Shear Wave Splitting and Mantle Deformation beneath Eastern Eurasia and Indo-Australia

Abstract:

The Eurasian and Indo-Australian plates comprise a highly complex and tectonically diverse system of lithospheric and asthenospheric deformational regimes. Nearly enveloped by convergent margins, Eurasia is bordered entirely along its eastern and southern boundaries by subduction and, in the only present-day example of its kind, the ongoing Himalayan continental collision. These phenomenal settings have made the region a natural laboratory for studying the deformational mechanics of the Earth’s interior on a near-global scale by utilizing the robust shear-wave splitting (SWS) technique. By acquiring and examining data recorded by 531 broadband stations belonging to numerous networks throughout eastern Eurasia and Indo-Australia, we obtained a data set consisting of over 11,200 high-quality XKS (consisting of PKS, SKKS, and SKS phases) shear-wave splitting measurements composed of fast polarization orientations and splitting delay times. The resulting measurements show relatively high spatial density throughout Central Asia (e.g. Tibet and the Tien Shan), whereas regions in southeastern Asia, India and Australia have relatively sparse coverage. Multiple stations located primarily in the Tien Shan, Tibet, and South China demonstrate a clear azimuthal variation in fast orientations, indicating the presence of strong complex anisotropy beneath these regions. Possible mechanisms generating these occurrences of complex anisotropic layering include the collision and underthrusting of India beneath the Eurasian plate along the Himalayan suture, the westward subduction of the Pacific plate along the Mariana arc, northward subduction of Australia along the Sunda Trench, and slab fragment downwelling beneath the intraplate Tien Shan orogenic belt and Tarim Craton.