The Geological Features Of The Changning Melange Belt Of West Yunnan

Changning-Menglian suture belt has been a hot spot for international and domestic geologists to study the evolution of the Paleo-Tethys for a long time. After years of research, new discoveries and insights keep imerging, and this greatly improve the research degree of this region. Despite all these achievements, different scholars still can’t research an agreement on some issues, such as the tectonic properties, scale and evolutionary history.The Changning melange belt of west Yunnan is the northern extension of the Changning-Menglian suture belt, trending NW-SE, the east side of it is the Chongshan Group and Triassic granodiorites, while the west side is the Ximeng Group Xiquelin Formation, both of the east and west sides show fault contact relationships with the melange belt.The regional geologic surveys and geological sections show that the Changning melange belt was made up of geologic bodies of different times and different geological origins. The melange belt include 5 geological unit, and they are faulted contact with each other. As the matrix, the Wenquan Formation formed in the deep-water basin environment which is close to continental slope, and it has been subjected to regional low-temperature dynamometamorphism and 4 phases of deformation since its formation. As the autochthonous blocks, Lancang Group experienced high pressure metamorphism, Ximeng Group experienced regional middle-temperature metamorphism. Among the exotic blocks, metabasalt belongs to Devonian ocean island basalt(OIB), and it has experienced 1 phase of metamorphism and 2 phases of deformation, of which the metamorphism is at the same phase of the first deformation, and they belong to greenschist facies regional low-temperature dynamometamorphism, while the second phase of deformation was manifested as the folding of the pre-existing schistosity, and S2 developed where the rock is strongly deformed. Meanwhile, the gneissic granodiorites is also the members of the exotic blocks, it experienced regional low-temperature dynamometamorphism.