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The Discovery and Significance of A-type Charnokite in Southeast Guangxi Province, China

PENG Songbai, FU Jianming, LIU Yunhua (Faculty of Sciences, China University of Geosciences, Wuhan 430074; Yichang Institute of Geological and Mineral Resources, Yichang 443003)  
The charnokite body and a lot of granulite, gneiss xenoliths were found in southern of Da-rongshan-Shiwandashan granite belt in Southeast Guangxi. The study on charnokite and granulites show that the isotermal-depression symplectic textures are generally developed in the granulites xenoliths, and main metamorphic reactions are Ga + Sill→Spl + Q, Ga+Q→Opx+Crd and Ga+Sill + Q→Crd. This midi-cates that the granulite is experienced the fast uplift and extensional exhumation once more. The research on genetic texture for zircons in the granulite and SHRIMP dating show a great deal of zircons are consist of the core and rim. The core is generally characteristic of metamorphic crystallization, and the rim is characteristic of magmatic crystallization. The ages of the core are concentrated abount ( 950-1100) Ma, and the magmatic crystallization age of the rim is at 248 Ma. the charnokite is characteristic of A-type granite which marks the end of Indosinian orogeny. According to this, It is consided that the protoliths of Indosin-ian A-type charnokite are the granulite facies metamorphic rocks formed in Sibao (Grenville) orogenic e-vent in the later Mesoproterzoic. A-type charnokite is formed in the fast lift and exhumation partial melting in post-collision orogenic environment during Indosinian. This provides the important evidence for the south extending of the Sibao(Grenvilla) Jiangshan-Saoxin orogenic belt in the late Mesoproterzoic and the east extending of the Tethys orogenic belt in late Paleozoic in Southchina, and indicates the end of Indosinian orogeny.
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