青藏东缘六合-香多镁铁质深源包体的岩石学和矿物学研究  

STUDY ON PETROLOGY AND MINERALOGY OF MAFIC DEEP-DERIVED ENCLAVES IN LIUHE-XIANGDUOAREA,EASTERN TIBET

作　　者：魏启荣[1] 王江海[2] 

机构地区：[1]中国地质大学材料科学与化学工程学院,湖北武汉430074 [2]中国科学院广州地球化学研究所,广东广州510640

出　　处：《矿物岩石》2004年第1期17-28,共12页Mineralogy and Petrology

基　　金：国家重点基础研究发展规划项目(编号:G1998040807);中科院知识创新项目(编号:KZCX2 SW 117);中国博士后科学基金

摘　　要：　对青藏东缘新生代六合 香多地区高钾岩系中镁铁质深源包体的岩石学和矿物化学成分的详细研究表明:六合 香多镁铁质深源包体为中 下地壳变质岩。包体有5种岩石类型,即石榴透辉岩、石榴斜长角闪岩、石榴角闪岩、斜长角闪岩和角闪石岩,其矿物组合分别为Grt+Di+Hbl,Grt+Pl+Hbl+Di,Grt+Hbl+Pl,Pl+Hbl和Hbl+Bt。包体具中 粗粒变晶结构,退变质作用强烈。石榴石主要为铁铝石榴石(Alm=64.86%～32.93%,Prp=41.80%～4.96%,Grs=35.83%～8.43%),发育后成合晶结构和角闪石冠状体。大颗粒石榴石内部保存有完好的生长环带,边部石榴石和小颗粒石榴石因受高钾岩浆热和流体的强烈改造致使其生长环带已被抹平;辉石为透辉石和次透辉石,富Ca(CaO=19.70%～24.64%)贫Na(Na2O=0.28%～2.72%);角闪石主要为韭闪石;斜长石成分变化大(An=0.90～82.95);云母为金云母(XMg=0.60～0.67),具有高Mg(MgO=14.20%～14.23%)的成分特征。温压估算表明,前3类包体主要来自下地壳,平衡温压较高(720℃～950℃,0.74GPa～1.50GPa);后两类包体主要来自中地壳,平衡温压较低(510℃～735℃,0.60GPa～0.98GPa)。包体属偶然包体,是起源深度大于50km的高钾岩浆在快速上升过程中于20km～50km部位随机俘获的中 下地壳变质岩。Study on petrology and mineral chemical compositions of deep-derived mafic enclaves from high-K igneous rocks in Liuhe-Xiangduo area, eastern Tibet showed that the enclaves belong to metamorphic rocks formed in the mid-lower crust. There are five types of enclaves,garnet diopsidite, garnet amphibolite, garnet hornblendite, amphibolite and hornblendite, whose mineral assemblages are Grt+Di+Hbl, Grt+Pl+Hbl+Di, Grt+Hbl+Pl, Pl+Hbl, and Hbl+Bt, respectively,with medium-coarse granular crystalloblastic texture and regressive metamorphism.Garnet in the enclaves mainly belong to almandite series (Alm=64.86%～32.93%, Prp=(41.80)%～4.96%, and Grs=35.83%～8.43%), and the simplectite and Hbl corona generally occur around the garnet. The garnet growth zoning was well preserved in the mega-porphyritic garnets, but completely erased due to high-K magma heating and fluid action in the rim and in fine-grained garnets.Pyroxenes are diopside and baicalite,enriched in Ca (w_(CaO)=19.70%～24.64%) and depleted in Na (Ww_(Na_2O)=0.28～(2.72)).Hornblende is mainly pargasite of calcic amphiboles. Mica is phlogopite with high Mg (w_(MgO)=14.20%～14.23%). The former three types of xenoliths mainly came from lower crust, whose equilibrium temperatures and pressures were high (720 ℃～950 ℃, and 0.74 GPa～1.50 GPa respectively), and the latter two formed in middle crust, whose temperatures and pressures were low (510℃～735℃, and 0.60 GPa～0.98 GPa respectively). The envlaves in Liuhe-Xiangduo area are middle-lower crust metamorphic rocks accidentally captured in 20 km～50 km depth by rapidly ascending high-K magma, whose source depth is more than 50 km.

关 键 词：青藏东缘 六合-香多 镁铁质深源包体 岩石学 矿物化学成分 

分 类 号：P588.3[天文地球—岩石学]