内蒙古狼山乌和尔图花岗岩岩体锆石U-Pb年代学及地球化学特征

摘要

The WuheErtu granite mass,with the main rock types of syenogranite and monzogranite,are distributed in Langshan area,Inner Mongolia,northern margin of the North China Plate.Zircon U-Pb ageis 236.1 ± 1.0Ma,indicating the WuherErtu granite mass formed in late Triassic.Geochemical results show high content of SiO2 (71.94 ～73.91％),K2O + Na2O (8.34 ～8.88％),low content of Ca and Mg,and weak content of aluminum (0.98 ＜ A/CNK ＜ 1.07).In SiO2-K2O diagram,sample points fall into the transitional region between high-K calc-alkaline and Shoshonite series.In the primitive mantle-normalized spider diagram,the geochemical characteristics of the granite mass show in some degree enrichment in Rb、Th、K、Nd、Zr、Hf、Sm and depletion in Ba、Nb、Ta、Sr、P、Ti,with medium to negligible Eu anomalies (SEu =0.47 ～ 0.66),which indicate the WuherErtu granite mass belong to the post-collisional granite formed in the tectonic setting transformed from compression system to extension system.Zircon Hf isotopic displays that εHf (t) values vary from-20.6 to +7.6 and Hf model ages (TDM2) vary from 780 ～ 2559 Ma,which suggest a mixed magma source of old continental crust with a small involvement of juvenile components.The comprehensive study of this granite mass helps to further understand and explore the tectonic-magmatic evolution of the northern margin of the North China plate in late Permian-Triassic.%乌和尔图花岗岩岩体位于华北板块北缘,内蒙古狼山地区,岩石类型主要为正长花岗岩及二长花岗岩.LA-ICP-MS锆石U-Pb年龄为236.1±1.0Ma,晚三叠世.岩石高硅(SiO2为71.94 ～73.91％)、富碱(K2O+Na2O为8.34 ～ 8.88％)、弱过铝(A/CNK为0.98 ～ 1.07),贫钙、镁.在SiO2-K2O图中,样品点落入高钾钙碱性系列-钾玄系列的过渡区域.在原始地幔标准化蛛网图上,不同程度富集Rb、Th、K、Nd、Zr、Hf、Sm,亏损Ba、Nb、Ta、Sr、P、Ti,具中等-弱的负Eu异常(δEu =0.47-0.66).主量元素、稀土元素和微量元素特征表明,乌和尔图花岗岩岩体形成于由挤压体制向拉张体制转换的构造背景,属后碰撞花岗岩类.锆石Hf同位素显示,乌和尔图花岗岩岩体的εHf (t)为-20.6～7.6,二阶模式年龄为780 ～ 2559Ma,变化范围较大,反映源区物质以古老地壳为主,可能有年轻组分的参与.对该岩体的综合研究有助于进一步认识和探讨华北板块北缘二叠纪末-三叠纪的构造-岩浆演化过程.