广西米场花岗岩及其暗色微粒包体的地球化学特征和成因分析  

Geochemistry and Genesis of Michang Granites and Their Dark Microgranular Enclaves in Guangxi

作　　者：付强[1] 葛文胜[1] 温长顺[1] 蔡克勤[1] 李世富[2] 张志伟[1] 李小飞[1] 

机构地区：[1]中国地质大学(北京),北京100083 [2]广西第六地质队,广西贵港537100

出　　处：《地球学报》2011年第3期293-303,共11页Acta Geoscientica Sinica

基　　金：广西壮族自治区地质矿产勘查开发局"广西陆川县米场钨钼矿床控矿因素;富集规律与成因机制研究"(编号:地勘【2006】);中国地质调查局项目(编号:200811008)联合资助

摘　　要：本文对博白-岑溪断裂带西南段的米场黑云母花岗岩体及其包体进行了岩石学和地球化学研究。结果表明,米场黑云母花岗岩体暗色包体广泛分布,暗色包体中发育有碱性长石斑晶、暗色镶边的眼球状石英、针状磷灰石和包裹有内环带的斜长石等。寄主岩及暗色包体两者都为准铝质、高钾钙碱性系列岩石,其主要氧化物含量在Harker图解中多呈直线变异趋势,反映了两者具有密切的亲缘关系;两者都富含大离子亲石元素和高场强元素,花岗岩的Nb/Ta比值11.51～13.34高于下地壳8.3,反映了岩体侵位前受过幔源物质的混染;其稀土元素的配分模式基本一致,也反映了岩浆的同源特征;用锆石饱和温度计和角闪石铝压力计估算了包体和寄主花岗岩结晶的温度和压力,结果表明两者的结晶温度和压力相近,分别在618～697℃和(3.64～4.61)×108Pa范围内。对包体及其寄主花岗岩的岩石学、地球化学特征和产出构造环境的综合分析表明,该岩体中的暗色微粒包体是在伸展的大地构造背景下,底侵的幔源岩浆与其诱发的壳源酸性岩浆混合作用的产物。The biotite granite on the southwestern margin of Bobai-Cenxi faulted zone contains abundant mafic magmatic enclaves. The pluton exhibits excellent evidence for magma mixing and mingling, such as the K-feldspar megacrysts in the mafic magmatic enclaves （MME）, augen quartz with dark edging, long prisms of apatite, and plagioclase with inner zone. The authors systematically studied petrological and geochemical charac- teristics of the pluton and the enclaves, and have concluded that the Michang pluton and the enclaves belong to meta-aluminous, high-K calc-alkaline rocks. The selected major oxides of MME and biotite granite show a linear correlation in Harker diagrams, and trace elements studies show that they are rich in both large ion lithophile elements and high field strength elements. The Nb/Ta ratio varies from 11.51 to 13.34, suggesting that the grantie probably experienced strong magma mixing. The similar REE pattern for MME and biotite granite gives an image of magma mixing; the crystallization temperature and pressure of enclaves and host granite are very close to each other, in the range of 595 - 697 ℃ and 3.64 - 4.61 kbar respectively. According to a comprehensive analysis of their tectonic settings as well as petrographical characteristics and geochemical data, it is suggested that the dark microgranular enclaves in Michang pluton were generated by mixing of underplating basic magma and its induced crustal felsic magma in an extension environment.

关 键 词：暗色包体 岩浆混合作用 地球化学 云开台隆 广西 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]