Shear Wave Anisotropy of the Upper Mantle Beneath the Region from Tingri of Tibet to Golmud of Qinghai

Measurements of shear wave splitting at 43 three–component seismic stations show very big difference in anisotropy on both sides of the Indus–Yarlung Zangbo suture (ITS), but little difference on both sides of the older Bangong–Nujiang suture (BNS) and the Jinsha River suture (JS) to its north. Obvious discrepancy exists between the anisotropy direction and the superficial tectonic trends, which is not explicable directly by the coherent upper mantle deformation usually supposed to occur in consistency with the trend of a collisional belt. On the other hand, strong spatial relationships are observed from the anisotropy results, such as the orthogonal directions of anisotropy on both sides of ITS and the good correlation between the region of larger magnitude of anisotropy and the zone of inefficient Sn propagation of Qiangtang as well as the systematic rotation of the directions of anisotropy, which should testify some much more complicated aspects of the continental convergence mechanism To the best of our data, we tend to suppose that the Qinghai—Tibet plateau might result from a mechanism complicated by the coexistence of Argand's underthrusting and Dewey's diffuse deformation.