Presenter: Hou-Ping Ho
Date: 2016/11/24
Abstract
India-Asia collision began from ca. 54 Ma and consistent with the uplift due to crustal thickening in eastern Tibet plateau. In Songpan-Ganzi Fold Belt, Cenozoic structures are large scale strike-slip faults. Paleostress reconstructions from fault plane kinematic data show a rotation compressive stress from NE-SW trending in the north to E-W trending in the south of the fold belt. There was also a clockwise rotation of upper crustal material during Cenozoic. In addition, the thickening of eastern Tibet crust was accommodated by viscous deformation in the depth. They constructed a model that lower and upper crust are decoupled. Upper crust is a laterally mobile thin-skinned veneer and lower crust is a homogeneously thickened tectonic basement. However, the combination of the result of apatite U-Pb, monazite U-Th, mica 40Ar/39Ar dating of the metamorphism age and structural observations indicated the peak of metamorphism in Danba area is ca. 65 Ma. The result implied that the eastern Tibet crust was already thick at the time of India-Asia collision. Thus it did not support the model of crustal thickening cause by lower crust flow.
Reference
C.J.L Wilson, M.J Harrowfield, A.J. Reid, 2006. Brittle modification of Trassic architecture in eastern Tibet: implications for the construction of the Cenozoic plateau. Journal of Asian Earth Sciences 27, 341-357.
S. Wallis, M. Aoya, T. tsujimori, T. Kawakami, K. Terada, K. Suzuki, H. Hyodo, 2003. Cenozoic and Mesozoic metamorphism in the Longmenshan orogen: Implications for geodynamic models of eastern Tibet. Geology 31, 475-478.