Establishment of tectonic evolution pattern of Longmenshan Orogen

Key words:  Longmenshan Orogen  thrust tectonic  overthmst tectonic  tectonic evolution pattern

Abstract:

Longmenshan Orogen is the western part of Yangtze plate and develops three main faults which are Wenchuan-Maowen, Beichuan-Yingxiu and Jiangyou-Guanxian fault. Because of the extrusion of Yangtze plate and Songpan-Aba block, Longmenshan began to fold uplift at late Indo-Chinese epoch. The three main faults became the reverse faults from the normal faults in the orogenic process. Based on the developed theory，through the field observation and the equilibrium section，the mountain-building process of Longmenshan Orogen was discovered, and the tectonic evolution pattern of orogen was established. The results show that at the early of orogen, Longmenshan was compressed by the force coming from northwest. At the latest trias, Longmenshan began to be compressed by Yangtze plate which is compressed by Pacific-oceanic plate from southeast. Longmenshan Orogen inherited overthrust structures of Indosinian to further uplift in Yanshanian. In Himalayan epoch, the overthrust structures developed, and at the same time, the unstable rock began to glide and became the stacked structure pattern of gliding nappe and thrust nappe and finally the contemporary format formed.