THE DEEP STRUCTURAL AND TECTONIC FEATURES OF THE CRUST IN PANXI AREA

This paper discusses the deep geological features in Panxi region obtained by deep seismic sounding from 1984 to 1985. This region has a thick crust of 50-60 km, and possesses multi-layed structure with lower velocity layers alternating with the higher velocity ones and fault-block tectonices. Of the five main velocity interfaces, R4 is steady and clear and may be regarded as the interface between the upper and lower crust; Re is steady and shows stronger reflection. It is the MOHO. The MOHO is deeper in the north and shallower in the south (56 -50 km) along the tectonic zone. It is deeper in the west and shallower in the east (60-48 km) across the zone. The upper-crustal thickness is thinner and the velocity is non-homogeneous. The lower-crustal is thicker and the yelocity is steady within the tectonic zone. The lower-velocity layers at the bottom of the upper-crust is thinner and shallower inside than outside of the zone. The P, velocity is lower, 7.54-7.80 km/s, and belongs to the crust-mantle transition zone. Its thickness is 13-22 km. Xiaojiang fault, Sikai fault, Anninghe fault and Jinhe fault etc. are crustal and ultracrust faults and they are mostly thrusts faults. Most of these structural and tectonic features show that this tectonic zone is a young erogenic zone of the continental plateau.