Abstract

To better constrain the probable timing of formation and evolution of the Altyn Tagh sinistral strike-slip system in the Mesozoic, a 40Ar/39Ar thermochronological study has been carried out in the north-central segment of the Altyn Tagh fault system, the northern margin of the Qaidam Basin, and the eastern Kunlun orogenic belt. Muscovite, biotite, and K-feldspar separated from mylonite, granite, pegmatite, and metamorphic rocks have been analyzed. The range of 40Ar/39Ar data and structural evidence indicate that a peak metamorphic event in terranes bordering the Altyn Tagh fault system occurred between 450 and 420 Ma. At ca. 250–230 Ma there is evidence for initial sinistral strike-slip shearing. Sinistral strike-slip deformation occurred later along the Altyn Tagh fault system at 165–160 Ma and 100–89 Ma, respectively.

Cooling histories in the northern margin of the Qaidam Basin and the eastern Kunlun orogenic belt show that these areas also experienced rapid cooling ca. 250–230 Ma, as was the case for the early Altyn Tagh fault system. This regional tectonic and cooling process indicates that the initial formation of the Altyn Tagh sinistral slip fault system occurred in latest Permian–Early Triassic time and was coupled with, or related to, suturing in the northern margin of the Qaidam Basin and the Kunlun orogenic belt. Cooling events along the Altyn Tagh fault system between 165 and 160 Ma and 100–89 Ma were accompanied by differential closure along the Bangong Lake–Nujiang suture zone in its eastern and western sectors during the Middle-Late Jurassic and Early Cretaceous, respectively (Zhao et al., 2001; Wang et al., 2002).

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