The Constitution And Tectonic Characteristics Of The Diancangshan Complex, Western Yunnan

The Diancangshan (DCS) metamorphic complex is a highly significant metamorphic complex along the Red River-Ailaoshan ductile shear zone which attracted the attention of many geologists because of its distinctive location and characteristics.This paper conducts the studies about the DCS metamorphic complex in several respects. 1) The constitutions of both of the western and eastern parts of the DCS metamorphic complex .2)The contrasts between the two parts in metamorphic rock associations. The author figured out that the main body of DCS metamorphic complex should be divided into two tectonic parts, i.e. the middle or deep metamorphic rock zone from west part to central part, and the retrogressive metamorphic zone in east part. The deep metamorphic rock zone is mainly composed by rock which is of upper greenschist facies to amphibolite facies. Rocks suffered strong sinistral slip shearing deformation. The eastern part is composed by 1.5km wide retrogressive metamorphic rocks, which is mainly composed by a suit of greenschist facies metamorphic rocks and granitic mylonite. 3) The studies of feldspar porphyroclasts and their deformational behaviors. The feldspar porphyroclasts can be subdivided into two types, the"hard porphyroclast"and the"soft porphyroclast". The latter can be further subdivided into two sub-types. One is that feldspar porphyroclasts obviously haveσ,δ, orΦtype tails and the other feldspar porphyroclasts show banding, stripe and striation textures. 4)By studying structural characteristics of the DCS metamorphic complex and geologic bodies around it, the author tries to understand their roles in the exhumation of DCS metamorphic complex.The DCS metamorphic complex possess many different microstructural phenomena in the eastern and western parts, which are caused by their different metamorphic and deformation characteristics. There are many microstructural phenomena in the granitic mylonites, e.g. subgrain rotation dynamic recrystallization, exsolution structure, kinking, microlayering,, banded structure, book shelf structure etc. They are of typical crystalline plastic deformation and brittle-ductile transition deformation evidences. The differences in metamorphism and deformation at the microscopic scale of rocks from the western part and eastern part are summarized. At the microscopic scale the rocks from the western part of the DCS show evidences of high temperature plastic deformation, but those from the eastern part mainly display evidences for brittle to ductile transition. In both the micro- and macro-scales the DCS metamorphic complex has undergone deformation superpositions.U-Pb dating of zircons from the granitic rocks in the revealed four stages of tectono-magmatic activities i.e. 760-780Ma, 240Ma, 30Ma and 23Ma, in the DCS area.