Episodic crustal anatexis and the formation of Paiku composite leucogranitic pluton in the Malashan Gneiss Dome, Southern Tibet

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• 作者：LiE Gao (1)
  LingSen Zeng (1)
  KeJun Hou (2)
  ChunLi Guo (2)
  SuoHan Tang (1)
  KeJia Xie (3)
  GuYue Hu (2)
  Li Wang (1)
  
• 关键词：Himalayan orogenic belt ; Northern Himalayan Gneiss Domes ; leucogranite ; crustal anatexis ; tectonic transition
• 刊名：Chinese Science Bulletin
• 出版年：2013
• 出版时间：October 2013
• 年：2013
• 卷：58
• 期：28-29
• 页码：3546-3563
• 全文大小：
• 作者单位：LiE Gao (1)
  LingSen Zeng (1)
  KeJun Hou (2)
  ChunLi Guo (2)
  SuoHan Tang (1)
  KeJia Xie (3)
  GuYue Hu (2)
  Li Wang (1)
  
  1. State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
  2. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China
  3. Non-Ferrous Mineral Exploration Engineering Research Center of Henan Province, Zhengzhou, 450016, China
  
• ISSN：1861-9541

文摘

The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite, two-mica granite and garnet-bearing leucogranite. Zircon U-Pb dating yields that (1) tourmaline leucogranite formed at 28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma; (2) two-mica granite formed at 19.8±0.5 Ma; (3) both types of leucogranite contain inherited zircon grains with an age peak at ～480 Ma. These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions. As compared to the two-mica granites, the tourmaline ones have higher initial Sr and zircon Hf isotope compositions, indicating that they were derived from different source rocks combined with different melting reactions. Combined with available literature data, it is suggested that anatexis at ～35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System (STDS), and led to the tectonic transition from compressive shortening to extension. Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt. Crustal anatexis at ～28 Ma and ～20 Ma represent large-scale melting reactions associated with the movement of the STDS.