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《Geoscience》 2018-01
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Characteristics of Chronology and Geochemistry for the Cenozoic Alkali-rich Porphyry in Lijiang Area,Western Yunnan and Their Significance

HUANG Yonggao;LUO Gai;ZHANG Tong;XIONG Changli;JIA Xiaochuan;YANG Xuejun;Sichuan Institute of Geological Survey;  
The Cenozoic alkali-rich porphyry in Lijiang region of Western Yunnan is located in the connection part between Sanjiang fold orogenic belt and southwest of Yangtze plate,including alkali rock and alkali-granite. Alkali rock includes orthophyre,syenite and trachyte-prophyry,while alkali granite includes granite-prophyry,monzonitic granite-prophyry and masanophyre. The zircon U-Pb dating indicates that the ages of those porphyry are between 34. 6 and 37. 1 Ma,which is consistent with the ages of Cenozoic alkali-rich porphyry in Western Yunnan. Geochemical results showed that alkali rock belongs shoshonite series,with SiO_2 content of 54. 54%-67. 70%,K_2O Na_2O. Alkali-granite belongs high-K calc-alkalic series,with SiO_2 content of 67. 16%-70. 66%,K_2O Na_2O. They are both enriched in alkali( Na_2O + K_2O = 7. 03%-11. 70%),showing metaluminous and weak peraluminous( A/CNK = 0. 64-1. 15) characteristics. The porphyry shows alkali and adakitic geochemical characteristics,with enrichment of LREE and LILE( Sr,Ba,K,Pb,and so on),deficit of HREE and HFSE( Nb,Ta,Ti,and so on),with high Sr content and ratio of Sr/Y,La/Yb,low Y and Yb contents,and low values of Mg~#( 0. 5). The comprehensive study shows that the porphyry is associated with partial melting of the base of thickened lower crust caused by decompression melting and underplating of mantle-derived magmas,formed from the structure transition phase of late-collisional between Indian and Asian continents,and was the magmatic event response to syn-collisional processes in the structural transform zone of southeast of the Tibetan orogen. It is considered that there is great gold-polymetallic prospective reserves of porphyry-hydrothermal deposits. This paper provides important constraints for understanding deeply the tectonicmagmatic-metallogenic processes of the Lijiang porphyry metallogenetic belt.
【Fund】: 中国地质调查局项目“西南三江有色金属资源基地调查”(DD20160016)
【CateGory Index】: P588.1
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