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Characteristics of Garnets from the Harlik Metamorphic Belt in Eastern Xinjiang

ZHAO Ming, WANG Ci-yin   

  1. Department of Earth Sciences, Nanjing University, Nanjing 210093
  • Received:2000-06-20 Revised:2000-06-20 Online:2000-06-20 Published:2000-06-20

Abstract: Garnet is often seen in the Harlik metamorphic belt. It is di stinguishe d as two different types by its morphology. The one is of a better crystal shape and formed during regional metamorphism, and the other is usually broken with c racks and recognized as a residue of early stage thermal metamorphism. Both garn ets may occur sometimes in the same samples. This study mainly focuses on the co mposi tions of garnets and their variations. The composition zoning characteristic s of the garnets, in which MnO and CaO decrease and MgO and FeO increase from co re to rim, indicate that the garnet crystallization temperatures were increasing from core to rim. The microprobe analyses reveal remarkable correlation between the MnO concentration in garnet core and its grain size. This suggests that the large garnet porphyoblasts nucleated at earlier stage and lower temperature.