And Paleo-Tethys Oceans in the Western Kunlun (Xinjiang, China)

Journal of Asian Earth Sciences 18 (2000) 637–650 www.elsevier.nl/locate/jseaes

Suturing of the Proto- and Paleo-Tethys oceans in the western Kunlun (Xinjiang, China)

F. Matterna,*, W. Schneiderb

aInstitut fu¨r Geologı¨e, Geophysik und Geoinformatik, Freie Universita¨t Berlin, Matteserstraße 74-100, D-12249 Berlin, Germany bInstitut fu¨r Geowissenschaften, Technische Universita¨t Braunschweig, Pockelsstraße 4, D-38106, Braunschweig, Germany Received 5 February 1999; accepted 30 September 1999

Abstract The Proto-Tethys Ocean between the North and South Kunlun began to form during the Sinian. Remnants of this ocean are preserved at the Oytag-Kudi suture. The presence of Paleozoic arc batholiths in the northern South Kunlun and their absence in the North Kunlun indicates southward subduction of the Proto-Tethys Ocean beneath the South Kunlun. Opposite subduction polarity can be demonstrated for the Late Paleozoic to mid-Mesozoic when the southerly located Paleo-Tethys Ocean was consumed beneath the South Kunlun and generated a Late Carboniferous to mid-Jurassic magmatic arc in the southern South Kunlun. Arc magmatism affected the southern South Kunlun and the large Kara-Kunlun accretionary prism (a suture sensu lato) which formed as a result of Paleo-Tethys’ consumption. The dextral shear sense of ductile faults which are located at the margins of the arc batholiths, and which parallel the South Kunlun/Kara-Kunlun boundary, suggests oblique plate convergence with a dextral component. Different lines of evidence encourage us to interpret the Proto-Tethys ophiolites of the Oytag-Kudi zone as at least partly derived from an oceanic back-arc basin. In contrast, we assume that Paleo-Tethys was a large ocean basin which was eliminated directly at the southern margin of the South Kunlun where no oceanic back-arc region existed. ᭧ 2000 Elsevier Science Ltd. All rights reserved.

1. Introduction Our main intention is to decipher the pre-Cenozoic plate tectonic processes which shaped the western Kunlun. Knowledge of the geology of the Kunlun was always Subduction of oceanic lithosphere plays a key role in this sparse, as it is difficult to access this geographic frontier. regard. At the same time we will also address problematic Until recently, fundamental geological knowledge of the aspects in the understanding of the tectonic history. western Kunlun remained obscure to the international geos- The western Kunlun is one of the Earth’s highest moun- cientific community because since 1949 foreigners were not tain ranges. It is located south of the Tarim Basin (Takla allowed to visit the area (Gaetani et al., 1990). Only as of Makan Desert) and north of the westernmost part of the 1988 could non-Chinese workers carry out investigations in Tibet Plateau which is referred to as the “Kara-Kunlun” the region again. The Italian expedition team was the first area (Fig. 1). To the northwest, parts of the Kunlun are one to resume foreign research efforts (Gaetani et al., 1990). morphologically and geologically transitional to the Pamirs. On the basis of recently collected data by Chinese and other The western Kunlun represents an accretion zone at which workers (e.g. Liu et al., 1988; Gaetani et al., 1990, 1991; Central Asia grew during the Phanerozoic. It is tectonostra- Matte et al., 1991; 1996; Pan et al., 1992; Yao and Hsu¨, tigraphically subdivided into the North Kunlun, i.e. the 1994; Mattern et al., 1996), it is now possible to review the southern margin of the Tarim Block, and the narrow main aspects of the geology of the western Kunlun. Our South Kunlun, which was the site of two Phanerozoic descriptions pay special attention to those aspects signifi- magmatic arc-related intrusion cycles. Both tectonic units cant for the reconstruction of the geodynamic development. are separated by the ophiolite-bearing Oytag-Kudi suture For more details on the regional geology the reader is (Fig. 1). The Kara-Kunlun is a sizeable mid-Phanerozoic referred to the quoted literature and the sources therein. accretionary wedge. We use the geological time table by Haq and van Eysinga (1987) in correlating radiometric ages with geological time * Corresponding author. units and corresponding stratigraphical time–rock units and E-mail address: [email protected] (F. Mattern). in assigning numerical time spans.

Fig. 1. Geological elements of the study area (simpliﬁed). Note that the Kudi ophiolite thrust unit appears to be much larger in map view than the ophiolite units of the suture trace. According to Yao and Hsu¨ (1994), ophiolites also occur in the Kara-Kunlun northwest and southeast of Mazar. They are not shown since their exact location was not indicated by Yao and Hsu¨ (1994). Ophiolite distribution after Liu et al. (1988). Fieldwork was carried out along the road from Yecheng to the area around Tianshuihai and in side valleys.

2. Sinian rifting of the North Kunlun and creation of the marine strata has been determined on the basis of micro- Proto-Tethys Ocean ﬂoral and small shelly fossils (Yao and Hsu¨, 1994). Along with Pan et al. (1992), we interpreted the Sinian The basement of the North Kunlun is characterized by succession as a rift sequence which formed during the Precambrian gneisses and migmatites (Pan et al., 1992; fragmentation of a subsiding shallow marine platform Matte et al., 1996). It is overlain by a mildly metamorphosed (Mattern et al., 1996). Following Sinian rifting of the south- Sinian (Late Proterozoic) succession of laminated carbo- ern margin of the Tarim Block, ocean spreading is assumed nates, volcanites, shales, marls and tufﬁtes, well-exposed to have taken place during the later Sinian and Lower Paleo- around Akaz Pass. Locally, we observed the alternation of zoic resulting in the formation of the Proto-Tethys Ocean parallel-bedded limestone and dolomite. The laminated whose remnants are found at the Oytag-Kudi suture (Pan et carbonates indicate a shallow marine depositional environ- al., 1992; Mattern et al., 1996). According to Chang et al. ment. According to Pan et al. (1992), the metavolcanites are (1989), this ocean developed during the Sinian and former oceanic tholeiites. The thickness of the Sinian Cambrian. We are unable to say which continental mass succession may reach 1 km or more. At Akaz Pass, a thick- drifted away from the southern margin of the Tarim ness of several hundred meters is exposed. Similar Sinian Block, but we do not consider the South Kunlun a likely rocks of great thickness occur in the Tarim Basin (Tian et candidate because it lacks a similar Sinian succession al., 1989). South of Hotan, the Sinian age of these shallow (Fig. 2). F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 639 considering that strike-slip rifts are low-volcanicity rifts at best (Mattern et al., 1998).

