华北古陆块北缘退变榴辉岩的矿物化学与退变质作用  

RETROGRADED ECLOGITES ON THE NORTHERN MARGIN OF NORTH CHINA CRATON, HEBEI PROVINCE, CHINA:MINERAL CHEMISTRY AND RETROGRESSIVE METAMORPHISM

作　　者：倪志耀[1] 翟明国[2] 王仁民[3] 童英[3] 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]中国科学院地质与地球物理研究所,北京100029 [3]北京大学地球与空间科学学院,北京100871

出　　处：《矿物学报》2004年第4期381-390,共10页Acta Mineralogica Sinica

基　　金：国家自然科学基金重点项目(批准号:40234050);中国科学院知识创新工程项目(批准号:KZCX1-07)

摘　　要：华北古陆块北缘退变榴辉岩呈透镜状产于角闪岩相变质的早元古宙红旗营子群黑云斜长片麻岩中,岩相学研究显示它经历了峰期榴辉岩相、减压过程中的高压麻粒岩相和角闪岩相变质作用。峰期榴辉岩相的矿物组合为石榴子石、绿辉石、金红石和石英等,变质条件为680～730℃和大于1 40～1 50GPa。在退变质早期,绿辉石分解形成钠质透辉石和斜长石(An=20 4～30 7)的蠕虫状后生合晶,榴辉岩转变成高压麻粒岩;晚期的退变质作用表现为高压麻粒岩相矿物组合转变成由钙质角闪石和斜长石(An=31 6～54 8)组成的角闪岩相矿物平衡共生组合。在结构上,主要表现为石榴子石颗粒边部的次变边、保留石榴子石假象的粒状后生合晶和保留辉石假象的蠕虫状后生合晶等,其变质温压条件为530～610℃和0 67～0 81GPa。The retrograded eclogites on the northern margin of the North China Craton occur as tectonic lenses within biotite-plagioclase gneisses in the Paleoproterozoic Hongqiyingzi Group characterized by amphibolite-facies parageneses. Petrographic studies revealed three main metamorphic stages: peak eclogite facies stage, high-pressure granulite facies stage and amphibolite facies stage during decompression. During the peak eclogite facies　stage of metamorphism, the eclogites had Ca-rich garnet+omphacite +rutile quartz assemblages and　must have equilibrated at 680-730 ℃ and more than (1.40-1.50)　GPa. Subsequently, during the early stages of decompression and continuing deformation, plagioclase exsolved from the omphacite to give rise to granulite facies fine-grained vermicular symplectite of sodic　diopside and plagioclase　(An=(20.4)-30.7). And garnet and sodic diopside　were variably recrystallised to give rise to the amphibilite facies mineral assemblages of pargasite,hornblende or tschermakite and plagioclase(An=31.6-54.8)that characterized by　kelyphitic rim around garnet, granular symplectite and vermicular symplectite.The geothermometry of the amphibolite facies assemblages suggests the conditions of 530-610℃　and 0.67-0.81 GPa.

关 键 词：高压麻粒岩 角闪岩 退变榴辉岩 退变质作用 岩相 绿辉石 石榴子石 GP 蠕虫 钙质 

分 类 号：P588[天文地球—岩石学] P571[天文地球—地质学]