tübinger geowissenschaftliche arbeiten (tga) - TOBIAS-lib ...

70
previously defined by Russian geologists as a Precambrian to Palaeozoic basement
window (Burtman and Molnar 1993, and Russian reference cited therein; Geological
map of Tadzhik SSR 1:500 000). This thesis and Schwab et al. (in press) demonstrated
that these basement rocks were formed mainly in Triassic/ Jurassic times during
subduction of the Jinsha oceanic crust and flysch sedimentation in the intervening
Sonpan-Ganzi basin. In contrast, the exhumation of the domal structure is a Tertiary
feature. Miocene apatite fission track ages were obtained from the Early Palaeozoic
intrusion P17 (~16 Ma), from the Tertiary intrusion P15 (~15 Ma), and from the Tertiary
aplitic dyke 96A6b (~20 Ma). The zircon fission track age of the sample P15 is around
16 Ma (Fig. 4.2). (5) Sandstone samples from Teriary intramontane basins along the
southern and northern margins of the Muzkol dome define different Tertiary histories
on both sides of the dome: (a) The zircon fission track grain age distribution of the
Palaeogene sandstone sample A96K1e of a Tertiary basin north of the Muzkol dome is
not reset. Hence, the age spectrum defines several age populations (Appendix C, Tab.
C7, Fig. C4): The oldest peak is around 370 Ma, a further peak is in Early Triassic
around 242 Ma, and the youngest peak age clusters around 165 Ma (Fig. 4.2). (b) Two
sandstone samples from an intramontane basin south of the Muzkol dome, the herein
called ‘Murgab section’ (Fig. 4.4), yielded single zircon fission track grain age
populations with central ages of ~20 Ma and ~19 Ma (M96A6b and A96M4b,
respectively).
Rushan Pshart arc
Triassic/Jurassic arc-type intrusions and a Triassic oceanic-basin-arc sequence in the
eastern Pshart constitute the Rushan Pshart arc. Sample L96M25a, a monzogranite,
yielded an zircon fission track age of 68.5±3.6 Ma (Fig. 4.2).
Shyok arc
Late Cretaceous granodiorites (P2 and P5) are the southernmost samples dated in this
study and are related to the Shyok arc. Apatite fission track ages of these samples are
around 10 Ma and so far the youngest fission track ages in the Pamirs (Fig. 4.2).