3. Oytag-Kudi suture and Kudi Ophiolite Complex

The Oytag-Kudi suture which separates the North and South Kunlun is marked by an alignment of ophiolite slices which appear narrow in map view (Fig. 1; Liu et al., 1988). The suture is inclined towards the South Kunlun (Pan et al., 1992, their Fig. A-2; Matte et al., 1996, their Fig. 2). Little is known about the geology of this suture trace (“suture trace” sensu Sengo¨r et al., 1988, their Fig. 21). Yang et al. (1996) reported peridotite, cumulate gabbro and basalt from the Kegang ophiolite occurrence (ca. 100 km NW of Kudi). Approximately 80 km east of Kudi, the structure along the suture trace appears to be complicated, in so far as there is a large lenticular, possibly fault-bounded rock unit, adjacent Fig. 2. Juxtaposition of the North and South Kunlun’s stratigraphy. Note the to the suture north of the ophiolites, which displays an en similar development as of the Devonian. e´chelon rock fabric (Matte et al., 1996). In Figs. 1 and 8 we assign it to the South Kunlun. The alternation of metacarbonates and metatholeiites Knowledge of the Kudi Ophiolite Complex, which indicates that marine conditions persisted during the rift appears much larger in map view than the ophiolite units process. Therefore, the visited area of the North Kunlun of the suture trace, is much more detailed. The Kudi Ophio- was probably not located on a rift dome, as this would lite Complex represents an obducted ophiolite unit which have likely caused uplift of the platform above sea-level. was thrust from the suture and emplaced on the South The Sinian rift sequence of the Akaz Pass area might have Kunlun (Fig. 3). We studied the northern and eastern part been located to the side (i.e. “north”, according to present of this complex in the north/south-trending Kudi Valley day directions) of such a dome. This interpretation implies a along the road north of the village of Kudi and in the dip-slip type of rifting. small, canyon-like Yishak Valley which trends approxi- Alternatively, one could argue that rifting was due to mately east/west and leads into the Kudi Valley from the strike-slip motion as this would neither require nor induce west (Fig. 3). We investigated the southern part of the a rift dome (Mattern et al., 1998). However, strike-slip rift- complex at the northern slope of the Boziwan Valley ing appears to be an unlikely option because of the abun- which joins the Kudi Valley from the west at the northern dance of volcanogenic strata in the Sinian succession, margin of Kudi (Fig. 3). Except for a sheeted dike complex

Fig. 3. Cross section sketch of the obducted Kudi Ophiolite Complex, constructed mainly from the investigations in the Boziwan Valley and Kudi Valley (road section). Fault marked with “x” is the one depicted on Fig. 6, ca. 15.5 km north of Kudi at the bridge. Fold vergence close to the Yishak Valley may be due to post-obductional shortening. Minor outcrops of metamorphic rocks are not shown. 640 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650

Fig. 4. Layering of the Kudi Ophiolite Complex. The total thickness measures more than 2 km (Wang, 1983). According to Yang et al. (1996), arc-typical lavas are a part of the complex. we found all main layers of a complete ophiolite section (Fig. 4). Instead of the sheeted dike complex we observed Fig. 5. Roadside outcrop of pillow lava belonging to the Kudi Ophiolite a thick layer of massive basalt. Yang et al. (1996), who Complex, ca. 8 km north of Kudi. investigated the Kudi Ophiolite Complex as well as some ophiolites of the suture trace, also noted the absence of or brown basalt. A debrite with a thickness of several deci- sheeted dikes. A summary of our findings pertaining to meters is associated with this layer in the Yishak Valley. the layering of the complex is shown in Fig. 4. At the base of the uppermost layer, lenses of up to 1 dm The Dunite as the lowermost layer, generally exhibits a thick hematitic chert occur. The bulk of the uppermost layer, coarse-grained, structureless fabric. Locally we observed however, comprises red shales and green tuffites which may thin parallel laminations of chromite which are intersected alternate in thin layers of only a few centimeters or form by only a few centimeters thick dikes of pyroxenite. More- monotonous successions of several meters or even tens of over, we found up to 1.5 m thick hornblendite dikes in the meters. The red shales are frequently intercalated with gray dunite. The peridotite above the dunite is partly serpenti- graded layers of several millimeters to centimeters in thick- nized. Among the rocks of this layer we distinguished two ness. The grain size of the tuffites ranges from dust to lapilli. varieties — a relatively fine-grained and massive one, and Coarse tuffites from the Yishak Valley bear lithic compo- another that displays layering of pyroxene cumulates. nents of basic volcanites, devitrified glass components, Within this layer also distinct pyroxenite bodies occur. plagioclase phenocrysts and fragments displaying flow The lithology of the peridotites is dominated by harzburgite fabrics, like deformed vesicles. All of these rock types (Yang et al., 1996). According to Yang et al. (1996), the appear to be silicified. peridotites are highly depleted. The next layer consists of The ratio between the amount of suture sediments and coarse-grained gabbro. basic to ultrabasic oceanic igneous rocks is relatively We can neither describe the transition from the gabbro small in the Kudi ophiolite complex. According to map layer to the next layer, nor do we know whether a transition analyses (e.g. Liu et al., 1988), this also holds true for the even exists. The next layer is thick and comprises a gener- suture trace. ally fine-grained, massive basalt (Fig. 4) above which a Age information pertaining to the Oytag-Kudi ophiolites layer of pillow basalt accumulated. The diameter of the is controversial. Moreover, radiometric literature informa- pillows usually does not exceed 1 m (Fig. 5). The pillows tion is often unspecific about the applied method, investi- display glassy rims and amygdales. According to Pan et al. gated minerals, sample location, type of age and so forth. (1992), the pillow basalts of the Oytag-Kudi suture repre- Rb–Sr isochron dating of basaltic rocks by Jiang et al. sent mature ocean ridge type tholeiites, but, according to (1992, as quoted by Yang et al., 1996) yielded an age of Yang et al. (1996), lavas from this suture zone display 360 Ma. According to the Institute of Geology and Mineral geochemical patterns suggesting a supra-subduction zone Resources, Urumqi, Xinjiang (correspondence), radiolarian environment. cherts of the Kudi ophiolites date as Carboniferous to Above the pillow basalts there are lenses of hematitic Permian. Wang (1983) reported an age of “earlier than chert (up to 2 cm thick), shales and tuffites. The following 860.5 Ma” for an ultrabasic rock. He also reported the age layer is represented by massive, amygdaloidal, slightly red of a quartz diorite which intruded volcanic rocks of the Kudi F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 641

Fig. 6. Southern margin of the 460 Ma granodiorite, 15.5 km north of Kudi. In the foreground on the right side, the pluton displays a mylonitic foliation (015/ 85), marked by the arrow on the lower right. The view is exactly parallel to the foliation towards 285Њ. Note that in the projected extension of the foreground mylonitic zone, the mountain crest of the background, displays a saddle (upper arrow). Note the more or less horizontally stratiﬁed unconsolidated river deposits in the south and the loess in the center covering the contact between the pluton and the more southerly located Kudi Ophiolite Complex.

