Earth Science Frontiers ›› 2020, Vol. 27 ›› Issue (4): 172-183.DOI: 10.13745/j.esf.sf.2020.4.9

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Petrogeochemistry and geochronology of biotite monzonitic granites in the Horqin Right Front Banner area, Inner Mongolia and the geological significance

CHEN Zehan1,2(), ZHANG Jia2, ZHAO Zhidan2, HAO Sen1, ZHANG Liqiang3, CAO Yuanbao1   

  1. 1. Langfang Center of Natural Resources Comprehensive Survey, Langfang 065000, China
    2. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China
    3. Liaoyang Natural Resources Bureau, Liaoyang 111000, China
  • Received:2019-12-28 Revised:2020-03-10 Online:2020-07-25 Published:2020-07-25

Abstract:

The Xing-Meng orogenic belt has very complex structural and distribution patterns. Its evolutionary process, especially the final time limit for the closure of the “scissors” type of the Paleo-Asian Ocean and the subsequent land-land collision process have not been determined. The study area is located in the eastern section of the Xing-Meng orogenic belt, where the geotectonic position is clamped between the Hegenshan-Heihe and Solon-Siramulon-Changchun fault zones. It provides an important window for studying the geological evolution of the eastern section of the Central Asian orogenic belt. The Qianqi biotite monzogranite body in the right wing of Horqin, Inner Mongolia has the shape of a rock plant, with a 400 m NE-trending long axis and a 150-250 m short axis. The north side intrudes into the Dashizhai Formation, and the south part is in fault contact with the Linxi Formation. The granite rocks had medium to fine-grained granitic and massive structures. They were mainly composed of potash feldspar (40%), plagioclase (25%), quartz (20%), biotite (14%) and a small amount of chlorite (1%), and had the LA-ICP-MS zircon U-Pb age of 221.1±2.1 Ma, consistent with formation in the Late Triassic. The geochemical characteristics of rocks were high in SiO2(68.46%-70.38%) and K2O+Na2O(9.02%-9.39%) and low in P2O5(0.09%-0.17%), MgO(0.60%-0.80%), TiO2(0.54%-0.58%) and medium K2O/Na2O(0.90-1.54) contents, with obvious fractionation of light and heavy rare earth elements (LREE and HREE), relative enrichment of LREE (ΣLREE content (163.55-226.55)×10-6) and depletion of HREE (ΣHREE content (11.96-21.67)×10-6). The granite type is peraluminous high-k calc alkaline I-type, indicating a post collisional/orogenic tectonic environment of the Late Permian Triassic magmatic rocks on the northern margin of the North China block. Based on previous research results and regional geological data, we infer that the Qianqi biotite monzogranite was formed under a lithosphere delamination and asthenosphere upwelling environment.

Key words: Horqin Right Front Banner area, Late Triassic, I-type granite, zircon U-Pb age

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