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Geoscience ›› 2020, Vol. 34 ›› Issue (06): 1245-1260.DOI: 10.19657/j.geoscience.1000-8527.2020.029

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Ages, Geochemical Characteristics and Tectonic Implications of the Riduoma Granodiorite in the Middle Section of Western Qinling Orogen

KOU Shaolei(), WEI Liyong, ZHANG Zhen, LI Guoying, ZHENG Xin, LU Zongyue, YANG Hanwen, MENG Wuyi   

  1. Xi’an Center of Mineral Resources Survey, China Geological Survey, Xi’an, Shaanxi 710100, China
  • Online:2020-12-22 Published:2020-12-22

Abstract:

Riduoma granodiorite is located near the Meiwu pluton in the middle section of the Western Qinling Orogen. A integrated study of petrography, U-Pb zircon dating and whole-rock geochemistry was carried out for the Riduoma granodiorite. The granodiorite contains numerous mafic microgranular enclaves (MMEs). LA-ICP-MS zircon U-Pb dating yielded a weighted mean age of (236.8 ± 3.6) Ma (MSWD=4.1) for the granodiorite and (242.7±1.6) Ma (MSWD=1.4) for the MMEs. The Riduoma pluton is weakly peraluminous (A/CNK=1.48-1.51) and high-K calc-alkaline, with high contents of K2O (2.58%-2.75%), K2O+Na2O (5.57%-5.76%), and belongs to I-type. The granodiorite is characterized by enrichment in LILEs (such as K, Rb, Ba, Th, and U) and depletion in HFSEs (such as Nb, Ta, Ti and P) with high LREE/HREE ratios (10.4-11.9) and moderately-negative Eu anomalies (δEu=0.68-0.81). Geochemical characteristics of the Riduoma granodiorite suggest that it was derived from partial melting of the lower crust high-K basaltic rocks. In addition, the granodiorite shows relatively high Mg # (57-61), Cr (149×10-6-185×10-6), and Ni (36×10-6-47×10-6), suggesting minor mantle-derived contribution. The MMEs may represent this source magma. Petrography, zircon U-Pb ages, and geochemical characteristics, combined with the regional setting, suggest that the Riduoma pluton emplacement was resulted from the subducted slab break-off in a post-collisional setting.

Key words: Western Qinling Orogen, Riduoma granodiorite, zircon U-Pb dating, geochemistry, tectonic setting

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