Ophiolite Complex to be 517 Ma. Pan et al. (1992) most part of the Kudi Ophiolite Complex, at the bridge mentioned a Rb–Sr isochron age of 816 Ma for a pegmatitic approximately 15.5 km north of Kudi. Microscopic kine- amphibolitic dike which intruded an ultramafic rock, and a matic evidence shows that the granodiorite was ductilely K–Ar whole rock age of 517 Ma for a diorite which intruded sheared in a strike-slip mode along the northwest/southeast volcanites north of Kudi. We wonder whether Pan et al. directions (Mattern et al., 1996). The main mylonitic folia- (1992) were referring to Wang’s (1983) data and whether tion of the granodiorite is conspicuous in the field (Fig. 6). the different numbers “860” of Wang (1983) and “816” of We also observed steeply dipping brittle faults (Mattern et Pan et al. (1992) resulted from a translation mistake or mix- al., 1996, p. 708–709), trending east/west (Fig. 7). The up in one of the two English texts as both numbers are contact between the Kudi Ophiolite Complex and the pluton phonetically very similar. According to Pan et al. (1992), is covered by a 300 m wide zone of unconsolidated sedi- this diorite was also dated as 458 Ma (Rb–Sr isochron) and ments (Fig. 6). The northernmost outcrop of the Kudi 480 Ma (40Ar/39Ar). They also reported ages pertaining to a Ophiolite Complex also exhibits signs of brittle fracturing. granite which intruded the volcanites of 384 Ma (40Ar/39Ar) The massive basalt was intruded by a mafic dike. We did not and 423 Ma (Rb–Sr isochron). Pan et al. (1992) also listed a find any evidence for an intrusive pluton/ophiolite contact. model age for pillow lavas, not located in the Kudi area, of Instead we interpret the contact relation between the pluton 900–600 Ma. Xu et al. (1992) determined the following and the Kudi Ophiolite Complex as a faulted one (Fig. 3). ages for a granodiorite which intruded the pillow lava: Although we saw many outcrops of the Kudi Ophiolite 474 Ma (40Ar/39Ar plateau age on hornblende), 449 ^ 24 Complex in the three valleys, we found no evidence of Ma (40Ar/39Ar– 39Ar/36Ar isochron age on biotite), and 458 granitoid intrusions into the complex. All contacts between Ma (U/Pb concordant age on zircon). The same age numbers granitoids and the ophiolites were covered by unconsoli- (partly different methods) were also published by Matte et dated sediment. Within the ophiolite complex, we also did al. (1996) for a schistose granodiorite south of Akaz Pass not observe any aplite or silicic pegmatite dikes which could which intruded mafic rocks. Its location is apparently indi- be associated with the granitoid intrusions. The literature cated on their Fig. 2 with the age information “gd4, 460 provides neither specific phenomenological nor formal Ma”. (location) details on the intrusive contact relations between We had the opportunity to investigate the zone between granitoids and ophiolites. the southernmost exposures of this pluton and the northern- Acknowledging the controversial age data, Pan et al. 642 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650

Fig. 7. Roadside outcrop of a brittle, steeply south-dipping, east/west-trending fault in the 460 Ma granodiorite; ca. 15.5 km north of Kudi, directly at the ﬁrst bridge north of Kudi.

(1992) and Mattern et al. (1996) considered the ophiolites of acidic dikes which experienced amphibolite facies conditions the Oytag-Kudi suture to have formed in the Proto-Tethys (Pan et al., 1992). Protoliths of the migmatites south of Kudi between the Sinian and Early Paleozoic. Further time seem to be of Proterozoic age (Matte et al., 1996). 40Ar/39Ar constraints on the formation of these rocks is provided by age spectra on K-feldspars suggested to Matte et al. (1996) a the age of subduction-related magmatites (see below) which minimum age of 380–350 Ma for metamorphism. formed during subduction of the Proto-Tethys Ocean since Zhang et al. (1992) distinguished two arc granitoid belts oceanic lithosphere must ﬁrst be created before it can be in the South Kunlun, an older, Paleozoic one in the north, subducted and since ocean-spreading can be coeval with and a younger, Late Paleozoic to Mesozoic one in the south. subduction. In this section we concentrate on the northern belt which is discontinuous at the surface, and relatively small compared to the southern belt (Fig. 8). Considering the geochemical 4. Paleozoic subduction of Proto-Tethys beneath the characteristics of the granitoids and their geological setting, South Kunlun which includes the presence of parallel-trending suture zones, as well as the long, linear, orogen-parallel extent of The basement of the South Kunlun is characterized by the the belts, Zhang et al. (1992) suggested that their genesis is occurrence of gneisses, amphibolites and migmatitic gneisses. closely related to subduction. Geochemical data (Pan et al., The gneisses and amphibolites were intruded by basic and 1992) support this interpretation. Hsu¨ (1988) had already F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 643

