Earth Science Frontiers ›› 2024, Vol. 31 ›› Issue (3): 20-39.DOI: 10.13745/j.esf.sf.2023.6.18

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Geochemical characteristics and petrogenesis of the Neoproterozoic Eshan highly fractionated I-type granites, western Yangtze block

LI Guangjie1(), CHEN Yongqing1,*(), SHANG Zhi1,2, LIU Shibo1   

  1. 1. School of Earth Science and Resources,China University of Geosciences(Beijing), Beijing 100083, China
    2. China Fire and Rescue Institute, Beijing 102202, China
  • Received:2022-10-04 Revised:2023-07-03 Online:2024-05-25 Published:2024-05-25

Abstract:

The Eshan highly fractionated I-type granites, situated in the western margin of the Yangtze block, represent a significant component of the Neoproterozoic magmatic belt within the region. A comprehensive investigation into their magma source, genesis, and tectonic settings can provide insights into the evolutionary trajectory of the Neoproterozoic crust. This study conducts zircon LA-MC-ICP-MS U-Pb dating and geochemical analyses on the Eshan highly fractionated I-type granites. The results indicate that these granites predominantly consist of red medium-coarse granite and gray-white medium-coarse granite, formed at approximately 746±34 Ma (MSWD=4.2) and 732±30 Ma (MSWD=3.3), respectively. Geochemical analysis reveals a highly fractionated I-type signature characterized by elevated levels of SiO2 (70.32%-78.41%), Na2O (3.09%-3.94%), and K2O (5.13%-7.35%), while exhibiting lower concentrations of CaO (0.52%-0.90%), TiO2 (0.001%-0.025%), and P2O5 (0.061%-0.097%). The rocks exhibit enrichment in K, Rb, Th, and depletion in Nb, P, and Ti. Sr-Nd isotope analysis shows εNd(t) values ranging from -10.8 to -7.5, with two-stage Nd model ages (TDM2) falling within the range of 2.3 to 2.0 Ga. Integrating these findings with regional geological studies, it is proposed that the Eshan highly fractionated I-type granites originated from the underplating of mantle- and/or juvenile mafic lower crust-derived magma that intruded the upper crust, triggering partial melting of Paleoproterozoic medium- to high-potassium basaltic rocks and biotite gneiss under an extensional tectonic regime. Subsequently, these granites were formed through a process of high fractional crystallization.

Key words: highly fractionated I-type granites, tectonic setting, Neoproterozoic, west margin of Yangtze block

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