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Early Jurassic low-angle normal faulting and thus earlier than in the Central Pamirs,
but coeval with ongoing subduction (Kapp et al. 2000). A sliver of garnet-amphibole
gneiss of the blueschist-bearing Gangma Co mélange derived zircon U/Pb ionmicroprobe
ages in the range of 556 to 419 Ma (Kapp et al. 2000) comparable to the
data of sample P17 of the Central Pamirs. Such basement slivers are constrained as
Pan-African basement that was eroded from the base of the Qiangtang block and
incorporated into the mélange during low-angle subduction (Kapp et al. 2000). Like the
mélange rocks in Central Qiangtang, the characteristic rock associations of the Central
Pamiran domes are monotonous siliciclastic and volcanoclastic rocks, as well as mafic
volcanic rocks, which are interpreted as a subduction-accretion association (Schwab et
al. in press).
The gabbro sample 96M9a, a representative for Triassic-Jurassic gabbros intruding the
biotite-gneisses in the Muzkol and Sares domes, has an upper intercept age at around
830 Ma; the most common age population of detrital zircons in the sedimentary rocks of
the Qiangtang mélange is between 1200-800 Ma (65% of all zircons, Kapp et al. 2003)
and around 830 Ma old granites constitute the basement of the Songpan-Ganze system
in eastern Tibet. These granites are interpreted as part of the South China craton
(Roger & Calassou 1997). The Pamiran gabbros and their likely equivalents in Central
Tibet indicate oceanic crust of Late Triassic/Early Jurassic age subducting southward
beneath the Central Pamirs and Qiangtang block. The Nd model age of 0.7 Ga from the
leucogabbro 96M9a is younger then all other determined model ages from the
Qiangtang and is more indicative for Kunlun and Karakul-Mazar affinity. The final
closure of the oceanic basin and the intervening Songpan-Ganze mélange was along
the Jinsha suture in Tibet and along the Tanymas suture in the Pamirs. The cryptic
Tanymas suture is therefore thought to be the westward continuation of the Jinsha
suture. Further similarities are granitoids intruding the Qiangtang block in the Pamirs
and in Central Tibet (see below).
Triassic/Jurassic intrusions of the Central Pamirs
Granitoids intruding the Qiangtang block have different ages or ion probe age
components of ~230-200 Ma and/or of ~200-160 Ma in the Pamirs and in Tibet. Some of
these intrusions with a major Triassic age component are herein attributed to early
Mesozoic southward subduction of oceanic crust along the Jinsha suture. Sample
L96M25a may received a lower intercept age of ~235±11 Ma, , whereas the mean of 12
SHRIMP spot ages of sample L96A9 is about ~201±4 Ma. A granitoid of a Qiangtang
core complex in Tibet yielded a comparable weighted mean 206 Pb*/ 238 U ion-mircroprobe
zircon age of 220±1 Ma (Kapp et al. 2000). According to Kapp et al. (2000) the closure
between the Qiangtang and Kunlun blocks was in the Late Triassic/Early Jurassic. The
exhumation of the Songpan-Ganze mélange in the extensional metamorphic core
complexes in the central Qiangtang block occurred in an intracontinental setting by
Late Triassic-Early Jurassic. Consequently, intrusions with a major mid-Jurassic age
component are interpreted to characterise basin closure in the Rushan Pshart zone,
probably with subduction of oceanic lithosphere below the southern margin of the
Qiangtang block. This suggests, that in the area of the narrow Qiangtang block of the
Central Pamirs a younger 200-160 Ma southern magmatic belt may have overprinted an