新疆阿尔泰造山带海西期花岗伟晶岩地球化学特征、年代学及地质意义

Geochemical Characteristics,Chronology and Geological Significance of Hercynian Granitic Pegmatites in the Altai Orogenic Belt,Xinjiang

阿尔泰是我国也是世界上最重要的伟晶岩分布区,伟晶岩作为一种独立的矿床类型,在矿床学研究中具有重要意义。本次研究选择阿尔泰造山带西段布尔津冬格列伟晶岩和青河北伟晶岩为研究对象,获得LA-ICP-MS锆石U-Pb年龄为(343.7±1.7)Ma,为早石炭世海西期运动产物。地球化学特征显示,伟晶岩具富硅、过铝质、中碱、中钙等特征,具低钾系列向高钾钙碱性系列过渡的特征。微量元素具有Ba,Ta,Nb,Sr,Zr,Ti相对负异常,Rb,K,Nb,P,Hf,Y相对正异常特征,接近原始地幔。分布曲线为“海鸥型”分布型式,具“四重效应”特征。稀土含量较低,轻重稀土分馏中等,轻稀土分馏明显,重稀土分馏不明显,分布曲线为右倾型,呈“V”型谷状。成因类型为分异变质成因伟晶岩,为NYF型。形成于俯冲增生阶段,处于挤压环境,构造活动强烈,不利于流动性很强的熔体-流体稳定,不易形成稀有金属伟晶岩矿床。

Altai is the most important pegmatite distribution area in my country and the world.As an independent deposit type,pegmatite is of great significance in the study of mineral deposits.In this study,the Burjin donggelei pegmatite and Qinghebei pegmatite in the western part of the Altai orogenic belt were selected as the research objects,and the LA-ICP-MS zircon U-Pb age was obtained as(343.7±1.7)Ma,which is the Early Carboniferous Pegmatites are the products of the Hercynian movement.Geochemical characteristics show that pegmatites are characterized by rich silicon,peraluminum,medium alkali and medium calcium.It has the characteristics of transition from low-potassium series to highpotassium calcium-alkaline series.The trace elements have relatively negative anomalies of Ba,Ta,Nb,Sr,Zr,and Ti,and relatively positive anomalies of Rb,K,Nb,P,Hf,and Y,which are close to the original mantle.The distribution curve is in the form of a“seagull”distribution,showing the characteristics of a“quadruple effect”.The content of rare earth is low,the fractionation of light and heavy rare earth is medium,the fractionation of light rare earth is obvious,and the fractionation of heavy rare earth is not obvious.The distribution pattern is right-leaning.Showing a“V”shaped valley.Its genetic type is differential metamorphic pegmatite,which is NYF type.Formed in the subduction and accretion stage,it is in an extrusion environment,and the tectonic activity is strong,which is not conducive to the stabilization of the melt-fluid with strong fluidity,and it is not easy to form rare metal pegmatite deposits.