Journal Article

Seismic Evidence of Basin Development in NE Tibetan Plateau in Response to Deep Crustal Dynamics From Joint Inversion of Rayleigh Wave Ellipticity and Phase Velocity

Wu, Xiaoyang, Luo, Bin, Guo, Zhen, Ren, Pengfei, Liu, Yiduo

2024

Overview

The NE Tibet experienced complex and distinct basin developments and uplifts in different areas. However, the reasons for such distinct surface deformation and their relationship to deep crustal geodynamic processes are not well understood. Here, we obtain a crust model of NE Tibet by jointly inverting Rayleigh wave ellipticity and phase velocity. Our results reveal that deep crustal strength contrasts across NE Tibet play an important role in controlling basin development. Extrusion of the significantly weak Qilian crust is obstructed by rigid Alxa block, resulting in deep foreland basin with dramatic topographic step. In contrast, the relatively weak crust of Longzhong absorbs outward extrusion of NE Tibet within a wide transition zone, leading to small intermontane basins. Furthermore, the systematic thinning of basins from north to south around the western Ordos Block demonstrates the tectonic transformation from extension to compression due to expansion of NE Tibet since the late Miocene. Plain Language Summary In this study, we obtain a high‐resolution model of NE Tibet by jointly inverting Rayleigh wave phase velocity and ellipticity (the radial‐to‐vertical amplitude ratio), which provides complementary constraints to the shallow structure. Our results show a clear correlation between velocity variations in the deep crust and basin structures at the surface. We infer that the extrusion of mechanically weak mid‐to‐lower crust of Qilian is obstructed by the strong Alxa block, leading to the steep topography and deep foreland Hexi Basin. To the east, in contrast, the outward extrusion of Songpan‐Ganzi is absorbed in a wide range by the relatively weak Longzhong region, developing gently sloping topography and small intermontane basins. Furthermore, the significant structural differences of rift basins from north to south around the western Ordos likely result from tectonic regime transformation induced by the continuous expansion of NE Tibet since the late Miocene. Our results improve the understanding of how deep crustal geodynamic processes influence surface uplift and basin developments in the expanding NE Tibet. Key Points A high‐resolution 3‐D crustal model of NE Tibet is obtained by joint inversion of Rayleigh wave ellipticity and phase dispersion We infer that deep crust extrusion and strength differences across plateau boundaries control distinct surface deformation in NE Tibet The systematic thinning of basins in west Ordos indicates tectonic regime transformation due to expansion of Tibet since Miocene

• Publisher: John Wiley & Sons, Inc
• Subject: 3‐D Vs model / basin evolution / Basins / Compacting / Compression / Compression zone / Compressive strength / Continuous extrusion / crustal deformation / Deformation / Earth crust / Ellipticity / high‐resolution / Longitudinal waves / Miocene / NE Tibet / Phase velocity / Plateaus / Rayleigh wave H/Z ratio / Rayleigh waves / Seismic response / Tectonics / Topography / Transition zone / Velocity / Wave phase / Wave velocity