One of the unique aspects of the Tibet plateau evolution is the apparent coherence of deformation in the mantle and crust across most of the eastern part of the plateau and around the Eastern Himalayan Syntaxis (EHS). This changes at abruptly 26°N where crustal and mantle deformation diverge. Measurements of the surface crustal velocities across the Southeastern Tibetan Plateau, western Sichuan, and Yunnan are characterized by clockwise rotation around the Eastern Himalayan Syntaxis. The crustal clockwise rotational deformation continues into northern Myanmar, accommodated by a series of East Northeast-West Southwest left-lateral strike-slip faults bounded between the Sagaing Fault and the Red River Fault. The relative contribution of crustal and mantle processes to surface clockwise rotational deformation remains debatable. GPS and fault slip data indicate that this rotational deformation in the crust extends to the Sagaing Fault, the eastern boundary of the Burma platelet; however the inferred upper mantle deformation measured from shear wave splitting indicates a strong east-west fabric. This lack of deformational coherence begins at approximately 26 degrees North.
The development of a comprehensive high-resolution P and S seismic model of the crust and mantle beneath Tibet and across southeast Asia via the application of full waveform inversion of three component teleseismic and regional broadband waveforms. This new model provides a clear image of the underthrusting of Indian beneath Tibet and subduction of the Indian plate along the Indo Burma Range. Furthermore, this model shows that nearly all of southeast Asia is underlain by an uppermost low velocity zone that extends from the Sai gang Fault to the South China Sea. This low velocity zone correlates reasonably well with the region of strong east-west fabric. We suggest that this low velocity zone is related to the Hainan plume in the south China sea. If correct, this would mean that mantle flow related to the Hainan plume is flowing primarily westward toward the subduction of the subducting Indian plate.
Speaker: Eric Sandvol, University of Missouri
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