北祁连造山带红石泉岩体地球化学特征及其构造意义

Geochemical Characteristics and Tectonic Significance of HongshiquanPluton in North Qilian Orogenic Belt

红石泉岩体地处北祁连造山带的龙首山成矿带西南缘,区内发育伟晶岩型铀矿床。本文对红石泉岩体进行岩相学、岩石地球化学研究,探讨其岩石成因、岩浆来源,厘定其构造环境。元素地球化学结果显示:岩体具中硅、富铝,富钠特征,为准铝质高钾碱性正长岩系列。在微量元素图解中,样品富集Rb、U、K、Nd等元素,亏损高场强元素Nb、Ta、Ti及元素P等;在稀土元素球粒陨石标准化图解中,样品富集轻稀土,轻重稀土分馏明显,Eu显示正异常。样品显示高的Zr+Nb+Ce+Y的值,属A型花岗岩。结合其元素地球化学特征及区域内岩浆岩的演化,厘定岩体为祁连板块与阿拉善板块碰撞后拉张环境下,壳源岩浆与幔源岩浆混合形成。

The Hongshiquan pluton is located in the southwest margin of Longshoushan metallogenic belt in north Qilian orogenic belt,where pegmatite type uranium deposit is developed.This paper studies the lithography and petrogeochemistry of Hongshiquanpluton,discusses its petrogenesis and magma source,and determines its tectonic environment.The results of elemental geochemistry show that the intrusions are characterized by moderate silicon,aluminum-rich and sodium-rich,and the meta-aluminous high-k alkaline syenite series.In the diagram of trace elements,the samples are enriched in Rb,U,K,Nd and depleted in Nb,Ta,Ti and P.In the chondrite standardization diagram,the samples are enriched in LREE,the fractionation of LREE is obvious,and positive Eu anomalies.The samples show high Zr+Nb+Ce+Y values and belong to A-type granite.Combined with the geochemical characteristics of the elements and the evolution of magmatic rocks in the region,it is determined that the Hongshiquanplutonwas formed by mixing of crust magma and mantle magma under the extensional environment after the collision of Qilian plate and Alashan plate.