[S-SS07] Environmental Seismology: from deep earth to surface process

[SSS07-17] Lithospheric rheology beneath the South China block revealed by Pn attenuation tomography

*Lin Shen¹, Lian-Feng Zhao¹, Xiao-Bi Xie², Li-Jun Liu¹, Xu Chang¹, Zhen-Xing Yao¹ (1.Institute of Geology and Geophysics, Chinese Academy of Sciences, 2.Institute of Geophysics and Planetary Physics, University of California at Santa Cruz)

Keywords:the South China block, Upper mantle, Attenuation, Pn attenuation, Lithospheric rheology

The detailed lithospheric rheological structure is key to understanding deep dynamic processes and regional tectonic evolution. The South China Block (SCB) experienced multiple episodes of compression and extension with intensive crust partial melting and deep material intrusion, controlled by Paleo-Pacific subduction and roll-back during the Mesozoic. However, how lithospheric rheology changes remains unclear due to the lack of the present fine rheological structure of the lithosphere. Seismic attenuation of Pn-wave which propagates within the uppermost mantle is a sensitive probe of the lithosphere's rheological strength because both attenuation and viscosity reflect the anelastic property of rocks. Here, we construct a high-resolution broadband Pn-wave attention model for the SCB to map the lithospheric rheology structure, with the aim of understanding the region’s tectonic evolution. Weak Pn attenuation is observed in the eastern Sichuan basin due to the cold, thick cratonic root and in the eastern Cathaysia block as well. In contrast, the western Cathaysia block between them is characterized by strong Pn attenuation, which correlates with the low seismic velocity previously obtained and possibly indicates thermal upwelling induced by lithospheric delamination. Eastern Cathaysia is featured by extremely weak Pn attenuation, albeit not a craton. Alongside the upper mantle anisotropy, the rigid lithosphere revealed by weak Pn attenuation beneath eastern Cathaysia may represent the residual of the cold paleo-Pacific slab within the upper mantle. This work was supported by the National Natural Science Foundation of China (U2139206) and the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation under Grant number GZC20232630.