The closing of Tethys and the tectonics of the Himalaya

M. P. SEARLE | Department of Geology, The University, Leicester LEI 7RH, United Kingdom M. P. COWARD Department of Geology, Imperial College, Prince Consort Road, London SW7 2BP, United Kingdom D.J.W. COOPER | Department of Geology, The University, Leicester LEI 7RH, United Kingdom A. J. REX D. REX Department of Earth Sciences, Leeds University, Leeds LS2 9JT, United Kingdom XIAO^XUCHANC } ^'nese Academy of Geological Sciences, Baiwanzhong, Beijing, China M. Q. JAN Department of Geology and National Centre of Excellence, Peshawar University, Peshawar, Pakistan V C THAKUR li ' r } Wadia Institute of Himalayan Geology, Dehra Dun, 248001, India o. K.UMAK J'

ABSTRACT of the Karakoram and Tibetan microplates north of the suture; as Recent geological and geophysical data from southern Tibet much as 1,000 km shortening occurred in Tibet. The more recent allow refinement of models for the closing of southern (Neo-) Tethys deformation, however, involved the spreading of this thickened crust and formation of the Himalaya. Shelf sediments of the Indian passive and the lateral motion of the Tibetan block along major approximately continental margin which pass northward into deep-sea Tethyan sed- east-west-trending strike-slip fault zones. iments of the Indtis-Tsangpo suture zone were deposited in the Late Cretaceous. An Andean-type margin with a 2,500-km-long Trans- INTRODUCTION Himalayan (Kohisitan-Ladakh-Gangdese) granitoid batholith formed parallel to the southern margin of the Lhasa block, together with The Indus-Tsangpo (also called "Yarlung-Tsangpo") suture zone extensive andesites, rhyolites, and ignimbrites (Lingzizong Forma- north of the Himalaya (Fig. 1) has long been recognized as a major crustal tion). The southern part of the Lhasa block was uplifted, deformed, suture separating the Indian plate to the south from the Lhasa and Xang and eroded between the Cenomanian and the Eocene. In the western Tang blocks in Tibet to the north (Dewey and Bird, 1970; Gansser, 1977; Himalaya, the Kohistan island arc became accreted to the northern Shackleton, 1981; Windley, 1983). Knowledge of the Tibetan sector of the plate at this time. The northern part of the Lhasa block was affected collision zone has until recently relied on reportings of a few explorers who by Jurassic metamorphism and plutonism associated with the mid- penetrated the Himalaya (Lydekker, 1883; Hayden, 1907; Auden, 1935; Jurassic closure of the Bangong-Nujiang suture zone to the north. Wadia, 1937; Heim and Gansser, 1939; Norin, 1946). Extensive field The timing of collision between the two continental plates (ca. work by Chinese geologists in the 1970s was followed by a number of 50-40 Ma) marking the closing of Tethys is shown by (1) the change symposia, field excursions, and joint cooperation projects (Bally and oth- from marine (flysch-like) to continental (molasse-like) sedimentation ers, 1980; Liu Dong-Sheng, 1981; Shackleton, 1981; Sengor, 1981; in the Indus-Tsangpo suture zone, (2) the end of Gangdese I-type Mitchell, 1984). A 3-yr Sino-French cooperation project in Tibet granitoid injection, (3) Eocene S-type anatectic granites and migma- (1981-1984) produced a vast amount of new geological and geophysical tites in the Lhasa block, and (4) the start of compressional tectonics in data (for example, Tapponnier and others, 1981a; Allegre and others, the Tibetan-Tethys and Indus-Tsangpo suture zone (south-facing 1984; Burg, 1983; Burg and others, 1984a). In 1985, there was a joint folds, south-direcled thrusts). Anglo-Chinese geotraverse across Tibet from the suture zone in the south After the Eocene closure of Tethys, deformation spread south- to the Tsaidam basin, north of the Tibet Plateau; preliminary results are ward across the Tibetan-Tethys zone to the High Himalaya. Deep published in Chang Cheng-fa and others (1986). crustal thrusting., Barrovian metamorphism, migmatization, and The western Himalaya shows a more complicated structural and generation of 0%ocene-Miocene leucogranites were accompanied by tectonic history than does the Nepal-southern Tibet sector (Tahirkheli and south-verging recumbent nappes inverting metamorphic isograds and Jan, 1979; Thakur and Sharma, 1983; Coward and others, 1986; Searle, by south-directedl intracontinental shear zones associated with the 1986; Windley, 1983). The geology of the Indus suture zone in the Kohis- Main Central thrust. Continued convergence in the late Tertiary re- tan and Ladakh regions of the northwest Himalaya is dominated by a very sulted in large-scale north-directed backthrusting along the Indus- large island-arc sequence termed the "Kohistan-Dras arc sequence," which Tsangpo suture zone. More than 500 km shortening is recorded in the separates the Karakoram microplate to the north from the Indian plate to foreland thrust zones of the Indian plate, south of the suture, and >150 the south. This arc is bounded by two sutures, a Shyok (or Northern) km shortening is recorded across the Indian shelf (Zanskar Range) suture and the southern Indus suture (or Main Mantle thrust = MMT) and the Indus suture in Ladakh. There was also large-scale shortening (Fig. 1).

Geological Society of America Bulletin, v. 98, p. 678-701, 12 figs., June 1987.

678

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 679

In recent years, a wealth of new geologic information has emerged Major unconformities occur between the Cambrian and Silurian and from both north Pakistan (for example, Calkins and others, 1975, 1981; at the base of the Permian in the Salt Ranges (Gee, 1980; Yeats and Tahirkheli and Jan, 1979; Bard and others, 1980; Coward and others, Lawrence, 1984). In the Hazara region, there are also unconformities at 1982a, 1982b, 1986; Bard, 1983; Yeats and Lawrence, 1984) and Ladakh the base of the Jurassic (Calkins and others, 1975) and at the base of the (for example, Sharma and Kumar, 1978; Thakur, 1981; Honegger and Paleocene (Yeats and Lawrence, 1984). others, 1982; Searle, 1983a, 1983b, 1986; Thakur and Sharma, 1983). It appears that the thick Mesozoic shelf carbonates, which are later- This paper reviews and synthesizes this information and compares it with ally more or less continuous from western Zanskar right across southern new information on Tibet and Kohistan. It includes some data collected on Tibet, end abruptly at the region of the Nanga Parbat syntaxis (Fig. 7). the Royal Society-Academica Sinica Tibet geotraverse in 1985 (Chang West of Nanga Parbat, the Mesozoic succession is drastically reduced. This Cheng-fa and others, 1986) and from ongoing Natural Environment Re- probably reflects the original western extent of the Indian continental search Council research projects in Kohistan. It aims to compare the margin. structure and stratigraphy along the length of the Himalaya, in particular the nature of the suture zones, the deformation of the northern plate, and Stratigraphy of the Northern Plate the effects of overthrusting on the Indian plate, to build up a tectonic sequence for the whole mountain chain. The origin of the Karakoram microplate is uncertain. Tapponnier Data are presented in simplified geologic maps of Tibet, Ladakh, and and others (1981b) considered it to be part of the Gondwana plate, and it Kohistan (Figs. 2,4, and 7), with their respective cross sections (Figs. 3,5, may be similar in origin to the Lhasa microplate, a separate micro-conti- and 8), and in time charts comparing the sequences of events in different nental fragment bounded to the north by the Bangong-Nujian suture parts of each region (Figs. 9, 10, and 11). which closed probably in the Late Jurassic-Early Cretaceous (Girardeau and others, 1984a; Xu Rong-Hua and others, 1985; Chang Cheng-fa and STRATIGRAPHY others, 1986). To the northwest of Kohistan, in the Hindu Kush, the oldest rocks of Paleozoic-Mesozoic Stratigraphy of the Indian Plate the Karakoram microplate are Paleozoic sediments between the Main Karakoram thrust (MKT) and the Afghanistan border (Pudsey and others, A relatively continuous Paleozoic and Mesozoic shelf succession oc- 1985; Pudsey, 1986). Only one isolated Ordovician outcrop is known, but curs in the Zanskar-Lahoul-Spiti regions of northwest India (Figs. 4 and 6) there is a prominent unit of Devonian limestones, dolomites, quartzites, along the northern margin of the Indian plate (Gupta and Kumar, 1975; and calcareous sandstones which provide evidence of very shallow marine Bassoullet and others, 1978; Fuchs, 1979; Thakur, 1981; Baud and others, conditions on a continental shelf (Talent and others, 1982). 1984). This succession, which is ~ 6 km thick, consists of upper Precam- To the northeast of Kohistan, along the Baltoro glacier toward K2, brian to Eocene sediments, stratigraphically divided into a Paleozoic La- well-cleaved Carboniferous slates are overlain by a Permian-Triassic and houl Supergroup and a Mesozoic Zanskar Supergroup separated by the Jurassic carbonate sequence (Desio, 1964, 1979; Desio and Zanettin, thick Permian Panjal Volcanic Group, commonly referred to as the "Pan- 1970). The Baltoro black slates are underlain by fissile shales and highly jal Traps." These continental tholeiitic and mildly alkaline flood basalts strained conglomerates interbedded by lithic tuffs and intruded by subvol- may have been erupted in early rifts which evolved into the passive conti- canic porphyries and quartz diorites (Searle and others, in press). A car- nental margin of Neo-Tethys during the early Mesozoic. bonate platform of Mesozoic age was stable on this Tethyan plate margin In the western Himalaya, a well-developed carbonate platform until initial collision of the Karakoram microplate with the Kohistan-Dras formed in the Triassic, and a widespread Jurassic transgression of the shelf island arc to the south during the mid-Cretaceous. At Hunza, the Karako- is marked by the thick, fossiliferous Spiti shales (Arkell, 1956). Deposition ram granodiorite batholith has a U-Pb date on zircons of ~95 m.y., which of shelf carbonate facies was characteristic of the Early Cretaceous, and is interpreted as an emplacement age (Le Fort and others, 1983). Younger relatively stable shallow-marine conditions continued until the Campa- mineral ages suggested to these authors Eocene regional metamorphism at nian-Maastrichtian when deep-water shales were deposited, notably the the time of Indo-Eurasian collision and Miocene uplift. Recent field inves- Kangi-la flysch in the Zanskar Range (Fuchs, 1979). In general terms, the tigations along the Baltoro glacier transect, however, suggest a close spacial Indian plate was bounded on the north by a passive continental margin and temporal relationship between the age of metamorphism and the age throughout the Mesozoic, and fossiliferous Eocene limestones in Zanskar of generation of the more S-type components of the Karakoram batholith and northern Hazara are the youngest shelf sediments in the Tibetan- such as the Baltoro plutonic unit (Searle and others, in press). These Tethys zone (Gaetani and others, 1983; Mathur and Pant, 1983). authors suggested the possibility that the Karakoram metamorphic series The Tibetan-Tethys zone section between Chiatsun and Gyangtse on the hanging wall of the Main Karakoram thrust, to the south of the along the Friendship Highway from Lhasa to Kathmandu probably repre- batholith, may represent metamorphosed equivalents of the Carboniferous sents the least deformed section of these rocks anywhere in the Himalaya to Jurassic (to Early Cretaceous?) shelf sediments of the Gasherbrum (Figs. 2 and 3), and Mu An-Tze and others (1973) described a continuous Range to the north of the batholith. stratigraphy from Ordovician to Eocene north of Everest. In the Lhasa block, there are gneisses of possible Precambrian age In Pakistan, the succession is not so continuous and has several (Xu Rong-Hua and others, 1985; Chang Cheng-fa and others, 1986), but stratigraphic gaps in the upper Paleozoic and Mesozoic. The earliest sedi- the earliest recorded Phanerozoic sediments are Carboniferous and contain ments, the Hazara slates, were deformed, metamorphosed, and then in- glacial-derived tilloids. These are overlain by shallow shelf facies sediments truded by granites, such as the Mansehra granite, which has been dated at and volcanics of Permian-Triassic to Cenomanian age. During the Cre- 514 Ma (Le Fort and others, 1980). There is a localized thick development taceous, marine carbonate sedimentation changed to terrestrial red-bed of lower Paleozoic conglomerates, quartzites, and limestones, possibly deposition with andesitic volcanism (Takena Formation). During the developed in fault-bounded basins, whereas to the south and west of Cenomanian-Eocene, the southern part of the Lhasa block was uplifted, Islamabad, the Cambrian strata are represented by red sandstones and folded, and eroded prior to the eruption of the calc-alkaline Lingzizong evaporites. Formation volcanics (Fig. 9).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 680 SEARLE AND OTHERS

U.S.S.R. Kongur Mustagh At a

Neogene - recent acidic volcanic centres

V Karakoram granite batholith y « < X X Trans-Himalayan granite batholith to, Neogene tourmaline granites Ophioliites & ophiolitic melanges Indus- Basin sediments & volcanic rocks Tsangpo Suture zone Indus Group (T) a Mesozoic shelf sediments Tibetan- Panjal Volcanic Group (Carb-P) INDIA Tethys zone Palaeozoic sediments a Central crystalline complex Higher Himalayan Granite gneiss zone ITSZ Indus-Tsangpo suture zone Lesser Himalaya thrust sheets MCT Main Central thrust Siwalik sediments (T) MBT Main Boundary thrust

Figure 1. Geologic map of the Himalayas (after Gansser, 1964). Boxes a, b, and c give locations of areas shown in Figures 2,4, and 7. (Note overlap in center.)

