Finding of high-pressure mafic granulites in the Amdo basement, central Tibet

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• 作者：XiaoRan Zhang (1)
  RenDeng Shi (1)
  QiShuai Huang (1)
  DeLiang Liu (1)
  SuoLang Cidan (2)
  JingSui Yang (3)
  Lin Ding (1)
  
• 关键词：high ; pressure granulite ; P ; T path ; Amdo basement ; Bangong ; Nujiang Suture ; Tibet
• 刊名：Chinese Science Bulletin
• 出版年：2010
• 出版时间：November 2010
• 年：2010
• 卷：55
• 期：32
• 页码：3694-3702
• 全文大小：952KB
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• 作者单位：XiaoRan Zhang (1)
  RenDeng Shi (1)
  QiShuai Huang (1)
  DeLiang Liu (1)
  SuoLang Cidan (2)
  JingSui Yang (3)
  Lin Ding (1)
  
  1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100085, China
  2. School of Sciences, Tibetan University, Lhasa, 850000, China
  3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
  
• ISSN：1861-9541

文摘

High-pressure mafic granulites with a peak mineral assemblage of garnet + clinopyroxene + rutile + quartz were found in the Amdo basement, central Tibet. Two kinds of symplectites were identified that are composed of orthopyroxene + plagioclase ± spinel and hornblende + plagioclase around garnet, which were interpreted to develop during the retrogressing stages in the granulites. P-T estimates suggested that peak metamorphic conditions were about 860-20°C and 1.46-.56 GPa, which retrogressed from post-peak phase at 820-90°C and 0.88-.15 GPa to amphibolite facies at 550-70°C and 0.52-.65 GPa. These three stages define a clockwise P-T path with near-isothermal decompression and cooling following the peak high-pressure metamorphism. This suggests that the Amdo granulites underwent an initial subduction to a deep crustal level of ?0 km and then were rapidly exhumed to a shallow crustal level (?0 km). The formation of Amdo granulites is considered to result from the arc-continent collision between the Amdo basement and the Qiangtang terrane in the middle Jurassic, which is a crucial step to the tectonic evolution of the Tibetan Plateau.