A huge oceanic-type UHP metamorphic belt in southwestern Tianshan, China: Peak metamorphic age and P-T path

详细信息    查看全文

• 作者：LiFei Zhang (1)
  JinXue Du (1)
  Zeng Lü (1)
  Xin Yang (1)
  LongLong Gou (1)
  Bin Xia (1)
  ZhenYu Chen (1)
  ChunJing Wei (1)
  ShuGuang Song (1)
  
• 关键词：oceanic UHP metamorphic belt ; coesite ; peak metamorphic age ; P ; T path ; southwestern Tianshan ; China
• 刊名：Chinese Science Bulletin
• 出版年：2013
• 出版时间：December 2013
• 年：2013
• 卷：58
• 期：35
• 页码：4378-4383
• 全文大小：
• 作者单位：LiFei Zhang (1)
  JinXue Du (1)
  Zeng Lü (1)
  Xin Yang (1)
  LongLong Gou (1)
  Bin Xia (1)
  ZhenYu Chen (1)
  ChunJing Wei (1)
  ShuGuang Song (1)
  
  1. Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing, 100871, China
  
• ISSN：1861-9541

文摘

Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan, China, is summarized in this paper. This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite, coesite pseudomorphs and other UHP minerals. It is the largest oceanic-type UHP metamorphic belt reported so far. It has formed due to northward subduction of the Tianshan Paleo-Ocean. U-Pb dating of metamorphic rims of zircons from a coesite-bearing garnet-phengite schist yields a peak UHP metamorphic ages of 320±3.7 Ma. Combined with ages of 233–226 Ma obtained from rims of zircons from retrograded eclogites, a long retrograde metamorphic evolution (>70 Ma) has been revealed. According to phase equilibria modeling, the P-T paths of both coesite-bearing eclogites and garnet-phengite schists are characterized by thermal relaxation, i.e., the metamorphic temperature peak lags behind the pressure peak, indicating that the UHP rocks experienced slow and long heating and decompression during exhumation in the subduction channel. On the basis of the field observation that a small amount of eclogite lenses is wrapped in large volumes of metapelites, and the similar P-T paths of both rock types, we propose that the exhumation of the UHP eclogites from southwestern Tianshan, China, may have resulted from the exhumation of large volumes of low-density metapelites, which carried the denser eclogites to the Earth’s surface.