Stratigraphy of the Suture Zone distal deep-sea fades. The oldest Tethyan basin rocks in the Indus-Tsangpo suture in south Tibet are in the Yamdrock melange, which contains large The Indus-Tsangpo suture zone in south Tibet contains Mesozoic isolated Permian exotic limestone blocks associated with alkali volcanics rocks which are time equivalents of shelf sediments of the Tibetan-Tethys (Fig. 9) accompanied by Triassic, Jurassic, and Lower Cretaceous deep- zone on the northern continental margin of India, but they are a more sea sediments (turbidites and radiolarian cherts) (Lin Baoyu, 1984). The

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 681

t N

QINGH A I - X / ZANT

CHINA

BURMA

0 Kilometres 300 +o 1 i i I O 0>

Figure 1. (Continued).

Xigase ophiolite has Albian-Aptian radiolaria in cherts conformably above Mesozoic Tethyan basinal sediments and volcanics deposited in an oceanic the pillow lava sequence (Girardeau and others, 1984b), and the overlying setting north of the Indian continental margin. A cross section through the Xigase Group sediments span the Upper Cretaceous. The Xigase Group Indian continental shelf and margin rocks of the Zanskar and Ladakh has clasts derived from the Gangdese granitoids to the north (Allegre and Range is shown in Figure 5, and a restored section of this is given in Figure others, 1984; Girardeau and others, 1984b). 6. Line balancing on the Cretaceous-Tertiary boundary shows that the In Ladakh, there is a structurally complex zone of predominantly present 98-km length from the Zanskar Valley normal fault to the Ladakh

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 Figure L Structural-tectonic map of southern Tibet and cen- tral and eastern Nepal, from England and Searle (1986), from mapping dome by Burg (1983) and the Chinese Academy of Geological Sciences. The contact between the High Himalayan Central Crystalline Complex and the Tibetan-Tethys zone of sed- iments is the thick line shown immediately north of Cho Oyu, Everest, Makalu, Kangchengunja, and the highest peaks of the Himalayas (Note overlap in center.)

TIBETAN (XIXANG) PLATEA!

GANGDESE TRANSHIMALAYAN % % * BATHOLITH

aiUWA FM. ui z XIGASE GP. OO XIOASE OPHJOLITES O.fUN J «il MESiOZOIC FLYSCH

KANGMAR GRANITE- GNEISS DOMES

INDIAN PLATE SHELF SEDIMENTS

CENTRAL CRYSTALLLINE COMPLEX AND HIGH HIMALAYAN Trisuli / Znanry LEUCOGRANITES bazar ( / sir*

Main Central Thrust _

LESSER HIMALAYA NAPPES

Main Boundary Thrust

SIWALIK MOLASSE Siwalik Hills Main Boundary Thrust

o \t * \

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 0

Boundary Thi^f4,

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 684 SEARLE AND OTHERS

HIGH HIMALAYAS

CENTRAL CRYSTALLINE COMPLEX TIBETAN - TETHYS ZONE

Figure 3. Geologic cross section of southern Tibet along the Friendship Highway from the Nepalese border at Zham along the Nyelam- Chiatsun road (from Shackleton, 1981). The Main Central thrust sheet rocks comprise garnet = (Gt), staurolite = (St), kyanite = (Ky), and sillimanite = (Sill bearing metapelites, paragneisses, and augen gneisses. Several leucogranitic (G) sheets, showing hornfels (H) contact metamorphism in places, are in many cases associated with the migmatites (M). The Tibetan-Tethys zone shelf sediments are of Ordovician (O), Devonian (D), Ciirboniferous (C), Permian, Triassic (Tr), and Jurassic (Jr) age in this section. Numbers below the section are kilometre posts (from Lhasa). Horizontal and vertical scales are equal.

batholith restores i:o an original length of 250 km. The implicit amount of rhyolites (Honegger and others, 1982) are associated with the exotic lime- shortening across the Zanskar Range is therefore a minimum of 152 km stone blocks. They are comparable to similar associations elsewhere in (Searle, 1986). The Lamayuru complex consists of shales, sandstone turbi- Tethys, for example the Mammonia complex in Cyprus and the Haybi dites, and rare deep-sea red radiolarian cherts which span the Triassic to complex in Oman (Searle and Graham, 1982) and the Mulbeck exotics in Cretaceous; these are the allochthonous preorogenic basin sediments of Ladakh (Searle, 1983a). In all of these areas, the volcanic-exotic limestone Tethys (Frank and others, 1977; Thakur, 1981; Thakur and Sharma, associations are thought to have formed as Triassic off-axis volcanoes with 1983; Searle, 1983a, 1983b, 1986). limestone cappings during Tethyan rifting. They are not related in age, Exotic limestone blocks containing abundant fossils of Late Permian chemistry, or origin to the adjacent MORB-related ophiolite complexes. and Triassic age are in tectonic contact with the Lamayuru sediments and The age of the Jungbwa ophiolite is unknown, but comparison with are termed the "Mulbeck exotics" (Searle, 1983a). They are similar to similar ophiolites along the Indus-Tsangpo suture zone suggests that it is well-known Tethyan exotic limestones in Oman, Cyprus, and the Zagros probably Cretaceous. The ophiolitic melange thrust sheets directly overlie suture of Iran and are interpreted as thrust seamounts that formed during Upper Cretaceous flysch, and the age of emplacement is thus assumed to the early stages of rifting (Searle and Graham, 1982). Alkaline and tholeii- be Late Cretaceous or earliest Tertiary. No Tertiary rocks underlie the tic volcanic rocks also occur in the Indus suture of Ladakh, mainly en- ophiolitic melange thrust sheets (Gansser, 1964). closed in ophiolitic melange belts (Honegger and others, 1982; Searle, 1983a). Spongtang Ophiolite

OPHIOLITE GENERATION AND EMPLACEMENT The Spongtang ophiolite klippe rests on allochthonous Lamayuru sediments and melanges similar to those exposed in the Indus suture zone Throughout l:he Himalayan region, ophiolite complexes occur in two ~30 km to the north (Fig. 4). It has yet to be studied in detail but appears main tectonic settings: in thrust sheets obducted southward onto the north- to preserve mainly the ultramafic and gabbroic levels, with some volcanic ern continental margin of the Indian plate and in discontinuous lenses rocks in distinct thrust slices (Reibel and Reuber, 1982; Searle, 1983a; tectonically disrupted within the Indus-Tsangpo suture zone. The best Reuber, 1986). Lithologies in the ophiolitic melange along the base of the examples of ophiolites obducted onto the Tethyan shelf sediments on the Spontang ophiolite include exotic limestones, Dras volcanic rocks, radio- Indian plate are the Jungbwa peridotite in southwest Tibet and the Spong- larian cherts, and amphibolites arid greenschists of the subophiolite meta- tang ophiolite in 2anskar (India). morphic sheet. The age of the Spontang ophiolite is unknown, but it is at present assumed to be Late Cretaceous. Jungbwa/Amlang-la Ophiolite Melange Sakhakot-Qila or Dargai Ophiolite The Jungbwa peridotite covers -3,500 km2 and structurally overlies thrust sheets of Mesozoic shelf sediments and flysch containing exotic The Sakhakot-Qila ophiolite is an incomplete, predominantly ultra- blocks (mostly Triassic limestones and alkali basalts) in the Amlang-la mafic ophiolite, which has an area of 25 x 5 km and an exposed thickness region of southwest Tibet (Heim and Gansser, 1939; Gansser, 1964). In of 3.5 km, and it is -30 km south of the Main Mantle thrust in Pakistan the Kiogar mountains, massive Upper Triassic Kioto limestone blocks are (Fig. 4). The complex is faulted against Precambrian greenschist facies embedded in serpentinized ultramafic rocks, forming a tectonic melange metasedimentary rocks. The crustal sequence is very thin and highly dis- (Gansser, 1964). Triassic alkali basalts, hawaiites, mugearites, and alkali membered, whereas the mantle sequence is well developed. Metagabbros

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 685

M VÜ *

X X X X .Batalik

£. A ^ T- «/^Spushkum j > / . — v—^

etc Is * Ï Sank a 10 Chang Tang .A 30 7 J

^ Spontanglttv^0 x 3Ü- Upschi (H/Rangdum; J^w^li : / ^ \ v; VingshedfLinflshed, )V v^ \ \\A\A. \\\\ . - • ' "»

^V \ T\ 1 ' Tso Morari - ' — v -r» \ \ ^crystalline complex

Indus Gp. Ladakh granitoids Spontang ophiolite / •><~-

Central crystalline complex km 40

Figure 4. Geologic map of Ladakh and Zanskar, northwest Indian Himalaya (from Searle, 1986). Location given by box b in Figure 1.

reach 350 km width. Ultramafic outcrops comprise roughly 65% harzbur- Xigase Ophiolite gite, 25% wehrlite, and 8% dunite. There are also metadolerite, rodingite, and pyroxenite dikes and chromite lenses in dunite. Neither the exact age Whereas the above described ophiolites were obducted considerable of the country rocks nor the age of emplacement are known (see Ahmed distances southward onto the Indian continental margin, the Xigase ophio- and Hall, 1984). lite complex of southern Tibet lies along the suture zone between the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 NE sw I

TIBETAN-TETHYS ZONE INDUS SUTURE TRANS-HIMALAYA LII/**LJ UIIIAI A W A f 1 » V«» 1 1 iimnun i n ZONh

Zanskar Valley Tsarap Ladakh Range

Central Crystalline Complex and leucogranites

y/fp///// ^

0 5 10 15 20 1 I 1 1 I V=H ^ T1 thrusts

Km. ^ T2 thrusts ^ T3 thrusts

Figure 5. Schematic section across the Tibetan-Tethys zone suture zone. Deep-level culminations of granite gneiss domes are of Zanskar and the Indus suture zone of Ladakh (Searle, 1986). extrapolated westward from the Tso Morari dome (TM). Pz = Paleozoic sediments, and Mz = Mesozoic shelf sediments. Upward-decreasing metamorphic isograds above the Tso Morari The Ladakh granitoids bound the northern edge of the Indus granite are shown as dashed lines.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 Zanskar HIGH Valley TIBETAN - TETHYS ZONE HIMALAYA Normal fault

SW

Figure 6. Restored cross section of the present-day structural section across Ladakh-Zanskar, shown in Figure 5. Symbols are the same as in Figure 5. Line balancing on the Cretaceous-Tertiary boundary shows that the present-day width of 98 km (Fig. 5) restores to 250 km, indicating that at least 152 km of shortening has occurred across the Zanskar and Indus suture zones. The diagram also shows that the Panjal Volcanic Group in the Kashmir Himalaya decreases in thickness northeastward across Zanskar. It also illustrates the facies change from the Mesozoic shelf sediments to Mesozoic Lamayuru basin sediments and the deepening of the Indus molasse basin beginning in the Eocene.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 Figure 7. Geologic map of Kohistan (after Coward and others, 1986). Location given by box c in Figure 1 (Note overlap in center.)

