Arnaud, N., Schärer, U., Brunel, M., Zhiqin, X., and Jingsui, Y., 2000, An Eocene magmatic belt across central Tibet: Mantle subduction triggered by the Indian collision: Terra Nova, v. 12, p. 102–108, doi:10.1046/j.1365-3121.2000.123282.x.

Rudnick, R.L., and Fountain, D.M., 1995, Nature and composition of the con-tinental crust: A lower crustal perspective: Reviews of Geophysics, v. 33, p. 267–309, doi:10.1029/95RG01302.

Schellart, W.P., Stegman, D.R., Farrington, R.J., Freeman, J., and Moresi, L., 2010, Cenozoic tectonics of western North America controlled by evolv-ing width of Farallon slab: Science, v. 329, p. 316–319, doi:10.1126/ science.1190366.

Schneider, W., Mattern, F., Wang, P.J., and Li, C., 2003, Tectonic and sedi-mentary basin evolution of the eastern Bangong-Nujiang zone (Tibet): A Reading cycle: International Journal of Earth Sciences, v. 92, p. 228–254, doi:10.1007/s00531-003-0311-5.

Scotese, C.R., Boucot, A.J., and McKerrow, W.S., 1999, Gondwana palaeo-geography and palaeoclimatology: Journal of African Earth Sciences, v. 28, p. 99–114, doi:10.1016/S0899-5362(98)00084-0.

Şengör, A.M.C., 1984, The Cimmeride Orogenic System and the Tectonics of Eurasia: Geological Society of America Special Paper 195, 82 p., doi:10.1130/SPE195.

Şengör, A.M.C., 1987, Tectonics of the Tethysides: Orogenic collage develop-ment in a collisional setting: Annual Review of Earth and Planetary Sci-ences, v. 15, p. 213–244, doi:10.1146/annurev.ea.15.050187.001241.

Şengör, A.M.C., Altiner, D., Cin, A., Ustaomer, T., and Hsu, K.J., 1988, Ori-gin and assembly of the Tethyside orogenic collage at the expense of Gondwana Land, in Audley-Charles, M.G., and Hallam, A., eds., Gond-wana and Tethys: Geological Society of London Special Publication 37, p. 119–181, doi:10.1144/GSL.SP.1988.037.01.09.

Shen, F., Royden, L.H., and Burchfi el, B.C., 2001, Large-scale crustal defor-mation of the Tibetan Plateau: Journal of Geophysical Research, v. 106, p. 6793–6816, doi:10.1029/2000JB900389.

Shen, S., Zhang, B., and Wei, Q., 1995, Volcanic rocks in southern Jomda–Weixi Arc in the Nujiang–Lancang–Jinsha Rivers area: Tethyan Geology, v. 19, p. 54–69.

Shi, D., Zhao, W., Brown, L., Nelson, D., Zhao, X., Kind, R., Ni, J., Xiong, J., Mechie, J., Guo, J., Klemperer, S., and Hearn, T., 2004, Detection of southward intracontinental subduction of Tibetan lithosphere along the Bangong-Nujiang suture by P-to-S converted waves: Geology, v. 32, p. 209–212, doi:10.1130/G19814.1.

Smith, A.B., and Xu, J.T., 1988, Paleontology of the 1985 Tibet Geotraverse, Lhasa to Golmud: Royal Society of London Philosophical Transactions, ser. A, v. 327, p. 53–105, doi:10.1098/rsta.1988.0122.

Stöcklin, J., 1980, Geology of Nepal and its regional frame: Journal of the Geo-logical Society, v. 137, p. 1–34, doi:10.1144/gsjgs.137.1.0001.

Stöcklin, J., and Bhattarai, K.D., 1977, Geology of the Kathmandu area and central Mahabharat Range, Nepal: Nepal Department of Mines and Geol-ogy Himalayan Report, 86 p.

Tseng, T.L., Chen, W.P., and Nowack, R.L., 2009, Northward thinning of Tibetan crust revealed by virtual seismic profi les: Geophysical Research Letters, v. 36, doi:10.1029/2009GL040457.

Turner, S., Arnaud, N., Liu, J., Rogers, N., Hawkesworth, C., Harris, N., Kelley, S., van Calsteren, P., and Deng, W.M., 1996, Postcollisional, shoshonitic volcanism on the Tibetan plateau: Implications for convective thinning of




the lithosphere and the source of ocean island basalts: Journal of Petrol-ogy, v. 37, p. 45–71, doi:10.1093/petrology/37.1.45.

Ustaömer, P.A., Ustaömer, T., Collins, A.S., and Robertson, A.H.F., 2009, Cadomian (Ediacaran–Cambrian) arc magmatism in the Bitlis Massif, SE Turkey: Magmatism along the developing northern margin of Gondwana: Tectonophysics, v. 473, p. 99–112, doi:10.1016/j.tecto.2008.06.010.

van der Pluijm, B., and Marshak, S., 2004, Earth Structure: An Introduction to Structural Geology and Tectonics (second edition): New York, W.W. Norton & Company, 672 p.

