Crustal azimuthal anisotropy in the lateral collision zone of the SE margin of the Tibetan Plateau and its tectonic implications

Author:

Shi Yutao1ORCID,Gao Yuan1ORCID,Zhang Hongshuang2,Zhang Ziqi3,Li Guohui1

Affiliation:

1. Key Laboratory of Earthquake Prediction, Institute of Earthquake Forecasting, China Earthquake Administration , Beijing 100036 , China

2. Key Laboratory of Deep Earth Dynamics, Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences , Beijing, 100037 , China

3. Department of Earth and Environmental Sciences, University of Rochester , Rochester, NY, 14627 , USA

Abstract

SUMMARYResolving the detail of crustal deformation of the seismically and technically active Sichuan-Yunnan block located in the southeast margin of the Tibetan Plateau is crucial for understanding the lateral extrusion of the Tibetan Plateau. Using seismic data from two regional seismograph stations of the China Earthquake Networks Center and twenty recently deployed broad-band temporary stations from the MCD Array (Middle ChuanDian block seismic array), we constrained crustal thickness and seismic anisotropy at the west boundary of the Sichuan-Yunnan block, near the east Himalayan syntaxis by receiver function techniques including CCP stacking and sinusoidal moveout of PmS conversions. Crustal thickness varies significantly across major faults inside the block which increases by >20 km from west to east. East of the Chenghai Fault, a clear positive phase lies above the Moho and is interpreted to be caused by the magma intrusion related to a late Permian Emeishan large igneous province (ELIP). The crustal anisotropy shows strong zoning features and clockwise rotation with respect to due north. To the west of the Lijiang-Xiaojinhe and the Honghe Faults, anisotropic fast orientations are near NS, indicating strong crustal deformation and movement of southward crustal flow along the Nujiang-Lancangjiang Fault; to the east of this fault, anisotropic fast orientations are near NE. The variation of the anisotropic fast orientations indicates that the southeastward crustal flow from the Tibetan Plateau may be prevented by fast velocity anomalies beneath the ELIP. These observations provided new evidence for strong crustal deformation along the tectonic boundary in the southeastern Tibetan Plateau with the expansion of the Tibetan Plateau.

Funder

National Natural Science Foundation of China

CEA

Publisher

Oxford University Press (OUP)

Subject

Geochemistry and Petrology,Geophysics

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