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Geoscience ›› 2022, Vol. 36 ›› Issue (03): 836-847.DOI: 10.19657/j.geoscience.1000-8527.2021.147

• Petrology • Previous Articles     Next Articles

Formation Age and Magma Source of the Shazhangtu Diorite Porphyry, Inner Mongolia: Constraints of Petrogeochemistry, Zircon U-Pb Geochronology and Hf Isotopes

LÜ Yunhe(), DONG Guochen(), ZHAO Liwei, SU Lin, YIN Guodong, TANG Jiahui   

  1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
  • Received:2021-07-08 Revised:2021-12-18 Online:2022-06-10 Published:2022-07-19

Abstract:

Diorite porphyry has been widely studied due to its genesis and ore-bearing characteristics. Many diorite porphyry intrusions were found in the north of Abagaqi (Inner Mongolia), accompanied by high-background geochemical anomalies. Studies on petrology, zircon U-Pb geochronology, geochemistry and Lu-Hf isotopes have been conducted for the formation age and magma source of diorite porphyry samples from the Shazhangtu mining area in Inner Mongolia. The diorite porphyry was emplaced at (311.1±1.7) Ma, and is the product of the middle Hercynian (Late Carboniferous) tectonomagmatic activities. The rocks have SiO2=56.19%-60.45%, Na2O+K2O=4.81%-5.87%, and aluminum saturation index (A/CNK)=1.00-1.43. It belongs to high potassium calc-alkaline and peraluminous rocks. The LREE LILE (K, Rb) and HFSE (Zr,Th and U) are enriched, and the HFSE (Nb, Ta, P, Hf and Ti) are depleted, indicating that the geochemical characteristics of island are magmatic rocks in subduction zone. The total REE contents ranges from 139.62×10-6 to 150.67 ×10-6, showing a right-inclined pattern of light rare earth enrichment and heavy rare earth depletion with weak negtive Eu anomaly. The Hf isotopic data of zircons show that the single-stage and two-stage model ages range from 637 to 905 Ma and from 827 to 1,259 Ma, respectively, and the εHf(t) value of zircons varies from 1.10 to 7.80, indicating the characteristics of mantle-derived magma. It is probably the partial melting magma in the mantle wedge due to the dewatering of the subduction plate that underplated under the bottom of the lithosphere and the molten body rises to cause under-invasion, heated and induced the partial melting of the new formed juvenile basic lower crust, forming the crust-mantle sources mixed magma.

Key words: diorite porphyry, U-Pb geochronology, geochemistry, zircon Hf isotope, Shazhangtu mining area

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