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 KOHISTAN BATHOLITH IN THE GlLGlT AREA

10 km X ^ Nanga A vaiaa^T^v rv\ Par bat Gneiss \ + J*>i\ • » • f\ * ^^VVt —' * IV _ J. 1 * \U \

vol cani cs

sediments T-r\ granite, tonalité, granodiorite

; I diorite, gabbro

1 gneiss

'Cs

»0 Lt A ^ Chilas ta il i_ j—i A A

/ -, LEGEND

«.oy bedding

Indian Plate Kohistan arc Northern plate <&y cleavage o a Kohistan batholith 0 Murree Fm. [ ** * I Granites —" thrust sediments

,-B— syncline sediments at Dir Cvvv , 1 Mesozoic vvvj volcanics & Kaiam Reshun Group — anticline r&j sediments volcanics 'greenstone' etc. Yasin Group Granites /t Chalt volcanics Basement Chitral Slate undifferantiated Precambriar I A j Amphibolic -'-/.-I sediments ! *; • ;! Darkot Group I j j Chilas complex

I^^J Ophiolite kVVN Blueschists E Alluvium tOöCI & granuli tes

Figure 7. (Continued).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 690 SEARLE AND OTHERS

Indian plate and the Lhasa block (Fig. 2). All components of the ophiolite of the Paleocene-Eocene Lingzizong volcanics imply a comagmatic origin are present, albeit mostly in thrust or strike-slip fault contact. For this with the Gangdese granitoids. reason, the original thickness of oceanic crust cannot be known for certain, Radiometric ages of the Gangdese intrusives span the Cenomanian to and there is no reason to suppose that it was anomalously thin crust as late Eocene and are remarkably consistent with ages derived from the suggested by Nicolas and others (1981). In some sections, the Xigase Ladakh plutonic complex (Figs. 9 and 10) (Honegger and others, 1982; ophiolite is tightly folded, but in general, it faces and dips steeply to the Reynolds and others, 1983; Scharer and others, 1984a, 1984b) and the north. Late Tertiary, north-directed back thrusts affect the ophiolite along Kohistan batholith (Petterson and; Windley, 1985). Recent precise U-Pb much of its length, and right-lateral strike-slip faulting has further disrupted radiometric dating (Scharer and others, 1984b) shows a range from 94 to the ophiolite sequence. The southern contact is always thrusted and 41 Ma. U-Pb dates on the Trans-Himalayan plutons led Xu Rong-Hua and marked either by a tectonic breccia or by foliated garnet amphibolites and others (1982) to suggest that collision of India with the southern Tibet quartzites that belong to the metamorphic sheet that formed during obduc- block occurred at 60 Ma in Ladakh but at 40 Ma in the Lhasa area. Recent tion (Girardeau and others, 1984b). Rb-Sr dates of 40 Ma on plutons in Ladakh (Reynolds and others, 1983) There is also evidence of an earlier phase of oceanic thrusting prior to and in north Pakistan (Petterson and Windley, 1985), however, indicate obduction of the ophiolite. The mantle sequence of the Xigase ophiolite that the main plutonic activity terminated at about the same time along comprises 4-6 km of harzburgite and lherzolite (with chrome-diopside) most of the Trans-Himalayan batholith, and, in turn, this suggests a similar intruded by many dolerite dikes and sills. This unusual association in the age for terminal collision. mantle sequence could be explained by thrusting of one slab over an active The U-Pb ages and isotopic compositions are compatible with a spreading center, enabling high-level dikes to intrude previously lower model of northward subduction of Tethyan oceanic lithosphere beneath mantle rocks. This explanation is supported by the totally different Pb the Lhasa block, formation of magma, and some continental crustal con- isotopic signatures of the harzburgites and of the crustal sequence. The tamination during rise of the plutons. The inherited radiogenic lead in mantle harzburgites have much higher 207Pb/204Pb values than does the zircons provides further evidence that some melting of lower continental gabbro-dike-lava sequence and cannot therefore be related (Gopel and crust was involved. others, 1984). Trace-element and REE geochemistry shows that the ba- There is one important difference between Tibet and the western salts and dolerites are identical to MORB (Prinzhofer and others, 1984), Himalaya. Whereas there is an intra-oceanic island arc complex in the and there seems no evidence to assume that an island arc was involved in latter, there is none preserved in the Tibetan part of the suture zone. In the their generation. west, in Kohistan, the Trans-Himalayan granitoids intrude an already For the ophiolites, a U-Pb whole-rock age of 120 ±10 m.y. (Gopel folded Kohistan island arc, indicating that the intra-oceanic subduction-arc and others, 1984) is reported from Xigase, and overlying conformable system docked with the Asian margin, forming a suture (the Shyok suture) radiolarian cherts have Albian-Aptian microfossils (Girardeau and others, and evolved with time into an Andean-type margin during the Paleogene 1984b; Xiao Xuchang, 1984). Flysch sediments belonging to the Xigase (Petterson and Windley, 1985; Coward and others, 1986). group north of the ophiolite are dated as Cenomanian to Danian and are The extrusive history of the Kohistan arc can be seen from the Chalt considered to lie conformably on top of the ophiolite (Allegre and others, and Dras volcanic sequences. In particular, the Dras volcanic group in 1984; Girardeau and others, 1984b). Ladakh comprises a 3-km-thick (maximum) sequence of Jurassic to Upper Cretaceous tholeiitic to andesitic volcanic rocks and volcanoclastic THE TRANS-HIMALAYAN BATHOLITH sediments and has a geochemical pattern comparable to that of island arc AND KOHISTAN ARC tholeiitic and calc-alkaline series of present-day island arcs (Honneger and others, 1982; Dietrich and others, 1983; Radhakrishna and others, 1984; A belt of granitoid rocks crops out immediately north of the Indus- Coward and others, 1986). Tsangpo suture zone for a distance of 2,500 km from Kohistan to Assam Within the Kohistan arc, the Chilas complex consists of layered basic (Figs. 1, 2,4, and 7). It is commonly referred to as the "Kohistan batho- cumulates and probably formed as the magma chamber to the arc (Fig. 7). lith" (Fig. 7) (Coward and others, 1982b, 1986; Petterson and Windley, It is >350 km long and 8 km thick, and its main constituents are norites, 1985) or the "Ladakh batholith" (Fig. 4) (Thakur, 1981) in the west, the gabbros, hypersthene gabbros, minor troctolites, and chromite-bearing du- "Kailas tonalite" in southwest Tibet (Heim and Gansser, 1939), and the nites. Probable equivalents in Ladakh occur in the Kargil area where "Gangdese plutonic complex" in south Tibet (Fig. 2) (Shackleton, 1981; mafic-rich gabbros, orthopyroxene-bearing norites, and hornblende- Tapponnier and others, 1981a; Allegre and others, 1984); regionally, it is pyroxene anorthosites represent a deep level of the Ladakh plutonic com- termed the "Trans-Himalayan batholith." plex (Rai and Pande, 1978). In southern Tibet, numerous intrusions of gabbro, diorite, granodior- At the southern edge of the Kohistan arc, the Jijal complex (Fig. 7) is ite, and granite arc widely interpreted to represent an Andean-type batho- an -200-km tectonic wedge of garnet granulites intruded by a 14-km lith at the southern margin of the Lhasa block (Allegre and others, 1984), body of ultramafic rock (Jan and Howie, 1981). The granulites are mostly in common with the Ladakh region (Honegger and others, 1982). The garnet gabbros with minor metanorites, and the ultramafic rocks include predominant rock type is a biotite- and hornblende-bearing granodiorite diopsidites, dunites with chromite seams, peridotites, harzburgites, and that appears remarkably uniform along the entire length of the Trans- hornblendites. The garnet granulites and ultramafic rocks are chemically Himalayan batholith. distinct and genetically unrelated; however, the origin of both these rock Geochemically, the Gangdese granitoids are very compatible with groups is still uncertain. They were metamorphosed at 690-700 °C and other I-type Cordilleran granites (Chappell and White, 1974; Pitcher, 12-14 kbar and at 800-850 °C and -8-12 kbar, respectively. An unpub- 1982) such as the coastal batholith of Peru (Atherton and others, 1979; lished Sm-Nd mineral isochron age of 103 ± 4 Ma on the garnet granulites McCourt, 1981). Initial Nd, Sr, and Pb isotopic compositions of the by M. Thirlwall (1986, personal commun.) probably resulted from high- Gangdese granitoids have a mantle-derived component, but they also pressure sub-island arc subduction-related metamorphism. Paragonite- show that anatexis of the lower continental crust was involved in the bearing assemblages were formed in shear zones at 505-540 °C and 8-9 magma genesis (Allegre and others, 1984). Similar isotopic characteristics kbar during uplift of the Jijal complex on the suture (Jan and others,

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 691

NW I ~ ~~ I ' ~ ¡E

E3 RED BEDS CO CRETACEOUS EOCENE SEDIMENTS CD METASEDIMENTS • PALEOZOIC E3 KOHISTAN-KARAKORUM ROCKS QU TERTIARY PLUTONICS Q GNEISSIC GRÄMTE CD PRE CAMBRIAN SLATES « G3 PHANEROZOIC (CHfTRAL) SLATES E3 KOHISTAN ROCKS I

20 km BREAK IN SECTION

Figure 8. Cross section through Kohistan along the line shown in Figure 7, based on data of Coward and others (1986), Pudsey and others (1985), and unpublished work by M. P. Coward.

1982). Between the Jijal and Kohistan-Chilas complexes, there is a wide sedimentation starts with the Eocene Quiwa Formation conglomerates zone of intensely deformed amphibolites and metasediments (the Kamila (Fig. 9). Clasts in these conglomerates are mostly granitoids and acid complex) which give 39Ar/40Ar ages on hornblendes of older than 75 Ma. volcanics derived from the Gangdese batholith to the north. It is not known whether they represent the southerly and more highly Immediately south of the Xigase ophiolite, there is a distinctive me- metamorphosed equivalents of the Kohistan island arc or, more likely, a lange (Yamdrock melange) which was described by Tapponnier and oth- second arc complex to the south which became accreted on the Kohistan ers (1981a) as "wildflysch with exotic blocks." The exotics include blocks arc during the Late Cretaceous. as much as 3 km long of Permian crinoidal limestones as well as lime- The Kohistan arc and its base, the MMT, have been folded into large stones of Triassic, Jurassic, and Cretaceous age. The youngest fossils in the north-south-trending antiforms, the largest of which occurs north of exotic blocks are Campanian-Maastrichtian Globotruncana sp. (Tappon- Nanga Parbat (Fig. 7). Across this fold, the arc rocks have been eroded nier and others, 1981a) and even Danian (J. Marcoux, 1984, personal away, and only Nanga Parbat gneisses of the Indian plate have been commun.). There are also distinctive blocks of Carnian "Ammonitico mapped south of the MMT. Rosso"-type limestones associated with alkali basalts. Some of the lower sections in the Yamdrock melange apparently LHASA BLOCK VOLCANISM have a flysch-like matrix; this was interpreted as a sedimentary melange by Shackleton (1981). The section around Qianggong village, ~ 100 km west North of the Gangdese batholith in south Tibet, many of the high of Xigase and toward the Cuola pass, however, is an excellent example of mountains around Lhasa are composed of ignimbrites, andesites, and al- a tectonic melange. In this area, a chaotic, nonbedded block melange with kali rhyolites of the Lingzizong Formation, which are >1,600 m thick and little or no matrix, juxtaposing numerous blocks of widely differing age overlie folded red beds of the Cretaceous Takena Formation (Coulon and and facies, cannot be described as a bedded olistostrome deposit; it must be others, 1984). Radiometric ages for the volcanics have been determined as of tectonic origin. A suitable environment to produce such a melange is a 60 and 48 Ma by 39Ar/40Ar (Maluski and others, 1982) and 60 and 56 trench, which palinspastic reconstruction places along the footwall of the Ma by Rb/Sr methods (Xu Rong-Hua and others, 1985). These volcanics basal Xigase ophiolite obduction plane (Fig. 12). are probably comagmatic with and represent the extrusive equivalents of the Gangdese batholith, as indicated by similar ages and isotopic character- HIGH HIMALAYAN DEFORMATION istics (Scharer and others, 1984b; Xu Rong-Hua and others, 1985). AND METAMORPHISM A separate and younger sequence of very thick well-bedded acid lavas, welded tuffs, and ash flow deposits of rhyolite-dacite composition The Central Crystalline Complex of the Higher Himalaya (Gansser, (Majang Formation) occurs in the Nyenqentangla range (Figs. 2 and 9). 1964) represents the metamorphic basement to the Phanerozoic sediments Enormous volumes of these acid lavas crop out around the Shukula Shan of the Tibetan-Tethys zone (the Tibetan Slab of Lombard, 1958; Bordet, mountain (7,053 m) on the road from Yangbajing to Xigase. Similar 1961; Caby and others, 1983). It is composed entirely of metamorphic volcanics throughout the Tibetan plateau were collected by Eric Norm in rocks and leucogranites and is separated from the Tibetan-Tethys sedi- 1946. These Majang volcanics have been dated by 40Ar/39Ar (H. Maluski ments to the north by a shallow north-dipping (25° to 45°) tectonic in Coulon and others, 1984) and Rb/Sr methods (Scharer and others, contact, which is interpreted, at least in upper crustal levels, to be a normal 1984c) as 14-10 Ma. fault (Caby and others, 1983; Burg and others, 1984b; Burg and Chen, 1984; Burchfiel and Royden, 1985) (see Fig. 12). Small-scale structures TERTIARY SEDIMENTATION IN THE SUTURE ZONE indicate down-to-the-north sense of movement, and the contact is proba- bly an original thrust reactivated as a normal fault during late Tertiary Sedimentation in the Indus-Tsangpo suture zone changes dramati- spreading of the thickened Tibetan/Himalayan crust (Burg and Chen, cally around the Cretaceous-Tertiary boundary. Upper Cretaceous marine 1984; Burchfiel and Royden, 1985; Coward and others, in press). South of flysch of the Xigase Group ends and coarse clastic, mostly conglomeratic, the contact, the high-grade metamorphic rocks, including sillimanite-,

