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Geoscience ›› 2021, Vol. 35 ›› Issue (02): 514-522.DOI: 10.19657/j.geoscience.1000-8527.2020.045

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Dating, Geochemical Characteristics, and Tectonic Significance of the Chaganobo Monzogranite in the Northern Margin of Alxa Block, Inner Mongolia

LI Jie1(), CONG Diange2,3, GU Yanchun4, TIAN Ying1   

  1. 1. Hebei Academy of Regional Geological Survey, Langfang, Hebei 065000, China
    2. Department of Geological Engineering, Qinghai University,Xining, Qinghai 810016, China
    3. Key Laboratory of Geological Process and Mineral Resources in the Northern Qinghai-Tibet Plateau,Qinghai Provincial Geological Survey Institute, Xining, Qinghai 810012, China
    4. Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-prospecting, Geological Survey Institute of Inner Mongolia, Hohhot, Inner Mongolia 010020, China
  • Received:2019-01-15 Revised:2020-06-29 Online:2021-04-25 Published:2021-05-25

Abstract:

The Chaganobo monzogranite is located in Alxa of Inner Mongolia. The intrusion is the main component of the large Norgong intrusive complex in the Norgong-Langshan tectonic belt, located in the northern margin of Alxa block. The monzogranite is LA-ICP-MS zircon U-Pb dated to be late Early Permian (279±1 Ma). The monzogranite has SiO2=72.88%-75.44%, total alkali (K2O+Na2O)=8.16%, K2O/Na2O=0.87-1.41, Al2O3=12.38%-13.98%, aluminum saturation index (ASI=A/CNK)=0.88-1.02, falling into the alkaline field in the AR-SiO2 diagram. These geochemical characteristics show that the Chaganobo monzogranite is high Si-K metaluminous granite. The right-inclining chondrite-normalized REE patterns indicate that they are enriched in LREEs (LREE/HREE=4.70-14.66) and show moderately to strongly negative Eu anomalies (δEu=0.18-0.87, average 0.37). The primitive mantle normalized trace element diagrams are characterized by obvious depletions of HFSEs, such as Nb, Ta, Ti, and P. The rocks contain very low average Sr (94.44×10-6) and high Yb (3.10×10-6). Geochemical characteristics show that the Chaganobo monzogranite formed in the post-collision setting, where extensional-related underplating may have started the magma intrusion event. Based on the regional data, we deduce that the northwestern margin of the north China plate (represented by the Alxa block) and the southern margin of the Tarim plate may have entered the post-collisional stage in the Early Permian.

Key words: Alxa block, granite, post-collision, northwestern margin of north China plate

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