S061-0010
Upper Mantle Radial Anisotropy Model Beneath South China from Multimode Surface Wave Tomography

Wednesday, 16 December 2020
Poster
Qingya Tang, Institute of Geology and Geophysics Chinese Academy of Sciences, Beijing, Beijing, China, Weijia Sun, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, Kazunori Yoshizawa, Hokkaido University, Department of Earth & Planetary Sciences, Faculty of Science, Sapporo, Japan and Li-Yun Fu, China University of Petroleum (East China), School of Geosciences, Qingdao, China
Abstract:
South China Block located in the southeastern part of Eurasia, is composed of Yangtze Block and Cathaysia Block. The convergence and extrusion of three tectonic domains in the Mesozoic and Cenozoic made the lithospheric structure of South China Block extremely complex, resulting in the differential evolution of Yangtze Block and Cathaysia Block.

In order to study the fine lithospheric structure of South China, we use the multimode surface wave tomography (Yoshizawa et al., 2010) to construct a upper mantle shear wave speed model and radial anisotropy model. Phase speeds are extracted from the waveform inversion of abundant event station pairs. The multimode phase speed maps of Rayleigh wave and Love wave, in the period of 30~200 s, are inverted to construct the SV and SH shear wave model in the depth range from 50 to 350 km.

The results show that pronounced distinctness of structural features are revealed from Cathaysia Block to Yangtze Craton. In Cathaysia Block, low-speed anomaly becomes obvious with the increase of depths. Nevertheless, the Yangtze Craton (especially the Sichuan Basin) is characterized by a high-speed anomaly, where anomalous feature can be clearly seen down to 350 km (Shan et al.,2016). Meanwhile, it's overt to see the slight negative anisotropy in Sichuan basin from 80 to 220 km. The negative anisotropy may be related to the eastward compression of Songpan-Ganzi Block. The Tibetan Plateau has changed from the compression type to the tension type, resulting in the extrusion of mantle flow from west to east along the channel, which may affect the directional arrangement of lithospheric materials. A remarkable negative anisotropy is found along the coastal region in asthenosphere, indicates that the vertical movement of mantle material plays a dominant role. The steady low-velocity anomaly and negative anisotropy surrounding the Hainan Island and Leizhou peninsula may suggest the existence of Hainan Mantle Plume.

References

Yoshizawa, K., & Ekström, G. (2010). Automated multimode phase speed measurements for high-resolution regional-scale tomography: application to north america.

Geophys. J. Int., 183 (3), 1538-1558.

Shan, B., Xiong, X., Zhao, K. F., Xie, Z. J., Zheng, Y., & Zhou, L. (2016). Crustal and upper mantle structure of south china from rayleigh wave tomography.

Geophys. J. Int., 208, 1643–1654.

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