GEODYNAMICS OF THE SHANXI RIFT SYSTEM, CHINA

The Pliocene-Quaternary Shanxi Rift system of northern China transsects the domal axis of the Shanxi Highlands an is defined by an S-shaped string of asymmetric basins, extending from Huailai-Yanqing in the north via Taiyuan to Yuncheng in the south. This rift system has a length of about 1200 km and a width of 20-80 km; it is characterized by strong earthquakes. Its central, NNE-trending, transtensional segment forms the main element of the Shanxi Rift system. Basin subsidence commenced during the early Pliocene along NNE oriented master-faults characterized by large strike-slip rates (5.68 7 mm/yr); crustal extension amounts to some 1.4 km; basins are separated by push-up blocks; destructive earthquakes (M = 7-8) are unevenly distributed. The ENE trending northern and southern branches of the Shanxi Rift system are characterized by orthogonal crustal extension along ENE striking normal faults, amounting to about 8 km; these areas are characterized by a basin-and-range type structural style and weak seismic activity. The Shanxi Rift system developed on a some 40 km thick, thermally cool Precambrian crustal segment that was overprinted during Mesozoic diastrophic events. There is only minor rift-related volcanic activity. The Moho is pulled up by a few kilometers only under the axial rift zone; sub-Moho compressional velocities are in the 8.0-8.1 km/s range. The Shanxi Rift system evolved in response to the build-up of regional stress fields related to the collision of India and Eurasia; its localization involved reactivation of pre-existing fracture systems.