Uppermost mantle velocities beneath China and surrounding regions

[ 1] Seismic P wave velocity variations in the uppermost mantle beneath China are tomographically imaged using Pn wave travel time data. The average velocity of the mantle lid beneath China is 8.05 km/s, with a range from -0.30 km/s to 0.35 km/s. Eastern China has slower mantle velocities and a thinner crust than western China. Different inversions performed for shorter ray path and longer ray path data sets separated the shallow and deep structure within the mantle lid. Velocities in the lower lid are no more than 0.2 km/s faster than at the top. The fastest velocities are beneath cratons, which remained relatively undeformed despite orogenic events around their margins. The Pn velocity beneath southern Tibet is faster than that beneath northern Tibet, suggesting that this contrast delineates the northern edge of the Indian lithosphere. On the southeastern margin of the Tibetan plateau, the Panxi rift, slow Pn velocity exists in the lithosphere due to the transextensional tectonic environment. In eastern China, extension of the North China Block produced a series of NNE-SSW trending rifts that cause slow mantle lid velocities. These slow velocities extend to the base of the mantle lid, suggesting that late Cenozoic Pacific subduction drove the rifting. Both high temperature and hydration may contribute to these low uppermost mantle velocities. The Shanxi rift, along the east margin of the Ordos platform, is characterized by a slow mantle velocity; in contrast, the Yinchuan rift, on the west margin, does not show any uppermost mantle velocity anomaly.