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Origin and Tectonic Setting of the Early Mesozoic Granitoids in Qinling Orogenic Belt

ZHANG Cheng-li1, WANG Tao2, WANG Xiao-xia3   

  1. 1. Key Laboratory of Continental Dynamics of Northwest University, Department of Geology, Northwest University, Xi'an 710069, China; 2. Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China; 3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
  • Received:2008-09-20 Revised:2008-09-20 Online:2008-09-20 Published:2008-09-20

Abstract: The Early Mesozoic granitoids in Qinling Mts are characterized by the metaluminous to peraluminous and moderateto high-K calc-alkaline rocks with enrichment in LILE and LREE and poorness in HFSE, as well as relative depletion in Nb and Ta, showing the geochemical features similar to those of post-collisional granitoids. Some of them are adakite-like and rapakivitextured granitoids. The adakite-like granitoids display high Sr and low Y contents, and rapakivi-textured granitoids show transitional geochemical characters from I- to A-type granites. The structure and geochemistry of these granitic intrusions, together with the bimodal features of the coeval lamprophyres and mafic dykes, suggest that the Early Mesozoic granitoids in Qinling Mts region were formed in a post-collisional setting. The early adakite-like granitoids were formed under the thickened crust during the early post-collision period. The large numbers of normal massive granitoids were produced under the crustal extension environment after delamination in Qinling Mts region, and the occurrence of rapakivi-textured and high differentiated granitoids indicates that Qinling region had evolved into the late stage of post-collisional environment.