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Sm-Nd and Rb-Sr Isotopic Ages of Shaba Granulite from Western Sichuan Province and Their Geological Significance

XU Shi-jin, YU Hang-bo, WANG Ru-cheng, LU Huai-peng, FANG Zhong   

  1. Department of Earth Sciences and State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China
  • Received:2002-12-20 Revised:2002-12-20 Online:2002-12-20 Published:2002-12-20

Abstract: Using the Sm-Nd and Rb-Sr mineral isochron methods. we have dated the Shaba granulite,which is one of the oldest basement rocks in the western margin of the Yangtze Plate. The Sm-Nd mineral isochron of 1 140 ± 1 10Ma represented the time of granulite facies metamorphism during the later Middle-Proterozoic era, when the Grenville-age Orogeny was developing around the world.The Rb-Sr mineral isochron of 218± 1 1Ma might be a thermal event age disturbed by the Late Permian -Triassic intrusion mass of. stratified gabbro. Its depleted mantle Nd model age of 1 1 58Ma and εNd= 5.5 showed that protolith of the Shaba granulite was experienced rapid granulite facies metamorphism after petrogenesis of the protolith. Based on above-mentioned dating results and the closure temperatures of Nd isotope in hypersthene and 40Ar/39Ar age of hypersthene, the authors suggest that the lower-crustal rocks in western margin of Yangtze Plate, including Shaba granulite, were slowly uplifted after 1140Ma.