Fig. 8. Map sketch of granitoids of the study area mainly after Matte et al. (1988) supplemented by data from Liu et al. (1988) for the South Kunlun. Note that the northern granitoid belt is much smaller than the southern one. Mazar pluton according to Liu et al. (1988), Gaetani et al. (1991), and own observations. Map depictions of the Kudi pluton differ greatly (compare, for example, Liu et al., 1988 and Matte et al., 1996). The anatectic laccoliths after Matte et al. (1996). attributed the presence of batholiths to a former active plate westnorthwest of Yecheng), at the transition between the margin. The two granites from the northwest-trending part Pamirs and the Kunlun, a slightly metamorphosed succes- of the western Kunlun dated by Fan and Wang (1990) as 445 sion of shallow marine Ordovician fossil-bearing limestones Ma (K/Ar) and 480.43 ^ 5 Ma (U/Pb) belong to this belt. and arc-related volcanites as well as Ordovician and Silurian These ages indicate Ordovician subduction. It cannot be clastic deposits occurs above the Sinian strata and below up ruled out that subduction occurred also during the Cambrian to 1350 m thick Upper Devonian terrestrial clastic red beds and Silurian. Southward subduction is indicated by the (Yao and Hsu¨, 1994, p. 79 and their Fig. 6). A pre-Devonian northern position of this older arc granitoid belt within the stratigraphic gap also exists in the western North Kunlun South Kunlun and its occurrence south of the Oytag-Kudi where there is no stratigraphic record between the Sinian rift suture. The interpretation of an Early Paleozoic episode of sequence and unconformably overlying Upper Devonian subduction is difficult to reconcile with coeval granitoid terrestrial red molasse deposits. intrusions into oceanic lithosphere, unless some ophiolite The Upper Devonian molasse consists of fluvial and allu- obduction occurred relatively early, or unless the upper vial fan arkoses and conglomerates as well as volcanogenic plate also had an oceanic back-arc region north of the strata. At a roadside outcrop, approximately 10 km east- South Kunlun, whose associated oceanic arc was first northeast of the Akaz Pass, these clastic rocks are compo- intruded by more or less M-type(?) arc granitoids (“M- sitionally and texturally immature. Lithic components were type” sensu Pitcher, 1982) and then obducted(?). eroded from nearby granitoids, rhyolites, acidic to intermediate altered pyroclastic rocks and basic volcanites. At the same outcrop we observed an angular unconformity 5. Mid-Paleozoic suturing of Proto-Tethys within these sediments with an angle close to the angle of repose. Only a larger angle would justify the interpretation In the Kongur Shan area (Mt. Kongur, 7719 m, 200 km of a tectonic cause for the formation of this unconformity. 644 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 The thickness of the Devonian molasse may be several hundred meters (Matte et al., 1996). Pan et al. (1992) noticed that the Devonian succession exhibits an overall fining-upward trend. The Devonian clastic rocks have been dated by plant fossils (reviews by Sengo¨r and Okur- ogullari, 1991; Yao and Hsu¨, 1994). Terrestrial red molasse deposits of Devonian age also occur in the South Kunlun (Pan et al., 1992). As shown in Fig. 2, the stratigraphic development of the North and South Kunlun is continuous and similar across the Oytag-Kudi suture as of the Devonian. Thus, the accretion of the South Kunlun against the southern margin of the Tarim Block must have been completed by that time. It appears reasonable to attribute the pre-Devonian stratigraphic gap in both terranes (Fig. 2) to uplift and erosion related to regional shortening in the course of accretionary processes. Since shallow marine Ordovician and Silurian strata are preserved in the Kongur Shan area we assume that significant short- Fig. 9. Juxtaposition of the South Kunlun and Kara-Kunlun stratigraphy. ening and uplift started after deposition of the Silurian clas- Note the similar development as of the Mesozoic. tic sediments. According to Yao and Hsu¨ (1994, their Fig. 6), uppermost Silurian to mid-Devonian sediments are miss- succession of distal allodapic limestones. Carbonates seem ing in the Kongur Shan area. This indicates to us that sutur- to be very scarce. ing, shortening, and mountain building started during the In the area of Mazar, fine- to coarse-grained laminated Late Silurian. Matte et al. (1996) concluded a Silurian colli- graywackes contain granitoid debris. Fine- to coarse- sion. They listed a U/Pb zircon age of 377 Ma and Rb/Sr grained graywackes at the Qitai Pass contain granitoid ages of 392 ^ 35 Ma on whole rock, and of 381 ^ 4Maon debris as well, but also subordinate amounts of chert, phyl- biotite on the potassic postkinematic Kudi granite, whose lite and quartzite fragments. Accessory constituents are intrusion postdates metamorphism and anatexis in the South zircon, apatite, muscovite, biotite and chlorite. The compo- Kunlun. This metamorphism and anatexis is indicated by a sition of metasiltstones from the Xaidulla area corresponds complex 40Ar/39Ar age spectra on K-feldspars of migmatites to that of the coarser material from the Qitai Pass. They south of Kudi, suggesting a minmum age of 380–350 Ma, contain quartz, feldspar, biotite, and muscovite. Tourma- due to Silurian collision (Matte et al. 1996). line, apatite, sphene and ore minerals represent accessory The Devonian molasse of both the North and South minerals. The main constituents in metatuffites are quartz, Kunlun grades upward into shallow marine Carboniferous feldspar and actinolite. and Permian carbonates (Fig. 2; Pan et al., 1992) which are The facies character of these clastic deposits (e.g. silici- well-dated by fusulinids, bivalves, brachiopods and corals clastic turbidites, allodapic limestone beds), compositional (De Terra, 1932 as quoted in Matte et al., 1996; BGMR, aspects (granitoid debris) as well as the occurrence of 1993). The carbonates may be 1 km thick (Matte et al., tuffites can be reconciled with an active margin setting 1996). The fact that these carbonates are marine indicates and is in support of the accretionary wedge interpretation. that the Silurian/Devonian Kunlun mountains were already Gaetani et al. (1990, 1991), who worked in the area of widely denuded when the carbonates accumulated. transition from the Kunlun to the Karakorum, estimated the thickness of these deposits (“Bazar Dara Slates”) to measure several thousand meters, and, according to Matte et al. 6. The Kara-Kunlun accretionary wedge (1992), as much as 6 km or more. The age of the unfossili- ferous Kara-Kunlun sediments could range from the Ordo- The Kara-Kunlun area is characterized by the occurrence vician to the Triassic (Pan et al., 1992) or from the Cambrian of thick monotonous and partly metamorphosed succes- to the Triassic (Matte et al., 1992) or from the Precambrian sions of clastic marine deposits which exhibit a flyschoid to the Mesozoic (Yao and Hsu¨, 1994). The sediments must character (Fig. 9). Dark shale is by far the predominant be older than the Mesozoic plutons which intruded them sediment type which probably gave the Kara-Kunlun its (Fig. 9 and below). Paleozoic to Triassic fossils are name (“kara” “black”). Besides shale we found silici- known to occur in exotic limestone slabs (Yao and Hsu¨, clastic turbidites and tuffites. The turbidite beds exhibit 1994). thicknesses mostly between 0.4 and 1.5 m. Bouma inter- From the Kara-Kunlun belt Yao and Hsu¨ (1994) reported vals “a” may be present. The pelitic intervals usually the occurrence of ophiolite me´langes northwest and south- measure only a few centimeters. Only at one locality east of Mazar, containing blocks of serpentinite, gabbro, (wadi 3 km west of Mazar) we observed a 30 m thick greenstone, radiolarite, metagraywacke, marble, gneiss F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 645 and volcanites, embedded in a pervasively sheared, cleaved implied internal thrust planes and with the dominant dip matrix of sericite-quartz schist, chlorite-sericite schist, two- direction of strata and the observed vergences. The Kara- mica schist and phyllite. Since the maps by Liu et al. (1988), Kunlun accretionary wedge can be correlated with the BGMR (1993), and Matte et al. (1996) do not indicate Sonpan Ganze Belt or parts of it (Bayan Har Group) farther ophiolites in the Mazar area, and since Yao and Hsu¨ east (Sengo¨r and Okurogullari, 1991; Matte et al., 1996; (1994) were unspecific about the location of the studied Mattern et al., 1996). The Songpan Ganze Belt occupies a ophiolite outcrops, we are unable to show them in Fig. 1. position south of the Kunlun, like the Kara-Kunlun accre- Another ophiolite unit occurs east of Dahongliutan (Fig. 1). tionary wedge, and is also characterized by a great thickness Also farther east, outside the study area, there is an ophiolite and by a dominance of fine-grained siliciclastic deposits body at Mt. Muztag (7723 m, 700 km eastsoutheast of Hotan (Leeder et al., 1988; Coward et al., 1988; Nie et al., — not to be confused with Mt. Muztag, 7282 m, 115 km 1994). It has also been interpreted as an accretionary southsoutheast of Hotan; Pan et al., 1992; Yao and Hsu¨, wedge south of the eastern Kunlun (Leeder et al., 1988). 