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 TIBET

HIMALAYA - YARLUNG - TIBET - N INDIAN PLATE ZANGPO LHASA BLOCK Ma SUTURE ZONE

N-backthrusting

O O O 7* U2 . C

40- 40*» gg 41* «ci- ca < 48* 50* n 50- O m Z 60- 60*

67* 70- Folding and a c. 40% shortening o of Lhasa block oc 80- a Ui c

s u. 100- < z HI cherts

X119 t 25 120 ~ XIGASE OPHIOLITE

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 INDIAN PLATE HIMALAYA ZANSKAR N INDUS-SUTURE ZONE CENTRAL TIBETAN- CRYSTALLINE TETHYS TRANSHIMALAYA Ma COMPLEX ZONE

CI- PLEISTOCENE

PLIOCENE N-backthrusting

10 —

MIOCENE

20 —

O CO 26- Z O

30 — OLIGOCENE IP2 S-thrusting 37- * 38.8 3 1.3 40 — Figure 10. Time chart for rocks of the Indian plate, Indus EOCENE KONG suture zone, and Trans-Hima- FM. layan batholith in the Ladakh 48.7 ±1.6 region (after Searle, 1986). Ra- 50 — LINGSHET FM. diometric ages shown are by U- 53- ? Spontang Pb (crosses), Rb-Sr (squares), ophiolite and '•"Ar-^Ar (stars). See text PALAEOCENE obduction * 60 ± 10 for sources of data. 60 — X 60.7 ±0.4

MAASTRICH -TIAN S-thrusting 70 - • 69.8 ±3.2 jjc 73.4 i 2.4 • 74.4 ±2.5 Blueschists

80 —

90-

CENOMAN -IAN

100 X 101± 2 X 103 ±3 KHALSI FM. 110-

DRAS VOLCANIC 120- GROUP

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 694 SEARLE AND OTHERS

kyanite-, staurolite-, garnet-, and muscovite-bearing schists and gneissic (Malinconico, 1986), which suggest that the dense basic rocks of the granites, show good evidence for southward thrusting (Burg and Chen, Kohistan complex are limited to the upper few kilometres of the crust, 1984; Brunei, 1986). although there are problems with this interpretation in that it does not take In northern Pakistan, similar metamorphic rocks crop out imme- into account the less dense Kohistan granites which lie above the MMT. diately south of the suture (Figs. 7 and 8). All of the small-scale structures Note that this interpretation is different from the previous one of a deep indicate thrusting to the south-southeast on a large ductile shear zone crustal MMT (Coward and otheis, 1982a). The previous interpretation which has itself been tightly folded and imbricated (Coward and others, in considered the folds within the Kohistan complex to be of the same age as press). The suture zone has thus cut down into the Indian plate and the MMT, decoupling above the shear zone, and the position of the MMT tectonically removed its northern boundary by scraping it to the south, at depth was constructed from the shape of these folds. Our present view is juxtaposing the Kohistan arc rocks and the high-grade metamorphic rocks. that these folds are earlier, related to the accretion of the Kohistan arc Brunei (1986) has mapped the thrust kinematic indicators around the complex with the Karakoram plate, and that the MMT slices through these Himalaya and shows them to have a radial pattern, from south-southeast structures. According to this interpretation, the MMT has eroded into the directed in Assam, to south directed in Nepal, southwest directed in Indian overthrusting Kohistan plate by a process of hanging-wall collapse or Kashmir, but reverting to south or south-southeast directed in Pakistan. break-back thrusting (Butler, 1982) and has removed the lower part of the The overthrust direction was thus outward, away from the thickened Kohistan arc by underthrusting it to the north. Tibetan crust. A discussion of the origin of this radial pattern is given in Break-back thrusts to the MMT occur in the central part of Kohistan, Butler and Coward (in press). near Dir and Chitral at the northwestern margin of the Kohistan arc (Figs. The Main Central thrust crops out just south of the border in Nepal 7 and 8). Near Dir, Upper Cretaceous to Paleocene sediments are tightly and is associated with characteristic reverse metamorphism (Le Fort, folded, cleaved, and thrust to the south-southeast and then later affected by 1975; Andrieux and others, 1981; Bouchez and Pecher, 1981; Caby and normal faults which drop down to the northwest, reactivating the earlier others, 1983; Arita, 1983; Windley, 1983). Ultrametamorphism at deep thrusts. Along the northwest margin of Kohistan, especially north of Chi- crustal levels (>15 km) resulted in in situ anatexis, migmatization, and tral (Fig. 8), there are large folds which are related to the southeast- generation of anatectic S-type (Chappell and White, 1974; Pitcher, 1982) directed overthrusting of Devonian rocks and Chitral slates over red clastic leucogranites, asso:iated with a widespread network of anastomosing sediments (Pudsey and others, 1985). These red beds rest unconformably dikes and sills. Extremely high 87Sr/86Sr ratios (0.7550 to 0.7800) indi- on previously deformed slates. The early deformation in the slates is cate that the granites were derived from partial melting of Precambrian- thought to be related to the closure of Kohistan's northern suture (the Paleozoic crustal reeks of the subducting Indian shield, north of the Main Shyok suture), to the later southeast-directed thrusts, to Tertiary deforma- Central thrust (Le Fort, 1981; Dietrich and Gansser, 1981; Vidal and tion, and to the collision with the Indian plate (Pudsey and others, 1985). others, 1982; Searle and Fryer, 1986). Late fluid phases played an impor- tant role in the crys tallization of the melt, which was rich in boron (tour- Karakoram maline), phosphorus (apatite), lithium (micas), F, and fyO. The fluids were driven off the underplating thrust slices, and they induced melting in There are similar major shear zones to the north of Kohistan. The the Main Central thrust slice by lowering the granite solidus (Searle and Hunza shear zone (or MKT, see Fig. 7), which forms the southern margin Fryer, 1986). of the Karakoram batholith in the Hunza valley, thrusts high-grade meta- Radiometric (cooling) ages of Himalayan leucogranites from Bhutan sediments over low-grade metasediments previously deformed along the (Dietrich and Gansser, 1981), Everest (Krummenacher and others, 1979; Shyok suture. The high-grade rocks in this thrust zone yield young K-Ar Kai, 1981), Makalu and Mustang (Krummenacher, 1971), and Manaslu cooling ages, as young as less than 10 Ma (D. Rex in Coward and others, (Vidal, 1978; Vidal and others, 1982; Le Fort, 1981) are consistently 1986), suggesting late Tertiary uplift along this thrust zone. Oligocene-Miocene (Fig. 9). The only reliable magmatic, whole-rock ages The Karakoram batholith is a composite intrusion made of up early for High Himalayan leucogranites are reported from Makalu (Scharer and biotite-hornblende-bearing granodiiorites which have a U-Pb zircon age of others, 1984b) and Manaslu (Deniel and others, 1983) of 18.1 ± 0.5 with 95 ± 5 Ma in Hunza (Le Fort and others, 1983) and Miocene peralumi- a 87Sr/86Sr ratio of 0.747. Inversion of metamorphic isograds during nous garnet and two-mica-bearing granites along the Baltoro glacier sec- large-scale thrusting (crustal subduction) along several major thrust zones tion (Debon and others, 1986; Searle and others, in press). K-Ar ages on in the High Himalaya followed the main thrusting event. two-mica granites and late leucocratic dikes, both in Hunza and the Bal- toro glacier areas, are Miocene and agree with Rb-Sr isochron ages of 8.8 DEFORMATION OF THE KOHISTAN-KARAKORAM- ± 0.3 Ma (Debon and others, 1986) and 14.13 ± 2.1 Ma (A. J. Rex in TIBETAN MICROPLATES Searle and others, in press) from the Baltoro plutonic units (Fig. 11). Both northern and southern contacts of the batholith are intrusive, Kohistan and P-T conditions of the metamoiphic aureole rocks either side indicate that at least 5 km of structural relief exists between the deeper, southern Apart from the: thrusting south of the suture, along the Main Mantle contact and the shallower northern contact (Searle and others, in press). thrust, there are several zones of southeast-directed thrusts and folds which The presence of a wide belt of kyanite- and sillimanite-grade rocks on the affect Kohistan and also rocks of the Karakoram microplate to the north hanging wall of the MKT, south of the Baltoro plutonic unit, shows that (Pudsey and others, 1985). Figure 8 shows a section line through Kohistan the throw on the MKT must be at least 4-5 km. This late Tertiary from near Abbottabad to Chitral (see Fig. 7 for location of section line). It break-back thrusting along the MKT is parallel to earlier structures formed shows that the Kohistan arc was folded prior to the intrusion of the along the Shyok suture zone north of Skardu. Kohistan batholith, but that all of the rocks of the arc were carried to the south-southeast on a gently dipping shear zone (the MMT) at a depth of Tibet only 10 to 15 km. The shallow dip and high crustal level of this shear zone are obtained from section construction in the thrust zone to the south, There was considerable Late Cretaceous to Tertiary deformation of where the MMT is projected to lie above the lower Paleozoic sediments of the Tibetan microplates, producing large-scale southeast-directed over- the Indian plate, gradually climbing down to lower crustal levels to the thrusts. Detailed cross sections through these structures are given in Chang north. A shallow level to the MMT is also supported by recent gravity data Cheng-fa and others (1986) (see also Hirn and others, 1984). Chang

