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地质学的证据表明 ,在喜马拉雅的冲断层带MCT和MBT处有大规模的地壳缩短 ;在雅鲁藏布缝合带附近也观测到冲断层 .但是 ,迄今还不知道这些冲断层向下俯冲多深 .我们根据地震学的证据 ,认为喜马拉雅及南藏的冲断层向下延伸至 80— 1 0 0km ,然后停止 .在MCT、MBT以及雅鲁藏布缝合带下面的冲断层与喜马拉雅以及南藏的多次地壳俯冲有密切关系 .这个现象为印度—欧亚的碰撞过程设定一个十分重要的框架 .该地区的地壳俯冲有一定深度 ,由于入侵的地壳太轻 ,使俯冲不能更深 ;此时由于印度板块的继续向北推进 ,在原俯冲带后方 ,出现另一个新的地壳俯冲带 .喜马拉雅与南藏的多重地壳俯冲与该地区地质活动的多幂性相吻合 .首先 ,在雅鲁藏布缝合带产生地壳俯冲 ,在到达 80— 1 0 0km处停止 .然后 ,在雅鲁藏布以南的MCT和MBT相继产生新的地壳俯冲 .它们也在 80— 1 0 0km的深处停止 .除了喜马拉雅和雅鲁藏布向北倾斜的地震带外 ,另外还观测到一个自地表从唐古拉山向南缓慢倾斜并到达雅鲁藏布地壳底部的地震带 .它可以解释为在唐古拉山附近的地壳向北仰冲 .喜马拉雅及南藏的多重地壳俯冲现象强有力地说明 ,入侵的印度地壳必与它的上地幔分裂开来 ,后者可以另行俯 (仰 )冲到更深的欧亚上地幔 .
Geological evidence suggests massive crustal shortening at the MCT and MBT thrusts in the thrust zone of the Himalayas and thrust faults in the vicinity of the Yarlung Zangbo suture, but so far it has not been known how far these thrusts subducted According to the seismological evidence, we believe that the thrust faults in the Himalayas and South Tibet extend downward to 80-10000 km and then cease.The thrust faults beneath the MCT, MBT, and the Brahmaputra suture zone connect with the Himalayas and the southern Tibet Is closely related to many crustal subductions.This phenomenon sets a very important framework for the collision process between India and Eurasia.The crustal subduction in this area has a certain depth and the subduction can not be deepened because the invading crust is too light. As the Indian plate continues northward, another new crustal subduction zone occurs behind the original subduction zone.The multiple crustal subduction of the Himalayas and South Tibet coincides with the multi-power of the geological activity in the region.First, in the Brahmaputra The suture zone produces crustal subduction, stopping at 80-100km, and then new crustal subduction of MCT and MBT south of the Brahmaputra occurred. In addition to the northwardly inclined seismic zone of the Himalayas and Brahmaputra, a seismic belt slowly sloped south from the Tanggula Mountains and reached the bottom of the Yarlung Zonal crust was observed. The multiple crustal subduction of the Himalayas and southern Tibet strongly suggests that the invaded Indian crust would split off from its upper mantle and the latter could plunge further down Eurasian upper mantle.