New constraints on the India–Asia collision: the Lower Miocene

Gangrinboche conglomerates, Yarlung Tsangpo suture zone, SE Tibet

Jonathan C. Aitchisona,*, Aileen M. Davisa, Badengzhub, Hui Luoa,c

aTibet Research Group, Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong SAR, People’s Republic of ChinabGeological Team#2, Tibet Geological Survey, Lhasa, Tibet, People’s Republic of China

cLaboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing 210008, People’s Republic of China

Received 5 September 2001; revised 30 November 2001; accepted 10 April 2002

Abstract

Lower Miocene conglomerates crop out along the length of the Yarlung Tsangpo suture zone on the southern margin of the Lhasa terrane.

These conglomerates, known by various local names, are correlated herein as the Gangrinboche conglomerates. All units exhibit broadly

similar stratigraphic histories and a basal depositional contact upon an eroded surface of rocks of the Lhasa terrane is ubiquitous. At most

localities the tops of sections are either removed by erosion or truncated by north-directed thrusts. These conglomeratic molasse units

developed in response to the India/Asia collision and record aspects of its development. In all units initial clast derivation was from the Lhasa

terrane on the northern margin of the Yarlung Tsangpo suture zone. Up-section the first appearance of clasts derived from terranes within the

suture zone and the northern margin of India, all of which lie to the south of any outcrops of Gangrinboche conglomerates, is observed.

Although these units were previously thought to be Eocene, analysis of fossil and structural constraints indicates Early Miocene deposition.

As development of the Gangrinboche conglomerates records a significant phase in the evolution of the India–Asia collision understanding of

their age and stratigraphic evolution has wider implications for regional tectonic models.

q 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Miocene; conglomerates; Yarlung Tsangpo suture zone; Indian-Asia collision

1. Introduction

The Yarlung Tsangpo suture zone (YTSZ) marks the

tectonic boundary between India and Asia (Fig. 1). The

rocks within, and along, this suture record the history of

what was once several thousand kilometres of Tethyan

ocean expanse. Most research in the area has concentrated

on the older rocks that have been brought together along the

suture. However, as well as the remnants of these oceanic

terranes, various conglomeratic ‘molasse’ units also crop

out along the suture. These conglomerates record phases in

the history of the India–Asia collision and the establishment

of the Tibetan Plateau. Despite the significance of the suture

the conglomerates have never been examined in detail. The

interpretation that their development was associated with

collisional orogensis has resulted in application of an

inferred Eocene age as an important constraint on models

relating to the timing of collision (Searle et al., 1987).

Over the past five field seasons we have examined

various conglomeratic units along the suture in order to

better understand their development and regional signifi-

cance. Significantly, results of our work indicate that more

than one phase of molasse sedimentation occurred along the

suture with two temporally and spatially distinct conglom-

erate facies being recognizable. The ‘Liuqu conglomerates’

developed during the Paleogene (Davis et al., 1999, 2002).

They crop out along the suture, entirely south of the Xigaze

terrane, for approximately 150 km from near Lhaze to SE of

Xigaze. These conglomerates are polymict and contain

abundant distinctive red chert cobbles but do not contain

any detritus from Xigaze or Lhasa terranes. They likely

record the history of collision between an intra-oceanic

island arc and the continental margin of India (Davis et al.,

1999, 2002).

Another significant and more laterally extensive con-

glomerate facies (‘Gangrinboche conglomerates’ herein)

crops out semi-continuously along the entire length of the

suture. The conglomerates extend from at least as far west

(818E) as Mt Kailas where they outcrop spectacularly to

1367-9120/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.

PII: S1 36 7 -9 12 0 (0 2) 00 0 37 -8

Journal of Asian Earth Sciences 21 (2002) 251–263

www.elsevier.com/locate/jseaes

* Corresponding author. Tel.: þ852-859-8047; fax: þ852-2517-6912.

E-mail address: jona@hku.hk (J.C. Aitchison).

near Namche Barwa (958E) at the eastern Himalayan

syntaxis. From west to east, this facies includes several

units known by a variety of local stratigraphic names

(Kailas, Qiuwu, Dazhuqu and Luobusa formations) applied

by geologists mapping independently in different areas

(Badengzhu, 1979, 1981; Gansser, 1964; Wei and Peng,

1984; Zhang and Fu, 1982). These units are nonetheless

correlatives and each records a similar depositional history.

Gangrinboche, meaning precious jewel of snows, is the

Tibetan name for Mt Kailas. The latter term is common in

western literature, presumably because this mountain is also

regarded as holy in other non-Tibetan cultures/religions that

Fig. 1. Geological sketch map of the YTSZ indicating the position of major tectonic features and locations mentioned in the text. The Gangrinboche

conglomerates (shaded) crop out intermittently along almost the entire length of the northern margin of the YTSZ from west of Gangrinboche (Mt Kailas) to

Namche Barwa. BNS ¼ Bangong–Nujiang suture; YTSZ ¼ Yarlung Tsangpo suture zone; MCT ¼ Main Central thrust of the Himalaya; MBT ¼ Main

Boundary thrust of the Himalaya.

Fig. 2. A: Geological map of the Zedong–Luobusa area indicating the disposition of the main tectonic entities and, in particular, the Gangrinboche

conglomerate (Luobusa Formation) in this region (modified after Badengzhu, 1979, 1981). The locations of sections measured and unconformity upon Lhasa

terrane at Zhu Mai Sha (Fig. 3) are indicated. RZT ¼ Renbu–Zedong thrust. B: Geological map of the Xigaze–Renbung area (modified after Wang et al.,

1987) indicating the disposition of the main tectonic entities and, in particular, the Gangrinboche conglomerate (Qiuwu Formation-west of Dazhuqu and

Dazhuqu Formation-east of Dazhuqu) in this region. The locations of sections measured and outcrop photos (Fig. 5B and C) are indicated. GCT ¼ Great

Counter thrust.

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263252

predominate in the areas from which Western geologists

have generally approached the mountain. However, we feel

it is somewhat inappropriate given the location of the

mountain in Tibet and suggest nomenclatural unification of

the conglomerate units under the name ‘Gangrinboche

conglomerates’. Units correlated under this name are

significantly younger than the Liuqu Formation conglom-

erates and record later, Early Miocene, tectonic events

(Aitchison and Davis, 2001a; Harrison et al., 1993; Miller

et al., 2000). In this paper we present the first detailed

descriptions of the stratigraphy of rocks assigned to the

Gangrinboche conglomerates and discuss the implications,

of the way in which this unit developed, for models of

regional tectonics. Locations mentioned were measured

using a Garmin GPS II Plus personal navigator with

manufacturers accuracy specifications of ^15 m.

2. Suture zone geology

Numerous important works synthesizing the results of

geological traverses and establishing the regional geological

framework of Tibet have already been published (Allegre

et al., 1984; Chang et al., 1986; Coward et al., 1988;

Gansser, 1977; Hirn et al., 1984; Hodges, 2000; Mercier

et al., 1984; Pearce and Deng, 1988; Searle, 1996; Searle

et al., 1987; Shackleton, 1981; Tapponnier et al., 1981). The

YTSZ is marked by a discontinuous belt of ophiolitic rocks

(Girardeau et al., 1984) and is the southernmost and

youngest amongst a southward younging series of similar

features that subdivide the Tibetan Plateau into several

east–west trending blocks (Bureau of Geology and Mineral

Resources of Xizang Autonomous Region, 1993; Chang

et al., 1986; Chang and Zeng, 1973; Gansser, 1977). It is

geographically located along, and just south of, the Yarlung

Tsangpo (Tsangpo ¼ River) in the Tibet Autonomous

Region of the People’s Republic of China where it separates

the Lhasa terrane to the north from the Indian terrane to the

south.

