Earth Science Frontiers ›› 2019, Vol. 26 ›› Issue (2): 137-156.DOI: 10.13745/j.esf.sf.2019.2.7

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Discussion on the dynamic mechanism of the Late Cretaceous magmatism-metallogenesis in Xiuwacu, northwestern Yunnan Province. 

JIANG Xiaojun, CHEN Zhengyu, LI Wenchang, YU Haijun, LI Chao, ZHANG Xiangfei, WANG Zhongqiang, YAN Qinggao   

  1. 1. Department of Earth Sciences, Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China
    2. Chengdu Geological Survey Center, China Geological Survey, Chengdu 610081, China
    3. MNR Key Laboratory of Sanjiang Metallogeny and Resource Exploration-Utilization, Yunnan Geological Survey, Kunming 650051, China
    4. National Research Center for Geoanalysis, Chinese Academy of Geological Sciences, Beijing 100037, China
  • Received:2018-10-20 Revised:2019-02-20 Online:2019-03-30 Published:2019-03-30
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Abstract: The Xiuwacu W-Mo deposit is a middle-large porphyry magmatic hydrothermal deposit located at the central section of the Yidun-Geza orogenic belt in northwestern Yunnan Province. Adverse natural environment in this region has delayed studies on Late Cretaceous tectono-magmatic activities in Late Yanshan, with focuses mainly on geochronology, petrogenesis, geodynamic background, fluid characteristics and source of ore-forming materials related to the Late Cretaceous alkali-rich granite, etc. However, discussion on structural stress field and dynamic mechanism is still rare. In this paper, we investigated in detail the structures and alteration-lithofacies of key sections and gallery in the east and west districts, Xiuwacu W-Mo deposits. Taking into account the zircon U-Pb, Lu-Hf and O isotopic characteristics, we believe that the Xiuwacu granitic pluton is a two phase complex pluton divided into east and west ore districts with a near S-N F4 fault as the boundary. The east district is dominated by Late Triassic (212201 Ma) porphyritic biotite granite, while mainly Late Cretaceou porphyritic quartz monzogranite and monzogranitic porphyry are in the west district. The situ-zircon U-Pb, Lu-Hf and O isotopic analysis on the porphyritic quartz monzogranite suggests that the monzogranite formation age is 80.18±0.80 Ma (LA-ICP-MC U-Pb) (negative zircon εHf(t)=-4.49-8.07, variable δ18O ranged 5.98‰7.45‰). Hf isotopic TDM2 model age is 14321239 Ma. Together with known geochemical characteristics, they show that the magmatic-mineralization material source of Late Cretaceous porphyritic quartz monzogranite was derived from the partial melting of thickened lower crust. Furthermore, Late Cretaceous regional tectonic stress field is characterized by NE-SW extension in the Yidun-Geza Area by regional structural analysis on 135 typical Late Cretaceous quartz monzogranite dykes and scheelite-molybdenite quartz veins. In summary, we believe that Late Cretaceous magmatic metallogenesis in this region is formed by the NW-SE extension of Neo-Tethys oceanic subduction resulting in partial melting of pre-existing thickened crust decompression.

 

Key words: Northwestern Yunnan Province, Xiuwacu W-Mo deposit, zircon U-Pb, Lu-Hf and O isotopes, regional structural analysis, dynamic mechanism

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