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Geological Journal of China Universities ›› 2023, Vol. 29 ›› Issue (4): 559-570.DOI: 10.16108/j.issn1006-7493.2021121

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Petrogenesis and Tectonic Implications of the Indosinian Fengxian Pluton, Western Qinling Orogeny

NI Chunyu,JIANG Yaohui*   

  1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
  • Online:2023-08-15 Published:2023-08-15

Abstract: This paper reports systematically petrological and SHRIMP zircon U-Pb dating, whole-rock geochemical and Sr-Nd-Hf isotopic research for the Fengxian Pluton. We discussed the magmatic evolution, source characteristics, tectonic and geodynamic settings of these plutons. Our study shows that: 1. The Fengxian pluton is composed of granodiorite and quartz monzonite, invaded in the Middle Triassic (~237.5 Ma). The SiO2 content of the rock is 61.7~66.7 wt %, belonging to the high potassium calc-alkaline series, with relatively high MgO content (1.49-2.43 wt%) and Mg# value (0.53-0.58), belonging to the high-K calc-alkaline series. They are enriched in light rare earth elements (LREE) and lack marked negative Eu anomalies. They are also enriched in LILE and depleted in HFSE. Their high Sr (474×10-6-629×10-6) low Y (6.85×10-6-7.60×10-6) and Yb (0.57×10-6- 0.72×10-6) value are similar to those of adakites. They show εNd(t) values of -4.2 to -5.8, initial 87Sr/86Sr ratios of 0.7072-0.7077 and εHf(t) values of -1.1 to -4.3. We believe that the Fengxian pluton is mainly derived from subducted sediments in the continental margin environment of the northward subduction of the Paleo-Tethys oceanic slab. The origin of the Fengxian pluton suggests that the Animaqing-Mianlue oceanic crust had subducted under the West Qinling before 237.5 Ma, and the eastern segment of the West Qinling remains a continental arc till the Middle Triassic.

Key words: West Qinling, Indosinian, Granitiods, subducted sediments, Paleo-Tethys

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