甘肃龙首山牛角沟地区中粗粒石英二长花岗岩年代学与元素地球化学特征及其地质意义

Geochronology, Geochemical Characteristics and Significances of Quartz Monzonite in Niujiaogou,Longshoushan,Gansu

通过对龙首山牛角沟地区芨岭花岗岩体中的灰白色中粗粒石英二长花岗岩中的锆石进行了U-Pb同位素测年,测得的加权平均年龄为(447.0±5.2)Ma,形成时代为晚奥陶世。灰白色中粗粒石英二长花岗岩主量、稀土及微量元素含量分析表明,其具有低硅、富铝、富钾的地球化学特征,为准铝-弱过铝质、高钾钙碱性I型花岗岩。结合区域其他岩体形成的构造环境研究,反映该岩体形成于北祁连洋壳的北向俯冲作用导致的北祁连岛弧与阿拉善地块碰撞期结束后的构造环境。芨岭岩体的中粗粒石英二长花岗岩I型花岗岩为后期碱交代型铀矿提供了铀源和赋矿空间。

U-Pb isotopic dating of zircons from Jiling gray white medium coarse grained quartz monzogranite in Niujiaogou area of Longshoushan is carried out.The weighted average age is(447.0±5.2)Ma,and the age of formation is late Ordovician.Through the analysis of the major elements,rare earth and trace elements of gray white medium coarse quartz monzogranite,it shows that it has the geochemical characteristics of low Si,high Al,K.It is metaluminous to weak peraluminous and high potassium calc alkaline I-type granite.Combined with the study of the tectonic setting of other rocks in this region,it is reflected that the Jiling quartz monzonite formed in the tectonic setting after the collision between the North Qilian island arc and the Alxa block caused by the North subduction of the North Qilian ocean crust.The Jiling medium coarse quartz monzogranite which is a I-type granite,provides uranium source and ore bearing space for the later alkali metasomatic type uranium deposit.