攀西地区的深部地壳结构与构造

根据1984-1985年地震测深资料,论述了攀西地区的深部地质特征。该区地壳厚50-60km;具高、低速相间的多层结构及断块构造;五个主要速度界面中,界面R₄稳定且清晰,为上、下地壳的分界面,R₆稳定并有较强的能量反射,为壳、幔之间的界面（莫霍面）,莫霍面沿构造带北深南浅（56-50km）,横穿构造带西深东浅（60-48km）。构造带内的上地壳较薄,纵横速度变化均较大,而下地壳较厚,速度较均匀,上地壳底部的低速层,在构造带内较带外薄而浅,P_n速度较低,为7.54-7.80km/s,属壳-幔过渡带,厚13-22km。小江、四开、安宁河及金河等断裂为超壳型或壳内断裂,多为逆冲断层。该构造带的各种深部特征表明它为大陆高原型年轻构造带。

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.