Abstract
The Tibetan Plateau results from the collision of the Indian and Eurasian Plates during the Cenozoic, which produced at least 2,000 km of convergence. Its tectonics is dominated by an eastward extrusion of crustal material that has been explained by models implying either a mechanical decoupling between the crust and the lithosphere, or lithospheric deformation. Discriminating between these end-member models requires constraints on crustal and lithospheric mantle deformations. Distribution of seismic anisotropy may be inferred from the mapping of azimuthal anisotropy of surface waves. Here, we use data from the CNSN to map Rayleigh-wave azimuthal anisotropy in the crust and lithospheric mantle beneath eastern Tibet. Beneath Tibet, the anisotropic patterns at periods sampling the crust support an eastward flow up to 100°E in longitude, and a southward bend between 100°E and 104°E. At longer periods, sampling the lithospheric mantle, the anisotropic structures are consistent with the absolute plate motion. By contrast, in the Sino-Korean and Yangtze cratons, the direction of fast propagation remains unchanged throughout the period range sampling the crust and lithospheric mantle. These observations suggest that the crust and lithospheric mantle are mechanically decoupled beneath eastern Tibet, and coupled beneath the Sino-Korean and Yangtze cratons.
Highlights
Quaternary fault slip rate data, and the mantle deformation inferred from several SKS shear-wave splitting datasets[15,16], which suggest a coherence between crust and mantle deformation
Because it can be related to rock deformation through lattice preferred orientation (LPO), seismic anisotropy is a key observation to understand the deformation of the Tibetan lithosphere
The anisotropic pattern in our model provides important clues on the dynamics of the Tibetan Plateau
Summary
Quaternary fault slip rate data, and the mantle deformation inferred from several SKS shear-wave splitting datasets[15,16], which suggest a coherence between crust and mantle deformation. The mapping of isotropic and anisotropic surface-wave velocity anomalies at selected periods is based on the measurements and inversion of a collection of dispersion curves. These maps can be linked to appropriate depth ranges through phase-velocity sensitivity kernels (Supplementary Figure S14). A special effort was made on the quality of the measurements to prevent scattered waves, multi-pathing or off-great-circle propagation from biasing our measurements We invert this collection of dispersion curves for maps of both isotropic and anisotropic anomalies of Rayleigh-wave phase velocity at selected periods[27,28,30,31].
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