内蒙苏尼特右旗吉布胡楞土岩体LA-ICP-MS锆石U-Pb定年、地球化学特征及地质意义

在华北板块北缘白乃庙岛弧岩浆活动带中发现了一套石榴石白云母花岗岩。锆石LA-ICP-MS U-Pb定年结果显示,该石榴石白云母花岗岩的结晶年龄为(500.8±2.4)Ma,为晚寒武世岩浆活动的产物。主量元素岩石地球化学特征方面:该岩体富硅、铝(w(SiO₂)=72.50%~74.11%;w(Al₂O₃)=14.73%~16.43%),贫铁、镁、钙(w(TFeO)=0.67%~1.14%;w(MgO)= 0.09%;w(CaO)=0.30%~0.61%),为高分异花岗岩(分异指数DI=91.99~93.20);铝饱和指数均大于1.1,发育富铝矿物石榴石和白云母,为过铝质花岗岩,但并非S型花岗岩;综合认为该石榴石白云母花岗岩是一套富铝、贫铁镁钙的高分异钙碱性I型花岗岩。微量元素特征方面:稀土总量较低,轻重稀土分馏不明显,具有强烈的负Eu异常;具明显的稀土元素四分组效应;并且部分岩石样品的Nb、Ta含量较高,暗示该岩体是分异岩浆与流体作用的产物。该岩体可为Nb、Ta等稀有金属成矿提供必要的物质基础。

Zircon LA ICP MS U Pb Dating,Geochemistry of the Jibuhulengtu Garnet-Bearing Muscovite Granitic Pluton in Mongolia and Its Geological Significance

There is a set of garnet-bearing muscovite granite in Bainaimiao island arc magmatic active belt that belongs to the northern part of the North China Craton.The Zircon LA ICP MS U Pb dating yields weighted mean 206 Pb/238 U age of (500.8 ± 2.4)Ma,indicating that the garnet-bearing muscovite granite was formed during the Late Cambrian.The petrogeochemistry is characterized by rich in Si,Al(w (SiO2 )=72.50% 74.1 1%,w (Al2 O3 )= 14.73% 1 6.43%)),poor in Fe,Mg and Ca (w (TFeO)= 0.67% 1.14%,w (MgO)= 0.09%,w (CaO)= 0.30% 0.61%).The garnet-bearing muscovite granite is highly differentiated with its DI of 91.99 93.20,the Shand Indexes of the garnet-bearing muscovite granitesare higher than 1.1,typical for high aluminum minerals,like garnet and muscovite. They are not S-type granite, but highly differentiated-Calc alkaline granite. The petrogeochemistry of rare earth element is characterized by low REE with strong depletion of Eu, showing a tetrad REE pattern.Some samples are rich in Nb,Ta,which indicates that the pluton was formed by magma differentiation and magma-fluid interaction.This pluton provided the necessary material foundation for other rare metal mineralization,such as Nb,Ta.