High‐Resolution 3‐D Shear Wave Velocity Model of the Tibetan Plateau: Implications for Crustal Deformation and Porphyry Cu Deposit Formation

Abstract

The high topography of the Tibetan Plateau was generated by the Cenozoic India‐Eurasia collision. A high‐resolution shear wave velocity model can provide improved understanding of the Tibetan structure and crustal deformation with complicated tectonic evolution. Based on continuous seismic observations at approximately 400 stations, we collected over 10,000 Rayleigh wave phase velocity dispersion curves extracted from ambient noise cross‐correlation functions. A direct surface wave inversion method was applied to obtain an S wave velocity model of the Tibetan crust. A heterogeneous structure including several prominent low‐velocity zones (LVZs) and relatively narrow low‐velocity bands connecting the LVZs is revealed. Our model shows significant crustal low‐velocity structures with lateral variations along the Himalayan front. In the eastern segment of the Lhasa terrane, the LVZ is spatially correlated with Miocene porphyry Cu deposits, which are probably related to strong tearing of the Indian lithosphere, while preexisting weak zones contribute to the LVZs in the western segment. Meanwhile, the LVZ along the Bangong‐Nujiang suture could be considered as a channel for eastward extrusion of ductile material, that is, crustal flow on geological timescales. This “flow” in the middle‐lower crust probably contributed to the formation of the V‐shaped conjugate strike‐slip fault system in central Tibet. The development of conjugate strike‐slip faults, however, ceased near 90°E, since the eastward “flow” was blocked by an intracrustal high‐velocity block in Amdo. This preexisting rigid zone (containing the Amdo microcontinent) hence influences the pattern of material transport inside the Tibetan crust and the deformation of the plateau.

Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Maduo earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data

“…Viscous flow in the mid-to-lower crust is proposed as a mechanism responsible for the eastward extrusion of the Tibetan Plateau (e.g., England & Molnar, 1997;Royden et al, 1997). Seismic and magnetotelluric data have revealed a mid-to-lower crustal low-velocity and high electric conductivity zone beneath the east Bayan Har block (Huang & Yao, 2020;Zhan et al, 2021). The nature of low shear velocity and/or high electric conductivity suggests a viscous or partially melted material at depth.…”

Crust and Upper Mantle Structure of the South China Sea and Adjacent Areas From the Joint Inversion of Ambient Noise and Earthquake Surface Wave Dispersions

“…In the last 2 decades, ambient noise tomography has been widely used to invert for the high‐resolution images of the shallow crust and upper mantle structure (S. Huang et al., 2020; Jiang et al., 2018; Liang & Langston, 2008; Lin et al., 2008; Shapiro et al., 2005; Shen et al., 2016; X. Yang & Gao, 2018; Y. Yang et al., 2011; H. Yao et al., 2008). Compared with earthquake surface wave tomography, the ambient noise tomography method is not affected by the uneven distribution of seismic events and has a better resolution in the shallow structure due to the use of short‐period dispersion data.…”

“…In the last 2 decades, ambient noise tomography has been widely used to invert for the high-resolution images of the shallow crust and upper mantle structure (S. Huang et al, 2020;Jiang et al, 2018;Liang & Langston, 2008;Lin et al, 2008;Shapiro et al, 2005;Shen et al, 2016;X. Yang & Gao, 2018;Y.…”

No mafic layer in 80 km thick Tibetan crust

“…Surface wave tomography results include a low shear wave velocity feature in the crust at the depth range of 20-40 km, which is interpreted as partial melting or mineral alignment in most of central Tibet [25][26][27] . The reference S-wave velocity model for China 26 includes low velocity down to Moho at 60-70 km depth in most of southern Tibet, but there is a trade-off between the velocity of the lower crust and the upper mantle, such that the lower crustal velocity determined from surface wave tomography has relatively large uncertainty.…”