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Geoscience ›› 2020, Vol. 34 ›› Issue (03): 532-544.DOI: 10.19657/j.geoscience.1000-8527.2019.014

• Petrology • Previous Articles     Next Articles

Identification and Geological Significance of Various Types of Muscovite in Jurassic Granite of Bengbu Area on the Southeast Margin of North China Craton

WU Tianhao1,2(), XU Lijuan1,2(), XIAO Yilin3,4, LIU Sheng’ao1,2   

  1. 1. Institute of Earth Sciences, China University of Geosciences, Beijing 100083, China
    2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
    3. School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
    4. CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China, Hefei, Anhui 230026, China
  • Received:2019-01-25 Revised:2019-12-10 Online:2020-07-04 Published:2020-07-05
  • Contact: XU Lijuan

Abstract:

The Triassic subduction of South China continental crust is generally considered to have extended to the Bengbu region (SE margin of the North China craton), yet whether the subduction there had caused ultra-high-pressure (UHP) metamorphism remains controversial. Primary phengite can be used as a geobarometer to estimate the pressure of rock formation. Petrographic observation, electron probe microanalysis (EPMA) and Raman spectral analysis have been performed on the muscovite in the restite, its granite host and the aplite vein from the Jurassic Jingshan granites in the SE margin of the North China Craton. The muscovite in the restite and granite host are coarser, and have higher Si and (Fe+Mg),but lower Al atomic contents than the muscovite in common granites. The muscovite in the restite and granite host also show similar Raman shift (421 cm-1) and aluminium atom bridge-bond (Al, O(br)), which are lower and higher than that of the white micas, respectively,in the UHP eclogite and non-UHP schist of this study. Therefore, major element contents and Raman shifts of the muscovite suggest that coarse-grained muscovite in the residual and granite are primary metamorphic phengite. Applying geobarometry, the melting pressure of the Jingshan granite is estimated to be 1.0 to 1.3 GPa. The source of the Jingshan granite may have been the subducted South China continental crust. The subducting depth of the South China plate beneath the NE margin of the North China Craton was at least 33 to 45 km, equivalent to the middle and lower crust there.

Key words: muscovite, phengite, restite, subducted continental crust, North China Craton

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