Remnants of oceanic terranes are recognizable (Fig. 2)

within, and bounding, the YTSZ (Aitchison et al., 2000) and

they provide evidence for reconstruction of the history of

Tethys in this region. Subduction of Tethyan oceanic

lithosphere along the YTSZ led to collision between India

and Asia and development of the Himalaya and Tibetan

Plateau. Based on several lines of indirect evidence,

collision between the continental masses of India and Asia

is widely regarded as having initiated in the Eocene (Chang

et al., 1986; Dewey and Bird, 1970; Molnar and Tapponnier,

1975). Subduction of Tethyan oceanic lithosphere beneath

the Lhasa terrane resulted in the production of a huge

volume of magma now represented by the Gangdese

batholith and its extrusive equivalents along the southern

margin of the Lhasa terrane (Allegre et al., 1984; Searle

et al., 1987). Radiometric age data from subduction-related

granites along the southern margin of the Lhasa terrane

indicate that subduction commenced in the Jurassic and

lasted through until at least the Oligocene (30 Ma) (Harrison

et al., 2000; Yin and Harrison, 2000).

During the Late Cretaceous predominantly deep-water

sedimentation occurred in a continental margin forearc

basin [Xigaze terrane; (Aitchison et al., 2000)] located to the

south of the Lhasa terrane. Deposition in the Xigaze terrane

was dominated by turbidite sedimentation by the late Albian

and lasted until at least the Coniacian (Durr, 1996; Einsele

et al., 1994; Wang et al., 1999). Erosion has removed all

rocks younger than this from the terrane. Clastic sediment

within the Xigaze terrane was largely derived from coeval

volcanic rocks developing upon the Lhasa terrane.

Ophiolitic rocks within the YTSZ, near the city of

Xigaze, were examined in detail as part of a Sino-French

collaboration (Girardeau et al., 1984, 1985a–c; Nicolas

et al., 1981a,b). Together with other ophiolitic rocks along

the suture they are assigned to the Dazhuqu terrane

(Aitchison et al., 2000). The terrane contains all elements

of an ophiolite complex although much of section is missing

due to tectonic attenuation along low angle normal faults

and later strike–slip faulting (Wang et al., 1987). Although

earlier interpreted as mid ocean ridge rocks (Nicolas et al.,

1981a) more recent work has revealed a characteristic

supra-subduction zone chemistry (Hebert et al., 2000; Zhou

et al., 1996). Detailed radiolarian biostratigraphy (Zyabrev

et al., 1999) indicates formation of the ophiolite in the

Barremian.

The Bainang terrane (Aitchison et al., 2000) is internally

characterised by an imbricate thrust zone containing

numerous south-directed thrust slices, which preserve an

ocean floor stratigraphy and lies south of the ophiolite.

Tectonic slices of radiolarian chert, and locally basalt,

dominate the northern portions of the terrane. To the south,

the quantity of chert diminishes and the terrane is

characterised by fine-grained, thinly bedded, deep marine

sediments. Structurally the unit is reminiscent of subduction

complexes such as those seen in the Circum-Pacific region.

However, the coarse-grained volcaniclastic turbidites, that

typically dominate such terranes where they have developed

along active continental margins, are not widespread and the

Bainang terrane mostly consists of material interpreted to

have been off-scraped from the down-going slab (Ziabrev

et al., 2001). Preliminary results of detailed systematic

sampling of the terrane indicate that Triassic to Early

Cretaceous cherts and other oceanic sediments were

accreted into this subduction complex during the late

Early Cretaceous (Ziabrev et al., 2001; Zyabrev et al.,

2000).

Liuqu Conglomerate is an Upper Cretaceous–Paleogene

molasse unit that crops out intermittently along the YTSZ

from Bainang to Lhaze. It contains detritus shed from

Indian, Tethyan and intra-oceanic terranes but not from

Xigaze and Lhasa terranes. Development of these thick

rapidly-deposited clastic strata is interpreted to have

occurred in response to collision of an intra-oceanic island

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 253

arc with India and predates final India/Asia collision (Davis

et al., 2002).

A vast zone of predominantly passive margin-derived

siliciclastic sedimentary rocks and carbonates lies south of

the Bainang terrane (Jadoul et al., 1998; Liu, 1992; Liu and

Einsele, 1994). These rocks constitute the leading edge of

the Indian terrane and range from Lower Paleozoic to

Paleogene. Locally, along the northern margin of the

terrane, they are disrupted into extensive zones of mud-

matrix melange (Liu and Einsele, 1996). Radiolarians in the

Yamdrok melange indicate its formation in the latest

Paleocene–earliest Eocene (Liu et al., 2000).

The order in which the ophiolitic Dazhuqu terrane is

tectonically juxtaposed against the Bainang terrane subduc-

tion complex to its south and the Zedong terrane, a Late

Jurassic–Cretaceous island arc sequence (McDermid et al.,

2000, 2001), to its north is consistent along strike. Together,

the arrangement of these coeval terranes suggests the former

existence of a south-facing intra-oceanic subduction system

inferred to have collided with, and been obducted onto, the

northern margin of India in the latest Cretaceous to

Paleogene (Aitchison et al., 2000). The formation of

significant units such as the Yamdrok melange and Liuqu

Conglomerate, appears to have been coeval with this

collision.

3. The Gangrinboche conglomerate

3.1. Lithostratigraphy

Four conglomerate units, known by a variety of local

geographic names (Luobusa, Dazhuqu, Qiuwu and Kailas

formations) crop out along over 2000 km of the strike length

of the suture from west of Mt Kailas (6714 m 318040N

0818190E) to near the eastern Himalayan syntaxis at Namche

Barwa (7782 m 298400N 0958100E). Each unit records the

Miocene cf. Eocene (Searle et al., 1987) deposition of

coarse clastic sediments and all record a broadly similar

stratigraphic evolution. The Gangrinboche conglomerates

formed after closure of the Tethyan Ocean in this region and

indicate the establishment of considerable relief in the area.

A basal depositional upon a basement of Lhasa terrane

rocks, which initially was the sole source of sediment, is

ubiquitous. Up-section the first appearance of southerly-

derived clastic detritus is observed and this material

gradually becomes dominant. Major changes in overall

source petrography may indicate the history of activity on

north-directed thrust faults. More local variations are likely

related to the immediate proximity of distinctive rock types

in localised source areas. In many areas these rocks are

folded and steeply dipping indicating they have been further

affected by on-going Tibetan orogenesis.

Fig. 3. Photo of the depositional unconformity between basal granitic

breccias of the Luobusa Formation (member R1) and felsic rocks of the

Gangdese batholith (Lhasa terrane). The contact between the southern

margin of the Lhasa terrane and rocks to its south was previously mapped in

this area (Yin et al., 1999) as the south-directed ‘Gangdese thrust’ for which

no evidence can be seen. This exposure is located on the south bank of the

Yarlung Tsangpo immediately below the road leading up to the Luobusa Cr

mine at a locality where a large rock within the river is named Zhu Mai Sha

(29814.6820N 092811.7870E 3580 m) and lies several metres below the

normal summer (flood) level of the Yarlung Tsangpo. Luobusa Formation

lies to the left (south) and is deposited directly on a weathered surface of

Lhasa terrane rocks that lie closer to the river (north).

Fig. 4. Measured logs through representative sections of Gangrinboche facies conglomerates. Inferred clast sources, listed in order of relative abundance, are

indicated on the left of the columns. Individual bed thicknesses are not shown. K1–K2: Kailas Formation observed in the Kuglung Chu (valley) (30858.3720N;

081829.9870) immediately north of old Barka a small hamlet on the northern side of Mapham Tso (Lake Manasarovar) located a few kilometres east of

Gangrinboche. The left column (K1) shows sediments representative of the lower member exposed on the western side of the valley. Column K2 is measured

over the transition from lower to middle members, as well as, the transition from the middle to upper members; G1–G3: Qiuwu Formation exposed along the

south side of the Yarlung Tsangpo between Giabulin and Xigaze. Section G1 was measured near Guibulin and shows sediments typical of units immediately

above and below the transition from lower to middle members. G2 shows the transition from middle to upper members and G3 shows sediments typical of the

upper member; Sections Z1–Z3 are from the Luobusa Formation near Zedong. Z1: from 20 km east of Zedong at Jerung where the basal member (R1) is

exposed; Z2: 2.5 km east of Zedong where member R2 is well exposed, Z3: from immediately east of Zedong where mid (R2) and upper (R3) members are

exposed.

