Complex deformation within the crust and upper mantle beneath SE Tibet revealed by anisotropic Rayleigh wave tomography

Abstract

Knowledge about Rayleigh-wave phase-velocity azimuthal anisotropy can provide important insight into the dynamic processes and complex deformation mechanisms beneath Southeastern (SE) Tibet. In this study, we imaged the azimuthal anisotropy of the Rayleigh-wave phase-velocity in the period range of 10–60 s beneath SE Tibet. The model provides seismological evidence for the existence of asthenospheric upwelling beneath the Indo-China block (ICB) and east-central Tibet. Stratified anisotropy architectures around the Eastern Himalaya Syntaxis (EHS) are observed, and the upper boundary of the subducting Indian slab at least extended to the center Lhasa block (LSB). Additionally, our models also reveal the complex deformation pattern of different blocks in the crust and upper mantle beneath SE Tibet, and the crustal deformation is much more complicated than that of the upper mantle. The EHS and LSB are deformed in the whole crust, which is affected by the subducting Indian lithosphere. The Qiangtang block, ICB and Songpan-Ganzi block deformation was mainly controlled by the strikes of the faults and the west-east tectonic movement of the plateau materials. The deformation of the Sichuan-Yunnan diamond block is related to mid-lower crustal flow. In the upper mantle, the fast-propagation directions of most of the blocks match the fast-polarization directions of SKS and the absolute plate motion, excluding the ICB and east-central Tibet. Based on the combined results of the isotropic and anisotropic models and previous studies, two dynamic models are proposed to shed new light on the complex deformation and dynamics processes in SE Tibet.