CRUSTAL STRUCTURE OF CHINA FROM DEEP SEISMIC-SOUNDING PROFILES

More than 36,000 km of Deep Seismic Sounding (DSS) profiles have been collected in China since 1958. However, the results of these profiles are not well known in the West due to the language barrier. In this pa per, we summarize the crustal structure of China with a new contour ma p of crustal thickness, nine representative crustal columns, and maps showing profile locations, average crustal velocity, and P-n velocity. The most remarkable aspect of the crustal structure of China is the w ell known 70+ km thickness of the crust of the Tibetan Plateau. The th ick (45-70 km) crust of western China is separated from the thinner (3 0-45 km) crust of eastern China by the north-south trending seismic be lt (105 degrees E). The average crustal velocity of China ranges from 6.15 to 6.45 km/s, indicating a felsic-to-intermediate bulk crustal co mposition. Upper mantle (P-n) velocities are 8.0.+/-0.2 km/s, equal to the global continental average. We interpret these results in terms o f the most recent thermo-tectonic events that have modified the crust. In much of eastern China, Cenozoic crustal extension has produced a t hin crust with a low average crustal velocity, similar to western Euro pe and the Basin and Range Province, western USA. In western China, Me sozoic and Cenozoic arc-continent and continent-continent collisions h ave led to crustal growth and thickening. Inferences on the process of crustal thickening are provided by the deep crustal velocity structur e as determined by DSS profiles and other seismological studies. A hig h velocity (7.0-7.4 km/s) lower-crustal layer has been reported in wes tern China only beneath the southernmost Tibetan Plateau. We identify this high-velocity layer as the cold lower crust of the subducting Ind ian plate. As the Indian crust is injected northward into the Tibetan lower crust, it heats and assimilates by partial melting a process tha t results in a reduction in the seismic velocity of the lower crust in the central and northern Tibetan Plateau. (C) 1998 Elsevier Science B .V. All rights reserved.