新疆拜城县波孜果尔A型花岗岩类矿物学特征及岩浆形成的温度条件

Mineralogy and temperature of magma generation for A-type granitoids in Boziguoer,Baicheng County,Xinjiang

新疆拜城县波孜果尔A型花岗岩类为富含铌、钽、锆等有用元素的含矿岩体。通过偏光显微镜、电子探针（EPMA）化学成分分析、电子探针背散射（BSE）对波孜果尔A型花岗岩类的矿物学特征进行了研究,并对岩浆形成的温度条件与构造背景进行了讨论。结果表明,波孜果尔A型花岗岩类包括霓石钠闪石英碱性长石正长岩、霓石钠闪碱性长石花岗岩、黑云母碱性长石正长岩3种岩石类型。主要造岩矿物包括石英、钠长石、钾长石、霓石、钠铁闪石和铁叶云母。副矿物包括锆石、烧绿石、钍石、萤石、独居石、氟碳铈镧矿、磷钇矿等。岩浆平均温度832~839℃,形成于非造山的板内构造环境,且具高温、无水、低氧逸度的成岩特点。

The Boziguoer A-type granitoids in Baicheng County of Xinjiang are ore-bearing rocks with abundant useful elements such as Nb,Ta and Zr.The petrological and mineralogical characteristics of the A-type granitoids were investigated on the basis of observation under polarized microscope,chemical analysis and detailed BSE images using EPMA,followed by the discussion on the p-T conditions of A-type magma generation and the tectonic setting.The results indicate that these A-type granitoids could be divided into three types,namely aegirine arfvedsonite quartz alkali feldspar syenite,aegirine arfvedsonite alkali feldspar granite and biotite alkali feldspar syenite.The major rock-forming minerals are quartz,albite,K-feldspar,aegirine,arfvedsonite and siderophyllite,whereas the accessory minerals include mainly zircon,pyrochlore,thorite,fluorite,monazite,bastnaesite and xenotime.The average temperatures of the magma are 832～839℃.A-type granitoids might have been formed in an anorogenic intraplate tectonic setting by which they generally show such features as hightemperature,anhydrous nature and low fugacity.