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263254

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 255

3.2. Luobusa Formation

The Luobusa Formation, which crops out along the

YTSZ south east of Lhasa, is a thick (1270 m at Luobusa)

succession of coarse clastic strata. Semi-continuous outcrop

can be traced eastwards for approximately 100 km along the

suture from Zedong township past Luobusa Cr-mine to

beyond Jindong. Rocks near Zedong are undeformed but as

the Namche Barwa syntaxis is approached the unit becomes

progressively more deformed. Distinct changes in sediment

sources are observed up-section. A depositional contact

upon a Lhasa terrane surface, represented by Late Cretac-

eous to Oligocene intrusives of the Gangdese batholith or

Late Jurassic to Early Cretaceous meta-sedimentary and

meta-volcanic units of the Sangri Group, can be observed

clearly (Fig. 3) at many localities (Badengzhu, 1979, 1981).

Coarse (boulder) conglomerates at the base of the formation

are dominated by clasts derived locally from the Lhasa

terrane such as Gangdese granites, porphyry volcanics,

limestone (marble), and chloritic meta-sediments and meta-

volcanics (lower member R1—360 m thick at Luobusa).

Up-section, overlying conglomerates (R2—270 m thick at

Luobusa) record the arrival of a conspicuous influx of

Dazhuqu and Bainang terrane-derived clasts (red chert,

ultramafic, diabase). While feldspar porphyritic volcanics of

Lhasa terrane origin are present they become less common

up-section (Fig. 4). Towards the top of the middle member

(R2) pebbly conglomerates, in which clasts are dominantly

Lhasa terrane-derived porphyritic volcanics (.75% of

clasts), are interbedded with finer-grained siltstones and

sandstones. Subordinate amounts of red chert and gabbro,

sourced from Bainang and Dazhuqu terranes, respectively,

are also present. Coarse conglomerates return in the

uppermost member (R3—640 m thick at Luobusa). This

member is polymict and sees the appearance of Indian

terrane-derived quartzite clasts. Clasts are derived from all

nearby terranes including the Zedong terrane. The upper

levels of the conglomerates are truncated by the north-

directed Renbu–Zedong thrust (Yin et al., 1994, 1999).

Luobusa Formation typically lies in the footwall of this fault

and locally exhibits asymmetrical folds associated with

north-directed thrusting. At some localities Luobusa

Formation is overthrust by constituent rocks of the YTSZ

such as those of the Zedong or Dazhuqu terranes (e.g. at

Luobusa; Zhou et al., 1996). Elsewhere shortening is greater

and it is overthrust by the Indian terrane.

3.3. Dazhuqu Formation

Dazhuqu Formation crops out to the southwest of

Lhasa and has its type area in the Yarlung Tsangpo

gorge near Renbung where it is over 1500 m thick. The

conglomerates were originally named Dazhuqu For-

mation by local geologists who mapped in this region as

part of a base metal exploration program along the

YTZS. They can be traced eastwards along strike to

south of Daga near the road bridge crossing the Yarlung

Tsangpo (Wei and Peng, 1984) where an extremely

small outcrop (a few m2) of these distinctive conglom-

erates occurs where the YTSZ passes through a small

col, Jiangdan Yako (visible from Lhasa airport). An

unconformable depositional contact upon rocks of the

Lhasa terrane (Sangri Group metamorphics) is particu-

larly obvious east of the summit of a major (6126 m)

glaciated peak (Burg, 1983) which, when not enveloped

in cloud, is clearly visible to the west of the main road

bridge over the Yarlung Tsangpo (Fig. 5A). Few

outcrops of Gangrinboche facies conglomerates or any

other suture zone rocks are seen between Lhasa Airport

and Zedong as the YTSZ is largely obscured by

Quaternary alluvium in the floor of the Yarlung

Tsangpo valley.

Dazhuqu Formation is dominated by coarse clastic strata

and was deposited directly on an eroded surface of Lhasa

terrane rocks such as intrusives of the Gangdese batholith or

Sangri Group metamorphics (Fig. 5B). Large boulder-sized

Lhasa terrane-derived clasts are common lower in the

formation and YTSZ ophiolitic, and subduction complex-

derived detritus then becomes abundant higher in the

section. Deposition was evidently very proximal. Near the

top of the preserved section Dazhuqu Formation grades

upwards into red and brown pebbly mudstones. Although

the northern contact is depositional upon the Lhasa terrane

all contacts with units to the south are faulted. Time and

weather constraints precluded the measurement of any

section through these rocks.

Fig. 5. A: Conglomerates of the Dazhuqu Formation observed on peak 6126 m looking west from the Lhasa–Xigaze highway a few km west of the main bridge

over the Yarlung Tsangpo. The other peak hidden in clouds to the left (south) of the pass is composed of Triassic rocks of Indian terrane affinity which have

been thrust northwards along the Great Counter (Renbu–Zedong) thrust system. Serpentinite and ultramafic rocks of the Dazhuqu terrane (um) crop out in the

saddle between the two peaks. The top of peak 6126 m consists of Dazhuqu Formation conglomerates which dip moderately to the south (left). A non-

conformable contact where these conglomerates rest depositionally upon an eroded surface of Sangri Group metamorphic rocks and granites (Lhasa terrane)

occurs on the slopes in shade below the summit of this peak. B: Dazhuqu Formation at 29818.3450N;089848.2620E east of Renbung observed looking up stream

(west) along the Yarlung Tsangpo. On the left hand (south) side of the photo a thick succession of Dazhuqu Formation unconformably overlies Sangri Group

metamorphic rocks (Lhasa terrane). Dazhuqu Formation dips gently to the south. The peak in the middle of the photo is capped by ophiolitic rocks of the

Dazhuqu terrane. C: Outcrop of Qiuwu Formation located on the south bank of the Yarlung Tsangpo east of Giabulin at 29819.7330N;088834.4380E observed

looking downstream (east). The contact between lower and middle members of the formation can be seen sloping from the saddle in the right of the photo down

towards the 4WD vehicle. D: Gangrinboche (6714 m—Mt Kailas), western Tibet. A thick succession of thickly-bedded conglomerate beds crops out as the flat-

lying horizons that form this holy mountain.

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263256

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 257

3.4. Qiuwu Formation

Qiuwu Formation crops out from about 15 km east of

Xigaze (898E) and extends westwards for hundreds of km

beyond Saga (858E) (Zhang and Fu, 1982). The easternmost

outcrops of Qiuwu Formation are essentially continuous

with the westernmost outcrops of the Dazhuqu Formation

with the area intervening between these two units obscured

by Quaternary alluvium in the Yarlung Tsangpo valley. The

base of the formation lies at a depositional contact upon

rocks of the Lhasa terrane. The uppermost levels of the

formation lie in the footwall of a major north-directed thrust

fault with Cretaceous turbidites of the Xigaze terrane in the

hanging wall thrust northwards over the Qiuwu Formation.

A maximum thickness of over 4000 m is attained west of

Xigaze.

As with the Luobusa Formation, the Qiuwu Formation

can be subdivided into three distinctive members. Distinct

changes in sediment sources are observed up-section (Wang

et al., 2000). Above the basal unconformity, where beds are

characterised by locally derived boulder beds, the formation

consists of tabular horizons of sandstone and pebble

conglomerates occur in more or less equal proportions.