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 695

Cheng-fa and others (1986) suggested that much of the considerable thick- tectonic model is presented in Figure 12 for the closing of Tethys and ening of the Tibetan crust could be due to shortening on these thrusts, a subsequent Himalayan deformation, based on the southern Tibet-Nepal shortening value of -1,000 km for Tibet as a whole. Medium- to high- section. grade metamorphic rocks, probably associated with the deeper levels of the Gangdese batholith, were uplifted to make the Nyenqentangla range Late Cretaceous (Chang Cheng-fa and others, 1986), and the basal thrust to this system forms an imbricate zone in Lingzizong Formation and Mesozoic sediments The sedimentary history of both the Indian plate margin and the to the southeast of the Yangbajin Valley (Fig. 2). The southeast side of the Lhasa block includes a continuous stratigraphic record until the mid- Nyenqentangla range is formed by a gently southeast-dipping major mylo- Cretaceous. The Lhasa block has Permian-Jurassic shallow-marine car- nite zone, which has a sense of displacement of top side down to the bonates which pass into more continental red beds with calc-alkaline southeast. This mylonite may be a low-angle extensional structure but is volcanics (Takena Formation) in the Cretaceous, when the Lhasa block probably an earlier southeast-directed thrust reoriented on the hanging emerged above sea level and became an Andean-type margin. The young- wall of the main Nyenqentangla thrust at depth (see Chang Cheng-fa and est sediments of the Takena Formation are Cenomanian (Fig. 9). A major others, 1986). phase of folding with -40% shortening occurred before the deposition of In the northern part of the Tibetan Plateau, the shortening is clearly the Lingzizong volcanics, possibly due to accretion of a minor arc or Tertiary in age, as it affects Eocene red beds south of the Kun Lun (Chang seamount along the southern margin of Tibet, although it is possible that Cheng-fa and others, 1986), but near Lhasa and in the southern part of the some of this deformation may be due to spreading from a thickened Tibet plateau, the age of the deformation is not certain. The Lingzizong Andean-type crust. The Late Cretaceous history of this margin is better Formation is affected by folds and southeast-directed thrusts, but itself seen in the west, where there has been less subsequent strike-slip move- overlies Cretaceous terrestrial red beds of the Takena Formation, which ment. Here, the main growth of the Kohistan-Dras island arc was in the show folds of a similar orientation. South of Lhasa, the Mesozsoic sedi- Cretaceous, and final sedimentation and volcanism was in the Albian- ments are tightly folded by structures which predate the Gangdese granite Aptian (Figs. 10 and 11). This arc collided and was sutured against the plutons and hence are probably part of this early set. The origin of this Karakoram plate in the Late Cretaceous (Coward and others, 1986; Pet- early deformation is uncertain; it clearly predates the collision of Tibet terson and Windley, 1985), with the result that the arc was then converted with India and may record an early collision or accretion event involving a into an Andean-type continental margin. The Kamila amphibolite com- Tethyan seamount or small island arc (Allegre and others, 1984). It also plex may be a second arc accreted onto the southern margin of the Kohis- supports, however, the suggestion of England and Searle (1986) that the tan arc. Farther northward, subduction of the Tethys plate below Kohistan Lhasa block was, in elevation as well as magma type, an Andean-type gave rise to the first intrusions of the Kohistan-Ladakh batholith in the margin by the end of the Cretaceous and that the Cretaceous deformation form of dolerite dikes at 75 m.y. (Petterson and Windley, 1985). Blue- may have been caused by spreading of this thickened crust. schists along the hanging wall of the MMT in Kohistan have been dated at Using the thin viscous sheet model for the continental lithosphere, 80 ± 5 Ma (Shams, 1980; Shams and others, 1980; Maluski and Matte, England and Searle (1986) predicted relatively homogeneous shortening 1984) and probably record subduction below the arc. migrating northward away from the Indus-Tsangpo suture zone during the On the Indian continental margin, stable shallow-marine sedimenta- Tertiary. The work reported by Chang Cheng-fa and others (1986), how- tion characterized the Late Cretaceous with a notable deepening event in ever, shows no northward progression in Tertiary sediment depocenters, as the Campanian-Maastrichtian, which gave rise to shales and mudstones. In would be expected if the deformation had migrated northward. Much of the Indus-Tsangpo suture zone, Albian-Aptian radiolarian cherts, lying the Tertiary deformation seems to have reactivated major Mesozoic struc- conformably on the Xigase ophiolite pillow lavas, indicate clastic-starved tures, so that many of the Tertiary structures have similar southward deposition far from any continental margin. During Cenomanian to Maas- vergences. There seems to have been a widespread shortening of the whole trichtian time, the Xigase Group flysch was progressively deriving debris of the Tibet Plateau during the Tertiary and not a northward progression from the north predominantly from the Gangdese granitoids. in shortening. The original nature of the Indus-Tsangpo suture in southern Tibet has Pal eocene-Early Eocene been destroyed. Much of the suture zone along the Tsangpo River south of Lhasa shows minor kinematic indicators of strike-slip sense, and the Trans- The collapse of the stable Mesozoic shelf on the Indian plate margin Himalayan batholith is so close to the suture that a considerable amount of around the Cretaceous-Tertiary boundary is thought to represent the time the pre-Tertiary margin of Tibet must have been removed either by strike- of emplacement of both the Jungbwa and Spongtang ophiolites in the slip movements or by uplift on south-directed early overthrusts. western Himalaya (Searle, 1983a, 1986); the ophiolite is considered to The later Tertiary and Quaternary deformation of Tibet is dominated have been obducted onto the Indian margin before final ocean closure, by north- to east-northeast-trending normal faults and associated comparable to the obduction of the Semail ophiolite onto the Oman shelf northwest-trending strike-slip faults which link the extension in the various which has not yet undergone continent-continent collision (Searle, 1985; basins (Tapponnier and others, 1982; Armijo and others, 1984). Chang Searle and Stevens, 1984). Cheng-fa and others (1986) recorded no major strike-slip faults in central In the Indus-Tsangpo suture zone, a widespread tectonic melange, the Tibet; much of the late Tertiary deformation is associated with the lateral Yamdrock melange, probably represents a trench deposit containing mate- extension of the thickened Tibetan crust. Chang Cheng-fa and others rial scraped off and underplated along a northward-dipping subduction (1986) did, however, describe large strike-slip displacement and rapid zone. All thrusting in the suture zone was southward directed during this Recent displacement rates along the Kun Lun fault systems of northern time, but little evidence remains of this early phase of deformation. Tibet. During the Paleocene and early Eocene, the Lhasa block became an uplifted Andean margin with I-type granodiorites and tonalites forming STRUCTURAL EVOLUTION the linear batholith parallel to the margin and with explosive subaerial calc-alkaline volcanics—the andesites, dacites, and ignimbrites of the The deformation which is associated with the Himalayan orogeny Lingzizong Formation. Plutons of the Kohistan-Ladakh batholith have began during the Late Cretaceous and continued throughout the Tertiary Rb-Sr ages of 60 Ma in the Kargil area (Figs. 10 and 11) (Scharer and to the present day—a span of -70-90 m.y. (Figs. 9, 10, and 11). A others, 1984a) and 54 ± 4 Ma around Gilgit (Petterson and Windley, Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 N 0 SHYOK SUTURE Ma KOHISTAN - LADAKH KARAKORAM w ZONE W 0 PLEISTOCENE <0 PLIOCENE c ai a >< ta œ S' oi TJ >> E I 10H T3 3 O O C ak- I I_ O a a> MIOCENE _ 3 .c "5 es ~ (A m m (0 20-1 S

26- C0 30 J CL o OLIGOCENE o • • IO • • 3 T3 37- £ • O O 40 -I • • !c O* co • • EOCENE co m 50 À 53" « • T° PALAEOCENE i + 60-^ o a EO l 0 65 a CM MAAST- 1 RICHTIAN * 7 OH

C AMP ANI AN

80 -A Si ANTONIAN

CONIACIAN co o TURONI AN 90 A LU O < c H I- CIENOMANIAN 3 C0 X LLl D 100-^ GC X O X ALBIAN A s co X u - Pb S • Rb - Sr

APTIAN 40 39 110H o Ar - Ar

• K - Ar c 3 X A Sm - Nd 120-J

Figure 11. Time chart for rocks of the Kohistan-Ladakh batholith, Shyok suture zone, and Karakoram plate. Radiometric ages shown are by U-Pb (croisses), Rb-Sr (squares), "°Ar-39Ar (circles), K-Ar (dots), and Sm-Nd (triangle). See text IFor sources of data.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 INDUS - TSANGPO INDIAN PLATE LHASA BLOCK SUTURE ZONE

0) CENTRAL CRYSTALLINE TIBETAN - TETHYS ZONE •C Ol Ü c to . to o 01 'jz à £ a O o HIGH HIMALAYA o Gangdese Majang Yangbaj/ng o o » Ordovician - Eocene N o -

Lesser Himalaya Thrust Sheets

U. MIOCENE

INDUS - TSANGPO LHASA BLOCK SUTURE ZONE TIBETAN TETHYS ZONE

Ordovician - Eocene Lingzizong „ . .. Gangdese Volcanics Yan9ba"n shelf sediments migmafites / Batholith leucogranites

U. EOCENE

INDIAN PLATE

Permian - Cretaceous Yamdrock Seamounts Trench Gangdese Indian Continental Margin Mesozoic Jurassic melange Batholith Lingzizong Shelf Sediments Flysch Cretaceous Volcanics e Mz Xigase Gp. ^ Pz

Prec

PALAEOCENE

Figure 12. Tectonic models for the closing of Tethys and tectonics of the Himalaya, based on the southern Tibet-Nepal section. See text for discussion.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 698 SEARLE AND OTHERS

1985), implying active subduction northward beneath the Asian margin Progressive steepening, overturning, and backthrusting occurred after intial during the Paleocene. collision. Late-stage break-back and breaching thrust systems occur in the A combination of paleomagnetic data and analysis of magnetic central Zanskar mountains, cutting upsection through previously as- anomalies in the Indian Ocean indicates that initial collision between India sembled stacks of thrust sheets, in places reversing the original stacking and Eurasia occurred at 55 Ma (Besse and others, 1984; Patriat and order. Along the Photoskar thrust, north of the Spongtang klippe, Triassic Achache, 1984). Marine sedimentation ceased, and continental molasse- shelf carbonates have been rethrust southward over previously emplaced type sedimentation began in the suture zone and at the edge of the Indian Lamayuru and Spongtang thrust sheets, reversing the original thrust stack- plate. ing order (Searle, 1986).

Mid-Eocene to Early Oligocene Miocene-Pliocene

In the period 50 to 40 Ma, crustal shortening occurred by considera- Crustal compression, folding, and thrusting continued throughout the ble thickening of continental crust along the northern margin of the Indian late Tertiary, with widespread Barrovian metamorphism and crustal ana- plate and possibly by the subduction and underplating of some of this crust texis in the Central Crystalline Complex along the High Himalaya. Rb/Sr beneath Tibet, giving rise to further deep partial melting and the produc- and K/Ar ages of leucogranites from the larger massifs of Makalu, Nuptse- tion of S-type leucogranites. The final plutonic activity of the Kohistan- Lhotse-Everest, and Manaslu have Oligocene to mid-Miocene ages Ladakh batholith is shown in Ladakh by a Rb/Sr date of 38.8 ± 1.3 Ma (Fig. 9). Subsequent thrusting associated with south-verging recumbent (Honneger and others, 1982) and in Kohistan by a Rb/Sr age of 40 ± 6 nappes inverted the metamorphic isograds. Le Fort (1975) and Vidal and Ma (Petterson and Windley, 1985). The Dir (= Utror) volcanics of Eocene others (1982) estimated that only 3% of the High Himalaya of Nepal is age in Kohistan probably represent the extrusive equivalents of the composed of leucogranite. In contrast, the volume of leucogranite (-30%), Kohistan-Ladakh granitoids. and hence the degree of partial melting, is much greater in northwest Fuchs (1979), Bassoullet and others (1978), and Baud and others India (Searle and Fryer, 1986). In Nepal, the MCT is the predominant (1984) considered (lie Spongtang ophiolite to have been emplaced after structure along which the metamorphic isograds are inverted (Le Fort, the deposition of the Eocene Nummulites-bearing limestones. Searle 1975; Bouchez and Pecher, 1981; Caby and others, 1983). In Kulu, La- (1983a, 1983b) and Searle and Stevens (1984), however, pointed out that houl, and Zanskar (northwest India), there are several major nappes with the ophiolite and Eocene limestones occur within separate but adjacent inverted isograds (Searle, 1983a) (see Fig. 8), and recent work by the late Tertiary thrust slices and are not in original contact with one another. authors shows a similar situation in north Pakistan. There are thus consid- Furthermore, ophiol ites are nowhere known to be directly obducted onto erable differences in the structure and metamorphic sequence along strike shallow-marine carbonates; they are usually emplaced into rapidly subsid- in the High Himalaya, although the basic processes were probably similar. ing basins accumulating syn-emplacement flysch-type sediments. On the In the Indus-Tsangpo suture zone, continued compression in the late Indian continental margin, in the Ladakh area, Eocene limestones contain- Miocene-Pliocene led to steepening of all earlier structures and to the ing Nummulites sp. and Assilina sp. were deposited unconformably on the northward backthrusting which affected the conglomerates of the Zanskar shelf carbonates and Lamayuru and Spongtang ophiolite thrust Oligocene-Miocene Liuqu Formation in southern Tibet and the Indus sheets. We regard these sediments as a neo-autochthonous cover to the Group molasse sediments in Ladakh. Crustal thickening in the Lhasa block Spongtang and Lamayuru rocks in the Zanskar mountains. Balanced and and throughout the Tibetan Plateau may have caused melting of the lower restored cross sections across the Zanskar Range (Figs. 5 and 6) indicate crust, giving rise to the calc-alkaline volcanics represented by the Majang that > 150 km of shortening has occurred after the middle Eocene, from Formation ignimbrites in the southern Nyenqentangla range in Tibet. the Zanskar Valley to the suture zone across the north Indian margin During the mid-Tertiary, two important molasse basins were devel- (Searle, 1986). oping and subsiding at rapid rates, the Indus-Tsangpo molasse basin along The youngest shelf sediments on the Indian continental margin in the suture zone north of the Himalaya and the Siwalik molasse along the Tibet are also middle Eocene (west of Tingri). Southward-directed thrusts southern margin of the Himalaya. The Indus Group molasse sediments in and south-facing folds have affected the Indian continental margin Ladakh formed in a major intermontane basin and are at least 4 km thick (Tibetan-Tethys zone) and the Indus-Tsangpo suture. The Eocene repre- and show very high averaged sedimentation rates (—340 m/m.y.). Debris sents the start of the main deformation north of the Himalayas; thrusting was derived both from Ladakh granitoids to the north and from the progressed southward and downward away from the suture zone. Coward Zanskar shelf sequences to the south (Frank and others, 1977; Searle, and Butler (1985) Butler and Coward (in press), and Coward and others 1983a). The origin of this basin is unknown; presumably it developed from (in press) recorded >500 km of shortening of the Indian plate in Pakistan extensional or strike-slip movements along the Indus suture zone. The since collision, suggesting a time-averaged shortening rate of 1 cm per year. 6-km-thick Siwalik sediments in Pakistan accumulated at a mean rate of Similarly, Chang Ctieng-fa and others (1986) argued for much of the 13 to 52 cm/1,000 yr in the past 13 m.y. (Johnson and others, 1982; shortening in Tibet north of the suture being early Tertiary in age. Burbank and Reynolds, 1984). They were derived from the Himalayan The structural complexity of the deformation is in many cases ex- ranges to the north, which have been uplifted >10 km in the past 10 m.y. treme, including several phases of thrusting and folding. In examples from In the late Tertiary, uplift rates were locally doubled to >5 mm/yr the Zanskar region, pDlyphase deformation occurred after the deformation (Zeitler, 1985). of the Nummulitic linestones which are preserved only as outliers around Singe-la (Mathur and Pant, 1983) and in tightly folded synclines around Pliocene-Pleistocene-Recent Kangi village (Fuchs, 1979). In the southern part of the Zanskar Range, folding is mainly south or southwest facing, and thrusting is south directed. Continued north-south compression occurred after deposition of the An increase in structural complexity toward the north is recorded in Indus Group molasse in the Ladakh region. The upper para-autoch- traverses across the Zanskar Range, with south-directed thrusts in the thonous units of the Indus Group (Bazgo and Kargil Formations) are south and north-direc ted back thrusts in the north (Searle, 1983a, 1986). affected by north-directed backthrusts along the Indus-Tsangpo suture

