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The discovery of pegmatite of the Chongshan orogenic belt in the Caojian area, Western Yunnan and its geological significance(Vol. 40, No.5, 2020) TEXT SIZE: A A A

HUANG Liang1,2, WU Jia-lin1, WANG Xiao-lin1, XIONG Bo1,2, PU Tao1, ZHU Xun-zao1, FANG Xiong1

(1. Yunnan Institute of Geological Survey, Kunming 650216, China;
2. MLR Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization, Kunming 650051, China)

Abstract: During the geological survey in the Caojian area, Dali Prefecture, western Yunnan, the authors had investigated and studied magmatic rocks in the Chongshan orogenic belt, and found a new set of white pegmatite whose main bodies are associated with the parent rock in forms of intercalated bands and local reticulated bands in a mixed magmatic rock zone. According to the difference of magma sources of pegmatites, there are two types of pegmatites, including the monzonitic granitic and alkaline granitic pegmatites, with majority of the monzonitic granitic pegmatite. The LA-ICP-MS zircon U-Pb dating ages of 34.47-18.66 Ma show that pegmatites were formed in a period from Eocene (late stage) to Miocene (early stage), indicating that the pegmatites were formed by magmas derived from long-term persistent partial melting. Geochemical studies show that the pegmatites belong to peraluminous granites of (high potassium) calc-alkaline series and shoshonitic series, with moderately enriched LREE, gently and weakly depleted HREE, enriched Rb and Th and depleted K, Ba, Hf, and Zr. The plotted results of R2-R1, A-B, and Sr-Yb diagrams show that the main body of pegmatites was mainly formed, in association with the late Himalayan orogeny, by the decompression melting process of crustal materials in depth under conditions of low pressure to extremely low pressure. Based on the comprehensive research, it is believed that the pegmatite represents a magmatic response of the rapid uplift process of the late Himalayan orogenic stage in the Chongshan orogenic belt. The end time of about 18.66 Ma for its melting process may indicate that the rapid uplift stage of the Chongshan orogenic belt was ended at that time.

Keywords: Chongshan orogenic belt; pegmatite; Himalayan period; Eocene; Miocene; late-stage of the orogeny; melting; uplift

ACTA MINERALOGICA SINICA Vol. 40, No.5, 2020, page 584-594

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