The lower member is approximately 650 m thick in the

Giabulin area west of Xigaze. Sandstones and conglomer-

ates contain clasts of serpentinite and mafic pebbles within

an arkosic matrix. The middle member of the formation

(2800 m thick) contains a series of fining-upward sequences

(Fig. 5C) with more or less equal proportions of conglom-

erate and finer-grained lithologies. A variety of clast types

are present with: gabbro, serpentinite, and diabase;

volcaniclastic sandstone, and tuffaceous mudstones; green

tuffaceous chert, and red chert; granite and porphyritic

volcanics derived from the Dazhuqu, Xigaze, Bainang and

Lhasa terranes, respectively. The upper member of the

formation (600 þ m thick) consists of fining-upward

sequences in which sandstone and red shale are predominant

and minor conglomerate also occurs. Conglomerates clasts

are mostly derived from the Bainang terrane and are

typically tuffaceous chert and red chert. Lesser amounts of

porphyritic volcanics, serpentinite, sandstone, mudstone,

limestone, quartzite, and vein quartz derived from Lhasa,

Dazhuqu, Xigaze, and Indian terranes are also present.

3.5. Kailas Formation

Conglomerates similar to those of the Qiuwu Formation

can be traced westwards from Xigaze at least as far

(1500 km) as the 6714 m peak of Gangrinboche (Mt Kailas)

where they outcrop spectacularly as thick flat-lying beds on

the upper slopes of the mountain (Fig. 5D). The Kailas

Formation is another thick succession of clastic strata with a

basal depositional contact, readily observed on the Kailas

Kora, upon the Gangdese batholith. It was first described by

Gansser (1964) who reported a thickness of approximately

4000 m. Distinct changes in sediment sources are obser-

vable up-section. Although lowermost sediments were

derived from the north, southerly-derived clasts become

increasingly dominant up-section.

As with other Gangrinboche conglomerate units, the

Kailas Formation can be subdivided into three members

(Yin et al., 1999). Locally derived Kailas granite boulders

occur in basal beds immediately above the unconformity. In

the lower member thick laterally extensive tabular beds of

sandstone and conglomerate predominate. Minor internal

unconformities are locally present. Clasts compositions are

dominated by porphyritic volcanics derived from the Lhasa

terrane to the north. A middle member consists of massive

conglomerates stacked in coarsening-upwards cycles.

Southerly-derived quartzose sandstone clasts of Indian

terrane origin are common and Lhasa terrane porphyritic

volcanics become subordinate up-section. A transition to the

upper member is observed with the gradual influx of beds of

extremely proximal breccia derived from terranes that lie to

the south of the Kailas Formation. Some clasts in the

breccias are more than 1 m in size and by the top of the

upper member breccias predominate. Most clasts are of

Tethyan origin with an abundance of Indian terrane-derived

boulders. Subordinate quantities of basalt, pelagic lime-

stone, and red siliceous mudstone clasts are also present.

Material derived from the Lhasa terrane is absent in the

upper member. The top of the formation is either faulted or

removed by erosion. The conglomerates are locally over-

thrust by the north-directed Great Counter thrust (Gansser,

1964; Heim and Gansser, 1939). This fault is also referred to

as the South Kailas thrust (Yin et al., 1999).

4. Age constraints

The ages of various Gangrinboche facies conglomerate

units along the YTSZ are of great significance to regional

tectonic models. The presence of these molasse units has

previously been used as geological evidence for the

development of relief associated with the India–Asia

collision and mass wasting of large volumes of coarse

sediments. These rocks have previously been accorded an

Eocene age and the timing of their accumulation has been

cited (Searle et al., 1987) as one of the main lines of

evidence in support of models invoking early Eocene

collision. Therefore any data which may better constrain the

ages of these rocks should provide important constraints for

testing the timing of collision inferred in models that are

based on more indirect geophysical lines of evidence

(Klootwijk et al., 1992; Molnar and Tapponnier, 1975;

Searle et al., 1987).

The age of the Luobusa Formation is constrained by the

presence of non-marine fossils reported by local workers on

map legends and in written reports accompanying these

maps. Fossils reported (Badengzhu, 1979, 1981) include:

Bivalvia Sphaerum aff. S. rivicolum Lamarck, Acuticosta

sp., Sphaerum sp., Lepidodesma sp; Gastropoda Planorbis

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263258

cf. P. rotundata Brong, Microlaminatus sp., Bitnynia sp.,

Planorbarius sp., Binynia? sp. cf. limbata (Deshayes),

Gyraulus sp., Fluminicola sp., Amnicola sp., Lymnaea sp;

Algae Charophyta gen. et sp. indet., Crofiella sp.,

Rhabdochara? sp., Ambnychara sp., Tectachara sp., and

Plantae Quecus cf. tofina, Colutea sp., Salix sp., Viburnum

spp. Palmocarpon? sp. and Rhododendron? sp. All known

fossils occurrences are in rocks of member R2 in the vicinity

of Luobusa and are regarded as indicative of an Oligocene–

Miocene depositional age (Badengzhu, 1981).

Stratigraphic relations can be used to further constrain

the age of the conglomerates. A basal depositional contact

where conglomerates are directly deposited upon strongly

foliated meta-sedimentary rocks within the Lhasa terrane, as

well as elements of the Gangdese batholith such as the Yaga

granodiorite, is clearly observable. This contact can be

walked for many kilometres in the field from east of Zedong

to beyond Luobusa. Emplacement of the Yaga granodiorite

at an estimated crustal depth of 13 km is constrained by

radiometric dates of 30.4 ^ 0.4 Ma (Harrison et al., 2000).

The deposition of the basal horizons of the Luobusa

Formation directly upon this mid Oligocene granodiorite

clearly indicates its surface exposure prior to sediment

accumulation. Harrison et al. (1992) and Copeland et al.

(1995) suggested that rapid cooling of Lhasa terrane plutons

occurred in this region between 29 and 24 Ma with uplift

completed by 23 Ma. Apatite fission track data indicate that

the nearby Dagze pluton passed through the apatite cooling

window (110 8C) by 22 Ma (Pan, 1993; Pan et al., 1993).

Thus development of the Luobusa Formation should

postdate this cooling event and deposition most likely

began in the Early Miocene. Additional radiometric

constraints on displacement along the Renbu Zedong thrust,

a structure that truncates the Luobusa Formation, indicate

that north-directed thrusting occurred between 18 and

10 Ma in this region (Yin et al., 1999). Fossil and

radiometric ages are therefore in accord with one another

and the best estimate for the timing of deposition of the

Luobusa Formation is during the Early Miocene.

No fossils have been reported from the Dazhuqu

Formation but the nature of its relationship to the Lhasa

terrane and the sedimentary succession within this unit

strongly support correlation with Luobusa, Qiuwu and

Kailas units. Were it not for the considerable quantity of

alluvium in the Yarlung Tsangpo valley the Dazhuqu

Formation would likely be continuous with Luobusa and

Qiuwu formations to the east and west, respectively.

Stratigraphy and sedimentology of rocks of the Qiuwu

Formation have been described in some detail (Wang et al.,

1999, 2000). On the basis of paleontological data they

excluded many rocks from the Qiuwu Formation referring

to them as a separate entity, the Giabulin Formation for

which a Cretaceous age was inferred. Wang et al. (1999,

2000) reported chert cobbles near the base of their Giabulin

Formation (lower Qiuwu Formation) that contain a

Turbocapsula costata zone (mid Cretaceous-Aptian) radi-

olarian fauna. They further reported Lower Cretaceous

gastropods from the upper part of the formation more than

3000 m above the lowermost reported cobbles containing

the radiolarian fauna. As the upper levels of the formation

cannot possibly be older than clasts in conglomerates within

the lower part of the formation we suggest that the presence

of older fossils at higher stratigraphic levels may be

explained by the fact that the gastropod fossils were

derived. The Qiuwu Formation contains red chert clasts

throughout and cannot be older than these clasts. The chert

clasts represent deep marine siliceous biogenic sediments

that must have experienced lithification, low-grade meta-

morphism and alteration prior to their being uplifted, eroded

and shed into a succession of fluvial sediments. Recent work

(Ziabrev et al., 2001; Zyabrev et al., 1999, 2000), which

provides new age constraints on various terranes and their

constituent lithologies within the YTSZ, indicates that the

ages of the radiolarian faunas in chert pebbles within the

Qiuwu Formation are entirely compatible with Bainang or

Dazhuqu terranes as possible sources for these clasts.