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 699

zone. These backthrusts affect all of the rocks of the suture zone and the tral Crystalline Complex. Deep-crustal thrusting and the formation of northern margin of the Tibetan-Tethys zone in Zanskar (Searle, 1983a). major basement-cover thrust systems thickened the crust, inducing wide- The net result of this backthrusting was the creation of a massive crustal- spread Barrovian metamorphism and generation of leucogranites or scale pop-up structure across the Tibetan-Tethys and Indus-Tsangpo su- two-mica S-type granites in the High Himalaya. Continued southward ture zones. thrusting inverted isograds around crustal-scale south-verging nappes and The Kohistan and Ladakh segments of the Kohistan arc are separated along major intracontinental shear zones such as the Main Central thrust. by a 40-km-wavelength fold with a north-south axis in the Nanga Parbat Rapid thrust culmination of the High Himalaya during the Miocene gneiss. This structure folds the MMT and all structurally overlying rocks; also resulted in dorsal culmination collapse, with normal faulting down- this is the northwestern syntaxis of Wadia (1937). Coward and others throwing the shelf sediments to the north and juxtaposing lower Paleozoic (1986) suggested that many of the Himalayan thrusts join the MMT along sediments against high-grade metamorphic rocks and leucogranites of the a branch line near the western margin of the syntaxis. Here, the Nanga High Himalaya. The normal fault zone along the Zanskar Valley (Figs. 4 Parbat gneisses locally overthrust Pleistocene glaciofluvial deposits (Law- and 5) has a throw of at least 5 km at the upper crustal level, although this rence and Ghauri, 1983). K/Ar dates of Kohistan rocks (D. Rex in does not imply extension in the lower crust. Coward and others, 1986) have progressively younger ages nearer to Continued convergence of the two continental plates led to (i) the Nanga Parbat, where Zeitler (1985) showed, using fission-track data, rapid development of thrusts which breached the tectonically assembled pile, to uplift rates of 0.5 cm/yr. Coward and others (1986, in press) argued that (ii) oversteepening of all structures in the Indus-Tsangpo suture zone, and this rapid uplift is partly due to interference of the predominant south- to (iii) backthrusting which created a crustal-scale pop-up with north- southeast overthrusting in Kohistan with the localized west-directed thrusts directed thrusts in the north and south-directed thrusts in the south. The of the western Himalaya. frontal thrust systems and foreland basin gradually propagated to the Within central and southern Tibet, fault-plane solutions of earth- south. Quaternary and Recent neotectonics have reactivated and trans- quakes indicate a vertical maximum principal compressive stress and a formed many of the thrust faults in the High Himalaya into strike-slip minimum principal stress that is east-west. Quaternary and Recent faulting faults, whereas others have been reactivated as normal faults during Re- in Tibet is indicated by extensive normal and strike-slip faults, some of cent spreading of the thickened Tibetan crust. which cut moraines and glacial terraces (Tapponnier and others, 1981a; Armijo and others, 1984). Geothermal geysers and hot springs find access Partitioning of Plate Motions to the surface along many of these north-south fault systems, which extend southward in the Everest region to the crest of the High Himalaya. The amount of crustal shortening recorded by the Himalayan thrust systems is >500 km, that is, a time-averaged displacement rate of ~1 CONCLUSIONS cm/yr. Lyon-Caen and Molnar (1985) obtained similar displacement rates from the time-averaged migration of the Ganges foreland basin in India. Abundant new stratigraphic, structural, radiometric, paleontological, Studies of the magnetic anomalies in the Indian Ocean (Patriat and Ach- and geophysical data from southern Tibet, Ladakh, and the Kohistan- ache, 1984), however, suggest that India has moved northward relative to Karakoram Ranges place tighter constraints on tectonic models for the Asia at a rate of ~5 cm/yr since collision. If collision took place at 50-55 closing of Tethys and for Himalayan tectonics. Ma, then the total shortening due to collision must be -2,500 km. Some of this may be accommodated by thickening of the Tibetan crust. The crust of Gosing of Tethys Kohistan-Karakoram and Tibet is now -70 km thick (England and Prior to continental collision, the southern margin of the Lhasa block Houseman, 1986) and had probably developed this twice-normal thick- formed an Andean-type margin with a Cenomanian-Eocene Trans- ness during the Tertiary. There is evidence for considerable shortening due Himalayan (Gangdese-Ladakh) granitoid batholith together with Paleo- to thrusting and folding north of the suture zone, much of which probably cene-lower Eocene andesites and ignimbrites of the Lingzizong For- occurred during the Tertiary, although there is also evidence of Recent mation. The Indian plate was a passive continental margin during this crustal shortening in several parts of central Tibet. Some of the crustal time with shelf facies in the south passing into deep-water Tethyan facies shortening near the northern suture of the Kohistan arc and along the to the north in the Indus-Tsangpo suture zone. southern part of the Tibet microplate, however, formed by earlier defor- At ~50 Ma, there were widespread and fundamental changes. Shelf mation and accretion along the north side of Tethys. sedimentation on the Indian plate, marine sedimentation of the Xigase If the thickness of the Tibetan crust was doubled during the Tertiary, Group, and trench melange formation (the Yamdrock melange) in the this allows for only 1,000 km shortening. Assuming the magnetic data are suture zone ended. Continental conglomeratic and red-bed sedimentation correct, then a further 1,000 km shortening needs to be found from other began in the north, and southward-directed folding and thrusting pro- sources. Some of the extra shortening may have occurred by strike-slip gressed southward from the suture zone across the Indian plate margin. deformation along the Kun Lun fault system and the line of the Indus Deep-level thrusting caused crustal thickening, anatexis, leucogranite suture, following the models of Molnar and Tapponnier (1975), Tappon- generation, and large-scale thrusting on both sides of the suture. These nier and others (1982), and Armijo and others (1984). Other shortening changes coincided with a sudden decrease in velocity and change in direc- may have occurred north of Tibet, in the Tien Shan and Qilian Shan, areas tion of motion of the Indian plate, as indicated by marine magnetic anom- which deserve study in the near future. alies in the Indian Ocean. We interpret all of these changes to record the collision of the two continental plates and the closure of Tethys. ACKNOWLEDGMENTS

Himalayan Tectonics Many of the field and laboratory data upon which these ideas are based were obtained on Natural Environment Research Council-funded After the Eocene terminal closure of Tethys, deformation progressed research projects GR3/4242 to B. F. Windley, M. P. Coward, and M. P. southward across the Tibetan-Tethys zone and the High Himalayan Cen- Searle to work in northern Pakistan and Ladakh and GR3/6113 to