1994, their Fig. 8). The presence of ophiolites in rocks of the Kara-Kunlun (Liu et al., 1988; Yao and Hsu¨, 1994) is impor- tant because it indicates that internal thrust planes exist in the 7. The Uygur Terrane and adjacent sutures siliciclastic Kara-Kunlun belt, such as one would expect to The Uygur Terrane located south of the Kara-Kunlun occur in an accretionary wedge. The ratio between the amount accretionary wedge (Fig. 1) is the southernmost unit we of suture sediments and basic to ultrabasic oceanic igneous inspected. Although the Uygur Terrane is a poorly under- rocks is relatively large in the Kara-Kunlun wedge. stood element of the regional tectonic collage there is In the westernmost part of the Kara-Kunlun, the clastic certainty that its rock facies contrasts sharply with that of rocks of the Kara-Kunlun are either unmetamorphosed or the Kara-Kunlun accretionary wedge. No stratigraphic rela- display a very low metamorphic grade (Gaetani et al., 1990). tionship exists between these two units. We observed a According to Matte et al. (1996), the clastic rocks are thrust contact between the two terranes in the Tianshuihai affected by only low-grade metamorphism. At several road- area (Mattern et al., 1996). The Uygur Terrane consists of a side outcrops between Mazar and Hez Pass and also farther fossiliferous and generally well-dated Paleozoic to Triassic east, for example, at the Qitai Pass, unmetamorphosed strata shallow marine succession (BGMR, 1993). The succession can be observed. At several places we found evidence of measures hundreds of meters in thickness and contains a contact metamorphism. These areas include the aureole of significant amount of carbonates. Because we could only the Mazar pluton, west of Mazar, the Dahongliutan area, and inspect a few of the formations within the terrane we a location 40 km eastsoutheast of Shanshilli (outcrop along decided not to depict its stratigraphic development. a new road, Mattern et al., 1996). At the latter we found To the south, the Uygur Terrane is separated from the south- sillimanite-bearing metashales. Ductile faults can be erly located Karakorum/Qiangtang Terrane by the “cryptic” observed in these zones (below). Longmu Co suture (Fig. 1) of Baud (1989), which is also We noticed that the strata of the Kara-Kunlun mainly dip referred to as the “Taaxi-Qiaoertianshan-Hongshanhanu to the north and northnortheast, that is inclined towards the suture” (Pan et al., 1992). Since we did not reach this suture, South Kunlun. Observations of the preferred dip include the following information is taken from the literature. those that were made on mountain-scale outcrops, for exam- Although most of this suture has been covered by post-accre- ple, in the areas around the Hez Pass, Dahongliutan, and the tionary deposits (Pan et al., 1992) ranging from the mid-Juras- Qitai Pass. Folds exhibit a south or southsouthwest sic to the Quaternary (Liu et al., 1988; BGMR, 1993), Pan et al. vergence. The observed slaty cleavage is genetically related (1992) identified this zone as a suture because it delineates to the folds (Mattern et al., 1996). These aspects are compa- blocks of marked geological and paleontological differences. tible with the interpretation of an accretionary wedge which Ophiolites do not occur in the suture segment south of the formed south of the South Kunlun in response to northward western Kunlun but are known from this suture farther east B-type subduction. As shown below, the Kara-Kunlun was (Pan et al., 1992). This zone also represents the northern intruded by subduction-related granitoids indicating an boundary for the distribution of marine Jurassic strata (Pan active margin environment in which the Kara-Kunlun et al., 1992). There isa mid-Jurassic suture overlap assemblage wedge became the site of arc magmatism. whose age is documented by a brachiopod fauna (BGMR, Whereas the stratigraphy and age of the Kara-Kunlun’s 1993), indicating that this segment of the Paleo-Tethys was rocks are poorly understood, the geodynamic significance of eliminated at the latest by the mid-Jurassic. the Kara-Kunlun zone appears to be clear. Hsu¨ (1988) interpreted the Kara-Kunlun area as an accretionary wedge which formed due to northward subduction of the Paleo- 8. Late Paleozoic to Early Mesozoic subduction of the Tethys Ocean beneath the South Kunlun. This view is Paleo-Tethys Ocean beneath the South Kunlun consistent with the flyschoid facies and composition of the thick clastic sediments and their association with tuffites, In the western Kunlun there is no rift sequence preserved ophiolite me´langes and arc granitoids as well as with the which could help to determine when the Paleo-Tethys 646 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 Ocean formed to the south of the South Kunlun. However, ages of 190 ^ 8 Ma and 177 ^ 3 Ma. The Kara-Kunlun there are arc magmatites whose ages indicate at least when accretionary wedge or part of it must have already formed melts developed in response to subduction of Paleo-Tethys before the intrusion of those granitoids with the Upper lithosphere. The onset of subduction must have predated arc Triassic ages. magma generation, and ocean spreading must have Matte et al. (1996) and Mattern et al. (1996) concluded predated, and may have been coeval with, subduction. that the magmatites of the southern South Kunlun and the From a Kunlun perspective one must conclude that ocean Kara-Kunlun formed as a result of the subduction of Paleo- spreading of the Paleo-Tethys must have started before the Tethys at a north-dipping Benioff plane beneath the South Late Carboniferous. Kunlun. Apparently, arc magmatism started to affect the Upper Carboniferous and Permian intermediate and basic South Kunlun already during the Late Carboniferous (volca- volcanites intercalated with the well-dated Upper Paleozoic nites) and the Kara-Kunlun only as of the Late Triassic. In shallow marine carbonates of the South Kunlun (Fig. 9) are both areas, arc magmatism seems to have ceased during the of the calc-alkaline arc type (Pan et al., 1992). They repre- mid-Jurassic. In Kara-Kunlun, arc activity could have sent the earliest evidence for a new subduction cycle. slightly outlasted that in South Kunlun. Mattern et al. Further evidence is provided by Late Paleozoic to Early (1996) hypothesized that with the growth of the Kara- Mesozoic orogen-parallel arc batholith belts (Fig. 8). As Kunlun accretionary wedge, the trench might have moved mentioned above, Zhang et al. (1992) distinguished an oceanwards and with it the magmatic front, so that the Kara- older Paleozoic arc granitoid belt in the north and a younger Kunlun became the site of arc granitoid intrusion. Late Paleozoic to Mesozoic one in the south of the South The subduction polarity is indicated by the geometry Kunlun. In this chapter we are concerned with the southern within the Kunlun/Kara-Kunlun subduction accretion zone belt which is significantly larger than the northern one (Fig. with the early magmatic arc in the northerly located South 8). The finding by Zhang et al. (1992) is based on radio- Kunlun and the Kara-Kunlun accretionary wedge to the metric and geochemical evidence as well as on considera- south. The observed vergences in the Kara-Kunlun wedge tions of the geological setting. lend further evidence for a north-dipping Benioff plane. An altered granodiorite at Xaidulla yielded a Rb/Sr One of our goals during fieldwork was to find and kine- isochron age of 267 Ma on biotite (Xu et al. 1992). From matically analyze ductile shear zones within arc batholiths a granite located 22 km northeast of Mazar an 40Ar/39Ar– or within their contact aureoles. The kinematic data 39Ar/36Ar isochron age of 211.8 ^ 10.8 Ma was published obtained by Mattern et al. (1996) are interpreted here as by Xu et al. (1992). For the same pluton an 40Ar/39Ar whole clues as to the kind of plate convergence. We reason that rock age of 211 ^ 8 Ma and an 40Ar/39Ar minimum age of arc magmatism is concurrent with subduction, and that 180 ^ 10 Ma on K-feldspars was reported (sources in Matte deformation observed within the “still hot” arc rocks and et al., 1996). A red porphyry volcanite located close to the adjacent country rocks should, therefore, have recorded granite yielded a Rb/Sr whole rock age of 180 ^ 10 Ma information of the tectonic regime controlled by the kind (source in Matte et al., 1996). According to Pan et al. of plate convergence. We found ductile faults in the vicinity (1992), the plutonic rocks of the South Kunlun belong to of, and with a trend parallel to, the South Kunlun/Kara- the calc-alkaline series and owe their genesis to subduction Kunlun boundary at Xaidulla in the southern South Kunlun and related arc magmatism. and 40 km eastsoutheast of Shanshilli in the northern Kara- The Kara-Kunlun accretionary wedge was also affected Kunlun (outcrop along a new road, Mattern et al., 1996). by this magmatic arc activity (Matte et al., 1996). Mesozoic The distance between both locations amounts to 55 km. arc batholiths intruded the Kara-Kunlun sediments, display- Mylonites of these faults were sampled and analyzed. In ing a trend parallel to the orogen. Gaetani et al. (1991) both cases we found microscopic evidence for dextral obtained a K/Ar biotite cooling age of 171.5 ^ 5.4 Ma for strike-slip motion (Mattern et al., 1996). the Mazar Pluton located west of Mazar. Xu et al. (1992) At the first location, the heat required for ductile shearing determined an 40Ar/39Ar plateau age of 184 Ma on biotite was provided by the previously mentioned altered Xaidulla and a low intercept age on zircon of 199.3 ϩ 2.2/Ϫ2.5 for granodiorite dated 267 Ma (Xu et al., 1992). According to the Mazar monzogranite. Xu et al. (1992) also determined the map by Matte et al. (1996), this granodiorite belongs to a an 40Ar/39Ar plateau age of 187 Ma for a granite which batholith from which the also mentioned granite located belongs to the batholith south of the road between Shanshilli 22 km northeast of Mazar was dated 211 ^ 10.8 Ma and Kengxiwar. They also published a lower intercept age (40Ar/39Ar– 39Ar/36Ar isochron) by Xu et al. (1992). For on zircon from a granite near Kengxiwar of 192 Ma. More- the same granite the above listed ages of 211 ^ 8Ma over, they dated a monzogranite (located 30 km southeast of (40Ar/39Ar whole rock) and 180 ^ 10 Ma (40Ar/39Ar mini- Kengxiwar?) 215 Ma (40Ar/39Ar, biotite) and 196.3 Ma mum age) were determined (sources in Matte et al., 1996). It (40Ar/39Ar plateau age, biotite). Matte et al. (1996) carried has to be noted that the granite of the Mazar area is located out 40Ar/39Ar measurements on muscovites and biotites at a distance of 80 km west of Xaidulla. The ages range from from granites along the Karakax Valley (area south of Shan- the Upper Permian to the uppermost Triassic to the mid- shilli and Kengxiwar and at Dahongliutan) yielding plateau Jurassic (minimum age). We are inclined to interpret these F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 647 the kinematic relation between the overriding and the downgoing plate, plate convergence should have been of dextral obliquity during the Early Mesozoic.

