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Geoscience ›› 2017, Vol. 31 ›› Issue (01): 20-32.

• Mineral Deposit and Petrology • Previous Articles     Next Articles

Geochemistry and Zircon U-Pb Dating of Granites in Early Cretaceous in Eastern Xilin Hot, Inner Mongolia and Its Geological Implications

YUAN Jianguo1,2(), GU Yuchao1,3(), XIAO Rongge1, QU Yunyan2, DUAN Kaibo2, HAN Yue4   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
    2. General Institute of Chemical Geology Survey, China Chemical Geology and Mine Bureau, Beijing 100013, China
    3. Shenyang Institute of Geology and Mineral Resources, China Geological Survey, Shenyang,Liaoning 110034, China
    4. Chinese Academy of Governance, Beijing 100089,China
  • Received:2016-02-24 Revised:2016-10-26 Online:2017-02-10 Published:2017-03-16

Abstract:

In this paper, a series of analyses including SHRIMP zircon U-Pb isotopic dating, major elements and trace elements, have been performed on the granite in Early Cretaceous in eastern Xilin Hot in order to make the discussion of tectonic environment in the study area. The results of the SHRIMP zircon U-Pb dating are (139.1±1.7) Ma for syenogranite(DS214) and (134.7±1.7) Ma for granite(DS220), which suggests that the granite formed in the early period of Early Cretaceous. The geochemical feature of major elements in the granites is found containing high SiO2 and K2O +Na2O contents, low Al2O3 content relatively. The average A/CNK value is 1.06, which belongs to weak peraluminous series. The trace element geochemistry shows evident enrichment of LILE(Th, U and K), deficit of HFSE (Nb, Ba, Sr, P and Ti). The REE patterns are the richment type of LREE/HREE value (5.71-14.36) with high total REE contents(122.90×10-6-368.77×10-6) and strong negative Eu anomalies(0.10-0.50), which implies that the samples are A-type granites. The K2O-Na2O diagram for tectonic environments also shows that they are A-type granite. The Y/Nb-Ce/Nb diagram of A-type granites of different tectonic environments displays the feature of A2-type granite. These geochemical characteristics of the granites reveal that the granites formed in the extending phase of the post-orogenic by the evolution of crustal magma with mantle mixing. The cause of the granite may be related to the procession from the extruding to extending environment which is the result of the lithosphere thinning after the plates collision (including Mongolia-Okhotsk ocean) with the close of Paleo-Asian Ocean during the Late Paleozoic to the Early Mesozoic. It was also effected by the westward subduction of the Paleo-Pacific Ocean.

Key words: A-type granite, SHRIMP zircon U-Pb dating, extensional environment, eastern Xilin Hot

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