Lithologically, the clasts have greatest affinity with the

Bainang terrane in which red ribbon-bedded radiolarian

cherts are abundant. The presence of cobble-sized clasts of

serpentinite within the Qiuwu (Giabulin) Formation indi-

cates minimal transportation and the Dazhuqu terrane seems

an eminently likely local source candidate. Having

examined sections from west of Giabulin to east of Xigaze

we see no stratigraphical or sedimentological reason to

regard the so-called Giabulin Formation as anything other

than part of the Qiuwu Formation. We therefore suggest that

there is no longer any need to invoke a ‘paleo-ophiolite’

source (Wang et al., 1999, 2000) and the so-called Giabulin

Formation should be regarded, as it is by most other

workers, as an integral part of the Qiuwu Formation.

Age estimates for deposition of the Qiuwu Formation,

rather than the ages of clasts within it, that are based on the

presence of fossils are imprecise and best estimated within

the range of late Eocene to Early Miocene. Non-marine

fossils include the plant fossils Ficeus, Palacocycas,

Yuceites, Rhamnites emines, Viburnum esperum sp. Fossils

locally occur in association with thin carbonaceous horizons

and numerous conflicting age calls exist. A minimum age

can be constrained from felsic dikes, which intrude both the

Qiuwu Formation and the Xigaze terrane. These dikes have

been radiometrically (40Ar/39Ar) dated at 18.3 ^ 0.5 Ma

(Yin et al., 1994). The dikes cross-cut folds in the Qiuwu

Formation, as well as the major north-directed thrust that

truncates the top of the formation, thus indicating

deformation prior to their intrusion in the late Early

Miocene. Thus, based on correlation with Gangrinboche

conglomerates elsewhere, we suggest that the Qiuwu

Formation is also Lower Miocene.

The age of the Kailas Formation is constrained both

paleontologically and radiometrically. The upper member

contains mid Eocene foraminifera Fasciolites Sheng et

Zhang, Fasciolites tibeticus Sheng et Zhang, Fasciolites

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 259

nuttalli Davies, Nummulites rotularius Deshayes (unpub-

lished data Tibet Geological Survey). These fossils occur

within limestone clasts and thus indicate the ages of rocks

within the source area rather than the timing of Kailas

deposition. Misunderstanding of this may be a reason for

previous incorrect assignment of an Eocene age. In situ

fossils occur in the form of plant fossils known from the

lower part of the formation and these include Populus

balsamoicles, Populus latior, Populus glanulifera, Populus

sp., Allbizzia sp., Lequminosites sp. (unpublished data Tibet

Geological Survey). Non-marine Unionidae bivalve fossils

reported from the middle part of the formation indicate

Miocene deposition (Miller et al., 2000).

Kailas conglomerates were deposited directly upon rocks

of the Kailas Igneous Complex which is dated radiometri-

cally at 38 ^ 1.3 Ma Rb–Sr; (Honegger et al., 1982).

Igneous clasts from this basement dominate conglomerates

low in the formation. Radiometric age constraints (Harrison

et al., 1993) indicate that these igneous rocks were not

uplifted, and thus not exposed and available for erosion,

until the late Oligocene. Thus fossil ages are in accord with

radiometric constraints on the timing of deposition.

Displacement on the South Kailas thrust, which truncates

the upper levels of the conglomerates, is bracketed between

20 and 4 Ma (Yin et al., 1999) thereby providing a minimum

age constraint. Thus the Kailas Formation must also be

Lower Miocene.

At all localities with fossil, radiometric or structural

constraints on the timing of deposition of the Gangrinboche

conglomerates a latest Oligocene to Early Miocene age is

indicated.

5. Discussion

Lower Miocene Gangrinboche facies conglomerates

within the Luobusa, Dazhuqu, Qiuwu and Kailas formations

are correlative molasse units that crop out in a narrow

elongate zone along the YTSZ and record aspects of the

history of the India/Asia collision. Sedimentary rocks in all

sections exhibit characteristics compatible with an interpret-

ation of their having accumulated in alluvial fan and braid-

plain environments (Wang et al., 1999, 2000; Yin et al.,

1999). Many of the sediments present are extremely

proximal and clast petrography is influenced strongly by

the nature of rocks in adjacent source terranes. A similar

stratigraphic history is recorded over a 1500 km strike

length. Each formation is subdivisible into three members

and the broad pattern of up-section evolution is correlative.

A depositional contact upon an eroded surface of Lhasa

terrane rocks with all sedimentary detritus being locally

derived from north of the suture zone is ubiquitous. Initial

clast derivation in all sections is very localised and is from

the north. Up-section the first arrival of clasts derived from

suture zone terranes and the northern margin of India, all of

which lie to the south of the Gangrinboche conglomerates, is

observed. Clasts derived from southern portions of, or south

of the suture zone, then become increasingly abundant until

they predominate in upper levels of the conglomerates. The

top of each unit either, lies at the present day erosional

surface or, is truncated by a north-directed thrust. This

structure is regionally extensive and constitutes part of the

Great Counter thrust system (Gansser, 1964; Heim and

Gansser, 1939). The same structure has been recognised

further east along the YTSZ where it is referred to as the

Renbu–Zedong thrust (Yin et al., 1994, 1999).

Late Oligocene regional uplift of the Lhasa terrane

(Harrison et al., 1992) must have created a landscape with

considerable relief with initial deposition of these conglom-

erates on alluvial fans and braided rivers that developed

along and parallel to the southern front of a cordilleran-type

mountain range. South-directed thrust faulting along a

structure referred to as the Gangdese thrust was suggested as

a mechanism to explain this uplift (Yin et al., 1994). This

hypothesis is of significance to any assessment of develop-

ment of the Gangrinboche conglomerates as, not only does it

suggest a mechanism for uplift of the Lhasa terrane, the

proposed Gangdese thrust reportedly places rocks of the

Lhasa terrane southwards over Tertiary conglomerates

(Harrison et al., 2000; Yin et al., 1994, 1999). Our

investigations (Aitchison et al., 2001) indicate, however,

that the conglomerates in question are not Tertiary. They are

pervasively foliated and metamorphosed, contain mostly

andesitic and limestone (marble) clasts, and constitute part

of an Upper Jurassic–Lower Cretaceous zone of meta-

sediments and meta-volcanics (Sangri Group) that com-

prises the basement of the southern part of the Lhasa terrane

(Burg, 1983). Observations along 1500 km strike length of

the Gangrinboche conglomerate indicate that the Gang-

rinboche conglomerates are everywhere in depositional

contact upon rocks of the Lhasa terrane. Detailed investi-

gations in the Zedong–Luobusa area indicate that this

depositional contact can be mapped along the entire strike

length of the proposed Gangdese thrust and we have not

seen Lhasa terrane rocks thrust over Gangrinboche

conglomerates at any locality. This observation is in

accordance with numerous other regional investigations

(Badengzhu, 1979, 1981; Bureau of Geology and Mineral

Resources of Xizang Autonomous Region, 1993; Burg,

1983; Gansser, 1964; Wei and Peng, 1984; Zhang and Fu,

1982) along the entire length of the suture zone. Thus,

although considerable relief must have been present within

the southern Lhasa terrane when Gangrinboche conglomer-

ates accumulated the mechanism for this uplift remains

enigmatic.

The gradual, then overwhelming, influx of detritus

derived from terranes that lie to the south of present day

outcrops of the Gangrinboche conglomerates provides

evidence for development of relief to the south of the

suture zone and is seen in all sections. While we see no

evidence for the existence of a south-directed ‘Gangdese

thrust’ we agree with the suggestion of Yin et al. (1999) that

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263260

these conglomerates, and coarse breccias in some localities

such as Mt Kailas, may reflect the development of north-

directed thrust systems such as the north-directed Great

Counter thrust or Renbu–Zedong thrust systems. Upper

levels of the Gangrinboche conglomerates presumably

developed in the foreland of a northward advancing

mountain front that lay to the south of the Lhasa terrane.

The elongate zone along which the Gangrinboche con-

glomerates are distributed reflects their original deposition

along a valley system axial to two sub-parallel, active,

mountain ranges.

It is presently a widely held, and remarkably unques-

tioned hypothesis that India–Asia collision occurred during

the latest Paleocene/early Eocene. The main lines of

evidence given in support of a latest Paleocene/early

Eocene collision (Searle et al., 1987) are: the slowdown in

the convergence rate between India and Asia; the initiation

of compressional tectonics along, and south of, the Indus–

Yarlung Tsangpo suture; a lack of data indicating subduc-

tion-related magmatic activity north of the suture between

India and Asia; and the accumulation of ‘Eocene’ molasse

deposits along the suture. From detailed studies of ‘molasse-

style’ conglomerate units that crop out along the YTSZ

(Aitchison and Davis, 2001a; Davis et al., 1999, 2002; this

paper) we recognize the existence of two discrete pulses of

sedimentation, one Paleogene, the other late Oligocene–

Early Miocene, but none of Eocene age. It is thus obvious

that not all conglomerates should, or can, be correlated.

Although a depositional contact of Indus Molasse upon

granitic rocks of the Ladahk Batholith can be observed in

Pakistan (Clift et al., 2001; Garzanti and Van Haver, 1988)

conglomerates in that area also rest depositionally upon

other terranes along and south of the Indus suture zone. We

therefore remain cautious about any direct correlation

between Indus and Gangrinboche conglomerates and

suggest further detailed work is required to resolve this

matter.

In other aspects of our investigations along the YTSZ we

have recognised evidence for the Late Cretaceous to

Paleocene collision of an intra-oceanic island arc with the

northern margin of India (Aitchison et al., 2000). We

suggest that the removal of the subduction zone associated

with this intra-oceanic island arc within Tethys would

provide an effective mechanism to slow what was an

anomalously high (20 cm/yr) convergence rate if a single

plate boundary existed between India and Asia. Paleogene

conglomerates of the Liuqu Formation are interpreted

(Aitchison et al., 2000; Davis et al., 1999, 2002) as having

developed in association with this collision which also

provides a plausible explanation for the initiation of

compressional tectonics along, and south of, the YTSZ.

If, as has been suggested by Searle et al. (1987), the

Gangrinboche conglomerates provide evidence for collision

between India and Asia then previous incorrect assumptions

of an Eocene age and potential misinterpretation of other

data may have lead to significant error in estimates of the

timing of collision between India and Eurasia. The timing of

deposition of these conglomerates can be well constrained

to the latest Oligocene–Early Miocene. Recently published

radiometric age data (Harrison et al., 2000) for granodiorites

in the southern Lhasa terrane indicate subduction-related

magmatism occurring as late as 30.4 ^ 0.4 Ma (end early

Oligocene), considerable later than previously known.

While the Gangrinboche conglomerates do not necessarily

constrain the timing of the initiation of collision they

certainly provide unequivocal evidence that it had hap-

pened. Their maximum age is considerably younger than

previously thought, as are the youngest known subduction-

related magmatic rocks in the Lhasa terrane and the

youngest known marine sediments in the Tethyan Himalaya

north of Qomolangma (the Zhaguo member of the Pengqu

Formation contains late Priabonian NP20 zone nannofos-

sils; Wang et al., 2002), thereby opening the possibility that

collision itself was later than presently believed. If two

continents were colliding in this region then we suggest

(Aitchison and Davis, 2001b) that the Eocene and much of

the Oligocene were times of remarkable sedimentary

quiescence in terms of the near absence of any succession

that could possibly be attributed to having developed in

association with collision. We further suggest that reassess-

ment of any models for the development of the India–Asia

collision should be on-going with no model more important

than any newly available data. Models for the tectonic

evolution of the India–Asia collision require on-going

modification to reflect complexity indicated by any newly

available data.

Acknowledgments

We thank members of the Tibetan Geological Survey

(Team 2) and Tibetan Geological Society whose efforts

have helped to make this research possible. Many of these

friends have assisted with arranging logistics and per-

mission. We thank Yani Najman, Erich Draganits and Kurt

Stuwe for their reviews and constructive comments on the

manuscript. The work described in this paper was supported

by grants from the Research Grants Council of the Hong

Kong Special Administrative Region, China (Project Nos.

HKU 7102/98P and HKU 7299/99P).

References

Aitchison, J.C., Davis, A.M., 2001a. Orogenic conglomerates indicate

timing of collision in Tibet. 16th Himalaya–Karakorum–Tibet work-

shop abstracts. Journal of Asian Earth Sciences 19/3A, 1–2.

Aitchison, J.C., Davis, A.M., 2001b. When did the India–Asia collision

really happen?, International Symposium and Field Workshop on the

Assembly and Breakup of Rodinia and Gondwana, and Growth of Asia.

International Symposium and Field Workshop on the Assembly and

Breakup of Rodinia and Gondwana, and Growth of Asia, Gondwana

Research, 4. Osaka City University, Japan, pp. 560–561.

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 261

Aitchison, J.C., Badengzhu, Davis, A.M., Liu, J., Luo, H., Malpas, J.,

McDermid, I., Wu, H., Ziabrev, S., Zhou, M.F., 2000. Remnants of a

Cretaceous intra-oceanic subduction system within the Yarlung-Zangbo

suture (southern Tibet). Earth and Planetary Science Letters 183,

231–244.

Aitchison, J.C., Davis, A.M., Badengzhu, Luo, H., 2001. The ‘Gangdese

thrust’ was not responsible for uplift of southern Tibet. EOS,

Transactions, American Geophysical Union Fall Meeting Abstracts

Supplement, T12F-08.

Allegre, 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., Xiao, X.,

Chang, C., Li, G., Lin, B., Teng, J.W., Wang, N., Chen, G., Han, T.,

Wang, X., Den, W., Sheng, H., Cao, Y., Zhou, J., Qiu, H., Bao, P.,

Wang, S., Wang, B., Zhou, Y., Ronghua, X., 1984. Structure and

evolution of the Himalaya–Tibet orogenic belt. Nature 307, 17–22.

Badengzhu, 1979. (Compiler) Xizang Autonomous Region Zhanang–

Sangri Regional Geology Reconnaissance Map 1:50,000. Xizang

Geological Survey Geological Team # 2, Group 2, Lhasa.

Badengzhu, 1981. (Compiler) Xizang Autonomous Region Sangri–Jiacha

Regional Geology Reconnaissance Map 1:50,000. Xizang Geological

Survey Geological Team # 2, Lhasa.

Bureau of Geology and Mineral Resources of Xizang Autonomous Region,

1993. Regional geology of Xizang (Tibet) autonomous region.

Geological Memoir of the Peoples Republic of China, Ministry of

Geology and Mineral Resources Series 1 31, 1–707.

Burg, J.P., 1983. Carte Geologique du Sud du Tibet, scale 1:500,000,

CNRS, Paris.

