STUDY ON THE NAPPE STRUCTURE IN MULI WESTERN STCHUAN

There occurs a huge thrust nappe structure, including the Jiantoushan, Housuo and Liewashan nappes, in the area of intersection the Yangtze paraplatform and the Songpan-Garze fold system. The hanging wall of the nappe structure consists of Upper Permian greenschist, metabasalt and tuffaceous sandy slate and crystalline limestone; the footwall（autochthonous rock series）is composed of Upper Triassic argillaceous rocks, which were mostly metamorphosed into phytlite. The difference in metamorphic grade between the rock series of the hanging wall and footwall is a distinctive feature of this thrush nappe structure. With the intensification of the intracontinental convergence and development of the thrust nappe structure, not only faulting within the Yangtze paraplatform was intensified, but some new faults also originated and developed, forming the Mishi-Jiang- zhou and Yalongjiang down-faulted basins respectively on the east and west sides of the "Xikang-Yunnan axis". Thus the teetonic framework of "one horst and two grabens" for the "Xikang-Yunnan axis" initiated.