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《Geochimica》 2017-06
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Magmatic properties and metallogenic analyses of magmatism triggered by early Neo-Tethys subduction in South Gangdese, Tibet

ZOU Yin-qiao;CHEN Xi-lian;HUANG Wen-ting;ZHANG Jian;LIANG Hua-ying;XU Ji-feng;CHEN Ling;Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences;University of Chinese Academy of Sciences;State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of sciences;Guangxi Key Laboratory of Marine Disaster in the Beibu Gulf, Qinzhou University;  
South Gangdese has experienced the Neo-Tethys subduction and subsequent collision between the Indian and Eurasian plates. Many post-collision-related porphyry Cu-Mo deposits have been found in the South Gangdese belt. However, only the Xiongcun super-large porphyry Cu-Au deposit was identified as relating to the Neo-Tethys subduction in the South Gangdese belt. This work reports several Cu-mineralized intrusions in the South Gangdese belt, which are distributed widely from the west to the east. Zircon U-Pb ages show that they were emplaced in the Early Mesozoic. Such Cu-mineralized igneous rocks generally develop quartz-epidote vein alterations, while the surrounding Cretaceous-Cenozoic Gangdese granitic batholith did not undergo any corresponding alteration and mineralization. This finding suggests that Cu mineralization and alteration occurred earlier than the batholith's formation. The chalcopyrite-magnetite-hematite mineral assemblage shows that Cu mineralization was related to the redox process of the magmatic magnetite. Thus, the mineralization was coeval with the intrusions. These Jurassic rocks have high hornblende content and quartz-magnetite-titanite and hematite-magnetite mineral assemblages, indicating they originated from highly oxidized and water-rich magmas. The primary fluid inclusions found in the magmatic sphere and apatite of mineralized intrusions indicate that their parental water-rich magmas existed in an exsolved volatile phase during the early stage of the magma evolution process. The temporal and spatial distributions of the Early Mesozoic magmatic rocks show the existence of a west-east magmatic rock belt parallel to the Yarlung Zangbo suture zone in the South Gangdese. These Early Mesozoic magmatic rocks show typical arc magma characteristics, and have high positive zircon ?Hf(t)(+10 ~ +16), providing evidence of a mantle-derived magma source. The above findings imply that South Gangdese developed large-scale magmatism associated with Cu mineralization in the Early Mesozoic. These Jurassic magmatic rocks originated from a juvenile lower crust, which provided a good Cu metal source. Further, their parental magmas were highly oxidized water-rich magmas, favoring the concentration and mineralization of chalcophile elements during the magma evolution process. Thus, it is proposed that the Early-Middle Jurassic subduction of the Neo-Tethys slab induced a west-east oxidized arc magmatic rock belt and contemporary Cu mineralization in the South Gangdese belt. The results reveal there was good potential for the creation of subduction-related porphyry Cu deposits. Given the strong uplift and denudation in South Gangdese after the Cretaceous, the domains of the Early-Middle Jurassic volcanic rocks or intrusions associated with Cu mineralization in this area are a good prospecting target for subduction-related porphyry Cu deposits.
【Fund】: 中国科学院战略性先导科技专项(B类)(XDB03010302);; 科技部国家重点研究计划(2016YFC0600407)
【CateGory Index】: P588.1;P618.2
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