Chang, C., Chen, N., Coward, M.P., Deng, W., Dewey, J.F., Gansser, A.,

Harris, N.B.W., Jin, C., Kidd, W.S.F., Leeder, M.R., Li, H., Lin, J., Liu,

C., Mei, H., Molnar, P., Pan, Y., Pearce, J.A., Shackleton, R.M., Smith,

A.B., Sun, Y., 1986. Preliminary conclusions of the Royal Society and

Academia Sinica 1985 geotraverse of Tibet. Nature 323, 501–507.

Chang, C.F., Zeng, S.L., 1973. Tectonic features of the Mount Jolmo

Lungma region in southern Tibet, China. Dizhi Kexue, Scientia

Geologica Sinica 1, 1–12.

Clift, P.D., Shimizu, N., Layne, G.D., Blusztajn, J., 2001. Tracing patterns

of erosion and drainage in the Paleogene Himalaya through ion probe

Pb isotope analysis of detrital K-feldspars in the Indus Molasse, India.

Earth and Planetary Science Letters 188, 475–491.

Copeland, P., Harrison, T.M., Yun, P., Kidd, W.S.F., Roden, M., Zhang, Y.,

1995. Thermal evolution of the Gangdese Batholith, southern Tibet; a

history of episodic unroofing. Tectonics 14, 223–236.

Coward, M.P., Kidd, W.S.F., Pan, Y., Shackleton, R.M., Zhang, H., 1988.

The structure of the 1985 Tibet Geotraverse, Lhasa to Golmud.

Philosophical Transactions of the Royal Society of London, Series A:

Mathematical and Physical Sciences 327, 307–336.

Davis, A.M., Aitchison, J.C., Badengzhu, Luo, H., Malpas, J., Zyabrev, S.,

1999. Eocene oblique-slip basin development, Tibet: terrane tracks on

the roof of the world. In: Evenchick, C.A., Woodsworth, G.J., Jongens,

R. (Eds.), Terrane Paths 99 Terrane Conference, Okanagan Valley,

Canada, September 26–October 1, 1999, pp. 28.

Davis, A.M., Aitchison, J.C., Badengzhu, Luo, H., Zyabrev, S., 2002.

Paleogene island arc collision-related conglomerates, Yarlung Tsangpo

suture zone, Tibet. Sedimentary Geology 150, 247–273.

Dewey, J.F., Bird, J.M., 1970. Mountain belts and the new global tectonics.

Journal of Geophysical Research 75, 2625–2647.

Durr, S.B., 1996. Provenance of Xigaze fore-arc basin clastic rocks

(Cretaceous, South Tibet). Geological Society of America Bulletin 108,

669–684.

Einsele, G., Liu, B., Durr, S., Frisch, W., Liu, G., Luterbacher, H.P.,

Ratschbacher, L., Ricken, W., Wendt, J., Wetzel, A., Yu, G., Zheng, H.,

1994. The Xigaze forearc basin; evolution and facies architecture

(Cretaceous, Tibet). Sedimentary Geology 90, 1–2.

Gansser, A., 1964. The Geology of the Himalayas, Wiley, New York, pp.

289.

Gansser, A., 1977. The great suture zone between Himalaya and Tibet; a

preliminary account. Colloques Internationaux du Centre National de la

Recherche Scientifique 268, 181–191.

Garzanti, E., Van Haver, T., 1988. The Indus clastics: forearc basin

sedimentation in the Ladakh Himalaya (India). Sedimentary Geology

59, 237–249.

Girardeau, J., Marcoux, J., Zao, Y., 1984. Lithologic and tectonic

environment of the Xigaze ophiolite (Yarlung Zangbo suture zone,

southern Tibet, China), and kinematics of its emplacement. Eclogae

Geologicae Helvetiae 77, 153–170.

Girardeau, J., Mercier, J.C., Xibin, W., 1985a. Petrology of the mafic rocks

of the Xigaze ophiolite, Tibet; implications for the genesis of the

oceanic lithosphere. Contributions to Mineralogy and Petrology 90,

309–321.

Girardeau, J., Mercier, J.C.C., Yougong, Z., 1985b. Origin of the Xigaze

Ophiolite, Yarlung Zangbo suture zone, southern Tibet. Tectonophysics

119, 1–4.

Girardeau, J., Mercier, J.C.C., Zao, Y., 1985c. Structure of the Xigaze

Ophiolite, Yarlung Zangbo suture zone, southern Tibet, China; genetic

implications. Tectonics 4, 267–788.

Harrison, T.M., Copeland, P., Kidd, W.S.F., Yin, A., 1992. Raising Tibet.

Science 255, 1663–1670.

Harrison, T.M., Copeland, P., Hall, S.A., Quade, J., Burner, S., Ohja, T.P.,

Kidd, W.S.F., 1993. Isotopic preservation of Himalayan/Tibetan uplift,

denudation, and climate histories of two molasse deposits. Journal of

Geology 100, 157–175.

Harrison, T.M., Yin, A., Grove, M., Lovera, O.M., Ryerson, F.J., Zhou, X.,

2000. The Zedong window: a record of superposed Tertiary

convergence in southeastern Tibet. Journal of Geophysical Research

105, 19211–19230.

Heim, A., Gansser, A., 1939. Central Himalaya; Geological observations of

the Swiss Expedition 1936, Gebruder Fretz, Zurich, 246 pp.

Hebert, R., Beaudoin, G., Varfalvy, V., Huot, F., Wang, C.S., Liu, Z.F.,

2000. Yarlung Zangbo ophiolites, southern Tibet revisited, 15th

Himalaya–Karakorum–Tibet workshop, Chengdu, China abstracts.

Earth Science Frontiers 7, 124–126.

Hirn, A., Nercessian, A., Sapin, M., Jobert, G., Xu, Z.X., Gao, E.Y., Lu,

D.Y., Teng, J.W., 1984. Lhasa block and bordering sutures; a

continuation of a 500 km Moho traverse through Tibet. Nature 307,

25–27.

Hodges, K.V., 2000. Tectonics of the Himalaya and southern Tibet from

two perspectives. Geological Society of America Bulletin 112,

324–350.

Honegger, K., Dietrich, W., Frank, A., Gansser, M., Thoni, M.,

Trommsdoff, V., 1982. Magmatism and metamorphism in the Ladakh

Himalayas (the Indus–Tsangpo suture zone). Earth and Planetary

Science Letters 60, 253–292.

Jadoul, F., Berra, F., Garzanti, E., 1998. The Tethys Himalayan passive

margin from Late Triassic to Early Cretaceous (South Tibet). Journal of

Asian Earth Sciences 16, 173–194.

Klootwijk, C.T., Gee, J.S., Peirce, J.W., Smith, G.M., McFadden, P.L.,

1992. An early India–Asia contact; paleomagnetic constraints from

Ninety east Ridge, ODP Leg 121; with Suppl. Data 92-15. Geology 20,

395–398.

Liu, G., 1992. Permian to Eocene sediments and Indian passive margin

evolution in the Tibetan Himalayas. Tubinger Geowissenschaftliche

Arbeiten 13, 1–268.

Liu, G., Einsele, G., 1994. Sedimentary history of the Tethyan basin in the

Tibetan Himalayas. Geologische Rundschau 83, 32–61.

Liu, G.H., Einsele, G., 1996. Various types of olistostromes in a closing

ocean basin, Tethyan Himalaya (Cretaceous, Tibet). Sedimentary

Geology 104, 203–226.

Liu, J., Aitchison, J.C., Badengzhu, Davis, A.M., Ziabrev, S.V., Luo, H.,

McDermid, I., 2000. Yamdrok Melange, South Tibet, 15th Himalaya–

Karakorum–Tibet workshop, Chengdu, China abstracts. Earth Science

Frontiers 7, 127.

McDermid, I., Aitchison, J.C., Badengzhu, Davis, A.M., Liu, J., Luo, H.,

Wu, H., Ziabrev, S.V., 2000. Zedong Terrane, a mid Cretaceous

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263262

intra-oceanic arc, South Tibet, 15th Himalaya–Karakorum–Tibet

workshop, Chengdu, China abstracts. Earth Science Frontiers 7, 265.

