The Uygur Terrane and adjacent sutures

and volcanites, embedded in a pervasively sheared, cleaved matrix of sericite-quartz schist, chlorite-sericite schist, two- mica schist and phyllite. Since the maps by Liu et al. 1988, BGMR 1993, and Matte et al. 1996 do not indicate ophiolites in the Mazar area, and since Yao and Hsu¨ 1994 were unspecific about the location of the studied ophiolite outcrops, we are unable to show them in Fig. 1. Another ophiolite unit occurs east of Dahongliutan Fig. 1. Also farther east, outside the study area, there is an ophiolite body at Mt. Muztag 7723 m, 700 km eastsoutheast of Hotan — not to be confused with Mt. Muztag, 7282 m, 115 km southsoutheast of Hotan; Pan et al., 1992; Yao and Hsu¨, 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 siliciclastic Kara-Kunlun belt, such as one would expect to occur in an accretionary wedge. The ratio between the amount of suture sediments and basic to ultrabasic oceanic igneous rocks is relatively large in the Kara-Kunlun wedge. In the westernmost part of the Kara-Kunlun, the clastic rocks of the Kara-Kunlun are either unmetamorphosed or display a very low metamorphic grade Gaetani et al., 1990. According to Matte et al. 1996, the clastic rocks are affected by only low-grade metamorphism. At several road- side outcrops between Mazar and Hez Pass and also farther east, for example, at the Qitai Pass, unmetamorphosed strata can be observed. At several places we found evidence of contact metamorphism. These areas include the aureole of the Mazar pluton, west of Mazar, the Dahongliutan area, and a location 40 km eastsoutheast of Shanshilli outcrop along a new road, Mattern et al., 1996. At the latter we found sillimanite-bearing metashales. Ductile faults can be observed in these zones below. We noticed that the strata of the Kara-Kunlun mainly dip to the north and northnortheast, that is inclined towards the South Kunlun. Observations of the preferred dip include those that were made on mountain-scale outcrops, for exam- ple, in the areas around the Hez Pass, Dahongliutan, and the Qitai Pass. Folds exhibit a south or southsouthwest vergence. The observed slaty cleavage is genetically related to the folds Mattern et al., 1996. These aspects are compa- tible with the interpretation of an accretionary wedge which formed south of the South Kunlun in response to northward B-type subduction. As shown below, the Kara-Kunlun was intruded by subduction-related granitoids indicating an active margin environment in which the Kara-Kunlun wedge became the site of arc magmatism. Whereas the stratigraphy and age of the Kara-Kunlun’s rocks are poorly understood, the geodynamic significance of the Kara-Kunlun zone appears to be clear. Hsu¨ 1988 inter- preted the Kara-Kunlun area as an accretionary wedge which formed due to northward subduction of the Paleo- Tethys Ocean beneath the South Kunlun. This view is consistent with the flyschoid facies and composition of the thick clastic sediments and their association with tuffites, ophiolite me´langes and arc granitoids as well as with the implied internal thrust planes and with the dominant dip direction of strata and the observed vergences. The Kara- Kunlun accretionary wedge can be correlated with the Sonpan Ganze Belt or parts of it Bayan Har Group farther east Sengo¨r and Okurogullari, 1991; Matte et al., 1996; Mattern et al., 1996. The Songpan Ganze Belt occupies a position south of the Kunlun, like the Kara-Kunlun accre- tionary wedge, and is also characterized by a great thickness and by a dominance of fine-grained siliciclastic deposits Leeder et al., 1988; Coward et al., 1988; Nie et al., 1994. It has also been interpreted as an accretionary wedge south of the eastern Kunlun Leeder et al., 1988.

7. The Uygur Terrane and adjacent sutures

The Uygur Terrane located south of the Kara-Kunlun accretionary wedge Fig. 1 is the southernmost unit we inspected. Although the Uygur Terrane is a poorly under- stood element of the regional tectonic collage there is certainty that its rock facies contrasts sharply with that of the Kara-Kunlun accretionary wedge. No stratigraphic rela- tionship exists between these two units. We observed a thrust contact between the two terranes in the Tianshuihai area Mattern et al., 1996. The Uygur Terrane consists of a fossiliferous and generally well-dated Paleozoic to Triassic shallow marine succession BGMR, 1993. The succession measures hundreds of meters in thickness and contains a significant amount of carbonates. Because we could only inspect a few of the formations within the terrane we decided not to depict its stratigraphic development. To the south, the Uygur Terrane is separated from the south- erly located KarakorumQiangtang Terrane by the “cryptic” Longmu Co suture Fig. 1 of Baud 1989, which is also referred to as the “Taaxi-Qiaoertianshan-Hongshanhanu suture” Pan et al., 1992. Since we did not reach this suture, the following information is taken from the literature. Although most of this suture has been covered by post-accre- tionary deposits Pan et al., 1992 ranging from the mid-Juras- sic to the Quaternary Liu et al., 1988; BGMR, 1993, Pan et al. 1992 identified this zone as a suture because it delineates blocks of marked geological and paleontological differences. Ophiolites do not occur in the suture segment south of the western Kunlun but are known from this suture farther east Pan et al., 1992. This zone also represents the northern boundary for the distribution of marine Jurassic strata Pan et al., 1992. There is a mid-Jurassic suture overlap assemblage whose age is documented by a brachiopod fauna BGMR, 1993, indicating that this segment of the Paleo-Tethys was eliminated at the latest by the mid-Jurassic.

8. Late Paleozoic to Early Mesozoic subduction of the Paleo-Tethys Ocean beneath the South Kunlun