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 700 SEARLE AND OTHERS

Coward. Coward was a member of the Royal Society-Academica Sinica Chappell, B. W., and White, A.J.R., 1974, Two contrasting granite types: Pacific Geology, v. 8, p. 173-174. Coulon, C., Maluski, H., and Wang, Song-chan, 1984, Volcanism of central and southern Tibet and its geodynamic geotraverse of Tibet in 1985, the preliminary results of which are pub- significance [abs.]: International Symposium on the Geology of the Himalayas, Chengdu, China. Coward, M. P., and Butler, R. W.H., 1985, Thrust tectonics and the deep structure of the Pakistan Himalaya: Geology, lished in Chang Cheng-fa and others (1986). Windley and Searle used v. 13, p. 417-420. GR3/4242 to fund field excursions to Tibet following the Baidaihe and Coward, M. P., Jan, M. Q., Rex, D., Tarney, J., Thirlwall, M., and Windley, B. F., 1982a, Structural evolution of a crustal section in the western Himalaya: Nature, v. 295, p. 22-24. Chengdu conferences of 1982 and 1984, respectively. Field work in Ko- 1982b, Geotectonic framework of the Himalaya of N. Pakistan: Geological Society of London Journal, v. 139, p. 299-308. histan and Ladakh is part of joint projects between the British group and Coward, M. P., Windley, B. F., Broughton, R., Luff, I. W, Petterson, M. G., Pudsey, C., Rex, D., and Khan, M. A., 1986, the University of Peshawar, Pakistan, and the Wadia Institute of Hima- Collision tectonics in the N.W. Himalayas, in Coward, M. P., and Ries, A., eds., Collision tectonics: Geological Society of London Special Publication, v. 19, p. 203-219. layan Geology, Dehra Dun, India. Coward, M. P., Butler, R.W.H., Khan, M. A., and Knipe, R. J., in press, The tectonic history of Kohistan and its implications for Himalayan structure: Geological Society of London Journal. We greatly appreciate discussions with our French colleagues work- Debon, F., Zimmerman, J. L., and Betrand, J. M., 1986, Le granite du Baltoro (batholite axial du Karakoram, nord Pakistan): une intrusion subalcaline d'age Miocene Superior: Comptes Rendus de l'Academie des Sciences, v. 303, ing in Tibet, particularly Jean Marcoux, Jean-Pierre Burg, Urs Scharer, p. 463-468. Christian Coulon, Paul Tapponnier, Roland Armijo, and Vincent Courtil- Deniel, C„ Vidal, Ph., and Le Fort, P., 1983, The Manaslu granite (Himalayan Nepal), new Sr and Nd isotopic data: Terra Cognita, v. 3, p. 266. lot. We acknowledge extremely helpful discussions and collaborative field Desio, A., 1964, Geological tentative map of the western Karakoram: Milan, Italy, Milano University Institute of Geology, scale 1:500,000. and laboratory research with our Chinese colleagues from Academia 1979, Geological evolution of the Karakoram, in Farah, A., and De Jong, K. A., eds., Geodynamics of Pakistan: Sinica and the Chinese Academy of Geological Sciences; members of the Quetta, Pakistan, Geological Survey of Pakistan, p. 111-124. Desio, A., and Zanettin, B., 1970, Geology of the Baltoro basin: Leiden, the Netherlands, Brill, 308 p. Tibet Geotraverse (l isted in Chang Cheng-fa and others, 1986); and Paki- Dewey, J. F., and Bird, J. M., 1970, Mountain belts and the new global tectonics: Journal of Geophysical Research, v. 75, p. 2625-2647. stani, Indian, British, and American workers in the Himalayas, in particular Dietrich, V. J., and Gansser, A., 1981, The leucogranites: of the Bhutan Himalaya: Schweizerische Mineralogische und Robert Shackleton, Rob Butler, Rob Knipe, Carol Pudsey, Bob Lawrence, Petrographische Mitteilungen, v. 61, p. 177-202. Dietrich, V. J., Frank, W., and Honegger, K., 1983, A Jurassic-Cretaceous island arc in the Ladakh Himalayas: Journal of Bob Yeats, M. Asif Khan, Professor R.A.K. Tahirkheli, and Dr. S. Sah. Volcanology and Geothermal Research, v. 18, p. 405-433. England, P. C., and Houseman, G. A., 1986, Finite strain calculations of continental deformation II, application to the This paper benefited greatly from reviews by Bob Lawrence and Bob India-Asia plate collision: Journal of Geophysical Research, v. 91, p. 3664-3676. Yeats. England, P. C., and Searle, M. P., 1986, The Cretaceous-Tertiary deformation of the Lhasa block and its implications for crustal thickening of Tibet: Tectonics, v. 5, p. 1-14. Frank, W., Gansser, A., and Trommsdorff, V., 1977, Geological observations in the Ladakh area (Himalayas): Schweize- rische Mineralogische und Petrographische Mitteilungen, v. 57, p. 89-113. REFERENCES CITED Fuchs, G., 1979, On the geology of western Ladakh: Geobgisches Jahrbuch, v. 122, p. 513-540. Gaetani, M., Nicora, A., Silva, I. P., Fois, E., Garzanti, E., and Tintori, A., 1983, Upper Cretaceous and Palaeocene in the Ahmed, Z., and Hall, A., 1984, Petrology and mineralization of the Sakhakot-Qila ophiolite, Pakistan, in Gass, I. G., Zanskar Range, N.W. Himalaya: Rivista Italiana di Paleontología e Stratigraphia, v. 89, p. 81-118. Lippard, S. J., and Skelton, A. W., eds., Ophiolites and oceanic lithosphère: Geological Society of London Special Gansser, A., 1964, Geology of the Himalayas: London, United Kingdom, J. Wiley, 289 p. Publication 13, p. 241-252. 1977, The great suture zone between Himalaya and Tibet, a preliminary account: Science de la Terre, Himalaya: Allegre, C. J., and others (35 aithors), 1984, Structure and evolution of the Himalayan-Tibet orogenic belt: Nature, Centre National de la Recherche Scientifique, v. 2(8, p. 147-166. v. 307, p. 17-22. Gee, E. R., 1980, Pakistan geological Salt Range series: Directorate of Overseas Surveys United Kingdom for the Andrieux, J., Arthaud, F., Brunei. M., and Sauniac, S., 1981, Geometrie et dnematique des chevauchements, en Himalaya Government of Pakistan and the Geological Survey of Pakistan, scale 1:50,000, 6 sheets. du Nord-Ouest: Société Géologique de France Bulletin, v. 23, p. 651-661. Girardeau, J., and others (8 authors), 1984a, Tectonic environment and geodynamic significance of the Neo-Cimmerian Arita, K., 1983, Origin of the ir verted metamorphism of the lower Himalayas, central Nepal: Tectonophysics, v. 95, Dongqiuo ophiolite, Banggong-Nujiang suture zone, Tibet: Nature, v. 307, p. 27-31. p. 43-60. Girardeau, J., Nicolas, A., Marcoux, J., Dupre, B., Wang;, Xibin, Cao, Youjong, Zheng, Haixang, and Xiao, Suchang, Arkell, W. J., 1956, Jurassic geology of the world: Edinburgh, Scotland, Oliver and Boyd. 1984b, Les ophiolites de Xigatse et la suture du Yarlung Zangbo (Tibet), in Mercier, J. L., and Li, Guangcen, eds., Armijo, R., Tapponnier, P., Mercier, J. L., and Han, Tonglin, 1984, Quaternary extension of the Tibetan plateau: Field Mission Franco-Chinoise au Tibet 1980: Paris, France, Centre National delà Recherche Scientifique, p. 189-197. observations and tectonic implications [abs.]: International Symposium on the Geology of the Himalayas, Gopel, C., Allegre, C. J., and Rong, Hua-Xu, 1984, Lead isotopic study of the Xigatse ophiolite (Tibet): The problem of Chengdu, China. the relationship between magmatites (gabbros, doltrites, lavas) and tectonites (harzburgites): Earth and Planetary Atherton, M., McCourt, W. J., îlanderson, L. M., and Taylor, W., 1979, The geochemica! character of the segmented Science Letters, v. 69, p. 301-310. Peruvian coastal bathoiith and associated volcanics, in Atherton, M., and Tamey, J., eds., Origin of granite Gupta, V. J., and Kumar, S., 1975, Geology of Ladakh, Laitaul and Spiti regions of Himalaya with special reference to the balholilhs—Geochemical evidence: Kent, United Kingdom, Shiva Publishing Ltd., p. 45-75. stratigraphie position of flysch deposits: Geotogischr Rundschau, v. 64, p. 540-563. Auden, J. B., 1935, Traverses in the Himalaya: Geological Survey of India Records, v. 69, p. 123-167. Hayden, H. H., 1907, The geology of the provinces of Tsang in Tibet: Geological Survey of India Records, v. 36, Bally, A. W., and others (10 authors), 1980, Notes on the geology of Tibet and adjacent areas—Report of American Plate p. 122-201. Tectonics Delegation to the People's Republic of China: U.S. Geological Survey Open-File Report 80-501. Heim, A., and Gansser, A., 1939, Central Himalaya—Geological observations of Swiss expedition, 1936: Société Bard, J. P., 1983, Metamorphism of an obducted island arc: Example of the Kohistan sequence (Pakistan) in the Helvetique Science Naturelle Mémoire, v. 73, p. 1-245. Himalayan collided range: Earth and Planetary Science Letters, v. 65, p. 133-144. Hirn, A., and others (8 authors), 1984, Lhasa block and bordering sutures—A continuation of a 500 km Moho traverse Bard, J. P., Maluski, H., Matte, P., and Proust, F., 1980, The Kohistan sequence: Crust and mantle of an obducted island through Tibet: Nature, v. 307, p. 25-27. arc University of Peshawar Geological Bulletin, v. 13, p. 87-94. Honegger, K., Dietrich, V., Frank, W., Gansser, A., Thoni, M., and Trommsdorff, V., 1982, Magmatism and metamor- Bassoulfet, J. P., Beilier, J. P., Cbichen, M., Barcoux, J., and Mascle, G., 1978, Découverte de Crétacé supérieur calcaire phism in the Ladakh Himalaya (the Indus-Tsangpo suture zone): Earth and Planetary Science Letters, v. 60, pelogique dans le Zanskar (Himalaya du Ladakh): Société Géologique de France Bulletin, v. 20, p. 961-962. p. 253-292. Baud, A., Gaetani, M., Garzanti, E., Fois, E., Nicora, A., andTintori, A., 1984, Geological observation in the S.E. Zanskar Jan, M. Q., and Howie, R. A., 1981, The mineralogy and geochemistry of the metamorphosed basic and ultrabasic rocks and adjacent Lahul area (N.W. Himalaya): Eciogae Geologicae Helvetiae, v. 77, p. 171-197. of the Jijal complex, Kohistan, N.W. Pakistan: Journal of Petrology, v. 22, p. 85-126. Besse, J., Courtillot, V., Pozzi, J. P., Westphal, M., and Zhou, Y. X., 1984, Palaeomagnetic estimates of crustal shortening Jan, M. Q., Wilson, R. N., and Windley, B. F., 1982, Piragonite pangenesis from the garnet granulites of the Jijal in the Himalayan thrusts and Zangbo suture: Nature, v. 311, p. 621-626. complex, Kohistan, N. Pakistan: Mineralógica! Magizine, v. 45, p. 73-77. Bordet, A., 1961, Recherches geol<)giques dans l'Himalaya du Nepal, region du Makalu: Paris, France, Centre National de Johnson, N. M., Opdyke, N. D., Johnson, G. D., Lindsíiy, E. H„ and Tahirkheli, R.A.K., 1982, Magnetic polarity la Recherche Scientifique, 175 p. stratigraphy and ages of Siwalik group rocks of the Potwar plateau, Pakistan: Palaeogeography, Palaeoclimatology, Bouchez, J. L., and Pecher, A., 1981, The Himalayan Main Central thrust pile and its quartz-rich tectonites in central Paleoecology, v. 37, p. 17-42. Nepal: Tectonophysics, v. ''8, p. 23-50. Kai, K., 1981, Rb-Sr geochronology of the rocks of the Himalayas, E. Nepal, Part 2. The age and origin of the granite of Brunei, M., 1986, Ductile thrusting in the Himalayas: Shear sense criteria and stretching lineations: Tectonics, v. 5, the Higher Himalayas: Kyoto University Memoir, Faculty of Science, Series Geology and Mineralogy, v. 47, p. 247-265. p. 149-157. Burbank, D. W., and Reynolds, R.G.H., 1984, Sequential late Cenozoic structural disruption of the northern Himalayan Krummenacher, D., 1971, Geochronometrie de l'Himalaya, in Recherches géologiques dans l'Himalaya du Nepal, region foredeep: Nature, v. 311, p 114-118. de la Thakkola: Paris, France, Comptes Rendus de l'Academie des Sciences, p. 187-202. Burchfiel, C., and Royden, L., 198$, N-S extension under the convergent Himalayan regime: Geology, v. 13, p. 679-682. Krummenacher, D., Bassett, A. M., Kingery, F. A., and Liyne, H. F., 1979, Petrology, metamorphism and K/Ar age Burg. J. P., 1983, Carte géologique du Sud de Tibet: Paris, France, Centre National de la Recherche Scientifique, and determinations in eastern Nepal, in Saklana, P. S., ed., Tectonic geology of the Himalaya: New Dehli, India, Today Beijing, China, Ministry of Geology. and Tomorrow Publishers, p. 151-166. Burg, J. P., and Chen, G. M., 1984, Tectonics and structural zonation of southern Tibet, China: Nature, v. 311, Lawrence, R. D., and Ghauri, A. A., 1983, Evidence of active faulting in Chilas district, northern Pakistan: University of p. 219-223. Peshawar Geological Bulletin, v. 16, p. 185-186. Burg, J. P., Guiraud, M., Chen, G, M., and Li, G. C., 1984a, Himalayan metamorphism and deformations in the North Le Fort, P., 1975, Himalayas: The collided range, present knowledge of the continental arc: American Journal of Science, Himalayan belt (southern Tibet, China): Earth and Planetary Science Letters, v. 69, p. 391-400. v. 275A, p. 1-44. Burg, J. P., Brunei, M., Gapais, D., Chen, G. M., and Liu, G. H., 1984b, Deformation of leucogranites of the crystalline 1981, Manaslu leucogranite: A collisional signature of the Himalaya, a model for its genesis and emplacement: Main Central thrust sheet in southern Tibet (China): Journal of Structural Geology, v. 6, p. 535-542. Journal of Geophysical Research, v. 86, p. 10545-10568. Butler, R.W.H., 1982, The termine logy of structures in thrust belts: Journal of Structural Geology, v. 4, p. 239-245. Le Fort, P., Debon, F., and Sonet, J., 1980, The 'Lesser Himalayan' cordierite granite belt, typology and age of the pluton Butler, R.W.H., and Coward, M. P., in press, Crustal-scale thrusting and continental subduction during Himalayan of Mansehra, Pakistan: University of Peshawar Geological Bulletin, v. 13, p. 51-62. collision tectonics on the NW Indian plate: NATO ASI volume, Istanbul Conference, J 985. Le Fort, P., Michard, A., Sonet, J., and Zimmermann, J. L, 1983, Petrography, geochemistry and geochronology of some Caby, R., Pecher, A., and Le Fol, P., 1983, Le grand chevauchement central himalayen: nouvelles données sur le samples from the Karakoram axial bathoiith (northern Pakistan), in Shams, F. A., ed., Granites of the Himalayas, métamorphisme inverse a 11 base de la Dalle du Tibet: Revue Géologique Dynamique Geographie et Physique, Karakoram and Hindu Kush: Lahore, India, Institute of Geology of Punjab University, p. 377-387. v. 24, p. 89-100. Lin, Baoyu, 1984, Les strates de Permian inférieur et la faura corallienne dans la region centre-sud du Tibet, in Mercier, Calkins, J. A., Offield, T. W., Abd jllah, S.K.M., and Tayyab, A. S., 1975, Geology of the southern Himalaya in Hazara, J. L., and Li, Guangcen, eds., Mission Franco-Chinoise au Tibet 1980: Comptes Rendues de l'Academie des Pakistan, and adjacent area;: U.S. Geological Survey Professional Paper 716-C, 29 p. Sciences, p. 77-107. Calkins, J. A., Jamiluddin, S., Kamaluddin, B., and Hussain, A., 1981, Geology and mineral resources of the Chitral- Liu, Dong-Sheng, éd., 1981, Geological and ecological studies of the Qinghai-Xixang Plateau, Volume 1: New York, Partsan area, Hindu Kush Range, northern Pakistan: U.S. Geological Survey Professional Paper 716-G, 33 p. Gordon and Breach, 974 p. Chang, Cheng-fa, and others (26 authors), 1986, Preliminary conclusions of the Royal Society-Academia Sinica 1985 Lombard, A., 1958, Un itinerarie géologique dans l'est du Nepal (Massif du Mont Everest): Société Helvetique Science geotraverse of Tibet: Nature, v. 323, p. 501-507. Naturelle Memoire, v. 82,107 p.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021 CLOSING OF TETHYS AND TECTONICS OF THE HIMALAYA 701