9. Mesozoic suturing of Paleo-Tethys

The latest shallow marine deposits of the western Kunlun are Upper Permian in age (Liu et al., 1988). The presence of these deposits indicates that uplift due to accretion/collision-related shortening postdates their deposition. There is a well-documented angular unconformity with a significant stratigraphic gap between the Upper Paleozoic rocks and the terrestrial Mesozoic molasse in the western Kunlun (Liu et al., 1988; Pan et al., 1992; Yao and Hsu¨, 1994). This gap and the onset of molasse deposition indicate that uplift had affected the region. Early uplift could be attributed to effects related to subduction. Later uplift was more likely due to shortening in the course of complex accretionary/collisional processes coeval with subduction. At the southern boundary of the South Kunlun we found one place where Upper Triassic red molasse overlies Permian shallow marine carbonates and volcanic strata at a (now overturned) angular unconformity (wadi north of the road at road mark 266, 26 road km east of Mazar, elevation 4000 m, Mattern et al., 1996). The Triassic succession consists of terrestrial conglomerates, sandstones and shales. The conglomerates and sandstones are alluvial fan deposits of low compositional and textural maturity. They contain reworked Carboniferous and Permian material (limestone and dolomite fragments) and clasts of chert, shale and quartzite. At this location, as well as on the southern slope of the Saliyak Pass (at an elevation of 4650 m, also at the southern boundary of the South Kunlun), we observed a fining- upward trend within the Upper Triassic succession. However, we did not see more than 70 m of exposed Trias- Fig. 10. Plate tectonic development of the western Kunlun and Kara- sic strata. At both places, the red Triassic shales grade into Kunlun. Note that only minor amounts of subduction-related melts reached slightly green Jurassic shales. In the Kongur Shan area, the northern South Kunlun during consumption of Proto- Tethys. Arc where there is also a stratigraphic gap between the Permian magmatism in the South Kunlun and Kara-Kunlun ended during the mid- Jurassic. Also note the age of overlap assemblages at terrane boundaries. and Triassic, the terrestrial Triassic succession is 850 m thick (Yao and Hsu¨, 1994). The Triassic rocks are dated in the eastern Kunlun by numerous kinds of fossils (Yang data as an indication that ductile deformation conditions and Long, 1990). have existed at Xaidulla during the Triassic and during In a wadi north of the road at road mark 272 (32 road km mid-Jurassic cooling. east of Mazar, elevation 4100 m), the Triassic is missing The granitoid which provided the heat for mylonitization above the Permo-Carboniferous shallow marine carbonates. of contact-metamorphic sillimanite-bearing shales at the Deposition of the terrestrial clastic molasse started here second location belongs to the batholith south of the road during the Early Jurassic and continued to the mid-Jurassic between Shanshilli and Kengxiwar, from which Xu et al. (Liu et al., 1988). The Jurassic succession contains (1992) determined the above mentioned 40Ar/39Ar plateau conglomerates, sandstones and shales. We observed coal age of 187 Ma and the lower intercept age on zircon of 192 seams which were also described for the Jurassic of the Ma. These are Early Jurassic ages. We assume that ductile North Kunlun by Pan et al. (1992). The depositional envir- deformation conditions may have existed during the Early onment of the Jurassic may have included lakes and Jurassic and possibly lasted to the mid-Jurassic during the swamps. In contrast to the Triassic strata, the Jurassic cooling process. deposits lack red color and contain a significant amount of If the finding of dextral ductile faults does indeed reflect granitoid debris. The lack of red color is also helpful in 648 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 distinguishing these Jurassic strata from Cretaceous and discussed and that is how a marine mid-Jurassic suture over- some Cenozoic terrestrial deposits. The presence of grani- lap assemblage was able to accumulate above a suture that toid debris shows that the magmatic arc was already eroded formed only during the Early Jurassic. Possible solutions to its granitoid level during the Lower Jurassic. The low are: 1. Accretion was “gentle” and did not result in a signif- compositional and textural maturity of the Jurassic deposits icant uplift (e.g. due to the shapes of the accretion zone and indicates a close provenance. The Jurassic sediments are of the microcontinent). 2. A time span of 30 million years rich in plant fossils. Some of them have been listed by elapsed between accretion (Pliensbachian?) and formation BGMR (1993). However, the listed fossil leaves are not of the overlap assemblage (Callovian?) allowing for denu- very conclusive as to the age of the succession. In the dation of a moderately uplifted region. 3. The suture zone outcrop zone in which we worked the Jurassic sediments was affected by extension (e.g. orogenic collapse or trans- are associated with a red volcanite which has been dated tension). 4. A combination of the above mentioned aspects. 180 ^ 10 Ma (Rb/Sr whole rock age, source in Matte et al., 1996). In the wadi at road mark 272, the Lower Jurassic rocks overlap the boundary between the South Kunlun and 10. Conclusions the Kara-Kunlun and exhibit only weak deformation. Arc magmatism is coeval with Late Triassic to mid-Juras- The comparison of both the northerly located Oytag-Kudi sic molasse deposition. It is also coeval with the formation ophiolite zone and the younger South Kunlun suture reveal of the terrane boundary overlap assemblages (Fig. 10). By striking differences. In contrast to the Kara-Kunlun accre- slightly modifying the model of Mattern et al. (1996) we tionary wedge (a suture zone s.l.) only minor amounts of suggest a model which implies successive accretion of two sediment are associated with the Oytag-Kudi ophiolite zone. relatively small units, the Kara-Kunlun accretionary wedge The ratio between the amount of suture sediments and basic and the Uygur Terrane, and, finally, the Karakorum/ to ultrabasic oceanic igneous rocks is relatively large in the Qiangtang microcontinent, all belonging to the realm of Kara-Kunlun wedge and relatively small in the Oytag-Kudi the Paleo-Tethys Ocean (Fig. 10). The accretion of these suture and Kudi complex. The fact that relatively large terranes was accompanied by successive oceanward shifts amounts of basic and ultrabasic oceanic material were of new, short-lived, north-directed subduction zones and preserved and obducted at the Oytag-Kudi suture may indi- successive slab break-offs. The broken-off slabs continued cate that relatively young, hot, buoyant and, therefore, to descend and generated arc melts (Fig. 10). This model “easy-to-obduct” oceanic lithosphere was consumed at the accounts for the regional uplift and arc magmatism concur- northern margin of the South Kunlun (compare Dewey, rent with accretionary/collisional processes and formation 1976). It may also indicate that the ocean basin was rela- of molasse-type overlap assemblages. tively small (if young!). Since oceanic back-arc basins meet The youngest known pre-Cretaceous shallow marine such characteristics we are inclined to assume that such a deposits of the Uygur Terrane are Triassic. It is generally basin was subducted and partly obducted at the Oytag-Kudi assumed that the flyschoid rocks of the Kara-Kunlun accre- suture (Fig. 10). It is intriguing that all major elements of a tion complex do not contain post-Triassic sediments (Liu et complete ophiolite section are represented at the Oytag- al., 1988; Pan et al., 1992; BGMR, 1993; Matte et al., 1996). Kudi suture, except for the sheeted dike complex. Instead, The youngest age of exotic limestone slabs within the accre- we observed thick massive basalt (Fig. 4). These circum- tionary wedge is Triassic (Liu et al., 1998; Yao and Hsu¨, stances might also be in line with the back-arc basin inter- 1994). Considering these aspects we suggest that the small pretation taking into account that sheeted dike complexes Uygur Terrane collided with the Kara-Kunlun accretionary most convincingly illustrate spreading (Moores, 1982) and wedge during the Late Triassic and put an end to wedge- that spreading of back-arc basins may be diffuse (Marsaglia, type accretion and marine sedimentation, due to shortening 