内蒙古巴林右旗晚侏罗世巴彦琥硕花岗岩地球化学特征、锆石U-Pb年龄及Hf同位素组成

巴彦琥硕花岗岩采自内蒙古巴林右旗北部，其主要岩性为中细粒花岗岩、细粒二长花岗岩。通过地球化学、锆石U-Pb定年及Hf同位素分析研究，探讨巴彦琥硕花岗岩成因及其地质意义。锆石U-Pb年代学研究结果表明，巴彦琥硕花岗岩锆石U-Pb年龄为150 Ma，形成于晚侏罗世。岩石学和地球化学研究表明:SiO₂质量分数不低于71.3%，Al₂O₃不低于12.15%，w(K₂O)+w(Na₂O)值为7.74%~8.29%，w(K₂O)/w(Na₂O)值为0.88~1.57，Sr质量分数为(61.7~197.5)×10^-6，Y为(17.3~33.2)×10^-6，w(Sr)/w(Y)值低，为1.77~3.56，巴彦琥硕花岗岩属低锶高钇型岩石；岩石轻、重稀土元素分馏明显，w(La)_N/w(Yb)_N值为3.06~10.89，显示出明显的Eu负异常。锆石Hf同位素分析显示ε_Hf(t)值介于6.1~12.3之间，显示源区亏损的特征。考虑到侏罗世—白垩世期间太平洋板块对中国东部边缘的俯冲作用，巴林右旗北部晚侏罗世巴彦琥硕花岗岩的形成受太平洋板块俯冲作用影响，形成于挤压向伸展体制转换的过渡期。

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

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.