青藏高原东北缘岩石圈缩短变形——深地震反射剖面再处理提供的证据

摘要

Although most researchers both in China and abroad have agreed that the Tibetan plateau is the largest highland induced by the India-Asia collision over the past 60-50 Ma, its formation mechanism has long been a problem of controversy. Deep seismic reflection profiling is an effective technique for revealing the fine structure of the lithosphere and detecting the deformation style of the crust. The reprocessing of the deep seismic reflection profile across Songpan block-West Qinling orogenic belt has revealed the details of lithosphere deformation. The superimposition of the thrust duplex structure in the upper crust and a sub-horizontal detachment in the middle crust and the vertical stacking of Moho at the bottom of the crust show that the lithospheric shortening deformation on the northeastern margin of the Tibetan Plateau was the main formation mechanism. The Kunlun fault 1000 km in length, one of the largest continental-scale strike-slip faults in Tibet, terminates at a sub-horizontal decollement with the depth of 35 km in the lowermost crust of Tibet. The study establishing the vertical structure of the lithosphere shows tectonic relationship between the western Qinling orogenic belt and the Zoige basin on the lithosphere scale.%青藏高原是由印度板块和亚洲板块于50～60 Ma碰撞而形成的全球最高最大的高原,已成为多数国内外学者的共识.然而,关于它的岩石圈变形机制却是长期争论的问题.深地震反射剖面是精细揭示岩石圈结构、分辨变形样式的有效技术.重新处理的松潘地块一西秦岭造山带深地震反射剖面揭示出岩石圈变形的细节,以地壳上部的双重逆冲构造、地壳中部一系列近水平拆离断层的叠置和地壳下部莫霍面的重叠为主要特征,展现出青藏高原东北缘岩石圈变形以缩短变形为主要机制.横向上上千公里展布的大规模左旋走滑的昆仑断层,自地表向下陡倾延伸到地壳中部的叠瓦状逆冲构造之上,在埋深约35 km处被近水平的拆离层所截断.本次研究建立的岩石圈垂向构造图也展现出西秦岭造山带与若尔盖盆地岩石圈尺度的构造关系.