EGU21-6843
https://doi.org/10.5194/egusphere-egu21-6843
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

40Ar/ 39Ar laser dating of Zongwulong ductile shear zone in northeastern Tibetan Plateau :Constrains on the closure time of the northmost Paleo-Tethys ocean

Wanli Gao and Zongxiu Wang
Wanli Gao and Zongxiu Wang
  • Institute of Geomechanics, Chinese Academy of Geological Sciences, China (gwanli851202@163.com)

Abstract:The Zongwulong tectonic belt (ZTB) is located between the northern Qaidam tectonic belt and the south Qilian orogenic belt and contains Late Paleozoic and Early- Middle Triassic strata. Structural features and geochronology of Zongwulong ductile shear zone have key implications for the tectonic property of the ZTB. This study integrated field structure, microscopic structure and 40Ar/39Ar laser probe analysis. The shear zone strikes ~NEE-SWW and dips at a high angle, with a NWW-SEE trending and WE stretching lineation, indicating the shear zone as a thrust- slip shear ductile shear. The asymmetric folds, rotating porphyroclast,structural lens and crenulation cleavage can be seen in the field. Mica fish, S − C fabrics, σ type quartz porphyroclastic and quartz wire drawing structure can also be observed under microscope, indicating that the strike- slip- related ductile deformation and mylonitization occurred under low- grade greenschist facies conditions at temperatures of 300° C − 400° C.  The highly deformed
mylonite schist yielded 40Ar/39Ar ages (245.8±1.7)Ma and (238.5±2.6)Ma for muscovite and biotite, respectively, indicating that the shear deformation occurred during the Early- Mid Triassic. Combined with comprehensive analysis of regional geology and petrology, the authors hold that the age of ductile shear deformation represents the time of Triassic orogeny in the ZTB. The oroginic activity was probably related to the oblique collision between the South Qilian block and the Oulongbuluke block after the closure of the northermost Paleo-Tethys ocean.

How to cite: Gao, W. and Wang, Z.: 40Ar/ 39Ar laser dating of Zongwulong ductile shear zone in northeastern Tibetan Plateau :Constrains on the closure time of the northmost Paleo-Tethys ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6843, https://doi.org/10.5194/egusphere-egu21-6843, 2021.

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