华北板块北缘中段姚五沟岩体锆石U-Pb定年、地球化学特征及其与区域构造演化的关系

Zircon U-Pb dating and geochemical characteristics of the Yaowugou granite in the middle section of northern margin of the north China plate and its implications to regional tectonic evolution

内蒙古太仆寺旗地区的姚五沟岩体位于华北板块北缘中段,主要岩石类型为花岗斑岩。岩体LA-ICP-MS锆石U-Pb测年结果为141.6 Ma±1.3 Ma(MSWD=0.78),形成于晚侏罗世。岩石化学特征显示岩体具高硅富碱的特征,A/CNK=0.93～1.07,为准铝质-弱过铝质,属高钾钙碱性系列。稀土配分模式呈右倾"V"字型,Eu负异常较显著(δEu=0.30～0.43),轻重稀土分异明显(w(La)N/w(Yb)N=34.04～48.59)。微量元素表现出富集Rb、Th、K等大离子亲石元素,亏损Ba、Sr和Nb、Ta、Ti、P等高场强元素,具有较高的10000×w(Ga)/w(Al)值(2.85～2.92)和w(Zr+Nb+Ce+Y)值(537.80×10^(-6)～584.10×10^(-6));表明其属A型花岗岩,由下地壳部分熔融而来,并伴随少量幔源组分参与,形成于非造山伸展环境。与研究区内的后淖S型花岗岩(255.8 Ma±1.6Ma,晚二叠世)和白旗A型花岗岩(134.6Ma±1.1Ma,晚侏罗世)的地球化学特征对比,发现由晚二叠世到晚侏罗世,岩浆源区由上地壳的泥质岩部分熔融转换为下地壳部分熔融,并伴随少量幔源组分参与,其大地构造背景由陆-陆碰撞环境转换为非造山伸展环境。

The Yaowugou granite in Taibus Bannner of Inner Mongolia is located in the middle section of northern margin of the North China plate mainly consisting of granite porphyry.LA-ICP-MS zircon U-Pb dating is 141.6 Ma±1.3 Ma(MSWD=0.78),showing Late Jurassic intrusives.The geochemistry of this rock is characterized by high concentrations of silica and alkali,A/CNK=0.93~1.07,belongs metaluminous to weakly peraluminous and high-K calc-alkaline to shoshonite granite.The REE distribution patterns is characterized by obvious negative anomalies(δEu=0.30~0.43)and exhibits right-dipping'V'patterns with LREE enrichment(w(La)N/w(Yb)N=34.04~48.59).In addition,the granite is riched in Rb,Th,K and other large ion lithophile elements(LILE),while Ba,Sr and Nb,Ta,P,Ti and other high field strength elements(HESE)are relatively depleted and it has high 10000×w(Ga)/w(Al)(2.85~2.92)and w(Zr+Nb+Ce+Y)(537.80×10-6~584.10×10-6)ratio values,showing the features of Atype granite and it is formed in the non-orogenic extensional tectonic setting.Compared with the geochemical characteristics of Late Permain Hounao S-type granite(255.8 Ma±1.6 Ma)and Late Jurassic Baiqi A-type granite(134.6 Ma±1.1 Ma),it is suggested that the granite formed by partial melting of argillaceous rock in the upper crust transformed into the lower crust with a few mantle-derived composition from Late Permain to Late Jurassic,while the tectonic setting is transformed from the continental collison tectonic setting into the non-orogenic extensional tectonic setting.