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Geoscience ›› 2021, Vol. 35 ›› Issue (02): 523-534.DOI: 10.19657/j.geoscience.1000-8527.2020.050

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Geochronology and Significance of Granites from Zhuozishan Region, Wuhai, Inner Mongolia

HE Zeyu1,2(), SHEN Junfeng1(), ZHANG Shanming1,2, LIU Jun3, DU Baisong1   

  1. 1. School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
    2. Inner Mongolia Eighth Geological Mineral Exploration Institute, Wuhai, Inner Mongolia 016000, China
    3. School of Earth Resources, China University of Geosciences, Wuhan, Hubei 430074, China
  • Received:2019-08-20 Revised:2020-07-19 Online:2021-04-25 Published:2021-05-25
  • Contact: SHEN Junfeng

Abstract:

The Zhuozishan granites in Wuhai (Inner Mongolia)are located at the intersection of the western margin of Ordos basin and the eastern margin of Alxa block, and comprise mainly syenogranite and monzogranite.LA-ICP-MS zircon U-Pb dating indicates that the syenogranite and monzogranite were emplaced in (2,039±79) Ma and (1,866±120) Ma, respectively, which are the products of Paleoproterozoic magmatsm.According to geochemical characteristics, the syenogranite and monzogranite are calc-alkaline, and both are rich in Si, Al and Ka, but relatively poor in Ti, Na and Ca. In addition, the granites are peraluminous (A/CNK=1.19-1.32).There is significant total REE difference between the monzogranite (17.36×10-6-11.70×10-6) and syenogranite(241.05×10-6).Meanwhile, our data show that LREEs are obviously enriched and HREEs are relatively depleted. The former shows obvious negative Eu anomaly (Eu/Eu*=0.36), and the latter shows obvious positive Eu anomaly (Eu/Eu*=3.39-4.89), indicating that the fractionation degree of syenogranite is higher.In terms of trace elements, syenogranite is characterized by enrichments in Th, U, Pb, and large ion lithophile elements (LILEs, e.g., Rb, K),but depleted in Ba, Nb, and Ti. Monzogranite is characterized by enrichments in LILEs and depletions in high field strength elements (HFSEs, e.g., Th, Nb, Ta, and Ti).Considering the regional geological background, these rocks were likely formed by partial melting of argillaceous rocks in different stages of the same magmatic phase, representing the products of the same collision stage. This indicates that there were two magmatic events in the Late Paleoproterozoic Zhuozishan.Considering the contact characteristics of strata and the mineralization distribution characteristics, we infered that the final orogenic event between the Alxa and Ordos blocks was completed by the end Paleoproterozoic.

Key words: Alxa block, North China Craton, disconformity, zircon U-Pb dating, amalgamation, Paleoproterozoic

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