龙门山多层分层拆离地壳结构:新构造变形与深部构造证据

2008年5.12汶川地震发生后,对于龙门山地壳结构及其与汶川地震的成生联系成为构造地质学研究极为关注的科学问题。然而,现有的多种龙门山地壳结构模式在综合解释表层构造变形及深部构造时与调查和探测资料均有不符。利用前人地球物理探测成果,结合穿过龙门山主要发震构造单元彭灌杂岩及雪隆包岩体的综合构造剖面,将地表构造与深部地壳探测资料结合进行了综合解释,认为龙门山逆冲构造带中的多重冲断推覆构造由约10 km深处的拆离断层分隔,因而应该只是浅层次构造变形的组合样式;在中、下地壳韧性流壳层的主导下,扬子地块基底被动?入并形成多层拆离的韧性流变构造组合。5.12汶川地震及余震是由于以彭灌杂岩和雪隆包岩体为代表的刚性体,在上部韧性流壳层前端的持续推挤作用下,发生破裂而形成的。

Multi-layer detachment crustal structure in the Longmen Mountains: Evidences from neo-tectonic deformation and geophysical data

The crustal structure and its affinity with the occurrence of 5.12 Wenchuan earthquake in the Longmen Mountains have become the focus of attention in the field of structural geology since 2008.However,present tectonic models for interpreting crustal structure in the Longmen Mountains only focus on surface structure,or only pay attention to deep structure;and thus,they could not furnish a comprehensive understanding.This paper reports a comprehensive structural section across the Pengguan complex and Xuelongbao pluton,which are the major tectono-petrological units generating the 5.12 Wenchuan earthquake,and re-interprets the geophysical data published by previous studies.We conclude that a detachment fault at a depth of ～10 km separated the in-sequence duplex imbricated thrust in the shallow tectonic level,while the rigid basement of the Yangtze Block northwestward wedged into the middle to lower crustal ductile channel,which produced multi-layer detachment crustal structure.The upper layer of the ductile channel flow pushed and ruptured the Pengguan complex and Xuelongbao pluton,which resulted in the occurrence of 5.12 Wenchuan earthquake.