1995). and related uplift. This interpretation is supported by the Considering the long time interval from the formation of onset of terrestrial molasse deposition during the Late the Sinian passive margin to the Silurian/Devonian end of Triassic in the Kunlun and during the Early Jurassic in the subduction, it appears likely that a large ocean basin existed Kara-Kunlun (e.g. above mentioned boundary overlap between the North and South Kunlun. If so, this oceanic assemblage). lithosphere was subducted at the Oytag-Kudi suture or at As indicated by the different pre-Jurassic development of the assumed intraoceanic subduction zone which caused the the blocks north and south of the Longmu Co suture and by inferred marginal basin to form. Such a marginal basin was the mid-Jurassic suture overlap assemblage, the Karakorum/ depicted by Pan et al. (1992) with a south-dipping Benioff Qiangtang microcontinent must have been added to the plane for the Early Paleozoic. In this regard it should be Asian tectonic collage during the Early Jurassic. According mentioned again that Yang et al. (1996) interpreted lavas to Dewey et al. (1988), the Qiangtang Terrane accreted to of the Oytag-Kudi ophiolite zone on geochemical grounds the Songpan-Ganze unit in the eastern part of the Tibetan as having formed in a suprasubduction zone environment. Plateau during the Late Triassic or earliest Jurassic. One In line with our interpretation of the Proto-Tethys’ aspect, which one might consider problematic, needs to be subduction setting is the relatively modest amount of arc F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650 649 granitoids generated during subduction. The Northern South Dewey, J.F., 1976. Ophiolite obduction. Tectonophysics 31, 93–120. Kunlun was located in a back-arc and, therefore, relatively Dewey, J.F., Shackleton, R.M., Chang, C., Sun, Y., 1988. The tectonic distant to the arc, so that only minor amounts of melts were evolution of the Tibetan Plateau. Philosophical Transactions of the Royal Society of London A 327, 379–413. able to reach the South Kunlun (Fig. 10). Fan, X., Wang, Y., 1990. Preliminary discussion on Caledonian granites in The formation of the large Kara-Kunlun accretionary western Kunlun. Xinjiang Geology 8, 153–157 (in Chinese, with wedge required sufficient plate coupling to strip off thick English abstract). clastic successions from the downgoing slab and to stack Gaetani, M., Gosso, G., Pognante, U., 1990. A geological transect from Kun them. However, the degree of plate coupling did not allow Lun to Karakorum (Sinkiang, China): the western termination of the Tibetan Plateau. Preliminary note. Terra Nova 2, 23–30. for incorporating significant amounts of basic and ultrabasic Gaetani, M., Gosso, G., Pognante, U., 1991. Geological report (Ch. IV) In: rock slices from the downgoing slab into the accretionary Desio A (Leader) Ev-K2-CNR Italian expedition to the Karakorum. wedge. Considering the small amount of preserved oceanic Geodesy, Geophysics and Geology of the Upper Shagsgam Valley basement rocks we conclude that the oceanic lithosphere (north-east Karakorum) and south Sinkiang, Scientific Reports, Consi- was relatively old and cold and, therefore, easy to subduct. glio Nazionale delle Richerche, Milano, pp. 99–168. This implies a relatively large ocean. Haq, B.U., van Eysinga, F.W.B., 1987. Geological Time Table. . 4th ed.El- sevier, Amsterdam. The interpretation of Paleo-Tethys as a large ocean basin Hsu¨, K.J., 1988. Relict Back-Arc Basins: Principles of Recognition and is also supported by the great volume of arc granitoids Possible New Examples from China. In: Kleinspehn, K.L., Paola, C. which intruded the immediate arc represented by the south- (Eds.). New Perspectives in Basin Analysis. Springer, New York, pp. ern South Kunlun and Kara-Kunlun during the elimination 245–263. of Paleo-Tethys (Fig. 1). Moreover, the long time span of Jiang, C.-F., Yang, J.-S., Feng, B.G., Zhu, Z.Z., Zhao, M., Chai, Y.C., Shi, X.D., Wang, H.D., Hu, J.Q., 1992. Opening-closing tectonics of Kunlun arc magmatism from the Late Carboniferous to the mid- Mountains. Geological Memoirs Series 5 (12), 1–224 (in Chinese, with Jurassic points to the likelihood of a relatively large ocean. English abstract). The older accretionary processes which took place at the Leeder, M.R., Smith, A.B., Jin, C., 1988. Sedimentology of the 1985 Tibet northern margin of the South Kunlun (Proto-Tethys realm) Lhasa to Golmud Geotraverse. Philosophical Transactions of the Royal are less understood than those along the South Kunlun’s Society of London A 327, 107–145. southern margin (Paleo-Tethys realm). We hesitate to Liu, Z., Jiao, S., Zhang, Y., Yi, S., Ai, C., Zhao, Y., Li, Y., Wang, H., Xu, J., Hu, J., Guo, T., 1988. Geological Map of Qinghai-Xizang (Tibet) accept the young age data on the Oytag-Kudi ophiolites Plateau and adjacent areas 1:1500000, Beijing. because they are difficult to reconcile with the arc granitoid Marsaglia, K.M., 1995. Interarc and backarc basins. In: Busby, C.J., Inger- age spectrum of the northern South Kunlun, the Devonian soll, R.V. (Eds.). Tectonics of Sedimentary Basins. Blackwell, age of the northern molasse, and, of course, with the older Cambridge, pp. 299–329. ages of the Oytag-Kudi ophiolites. Matte, P., Tapponnier, P., Arnaud, N., Bourjot, L., Avouac, J.P., Vidal, Ph, Liu, Q., Pan, Y., Wang, Y., 1996. Tectonics of Western Tibet, between the Tarim and the Indus. Earth and Planetary Science Letters 142, 311– Acknowledgements 330. Matte, P., Tapponnier, P., Bourjot, L., Pan, Y., Wang, Y., 1991. Tectonics of western Tibet, from the Kunlun to the Karakorum. Terra Abstracts 3, We thank Mark B. Allen and Brian Windley for their 258. constructive comments on the manuscript. We also thank Matte, P., Tapponnier, P., Bourjot, L., Pan, Y., Wang, Y., 1992. Tectonics the VW Foundation for its generous support of our field of western Tibet, from the Kunlun to the Karakorum.. International investigations in the Kunlun and Kara-Kunlun. Symposium on the Karakorum and Kunlun Mountains, Abstracts, June 1992, Kashi. , p. 36. Mattern, F., Schneider, W., Li, Y., Li, X., 1996. A traverse through the References western Kunlun (Xinjiang, China): tentative geodynamic implications for the Paleozoic and Mesozoic. Geologische Rundschau 85, 705–722. Baud, A., 1989. The western end of the Tibetan Plateau. In: Sengo¨r, A.M.C. Mattern, F., Schneider, W., Wang, P., Li, C., 1998. Continental strike-slip (Ed.). Tectonic Evolution of the Tethyan Region. NATO ASI Series C rifts and their stratigraphic signature: application to the Bangong/ 259Kluwer, Dordrecht, pp. 505–506. Nujiang zone (Tibet) and the South Penninic zone (Alps). Geologische BGMR., 1993. Geological Map of the Xinjiang-Tibet Highway (within the Rundschau 87, 206–224. Xinjiang area) 1:1000000. No. 1 Regional Geological Surveying Party Moores, E.M., 1982. Origin and Emplacement of Ophiolites. Reviews of of Xinjiang Bureau of Geology and Mineral Resources, Urumqi (in Geophysics and Space Physics 20, 735–760. Chinese). Nie, S., Yin, A., Rowley, D.B., Jin, Y., 1994. Exhumation of the Dabie Shan Chang, C., Pan, Y., Sun, Y., 1989. The tectonic evolution of Qinghai-Tibet ultra-high-pressure rocks and accumulation of the Songpan-Ganzi plateau: a review. In: Sengo¨r A.M.C. (Ed.), Tectonic Evolution of the flysch sequence, central China. Geology 22, 999–1002. Tethyan Region, NATO ASI Series C 259. Kluwer, Dordrecht, pp. Pan, Y., Zheng, D., Zhang, Q., 1992. Introduction to Integrated Scientific 415–476. Investigation on Karakorum and Kunlun Mountains. China Meterolo- Coward, M.P., Kidd, W.S.F., Pan, Y., Shackleton, R.M., Zhang, H., 1988. gical Press, Beijing. The structure of the 1985 Tibet Geotraverse, Lhasa to Golmud. Philo- Pitcher, W.S., 1982. Granite type and tectonic environment. In: Hsu¨, K.J. sophical Transactions of the Royal Society of London A 327, 307–336. (Ed.). Mountain Building Processes. Academic Press, London, pp. 19– De Terra, H., 1932. Geologische Forschungen im westlichen K’un-Lun und 40. Karakorum-Himalaya. Wissenschaftliche Ergebnisse der Dr. Trink- Sengo¨r, A.M.C., Altiner, D., Cin, A., Ustao¨mer, T., Hsu¨, K.J., 1988. Origin ler’schen Zentralasien-Expedition, vol. 2. Dietrich Reimer/Ernst and assembly of the Tethyside orogenic collage at the expense of Gond- Vohsen, Berlin. wana Land. In: Audley-Charles, M.G., Hallam, A. (Eds.). Gondwana 650 F. Mattern, W. Schneider / Journal of Asian Earth Sciences 18 (2000) 637–650