Veevers, J.J., and Powell, C.M., 1987, Late Paleozoic glacial episodes in Gond-wanaland refl ected in transgressive-regressive depositional sequences in Euramerica: Geological Society of America Bulletin, v. 98, p. 475–487, doi:10.1130/0016-7606(1987)98<475:LPGEIG>2.0.CO;2.

von Huene, R., and Scholl, D.W., 1991, Observations at convergent mar-gins concerning sediment subduction, subduction erosion, and the growth of continental crust: Reviews of Geophysics, v. 29, p. 279–316, doi:10.1029/91RG00969.

Wang, C., Zhao, X., Liu, Z., Lippert, P.C., Graham, S.A., Coe, R.S., Yi, H., Zhu, L., Liu, S., and Li, Y., 2008, Constraints on the early uplift history of the Tibetan Plateau: National Academy of Sciences Proceedings, v. 105, p. 4987–4992, doi:10.1073/pnas.0703595105.

Wang, G.H., Han, F.L., Yang, Y.L., Li, Y.Q., and Cui, J.L., 2009, Discovery and geologic signifi cance of Late Paleozoic accretionary complexes in Central Qiangtang, northern Tibet, China: Geological Bulletin of China, v. 28, p. 1182–1187.

Wang, L., Pan, G., Li, D., Xu, Q., and Lin, S., 1999, The spatio-temporal frame-work and geological evolution of the Jinshajiang arc–basin systems: Acta Geologica Sinica, v. 73, p. 206–218.

Wang, Q., Wyman, D.A., Xu, J., Dong, Y., Vasconcelos, P.M., Peason, N., Wan, Y., Dong, H., Li, C., Yu, Y., Zhu, T., Feng, X., Zhang, Q., Zi, F., and Chu, Z., 2008a, Eocene melting of subducting continental crust and early uplifting of central Tibet: Evidence from central-western Qiangtang high-K calc-alkaline andesites, dacites and rhyolites: Earth and Planetary Science Letters, v. 272, p. 158–171, doi:10.1016/j.epsl.2008.04.034.

Wang, Q., Wyman, D.A., Xu, J., Wan, Y., Li, C., Zi, F., Jiang, Z., Qui, H., Chu, Z., Zhao, Z., and Dong, Y., 2008b, Triassic Nb-enriched basalts, magne-sian andesites, and adakites of the Qiangtang terrane (Central Tibet): Evi-dence for metasomatism by slab-derived melts in the mantle wedge: Con-tributions to Mineralogy and Petrology, v. 155, p. 473–490, doi:10.1007/s00410-007-0253-1.

Wang, X., Metcalfe, I., Jian, P., He, L., and Wang, C., 2000, The Jinshajiang-Ailaoshan suture zone, China; tectonostratigraphy, age and evolution: Journal of Asian Earth Sciences, v. 18, p. 675–690, doi:10.1016/S1367-9120(00)00039-0.

Wang, Y.J., and Mu, X.N., 1983, Upper Carboniferous and Lower Permian strata in the Gondwana–Tethys province of Xizang (Tibet): Palaeontol Cathayana, v. 1, p. 411–419.

Wang, Y.J., Wang, J.P., Wang, Y.M., Li, Q.S., and Pei, F., 2002, Characteristics and age of the Dingqing ophiolite in Xizang (Tibet) and their geological signifi cance: Acta Micropalaeontologica Sinica, v. 19, p. 417–420.

Wang, Y.J., Wang, J.P., and Pei, F., 2006, A Late Triassic radiolarian fauna in the Dingqing ophiolite belt, Xizang (Tibet): Acta Micropalaeontologica Sinica, v. 19, p. 323–336.

Wei, W., Unsworth, M., Jones, A., Booker, J., Tan, H., Nelson, D., Chen, L., Li, S., Solon, K., Bedrosian, P., Jin, S., Deng, M., Ledo, J., Kay, D., and Roberts, B., 2001, Detection of widespread fl uids in the Tibetan crust by magnetotelluric studies: Science, v. 292, p. 716–719, doi:10.1126/ science.1010580.

Weislogel, A.L., 2008, Tectonostratigraphic and geochronologic constrains on evolution of the northeast Paleotethys from the Songpan-Ganzi complex, central China: Tectonophysics, v. 451, p. 331–345.

Weislogel, A.L., Graham, S.A., Chang, E.Z., Wooden, J.L., and Gehrels, G.E., 2010, Detrital zircon provenance from three turbidite depocenters of the Middle–Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment produc-tion: Geological Society of America Bulletin, v. 122, p. 2041–2062, doi:10.1130/B26606.1.

Williams, H.M., Turner, S.P., Pearce, J.A., Kelley, S.P., and Harris, N.B.W., 2004, Nature of the source regions for post-collisional, potassic mag-matism in southern and northern Tibet from geochemical variations in inverse trace element modeling: Journal of Petrology, v. 45, p. 555–607, doi:10.1093/petrology/egg094.

Xu, R.-H., Schärer, U., and Allègre, C.J., 1985, Magmatism and metamorphism in the Lhasa block (Tibet): A geochronological study: The Journal of Geology, v. 93, p. 41–57.