McDermid, I., Aitchison, J.C., Badengzhu, Davis, A.M., 2001. The Zedong

Terrane: an intra-oceanic magmatic arc assemblage Tibet. 16th

Himalaya–Karakorum–Tibet workshop abstracts. Journal of Asian

Earth Sciences 19/3A, 44.

Mercier, J.L., Tapponnier, P., Proust, F., Andrieux, J., Armijo, R.,

Bassoullet, J.P., Brunel, M., Burg, J.P., Colchen, M., 1980. La collision

Inde–Asie cote Tibet. In: Mercier, J.L., Guangcen, L. (Eds.), Mission

Franco–Chinoise au Tibet 1980. Etude geologique et geophysique de la

croute terrestre et du manteau superieur du Tibet et de l’Himalaya,

CNRS, Paris, pp. 1–13.

Miller, C., Schuster, R., Klotzli, U., Frank, W., Grasemann, B., 2000. Late

Cretaceous–Tertiary magmatic and tectonic events in the Transhima-

laya batholith (Kailas area, SW Tibet). Schweizerische Mineralogische

und Petrographische Mitteilungen 80, 1–20.

Molnar, P., Tapponnier, P., 1975. Cenozoic tectonics of Asia; effects of a

continental collision. Science 189, 419–426.

Nicolas, A., Girardeau, J., Marcoux, J., Dupre, B., Wan, X., Cao, Y., Zheng,

H., Xiao, X., 1981a. The Xigaze ophiolite (Tibet); a peculiar oceanic

lithosphere. Nature 294, 414–417.

Nicolas, A., Girardeau, J., Wang, X.B., Cao, Y.G., Zheng, H.X., 1981b.

Complete ophiolitic sequences in southern Xizang (Tibet); discovery of

cumulates, dike and sill layers. Dizhi Lunping (Geological Review) 27,

457–459.

Pan, Y., 1993. Unroofing history and structural evolution of the southern

Lhasa Terrane, Tibetan Plateau. Implications for the continental

collision between India and Asia. PhD Thesis, State University of

New York, Albany, 395 pp.

Pan, Y., Copeland, P., Roden, M.K., Kidd, W.S.F., Harrison, T.M., 1993.

Thermal and unroofing history of the Lhasa area, southern Tibet—

Evidence from apatite fission track thermochronology. Nuclear Tracks

and Radiation Measurements 21, 543–554.

Pearce, J.A., Deng, W., 1988. The ophiolites of the Tibet Geotraverses,

Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986). Philosophi-

cal Transactions of the Royal Society of London, Series A:

Mathematical and Physical Sciences 327, 215–238.

Searle, M.P., 1996. Cooling history, erosion, exhumation, and kinematics

of the Himalaya–Karakorum–Tibet orogenic belt. In: Yin, A.,

Harrison, M. (Eds.), The Tectonic Evolution of Asia, Cambridge

University Press, New York, pp. 110–137.

Searle, M.P., Windley, B.F., Coward, M.P., Cooper, D.J.W., Rex, A.J., Rex,

D., Li, T., Xiao, X., Jan, M.Q., Thakur, V.C., Kumar, S., 1987. The

closing of Tethys and the tectonics of the Himalaya. Geological Society

of America Bulletin 98, 678–701.

Shackleton, R.M., 1981. Structure of southern Tibet; report on a traverse

from Lhasa to Khatmandu organised by Academia Sinica. Journal of

Structural Geology 3, 97–105.

Tapponnier, P., Mercier, J.L., Proust, F., Andrieux, J., Armijo, R.,

Bassoullet, J.P., Brunel, M., Burg, J.P., Colchen, M., Dupre, B.,

Girardeau, J., Marcoux, J., Mascle, G., Matte, P., Nicolas, A., Li, T.,

Xiao, X., Chang, C., Lin, P., Li, G., Wan, N., Chen, G., Han, T., Wang,

X.b., Den, W., Zheng, H., Sheng, H., Cao, Y., Zhou, J., Qin, H., 1981.

The Tibetan side of the India–Eurasia collision. Nature 294, 405–410.

Wang, C.S., Liu, Z.F., et al., 1999. Xigaze Forearc Basin and Yarlung

Zangbo Suture Zone, Tibet, Geological Publishing House, Beijing, pp.

237.

Wang, C.S., Liu, Z.F., Herbert, R., 2000. The Yarlung-Zangbo paleo-

ophiolite, southern Tibet: implications for dynamic evolution of the

Yarlung-Zangbo Suture Zone. Journal of Asian Earth Sciences 18,

651–661.

Wang, C.S., Li, X.H., Hu, X.M., Jansa, L.F., 2002. Latest marine horizon

north of Qomolangma (Mt Everest): implications for closure of Tethys

seaway and collision tectonics. Terra Nova 14, 114–120.

Wang, X.B., Bao, P.S., Deng, W.M., Wang, F.G. (Eds.), 1987. Tectonic

Evolution of the Lithosphere of the Himalayas: Xizang (Tibet)

Ophiolite, People’s Republic of China Ministry of Geology and

Mineral Resources Geological Memoirs Series 3, 8. Geological

Publishing House, Beijing, p. 336.

Wei, B.J., Peng, Y.H., 1984. (Compilers) Xizang Autonomous Region

Xigaze — Qushui Geological Traverse Map 1:200,000. Xizang

Geological Survey Geological Team # 2, Lhasa.

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan–

Tibetan orogen. Annual Review of Earth and Planetary Sciences 28,

211–280.

Yin, A., Harrison, T.M., Ryerson, F.J., Chen, W.J., Kidd, W.S.F.,

Copeland, P., 1994. Tertiary structural evolution of the Gangdese

thrust system in southeastern Tibet. Journal of Geophysical Research

99, 18175–18201.

Yin, A., Harrison, T.M., Murphy, M.A., Grove, M., Nie, S., Ryerson, F.J.,

Wang, X., Chen, Z., 1999. Tertiary deformation history of southeastern

and southwestern Tibet during the Indo-Asian collision. Geological

Society of America Bulletin 111, 1644–1664.

Zhang, S.M., Fu, X.L., 1982. (Compilers) Xizang Autonomous Region

Xigaze — Saga Geological Traverse Map 1:200,000. Xizang

Geological Survey Geological Team # 2, Lhasa.

Zhou, M.F., Robinson, P.T., Malpas, J., Li, Z., 1996. Podiform chromitites

in the Luobusa Ophiolite (southern Tibet); implications for melt-rock

interaction and chromite segregation in the upper mantle. Journal of

Petrology 37, 3–21.

Ziabrev, S.V., Aitchison, J.C., Badengzhu, Davis, A.M., Luo, H., Liu, J.,

2001. More about the missing Tethys: Bainang terrane Tibet. 16th

Himalaya–Karakorum–Tibet workshop abstracts. Journal of Asian

Earth Sciences 19/3A, 82–83.

Zyabrev, S.V., Aitchison, J.C., Badengzhu, Davis, A.M., Luo, H., Malpas,

J., 1999. Radiolarian biostratigraphy of supra-ophiolite sequences in the

Xigaze area, Yarlung Tsangpo suture, Southern Tibet (preliminary

report). Radiolaria 17, 13–19.

Zyabrev, S.V., Aitchison, J.C., Badengzhu, Davis, A.M., Luo, H., Liu, J.B.,

2000. Tethyan relics in the Yarlung Tsangpo suture, Tibet: structural

setting, radiolarian ages and their tectonic significance. Ninth Meeting

of the International Association of Radiolarian Paleontologists

INTERRAD 2000 Program with Abstracts 72.

J.C. Aitchison et al. / Journal of Asian Earth Sciences 21 (2002) 251–263 263