Petrogenesis and tectonic significances of Late Mesozoic granitoids in the Dahutang area, Jiangxi Province: constraints from zircon U- Pb dating, mineral- chemistry, geochemistry and Hf isotope
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    Abstract:

    The Dahutang area in Jiangxi Province developed multiple- phased granitiods during the Late Mesozoic, which are closely associated with W- Cu- Mo mineralization. This paper performed the study of mineral chemistry, geochemistry, zircon U- Pb chronology and Lu- Hf isotope for porphyric- like biotite monzogranite and biotite granite porphyry from the study area. The results show that the porphyric- like biotite monzogranite formed at 145.6±1.4 Ma (Kunshan Pluton), 148.4±2.4 Ma (in the center of Yanziya Pluton) and 145.7±2.9 Ma (the edge of Yanziya Pluton), and the biotite granite porphyry formed at 143.7±2.4 Ma (Shiweidong Pluton). All the captured zircons in four samples were derived from the surrounding granitoids of Neoproterozoic. The geochemical characteristics show that the porphyric- like biotite monzogranite and biotite granite porphyry are similarly high in SiO2 (72.37%~73. 33% and 70. 16%~73. 8%, respectively), rich in Al with the aluminum saturation index A/CNK of 1. 23~1. 47 and 1. 30~3. 02, respectively; suggesting a high high- K calc- alkaline series. Rare earth and trace elements analyses show distinct differences between the porphyric- like biotite monzogranite and biotite granite porphyry. The porphyric- like biotite monzogranite is characterized by distinct HREE and LREE fractionation with an average (La/Yb)N of 26. 18 and obvious right leaning of REE distribution patterns, apparent negative Eu anomaly, enrichment in LILE (Cs, Rb, Th, U, K and Pb) and depletion in HFSE (Zr, Nb, Ti and Y), and low Ba and Sr. However, the biotite granite porphyry shows weak fractionation of LREE and HREE, with an average (La/Yb)N of 9.76, apparent Eu negative anomaly, “sea gull”- type REE patterns, and “M”- type four group effect, enrichment in LILE and depletion in HFSE. The εHf(t) of the porphyric- like biotite monzogranite has a range of -7.39~-5.19, with a two- stage model age (TDM2) of 1. 53~1. 67 Ga. Comprehensive analysis shows that the porphyric- like biotite monzogranite of Late Jurassic in the Dahutang area may be originated from partial melting of the Neoproterozoic biotite- granodiorite in middle- upper crust in the tectonic background of subduction of the Paleo- Pacific Plate into the South China Plate; while the biotite granite porphyry of Early Cretaceous originated from partial melting of the Neoproterozoic biotite- monzogranite in upper crust due to upwelling of the asthenosphere mantle in a tectonic transition background from subduction of the Paleo- Pacific Plate into the South China Plate to post- subduction extension. Besides, the biotite granite porphyry was replaced by Cl- rich fluids during the process of crystallization differentiation.

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CHU Pingli, DUAN Zheng, LIAO Shengbing, HUANG Wencheng, HONG Wentao, ZHU Yanhui, SHU Xujie.2019. Petrogenesis and tectonic significances of Late Mesozoic granitoids in the Dahutang area, Jiangxi Province: constraints from zircon U- Pb dating, mineral- chemistry, geochemistry and Hf isotope[J]. Acta Geologica Sinica,93(7):1687-1707

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History
  • Received:May 07,2018
  • Revised:June 12,2018
  • Adopted:June 12,2018
  • Online: December 20,2018
  • Published: