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Paleoproterozoic High Temperature Paired Metamorphic Belt in Central Part of Sounthern Inner Mongolia and Its Tectonic Implication

LIU Shou-jie,LI Jiang-hai   

  1. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, China; School of Earth and Space Sciences,Peking University, Beijing 100871, China
  • Received:2009-03-20 Revised:2009-03-20 Online:2009-03-20 Published:2009-03-20

Abstract: An ultra-high temperature (UHT) metamorphic rock belt occurs in Jining-Fengzhen-Tuguiwula, central part of southern Inner Mongolia. Detailed study on the mineral assemblages shows UHT indicators such as Spl+Qtz, Spr+Qtz and Opx+Sil+Qtz.UHT rocks underwent initial isobaric cooling followed by isothermal decompression in the field of UHT metamorphism. Available age data suggest peak metamorphism at 1 920 Ma followed by retrogressive metamorphism at 1 850 Ma of the UHT rocks. To the southeast, including Huai'an-Xuanhua area, outcropped a high pressure granulite, which has a isothermal decompression retrograde metamorphic history along a clockwise P-T path. Most of the ages show a peak metamorphism at ~1 900 Ma followed by a ca. 1 850 Ma retrograde metamorphism. Both the UHT rocks and high pressure granulite have a foliation striking NEE and dipping to NNW at ca. 70°. UHT rock belt and high pressure granulite formed a paired metamorphic belt due to the coincidence of distribution, attitude and metamorphic age. Since the metamorphic temperature is relatively higher than the traditional paired metamorphic belt, it could be defined as high temperature paired metamorphic belt, which is one of the oldest paired metamorphic belts. This high temperature paired metamorphic belt indicates that the crustal material at different levels in mid-southern Inner Mongolia underwent metamorphisms with entirely different P-T paths during a collision event at ca. 1 900 Ma, then the UHT rocks and high pressure granulite were uplifted as a whole block. Further research on the high temperature paired metamorphic belt provides a chance to study the early structural framework and crustal thermal evolution of North China Craton, especially the plate tectonics and structural process at different crustal levels.