Lydekker, R„ 1883, The geology of (he Kashmir and Chamba territories and the British district of Khagan: Geological Searle, M. P., and Fryer, B. J., 1986, Garnet, tourmaline and muscovite-bearing leucogranites, gneisses and migmatitesof Survey of India Memoir, v. 22, p. 108-122. the Higher Himalaya from Zanskar, Kulu, Lahoul and Kashmir, in Coward, M. P., and Ries, A. C., eds., Collision Lyon-Caen, H., and Molnar, P., 198S, Gravity anomalies, flexure of the Indian plate, and the structure, support and tectonics: Geological Society of London Special Publication 19, p. 185-201. evolution of the Himalaya and Ganga basin: Tectonics, v. 4, p. 513-538. Searle, M. P., and Graham, G. M., 1982, The "Oman Exotics"—Oceanic carbonate build-ups associated with the early Malinconico, L. L., 1986, The structure of the Kohistan arc terrane in northern Pakistan as inferred from gravity data: stages of continental rifting: Geology, v. 10, p. 43-49. Tectonophysics, v. 124, p. 297-307. Searle, M. P., and Stevens, R. K., 1984, Obduction processes in ancient, modern and future ophiolites, in Gass, I. G„ Maluski, H., and Matte, P., 1984, Age of Alpine tectono-metamorphic events in the northwestern Himalaya (northern Lippard, S. J., and Shelton, A. W., eds., Ophiolites and oceanic lithosphere: Geological Society of London Special Pakistan) by ^Ar/^Ar methods: Tectonics, v. 3, p. 1-18. Publication 13, p. 303-320. Maluski, H., Proust, F., and Xiao, Xuchang, 1982, First results of Ar39/Ar40 dating of Transhimalayan calcalkalioe Searle, M. P., Rex, A. J., Tirrel, R., Windley, B. F., St Onge, M., and Hoffman, P., in press, A geological profile across the magmatism and volcanism of southern Tibet: Nature, v. 298, p. 152-154. Baltoro Karakoram Range, N. Pakistan: University of Peshawar Geological Bulletin. Mathur, N. S., and Pant, P. C., 1983, Early Eocene foraminifera from Singhe La area, Zanskar region, Ladakh Himalaya, Sengor, A.M.C., 1981, The geological exploration of Tibet: Nature, v. 294, p. 403-404. in Thakur, V. C., and Sharma, K. K., eds., Geology of the Indus suture, zone of Ladakh: Dehra Dun, India, Wadia Shackleton, R. M., 1981, Structure of southern Tibet: Report on a traverse from Lhasa to Khatmandu organized by Institute of Himalayan Geology, p. 151-156. Academia Sinica: Journal of Structural Geology, v. 3, p. 97-105. McCourt, W. J., 1981, The geochemistry and petrography of the coastal batholith of Peru, Lima segment: Geological Shams, F. A., 1980, Origin of the Shangla blueschists, Swat, Himalayan Pakistan: University of Peshawar Geological Society of London Journal, v. 138, p. 407-420. Bulletin, v. 13, p. 67-70. Mitchell, A.H.G,, 1984, Post-Permian events in the Zangbo suture zone, Tibet: Geological Society of London Journal, Shams, F. A., Jones, G. C., and Kempe, R.D.C., 1980, Blueschists from Topsin, Swat district, N.W. Pakistan: Mineralogi- v. 141, p. 129-136. cal Magazine, v. 43, p. 941-942. Molnar, P., and Tapponnier, P., 1975, Cenozoic tectonics of Asia: Effects of a continental collision: Science, v. 189, Sharma, K. K., and Kumar, S., 1978, Contribution to the geology of Ladakh, N.W. Himalaya: Himalayan Geology, v. 8, p. 419-426. p. 252-287. Mu, An-Tze, Wen, Shih-Hsuan, Wang, Yi-Kang, and Chang, Ping-Kao, 1973, Stratigraphy of the Mount Jolmo Lungma Tahirkheli, R.A.K., and Jan, M. Q., 1979, Geology of Kohistan, Karakorum Highway, northern Pakistan: University of region in southern Tibet, China: Scientia Sinica, v. 16, p. 96-111. Peshawar Geological Bulletin Special Issue II, p. 1-30. Nicolas, A., and others (8 authors), 1981, The Xigaze ophiolite (Tibet): A peculiar oceanic lithosphere: Nature, v. 294, Talent, J. A., Conaghan, P. J., Mawson, R., Molloy, P. D., and Pickett, J. W., 1982, Intricacy of tectonics in Chitral p. 414-417. (Hindu Kush): Faunal evidence and some regional implications: Himalayan Geology, Section Ha: Geological Norm, E„ 1946, Geological exploration in western Tibet: Report on Sino-Swedish Expedition 29: Stockholm, Sweden, Survey of India Miscellaneous Publications 41, p. 77-101. Aktiebolaget Thule, 214 p. Tapponnier, P., and others (29 authors), 1981a, The Tibetan side of the India-Eurasia collision: Nature, v. 294, Patriat, P., and Achache, J., 1984, India-Eurasia collision chronology and implications for crustal shortening and driving p. 405-410. mechanisms of plates: Nature, v. 311, p. 615-621. Tapponnier, P., Mattauer, M., Proust, F., and Carsaigneau, C., 1981 b, Mesozoic ophiolites, sutures and large-scale tectonic Petterson, M. G., and Windley, B. F., 1985, Rb-Sr dating of the Kohistan arc-batholith in the Trans-Himalaya of N. movements in Afghanistan: Earth and Planetary Science Letters, v. 52, p. 355-371. Pakistan and tectonic implications: Earth and Planetary Scinece Letters, v. 74, p. 45-57. Tapponnier, P., Peltzer, G„ Ledain, A. Y., Armijo, R., and Cobbold, P., 1982, Propagating extrusion tectonics in Asia: Pitcher, W. S., 1982, Granite type and tectonic environment, in Hsu, K J., ed., Mountain building processes: London, New insights from simple experiments with plasticene: Geology, v. 10, p. 611-616. United Kingdom, Academic Press, p. 19-40. Thakur, V. C., 1981, Regional framework and geodynamic evolution of the Indus-Tsangpo suture zone in the Ladakh Prinzhofer, A., Allegre, C. J., Bao, Peishing, and Wang, Xibin, 1984, Magmatism in the southern Tibet ophiolite: Trace Himalayas: Royal Society of Edinburgh Transactions, Earth Sciences, v. 72, p. 890-897. element constraints [abs.]: International Symposium on the Geology of the Himalayas, Chengdu, China. Thakur, V. C., and Sharma, K. K., eds., 1983, Geology of the Indus suture zone of Ladakh: Dehra Dun, India, Wadia Pudsey, C. J., 1986, The Northern Suture, Pakistan: Margin of a Cretaceous island arc: Geological Magazine, v. 123, Institute of Himalayan Geology, 205 p. p. 405-423. Vidal, P. L., 1978, Rb-Sr and systematic in granite from central Nepal (Manaslu): Significance of the Oligocene age and Pudsey, C. J., Coward, M. P., Luff, I. W., Shackleton, R. M., Windley, B. F., and Jan, M. Q., 1985, The collision zone high ratio in Himalayan orogeny: Geology, v. 6, p. 196. between the Kohistan arc and the Asian plate in N.W. Pakistan: Royal Society of Edinburgh Transactions, Earth Vidal, P. L., Cocherie, A., and Le Fort, P., 1982, Geochemical investigations of the origin of the Manaslu leucogranite Sciences, v. 76, p. 463-479. (Himalaya, Nepal): Geochimica et Cosmochimica Acta, v. 46, p. 2279-2292. Radhakrishna, T., Rao, V. D., and Murali, A. V., 1984, Geochemistry of Dras volcanics and the evolution of the Indus Wadia, D. N., 1937, The Cretaceous volcanic series of Astor-Deosai, Kashmir and its intrusives: Geological Survey of suture ophiolites: Tectonophysics, v. 108, p. 135-153. India Records, v. 72, p. 151-161. Rai, H., and Pande, K., 1978, Geology of the Kargil igneous complex, Ladakh, Jammu and Kashmir, India: Recent Windley, B. F., 1983, Metamorphism and tectonics of the Himalaya: Geological Society of London Journal, v. 140, Research in Geology, v. 5, p. 219-228. p. 849-865, Reibel, G., and Reuber, I., 1982, La klippe ophiolitique de Spongtang-Photoksar (Himalaya du Ladakh): une ophiolite Xiao, Xuchang, 1984, Les ophiolites de Xigatse au Tibet meridional et quelques problems tectonique les concernant, in sans cumulats: Comptes Rendus de rAcademic des Sciences, v. 29, p. 557-562. Mercier, J. L., and Li, Guangcen, eds.. Mission Franco-Chinoise au Tibet 1980: Paris, France, Centre National de Reuber, I., 1986, Geometry of accretion and oceanic thrusting of the Spontang Ophiolite, Ladakh Himalaya: Nature, la Recherche Scientifique, p. 167-188. v. 321, p. 592-596. Xu, Rong-Hua, Scharer, U., and Allegre, C. J., 1982, Timing of the Tibetan collision by radiometric dating [abs.]: EOS Reynolds, R. H., Brookfield, M. E„ and McNutt, R. H., 1983, The age and nature of Mesozoic-Tertiary magmatism across (American Geophysical Union Transactions), v. 62, p. 1094. the Indus suture zone in Kashmir to Ladakh (N.W. India and Pakistan); Geologische Rundschau, v. 72, 1985, Magmatism and metamorphism in the Lhasa block (Tibet): A U-Pb geochronological study: Journal of p. 981-1004. Geology, v. 93, p. 41-57. Scharer, U., Hamet. J., and Allegre, C. J., 1984a, The Trans-Himalaya (Gangdese) plutonic belt in the Ladakh region: A Yeats, R. S„ and Lawrence, R. D., 1984, Tectonics of the Himalayan Thrust Belt in northern Pakistan, in Haq, B. U., and U-Pb and Rb-Sr study: Earth and Planetary Science Letters, v. 67, p. 327-339. Hilliman, J. D., eds., Marine geology and oceanography of Arabian Sea and coastal Pakistan: p. 177-198. Scharer, U., Xu, Ronghua, and Allegre, C. J., 1984b, The magmatic events in the Himalayas and the Tibetan plateau: Zeitler, P. K., 1985, Cooling history of the NW Himalaya, Pakistan: Tectonics, v. 4, p. 127-151. Colloque Franco-Chinois sur la Geoiogie de 1'Himalaya—Tibet: Montpellier, France, Centre National de la Recherche Scientifique, p. 70. 1984c, Plutonism and metamorphism in the Lhasa block [abs.]: International Symposium on the Geology of the Himalaya, Chengdu, China. Searle, M. P., 1983a, Stratigraphy, structure and evolution of the Tibetan-Tethys zone in Zanskar and the Indus suture zone in the Ladakh Himalaya: Royal Society of Edinburgh Transactions, Earth Sciences, v. 73, p. 205-219. 1983b, On the tectonics of the western Himalaya: Episodes, p. 21-26. 1985, Sequence of thrusting and origin of culminations in the northern and central Oman Mountains: Journal of MANUSCRIPT RECEIVED BY THE SOCIETY FEBRUARY 20,1985 Structural Geology, v. 7, p. 129-144. REVISED MANUSCRIPT RECEIVED DECEMBER 5,1986 1986, Structural evolution and sequence of thrusting in the High Himalayan, Tibetan-Tethys and Indus suture MANUSCRIPT ACCEPTED DECEMBER 31,1986 zones of Zanskar and Ladakh, western Himalaya: Journal of Structural Geology, v. 8, p. 923-936. FINAL ILLUSTRATIONS ACCEPTED FEBRUARY 12,1987

Printed in U.S.A.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/98/6/678/3434697/i0016-7606-98-6-678.pdf by guest on 27 September 2021