Petrographical and Mineralogical Characteristics of Bengge Alkaline Igneous Complex in Zhongdian, Western Yunnan and Its Geological Significance

Bengge alkaline igneous complex in Zhongdian, Western Yunnan has the variety of rock types, which is production after a complex magma—fluid process. The petrographical and mineralogical analysis of the host rock and its xenolith suggests that the igneous complex has magma mixing and contamination, and metasomatism features. The light-colored minerals in different rock types of Bengge pluton are orthoclase, and individual sample which represent s magma mixing and metasomatism residual has the plagioclase. The dark minerals show the characters of rich-Si, Mg, and poor-Al, alkali. The magmatic source of different rock types is different. The production of syenite was related to Ganze-Litang oceanic flat subduction in late Triassic, and its origin was crust-mantle mixing source. While the lamprophyre was the production that the mantle source of potassic-ultrapotassic magmatism was caused by India-Eurasia plate collision in Cenozoic. The two magmas with different properties coexisted in the same closed system, and magma mixing, contamination, metasomatism had occurred in the magma transfer and petrogenetic process. Therefore, the petrogenesis of Bengge alkaline igneous complex subjects to the multi-stages overlying process of magma-fluid-tectonism which is mainly oceanic crust subduction.