data as an indication that ductile deformation conditions have existed at Xaidulla during the Triassic and during
mid-Jurassic cooling. The granitoid which provided the heat for mylonitization
of contact-metamorphic sillimanite-bearing shales at the second location belongs to the batholith south of the road
between Shanshilli and Kengxiwar, from which Xu et al. 1992 determined the above mentioned
40
Ar
39
Ar plateau age of 187 Ma and the lower intercept age on zircon of 192
Ma. These are Early Jurassic ages. We assume that ductile deformation conditions may have existed during the Early
Jurassic and possibly lasted to the mid-Jurassic during the cooling process.
If the finding of dextral ductile faults does indeed reflect the kinematic relation between the overriding and the down-
going 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 accretioncolli- sion-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 accretionarycollisional
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 quart- zite. 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-
sic strata. At both places, the red Triassic shales grade into slightly green Jurassic shales. In the Kongur Shan area,
where there is also a stratigraphic gap between the Permian 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
and Long, 1990.
In a wadi north of the road at road mark 272 32 road km east of Mazar, elevation 4100 m, the Triassic is missing
above the Permo-Carboniferous shallow marine carbonates. Deposition of the terrestrial clastic molasse started here
during the Early Jurassic and continued to the mid-Jurassic Liu et al., 1988. The Jurassic succession contains
conglomerates, sandstones and shales. We observed coal seams which were also described for the Jurassic of the
North Kunlun by Pan et al. 1992. The depositional envir- onment of the Jurassic may have included lakes and
swamps. In contrast to the Triassic strata, the Jurassic deposits lack red color and contain a significant amount of
granitoid debris. The lack of red color is also helpful in
F. Mattern, W. Schneider Journal of Asian Earth Sciences 18 2000 637–650 647
Fig. 10. Plate tectonic development of the western Kunlun and Kara- Kunlun. Note that only minor amounts of subduction-related melts reached
the northern South Kunlun during consumption of Proto- Tethys. Arc magmatism in the South Kunlun and Kara-Kunlun ended during the mid-
Jurassic. Also note the age of overlap assemblages at terrane boundaries.
distinguishing these Jurassic strata from Cretaceous and some Cenozoic terrestrial deposits. The presence of grani-
toid debris shows that the magmatic arc was already eroded to its granitoid level during the Lower Jurassic. The low
compositional and textural maturity of the Jurassic deposits indicates a close provenance. The Jurassic sediments are
rich in plant fossils. Some of them have been listed by BGMR 1993. However, the listed fossil leaves are not
very conclusive as to the age of the succession. In the outcrop zone in which we worked the Jurassic sediments
are associated with a red volcanite which has been dated 180 10 Ma RbSr 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
the Kara-Kunlun and exhibit only weak deformation.
Arc magmatism is coeval with Late Triassic to mid-Juras- sic molasse deposition. It is also coeval with the formation
of the terrane boundary overlap assemblages Fig. 10. By slightly modifying the model of Mattern et al. 1996 we
suggest a model which implies successive accretion of two relatively small units, the Kara-Kunlun accretionary wedge
and the Uygur Terrane, and, finally, the Karakorum Qiangtang microcontinent, all belonging to the realm of
the Paleo-Tethys Ocean Fig. 10. The accretion of these terranes was accompanied by successive oceanward shifts
of new, short-lived, north-directed subduction zones and successive slab break-offs. The broken-off slabs continued
to descend and generated arc melts Fig. 10. This model accounts for the regional uplift and arc magmatism concur-
rent with accretionarycollisional processes and formation of molasse-type overlap assemblages.
The youngest known pre-Cretaceous shallow marine deposits of the Uygur Terrane are Triassic. It is generally
assumed that the flyschoid rocks of the Kara-Kunlun accre- tion complex do not contain post-Triassic sediments Liu et
al., 1988; Pan et al., 1992; BGMR, 1993; Matte et al., 1996. The youngest age of exotic limestone slabs within the accre-
tionary wedge is Triassic Liu et al., 1998; Yao and Hsu¨, 1994. Considering these aspects we suggest that the small
Uygur Terrane collided with the Kara-Kunlun accretionary wedge during the Late Triassic and put an end to wedge-
type accretion and marine sedimentation, due to shortening and related uplift. This interpretation is supported by the
onset of terrestrial molasse deposition during the Late Triassic in the Kunlun and during the Early Jurassic in the
Kara-Kunlun e.g. above mentioned boundary overlap assemblage.
As indicated by the different pre-Jurassic development of the blocks north and south of the Longmu Co suture and by
the mid-Jurassic suture overlap assemblage, the Karakorum Qiangtang microcontinent must have been added to the
Asian tectonic collage during the Early Jurassic. According to Dewey et al. 1988, the Qiangtang Terrane accreted to
the Songpan-Ganze unit in the eastern part of the Tibetan Plateau during the Late Triassic or earliest Jurassic. One
aspect, which one might consider problematic, needs to be discussed and that is how a marine mid-Jurassic suture over-
lap assemblage was able to accumulate above a suture that formed only during the Early Jurassic. Possible solutions
are: 1. Accretion was “gentle” and did not result in a signif- icant uplift e.g. due to the shapes of the accretion zone and
of the microcontinent. 2. A time span of 30 million years elapsed between accretion Pliensbachian? and formation
of the overlap assemblage Callovian? allowing for denu- dation of a moderately uplifted region. 3. The suture zone
was affected by extension e.g. orogenic collapse or trans- tension. 4. A combination of the above mentioned aspects.
10. Conclusions
