广西钦甲花岗岩体岩石地球化学特征及成因研究

华南地区加里东期花岗岩远不如燕山期那么发育,位于广西西南部的钦甲岩体是较为著名的加里东岩体之一。钦甲岩体位于扬子板块西南缘,属早古生代花岗岩体。本文在前期年代学研究的基础上对钦甲岩体的岩石地球化学特征进行了分析探讨,其SiO2含量为65.94%~72.23%,全碱含量(K2O+Na2O)为6.27%~9.11%,K2O的含量普遍大于Na2O,A/CNK值为1.02~1.24,属弱过铝质花岗岩类。岩石稀土元素含量偏低,变化范围为17.18×10-6~128.33×10-6,其配分曲线呈轻稀土富集并缓向右倾斜、重稀土较为平坦、具较明显的铕负异常。微量元素以富集大离子元素Rb、Th,亏损Ba、Sr为特征,其形成可能和扬子板块与华夏板块之间的汇聚挤压有关,其源岩主要由含少量泥质的砂质岩组成,并可能有具Ce负异常的沉积物参与部分熔融。

Geochemistry and petrogenesis of the Qinjia granite in Guangxi

The Caledonian granites in South China are not so well developed as Yanshanian granites,and the Qinjia granite in southwest Guangxi is one of the famous Caledonian granites.The Qinjia granitoid pluton,located at the southwestern edge of Yangtze plate,is a typical Early Paleozoic pluton.Based on previous research result of geochronology,the authors performed a lot of detailed work on geochemistry.The SiO2 content of rocks is in the range of 65.94%～72.23%, the total alkalis content(K2O+Na2O) is in the range of 6.27%～9.11%,and the K2O content of most rocks is higher than Na2O content.The A/CNK values are 1.02～1.24,assigned to species of weakly peralumious.The rocks have low and remarkably varying REE,ranging from 17.18×10-6 to 128.33×10-6,and their distribution patterns show LREE enrichment with gentle rightly-oblique deviation,relatively flat HREE and significant negative Eu anomaly.In trace elements,the Qinjia pluton is enriched in LILE Rb,Th and depleted in Ba,Sr.The research results show that the formation of Qinjia granite was probably linked with the collision between Yangtze plate and Cathaysia plate,and the source rocks of Qinjia granite were mainly composed of politic sandstone rocks,and some sediments with negative Ce anomalies probably entered magma source.