内蒙古乌拉特中旗乌兰地区含石榴石花岗岩锆石U-Pb年龄及地质意义

Zircon U-Pb Dating of the Garnet-Bearing Granite from Wulan Area of Urad Zhongqi in Inner Monglia and Its Geological Significance

对乌拉特中旗乌兰地区含石榴石花岗岩进行了同位素地质年代学和岩石地球化学研究,探讨了其形成时代和构造背景。利用锆石SHRIMP U-Pb法测得含石榴石花岗岩岩体的年龄为(256.4±2.2)Ma,表明其形成于晚二叠世;岩石地球化学特征显示属弱过铝质Ⅰ型花岗岩,物源主要为上陆壳硬砂岩,形成于后碰撞构造环境,源区岩浆部分熔融程度较低,可能是由Ⅰ型花岗质流体与岩浆演化后期热液流体反应而分异结晶形成的。根据含石榴石花岗岩产出的大地构造位置、形成环境及侵位时代,推断研究区内华北板块北缘与西伯利亚板块南缘的碰撞缝合时间上限早于256.4 Ma。

Geochronology and petro-geochemistry of garnet-bearing granite from Wulan area of Urad Zhongqi are investigated,and its forming age and tectonic background are discussed.The age of garnet-bearing granite dated by SHRIMP U-Pb of zircons is（256.4±2.2） Ma,indicating that it was formed at the Later Permian.Petro-geochemical characteristics show that the granite is weakly peraluminous I-type ones formed in post-collision tectonic settings and its sources is the greywacke in upper continental crust.The partial melting degree of the source rocks is lower.The granite was derived from interaction of an I-type granitic liquid as a result of strong with hydrothermal fluid during the magmatic stage.According to tectonic settings,forming conditions and emplacement times of garnet-bearing granites,it is referred that the suturing between the Northern margin of North China plateform and the Southern margin of Siberian plate in research area took place before 256.4 Ma.