T21C-2837
Weakly Coupled Lithospheric Extension in Southern Tibet

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Xiaobo Tian1, Yun Chen1, Tai-Lin Tseng2, Simon L Klemperer3, Hans Thybo4, Zhen Liu5, Tao Xu5, Xiaofeng Liang1, Zhiming Bai1, Xi Zhang5, Shaokun Si6, Changqing Sun Sr7, Haiqiang Lan1, Erchie Wang5 and Jiwen Teng1, (1)Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, (2)NTU National Taiwan University, Taipei, Taiwan, (3)Stanford University, Stanford, CA, United States, (4)University of Copenhagen, Copenhagen, Denmark, (5)IGG Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, (6)National Deep Sea Center, State Oceanic Administration, Department of Deep-sea Investigation, Qingdao, China, (7)Institute of Crustal Dynamics, China Earthquake Administration, Key Laboratory of Crustal Dynamics, Beijing, China
Abstract:
West-east extension is a prominent tectonic feature of southern and central Tibet despite ongoing north-south (N-S) convergence between India and Eurasia. Knowledge of deep structure beneath the N-S trending rifts is key to evaluating models proposed for their origin, including gravitational collapse, oblique convergence along the arcuate plate boundary, and mantle upwelling. We model direct S and Moho-reflected SsPmp phases at teleseismic distances to constrain variations in crustal thickness across the major rifts crossed by a ~900-km long, W-E broadband array in the Lhasa Terrane. Crustal thicknesses are ~70–80 km. However, Moho depth decreases by ~10 km within a horizontal distance of 100 km west of the Yadong-Gulu rift (YGR) and Nyainquentanghla mountains (NQTL). This Moho uplift, taken with deep, extensional focal mechanisms and reduced seismic velocity in the upper mantle, suggests that asthenospheric upwelling has significantly contributed to the pattern of extension across the YGR and NQTL. The ~100-km separation between surface rift and Moho uplift is likely enabled by partial decoupling across a ductile middle crust.
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