贺兰山——阿拉善地区下、中前寒武系的划分对比及其变质、成矿作用特征

THE DIVISION, CORRELATION, METAMORPHISM AND MINERALIZATION FEATURES OF THE LOWER AND MIDDLE PRECAMBRIAN IN THE HELANSHAN MOUNTAIN -ALASHAN REGION, CHINA

据近期成果,贺兰山—阿拉善地区出露的巨厚变质杂岩可划分为中太古界贺兰山群和叠布斯格群(其全岩Rb—Sr等时年龄为3108.3和3218.8Ma),上太古界阿拉善群和下元古界的赵池沟群、阿拉坦敖包群;它们具不同的变质矿物共生组合,太古界变质岩属低压高温变质的麻粒岩相;下元古界为低—低中压区域动力(热流)变质的绿片岩相岩石。太古界有较强的混合岩化、花岗岩化作用,并蕴藏有铁、石墨、矽线石、刚玉等多种矿产。

In the Helanshan Mts. -Alashan region there are well exposed metamorphic complexes of the lower and middle Precambrian of more than 20000m thick. Based on the data obtained in recent years, the lower-middle Precambrian of the Helanshan Mts.can be divided into the middle Archean Helanshan Group and the lower Proterozoic Zhaochigou Group and thous of Alashan Region, into the middle Archean Diebusige Group,the upper Archean Alashan Group and the lower Proterozoic Alatan aobao Group.The Helanshan Gr.consists of various gneisses,granulites and their megmatites, with the lower part giving an isochron age of 2056.1Ma.The rocks are assigned to granulite metamorphic facies of regional hith temperature metamorphism of low pressure metamorphic facies and most of its upper part are assigned to amphibolite facies.The rocks of Zhaochigou Gr.are dominantly composed of mica-bearing quart-zite biotite-granulite belonging to green schist facies of regional kinetic metamorphism of low-median pressure metamorphic facies series.The Diebusige Gr.belongs to silliceous ferruginous formation.The Rb-Sr.Whole rock age is 3108.3 Ma-3218.8Ma. The rocks are assigned to granulite facies of regional high temperature metamorphism of low pressure metamorphic facies series.The Alashan Gr. consists mainly of biotite-hornblendegneiss; gabbro intruding in its upper part gives a meta morphic age of 1982Ma. They belong to amphibolite facies of regional high temperature metamorphism of low-median pressure metamorphic facies series.The Alatan'aobao Gr.consists of biotite-gneiss, granulite, muscovite-quartzite, metamorphic conglomerate and marble. The rocks of this Gr.are assigned to green schist facies of regional kinetic thermal metamorphism of low pressure metamorphic facies series.In the metamorphic rocks aboved-memtioned there are iron, muscovite, cystal-line graphite, sillimanite and emery ore deposits.