Uppermost Mantle Seismic Pn-Velocity in Continental China and Its Tectonic Implications

Abstract

We construct a high-resolution Pn-velocity model in continental China through a new tomographic scheme simultaneously inverting event epicenter location and Pn-velocity and accurately accounting for the Pn propagation effects of irregular crustal thickness variation. The inversion integrates a combined data set of 32,427 absolute Pn travel times and 62,431 interstation Pn differential travel times manually picked from the recordings of 2,989 stations in and around continental China, yielding a model of spatial resolutions ranging from 0.75° × 0.75°–3° × 3°. Major Pn-velocity features revealed by the model and the tectonic processes we attribute to include: (a) high Pn-velocities beneath major cratonic blocks and the southern Tibetan Plateau attributed to low temperatures of cratons, (b) low Pn-velocities beneath the eastern North China craton around the Tan-Lu fault and the central South China block attributed to high temperatures and low-Mg# ((Formula presented.)) peridotites in response to the Mesozoic-Cenozoic subduction of the Pacific plate, and beneath the Trans-North China orogen, most regions of the Tibetan blocks and the central Tianshan orogen attributed to high temperatures after multiple tectono-thermal events in response to the Mesozoic-Cenozoic subduction of the Pacific plate, the Triassic convergence of the North China, Yangtze, and northern Tibetan blocks and the Cenozoic India-Eurasia collision, and (c) intermediate Pn-velocities beneath the marginal regions of the Ordos block and Micang-Daba region attributed to possible extrusion of hot asthenospheric flow from the Tibetan Plateau in response to far-field effects of the India-Eurasia collision.