and Tethys. Geological Society Special Publication 37Oxford Univer- Yang, J.-S., Robinson, P.T., Jiang, C.-F., Xu, Z.Q., 1996. Ophiolites of the sity Press, New York, pp. 119–181. Kunlun Mountains, China and their tectonic implications. Tectonophy- Sengo¨r, A.M.C., Okurogullari, H., 1991. The roˆle of accretionary wedges in sics 258, 215–231. the growth of continents: Asiatic examples from Argand to plate Yang, Z., Long, N., 1990. A discussion on Triassic system of Karakorum tectonics. Eclogae geologicae Helvetiae 84, 535–597. Mountain and eastern Kunlun Mountain, Xinjiang. Xinjiang Geology 8, Tian, Z., Chai, G., Kang, Y., 1989. Tectonic evolution of the Tarim Basin. 321–332. In: Zhu, X. (Ed.). Chinese Sedimentary Basins, Sedimentary Basins of Yao, Y., Hsu¨, K.J., 1994. Origin of the Kunlun Mountains by arc-arc and the World 1. Elsevier, Amsterdam, pp. 33–43. arc-continent collisions. Island. Arc. 3, 75–89. Wang, Y., 1983. The age of the Yisak Group of West Kunlun, and tectonic Zhang, Y., Xie, Y., Xu, R., Vidal, P., Arnaud, N., 1992. Elements geochem- signiﬁcance. Xinjiang Geology 1, 1–8 (in Chinese, with English istry of granitoid rocks in the west Qinghai-Xizang Plateau. Interna- abstract). tional Symposium on the Karakorum and Kunlun Mountains, Abstracts, Xu, R., Zhang, Y., Vidal, P., Arnaud, N., 1992. Two plutonic belts in June 1992, Kashi. , p. 64. western Kunlun. International Symposium on the Karakorum and Kunlun Mountains, Abstracts, June 1992, Kashi, p. 62.