Yang, T.N., Zhang, H.R., Liu, Y.X., Wang, Z.L., Song, Y.C., Yang, Z.S., Tian, S.H., Xie, H.Q., and Hou, K.J., 2011, Permo-Triassic arc magmatism in central Tibet: Evidence from zircon U-Pb geochronology, Hf isotopes, rare earth elements, and bulk geochemistry: Chemical Geology, v. 284, p. 270–282, doi:10.1016/j.chemgeo.2011.03.006.

Yin, A., and Harrison, T.M., 2000, Geologic evolution of the Himalayan-Tibetan orogen: Annual Review of Earth and Planetary Sciences, v. 28, p. 211–280, doi:10.1146/annurev.earth.28.1.211.

Yin, H., 2003, Triassic biostratigraphy of China, in Zhang, W.T., et al., eds., Biostratigraphy of China: Beijing, China, Science Press, p. 379–422.

Yin, J., Xu, J., Liu, C., and Li, H., 1988, The Tibetan plateau: Regional strati-graphic context and previous work: Royal Society of London Philosophi-cal Transactions, ser. A, v. 327, p. 5–52, doi:10.1098/rsta.1988.0121.

Zhai, Q.G., Zhang, R.Y., Jahn, B.M., Li, C., Song, S.G., and Wang, J., 2011, Triassic eclogites from central Qiangtang, northern Tibet, China: Petrol-ogy, geochronology and metamorphic P-T path: Lithos, v. 125, p. 173–189, doi:10.1016/j.lithos.2011.02.004.

Zhang, K.J., and Tang, X.C., 2009, Eclogites in the interior of the Tibetan Pla-teau and their geodynamic implication: Chinese Science Bulletin, v. 54, p. 2556–2567.

Zhang, K.J., Xia, B., and Liang, X., 2002, Mesozoic–Paleogene sedimentary facies and paleogeography of Tibet, western China: Tectonic implica-tions: Geological Journal, v. 37, p. 217–246, doi:10.1002/gj.911.

Zhang, K.J., Cai, J.X., Zhang, Y.X., and Zhao, T.P., 2006a, Eclogites from central Qiangtang, northern Tibet (China) and tectonic implications: Earth and Planetary Science Letters, v. 245, p. 722–729, doi:10.1016/j.epsl.2006.02.025.

Zhang, K.J., Zhang, Y.X., Li, B., Zhu, Y.T., and Wei, R.Z., 2006b, The blueschist-bearing Qiangtang metamorphic belt (northern Tibet, China) as an in situ suture zone: Evidence from geochemical comparison with the Jinsha suture: Geology, v. 34, p. 493–496, doi:10.1130/G22404.1.

Zhang, K.J., Tang, X.C., Wang, Y., and Zhang, Y.X., 2011, Geochronol-ogy, geochemistry, and ND isotopes of early Mesozoic bimodal volca-nism in northern Tibet, western China: Constraints on the exhumation of the central Qiangtang metamorphic belt: Lithos, v. 121, p. 167–175, doi:10.1016/j.lithos.2010.10.015.

Zhang, K.J., Zhang, Y.X., Tang, X.C., and Xia, B., 2012, Late Mesozoic tec-tonic evolution and growth of the Tibetan plateau prior to the Indo-Asian collision: Earth-Science Reviews, v. 114, p. 236–249, doi:10.1016/j.earscirev.2012.06.001.

Zhang, Z.M., Dong, X., Liu, F., Lin, Y.-H., Yan, R., and Santosh, M., 2012, Tectonic evolution of the Amdo terrane, central Tibet: Petrochemistry and zircon U-Pb geochronology: Journal of Geology, v. 120, p. 431–451, doi:10.1086/665799.

Zhou, D., and Graham, S.A., 1996, Songpan-Ganzi complex of the west Qin-ling Shan as a Triassic remnant ocean basin, in Yin, A., and Harrison, T.M., eds., The Tectonic Evolution of Asia: Rubey Volume 9: Cambridge, UK, Cambridge University Press, p. 281–299.

Zhu, D.C., Zhao, Z.D., Niu, Y., Mo, X.X., Chung, S.L., Hou, Z.Q., Wang, L.Q., and Wu, F.Y., 2011, The Lhasa Terrane: Record of a microcontinent and its histories of drift and growth: Earth and Planetary Science Letters, v. 301, p. 241–255, doi:10.1016/j.epsl.2010.11.005.

Zhu, D.C., Zhao, Z.D., Niu, Y., Dilek, Y., Hou, Z.Q., and Mo, X.X., 2012, The origin and pre-Cenozoic evolution of the Tibetan Plateau: Gondwana Research, v. 23, p. 1429–1454, doi:10.1016/j.gr.2012.02.002.

MANUSCRIPT ACCEPTED BY THE SOCIETY 28 FEBRUARY 2014

Printed in the USA



|| mesozoic tectonic history and lithospheric structure of the qiangtang terrane: insights from the...

Documents