Reconstruction of Archaean basement in the Dabie orogen: Constraints from geochronology and Sr-Nd-Hf isotope of the Early Cretaceous Daqishan granite
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1. Wuhan Center, China Geological Survey, Wuhan, Hubei 430205, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Research Center of Granitic Diagenesis and Mineralization, China Geological Survey, Wuhan, Hubei 430205, China;4. School of Earth Sciences, Yunnan University, Kunming, Yunnan 650500, China

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    Abstract:

    We present detailed geochronological, geochemical and Sr-Nd-Hf isotopic data for the late Mesozoic granitic rocks in the Daqishan region of the Dabie orogen. LA-ICP-MS U-Pb dating indicates that the Daqishan granites formed in the Early Cretaceous with an age of 124~120 Ma. These granites have high SiO2(69.3%~75.2%),Al2O3 (13.4%~15.3%), and a total alkali of Na2O+K2O (7.94%~8.71%) with A/CNK=1.01~1.03, low MgO (0.23%~0.84%), TiO2(0.16%~0.49%) and TFeO (1.05%~2.66%). In addition, these granites are distinctively enriched in LILE and LREE, depleted in HSFE, HREE, with obvious negative Eu anomaly (δEu=0.34~0.51), and belong to calc-alkaline I-type granite. The parental magmas likely experienced fractional crystallization of plagioclase, K-feldspar and apatite. The Cretaceous zircons have negative εHf( t ) values and εNd( t ), ranging from 32.9 to 15.2 and 22.5 to 15.8, respectively, with corresponding t DM2 of 3258 Ma to 2140 Ma and 2754 Ma to 2209 Ma, indicating a significant ancient materials involved in the Cretaceous magmatism. Because of approximate U-Pb age and Hf isotopic composition, it is speculated that the inherited zircons of ~2.65 Ga age in Daqishan granites have a certain genetic relationship with the granites of 2.65~2.63 Ga in Jiamiao area. The Daqishan granites may have been generated from the partial melting of Archean crust in the Dabie orogen, and were dominated by the extensional regime in the middle-late Mesozoic relating to the westward subduction of the Pacific plate.

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JIN Wei, TIAN Yang, WANG Jing, ZHANG Weifeng, DENG Xin, PENG Ni.2023. Reconstruction of Archaean basement in the Dabie orogen: Constraints from geochronology and Sr-Nd-Hf isotope of the Early Cretaceous Daqishan granite[J]. Acta Geologica Sinica,97(6):1780-1796

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  • Received:May 07,2022
  • Revised:
  • Adopted:
  • Online: July 05,2023
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