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amphibole, white mica, and biotite as well as K/Ar dating of sericite (Appendix A, Tab.
A3, A4, A5). These dating methods were determined on samples from the Muzkol and
Sares domes (Fig. 4.1):
(1) Rb/Sr whole rock-muscovite ages of basement rocks, e.g. biotite schists and
gneisses, were determined on two samples from the southern side of the Sares
dome. Sample 96A5i yielded 37.1±0.4 Ma and sample A96A5k 30.0±1.2 Ma. The
sample 96Ak3d from the northern side of the Muzkol dome obtained an age of
68.0±7.7 Ma. As the error is very high, the date will not be included into the
discussion or conclusion.
(2) Several intrusions and dykes of likely Tertiary age were probed in the Muzkol and
Sares domes. Sample P17, an undeformed aplite dyke that cuts high-grade biotite
gneiss in the Muzkol dome is already described in chap. 3: the sample contains
inherited zircons with spot ages in the range of 561 to 424 Ma, which are attributed
to characterise the Qiangtang basement. Conventional U/Pb zircon dating points to
an upper intercept age of 539±5 Ma with assumed Pb-loss at 44±22 Ma. Such a
crystallisation/Recent Pb-loss model infers Tertiary disturbance of the U/Pb
system, even so no Tertiary rims could be detected with SHRIMP analyses.
Nevertheless, it was suggested that the dike was emplaced in the Tertiary
(Schwab et al. in press). Another Tertiary intrusion (P15) into the Muzkol dome and
a dyke of the Sares dome (96A6b) yielded conventional U/Pb zircon upper intercept
ages of 540±4 Ma and 570±230 Ma, respectively. The lower intercept age is
around 31±2 Ma in case of sample P15, and around 17±8 Ma for sample 96A6b.
The U/Pb data are included in Appendix A, Tab. A7.
(3) Rb/Sr whole rock-muscovite dating of sample L96A11a, a pegmatitic dyke crosscutting
basement units of the Sares dome, gave an age of 13.7±0.1 Ma (see
Appendix A, Tab. A5).
(4) Ar/Ar amphibole, muscovite, and biotite ages of the Muzkol and Sares domes were
obtained from basalts, basement, and intrusive rocks. The data are summarised in
Appendix A, Tab. A3. The metamorphic mineral ages are in the range of 28 to 14
Ma. Tertiary basalts crosscut the Muzkol and Sares domes and extruded in an
extensional setting as indicated by structural analyses and preliminary
geochemical classifications (see Appendix A, Tab. A2). The basalts yield Ar/Ar
whole rock ages of about 20 Ma.
(5) Sandstones from Tertiary sediments from the Murgab profile (Fig. 4.4) show anchi-
to greenschist facies overprint. Five samples of metamorphic grown sericite were
dated by the K/Ar method (see Appendix A, Tab. A4). The ages range from 14 Ma
in the north of the section to 33 Ma further to the south.
4.3 Discussion
South Tien Shan
Fission track ages of Tertiary sediments from the southernmost Tien Shan confirm
the Palaeozoic and Mesozoic history of the Tien Shan as suggested in chapter 3: the
basement of the Tien Shan is composed of different terranes which were originally
sutured together during two collisions in Late Devonian-Early Carboniferous and Late
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