内蒙古中部商都县库伦图地区晚三叠世花岗岩的地球化学特征及构造意义

Geochemical Characteristics and Geotectonic Implications of Late Triassic Granite from Kuluntu Region of Shangdu County,Central Inner Mongolia

内蒙古商都县位于中朝陆块北部、华北地台北缘,区内岩浆岩分布广泛。对商都县库伦图地区的铜顶山二长花岗岩和和眭村—民主村正长花岗岩进行了锆石TIM SU-Pb定年,结果表明两岩体分别形成于(236.5±4.2)Ma和(231.8±1.1)Ma。岩石学和地球化学研究表明二长花岗岩和正长花岗岩均属于高硅、准铝—过铝质高钾钙碱性岩石,其Rb、Th相对富集,Ba、Nb、Sr和Eu具明显的负异常,亏损Zr和Hf。铜顶山和和眭村-民主村岩体可能形成于由挤压向伸展过渡的构造体制转换的构造背景。

Shangdu County,250 km south of Sonid Zuoqi,Inner Mongolia,is located in the north margin of North China plate,in which magmatic rocks are widely distributed.The U-Pb zircon ages of the monzonite granite from Tongdingshan and syenogranite from Hemu-Minzhu are respectively（236.5±4.2） Ma and（231.8±1.1） Ma.Petrology and geochemical characteristics reveal that the monzonite granite and syenogranite belong to peraluminous,high-K,calc-alkaline granitods.These granitods are relatively rich in Rb and Th,lack of Zr and Hf,meanwhile they contain Ba,Nb,Sr and Eu with obviously negative abnormality.Tongdingshan and Hemu-Minzhu granitods are formed in tectonic setting of transition from compressional to extensional environment.