西秦岭—东昆仑及邻近地区地壳结构——深地震宽角反射/折射剖面结果

Crustal structures beneath West Qinling-East Kunlun orogen and its adjacent area——Results of wide-angle seismic reflection and refraction experiment

在青藏高原东北缘，穿过阿尼玛卿缝合带东端完成了一条637km的近南北向深地震宽角反射，折射剖面．获得的地壳结构剖面表明，该地区Moho界面埋深48～51km，北浅南深，横向变化不大，而地壳内部构造在不同的地质构造块体差异明显．在下地壳内出现的两组能量较强的P3、P4波组，反映了研究区下地壳的反射性质和多层结构特征．阿坝弧形断裂以南和阿尼玛卿缝合带附近壳内界面变形强烈，壳内低速异常结构明显，特别是在缝合带下方20km以下的中下地壳异常的低速结构可以解释为存在延伸至中下地壳的破碎带构造特征．在剖面南段反映西秦岭褶皱带至松甘块体相应的地震记录出现复杂、强烈的中下地壳反射和相对较弱的Moho反射震相是该地区地壳结构的明显特征．

A 637 km long wide-angle seismic reflection and refraction profile in the north-south direction was carried out in the northeast margin of Tibet plateau, which crosses A＇nyemaqen suture belt. The crust section obtained from the seismic data shows that the depth of the Moho is about 48 - 51 km. The crust is slightly thicker in the south and it varies smoothly toward the north along the profile with different structures in the various tectonic blocks. The clearly identified overcritical reflections P3, P4 on the seismic record sections indicate that the lower crust features multi-layer structure and strong reflectivity in this area. There are severe deformations on the interfaces of the crust, and low velocity distributions on the south of Aba arcuate fault and near A＇nyemaqen suture belt. The low velocity zone in the mid and low crust beneath A＇nyemaqen suture belt may be explained as the extension of the suture belt into the crust. The crust structure from the West Qinling fold zone to Songpan-Garze block is characterized by strong reflections from the mid and lower crust, andrelatively weak Moho reflections on the seismic record sections.