Protolith age and exhumation history of metagranites from the Dabie UHP metamorphic belt in east-central China: A multi-chronological study

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  • Wang Ru-Cheng
    Department of Earth Sciences, and State Key Laboratory for Mineral Deposits Research, Nanjing University
  • Xu Shi-Jin
    Department of Earth Sciences, and State Key Laboratory for Mineral Deposits Research, Nanjing University
  • Fang Zhong
    Department of Earth Sciences, and State Key Laboratory for Mineral Deposits Research, Nanjing University
  • Shieh Yuch-Ning
    Department of Earth and Atmospheric Sciences, Purdue University
  • Li Hui-Min
    Tianjin Institute of Geology and Mineral Resources
  • Li Da-Ming
    Institute of Geology, China Seismological Bureau
  • Wan Jing-Lin
    Institute of Geology, China Seismological Bureau
  • Wu Wei-Ping
    Anhui Institute of Geology

書誌事項

公開日
2004
DOI
  • 10.2343/geochemj.38.345
公開者
一般社団法人日本地球化学会

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説明

Metagranites (granitic orthogneisses) constitute one of the important lithologic units in the Dabie ultrahigh pressure metamorphic belt. They often display direct contact with paragneisses and eclogites. TIMS zircon U-Pb dating on the metagranites reveal that their protolith was crystallized as granitoids in Neoproterozoic ages of 755 to 611 Ma and thus correspond to rift magmatism associated with breakup of the Rodinia supercontinent in the northern margin of the Yangtze Block. Zircon U-Pb age and Ar-Ar ages of amphibole and biotite indicate that the granitoids experienced eclogite-facies metamorphism in Early Mesozoic with rapid exhumation at cooling rates of 8.7 to 10.2°C/Ma from 225 ± 6 to 181 ± 3 Ma in response to amphibolite-facies retrogression. Fission track ages of sphene, zircon and apatite indicate that the metagranites experienced slow exhumation with cooling rates of 0.88 to 1.25°C/Ma in Late Mesozoic. It is possible that in the first period of exhumation, the metagranites were uplifted from the mantle depth to lower crustal level at ca. 225 Ma, then rapidly reached middle to upper crustal levels between 204 Ma and 180 Ma. After the intensive magmatism in Early Cretaceous, the Dabie terrane was uplifted at the slow rate in response to unroofing. Either the rapid exhumation in the Early Mesozoic or the slow uplift in the Late Mesozoic in the Dabie terrane were contemporaneous with two rapid subsidence and sedimentation of the Hefei Basin in Early Jurassic and Paleogene, respectively. This suggests that the orogeny and basin-forming events were closely related to each other rather than independently separated.

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