Abstract

Info

Title:: Geochemical Characteristics, Zircon U-Pb Age and Hf Isotopic Composition of Late Jurassic Bayanhushuo Granites in Balinyou Banner of Inner Mongolia

Author(s):: FENG Gang; WAN Le; LIU Zheng-hong; BAI Xin-hui; GUAN Qing-bin; LI Peng-chuan; 1. Inner Mongolia Second Hydrogeology Engineering Geological Prospecting Institute, Erdos 017000, Inner Mongolia, China; 2. School of Earth Sciences, Jilin University, Changchun 130061, Jilin, China

Keywords:: granite; geochemistry; Jurassic; zircon; U-Pb age; Hf isotope; calc-alkaline series; Inner Mongolia

Abstract:: Bayanhushuo granites are collected from the northern part of Balinyou banner, Inner Mongolia. The main lithology includes fine grained granite and fine grained monzonitic granite. Based on geochemistry, zircon U-Pb dating and Hf isotopic analysis, the genesis of Bayanhushuo granites and the geological significance were discussed. Zircon U-Pb dating indicates that the zircon age of Bayanhushuo granite is 150 Ma, forming in Late Jurassic. Petrological and geochemical results show that the mass fraction of SiO₂ is not lower than 71.3%, Al₂O₃ is not lower than 12.15%, w(K₂O)＋w(Na₂O) is 7.74%-8.29%, w(K₂O)/w(Na₂O) is 0.88-1.57; the mass fraction of Sr is (61.7-197.5)×10^-6, Y is (17.3-33.2)×10^-6, w(Sr)/w(Y) is low with the value of 1.77-3.56; Bayanhushuo granite belongs to the rock with low Sr and high Y; the fractionation between LREE and HREE of the rock is significant, w(La)_N/w(Yb)_N is 3.06-10.89 with obvious negative Eu anomaly. The zircon Hf Isotopic analysis demonstrates that ε_Hf(t) is 6.1-12.3, showing the magma originates from depleted source. Considering the subduction of Pacific Plate on the edge of the eastern China in Jurassic-Cretaceous, the formation of Late Jurassic Bayanhushuo granite in the northern of Balinyou banner, which is affected by the subduction of Pacific Plate, is in a tectonic transition setting from compression to extension.