Complex subduction beneath the Tibetan plateau: A slab warping model

Abstract

Morphology of the subducting Indian lithosphere beneath Tibet is the key to understanding the tectonic evolution of the Tibetan plateau. In the present study we determine three-dimensional P-wave velocity images of the mantle under the entire Tibetan plateau and its adjacent areas by inverting ~200,000 teleseismic relative travel-time residuals recorded at 893 stations belonging to >32 portable seismic networks deployed in and around the plateau. An east-west varying high-velocity anomaly with a large dip angle down to the mantle transition zone is revealed clearly, which represents the subducting Indian slab. On the basis of the tomographic results, we propose a slab warping model to describe the complex subduction of the Indian plate beneath the plateau, which is characterized by lateral bending in addition to downward subduction. The complex geometry of the present Indian slab is possibly caused by non-uniform pulling of an earlier subducted slab in a process with the Indian slab detachment propagating laterally. As a result, a warping arc has formed beneath the Himalaya block to keep the Indian lithosphere intact. This slab warping model agrees well with many observations, such as magmatism and surface deformations in the western and southern Tibetan plateau.