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Geoscience ›› 2020, Vol. 34 ›› Issue (03): 483-493.DOI: 10.19657/j.geoscience.1000-8527.2020.009

• Petrology • Previous Articles     Next Articles

Zircon U-Pb Age, Geochemical Characteristics and Tectonic Implications of Granites in the Wulanhaote Area, Central Daxing’an Mountains

ZHANG Haihua(), LI Yongfei, ZHANG Jian, SU Fei, ZHENG Yuejuan, BIAN Xiongfei, ZHANG Dejun   

  1. Shenyang Center of Geological Survey, China Geological Survey, Shenyang, Liaoning 110034, China
  • Received:2018-05-05 Revised:2019-12-11 Online:2020-07-04 Published:2020-07-05

Abstract:

Zircon U-Pb geochronological and geochemical data are presented on the granites in Wulanhaote (Inner Mongolia), and we discussed the granite ages, types and regional tectonic evolution.The Wulanhaote granites are monzogranite, and zircon U-Pb dating yielded a weighted mean 206Pb/238U age of (214.4±2.6) Ma, indicating a Late Triassic granite emplacement. The rocks are characterized by having high SiO2 and alkali, but low CaO, MgO and TiO2 contents. Chondrite-normalized REE diagram shows a weak right-inclining, low-MREE pattern with strong negative Eu anomaly. The rocks show enrichments in Rb, Th, Zr, Y and Yb, but depletions in Ba and Sr. They have high Rb/Sr and Rb/Nb values and show features of low-Sr- and high-Yb-type granites. Our results show that the granites were formed under relatively low pressure by partial melting of the delaminated crust. Integrating regional tectonic evolution and tectonic discrimination diagrams, we suggest that the granites were emplaced in a post-orogenic extensional setting. This indicates that the regional tectonics has changed from Middle Triassic collisional orogenic to post-Triassic orogenic extensional, and that the Siberia-North China collision may have lasted till the Middle Triassic.

Key words: zircon U-Pb dating, geochemistry, monzogranite, Late Triassic, Wulanhaote

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