内蒙古阿拉善地区前寒武纪变质基底阿拉善群的再厘定  

Redefinition of the Alxa Group-complex (Precambrian metamorphic basement) in the Alxa area, Inner Mongolia

作　　者：耿元生[1] 王新社[1] 沈其韩[1] 吴春明[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《中国地质》2006年第1期138-145,共8页Geology in China

基　　金：中国地质调查局地质大调查项目(199913000006)资助。

摘　　要：原划分的阿拉善群包含了时代、成因各异、构造样式有别、变质程度不同的变质地层和变形深成片麻岩体。作为一个岩石地层单元已不合适,应予解体并重新厘定。根据目前的研究,原阿拉善群可划分成3套变质地层单元和两个变形深成片麻岩杂岩。本区最古老的岩石地层单元为迭布斯格岩群,由深变质的变质表壳岩系组成,是区内的基底岩系。初步的锆石SHRIMPU-Pb年代学研究表明,它们形成于27亿年左右,属于新太古代。新建立的巴彦乌拉山岩组主要由变质火山岩组成,是区内的火山岩系。目前获得的年龄为2264Ma和2271Ma,属于古元古代。重新厘定的阿拉善岩群主要由变质碎屑岩和变质碳酸盐岩组成,是陆缘沉积岩系,形成于古元古代晚期或更晚。波罗斯坦庙英云闪长质-花岗质片麻岩杂岩,由早期的英云闪长质片麻岩和晚期的花岗质片麻岩组成。早期英云闪长质片麻岩形成于18亿年左右,晚期的花岗质片麻岩大致形成于古生代期间。毕及格台花岗闪长质片麻岩杂岩主要由角闪斜长片麻岩、黑云斜长片麻岩等组成,初步的同位素年龄测定结果显示它们的主期形成于8￣10亿年的晋宁期。The original Alxa Group-complex consists of metamorphic strata and deformed orthogneisses of different ages, geneses, tectonic styles and metamorphic grades; so it is not suitable for a lithostratigraphic unit and should be disintegrated and redefined. Based on recent studies, the original Alxa Group-complex may be divided into three metamorphic stratigraphic units and two deformed orthogneiss complexes. The oldest lithostratigraphic unit in the area is the Diebusige Group-complex, which consists of high-grade metamorphic supracrustal rocks and is the basement rock series in this area. Preliminary zircon SHRIMP U-Pb dating suggests that the Diebusige Group-complex formed at -2700 Ma and is considered to be of Neoarchean age. The newly established Bayan U1 Formation-complex, which is principally composed of metavolcanic rocks, is a volcanic rock series in this area. Its newly obtained ages are 2264 and 2271 Ma, indicating a Paleoproterozoic age. The redefined Alxa Group-complex, which consists predominantly of meta-clastic rocks and meta-carbonate rocks, is a continentalmargin sedimentary series and formed in the late Paleoproterozoic or still later. The Boluosutanmiao tonaliticgranitic gneiss complex is composed of early-stage tonalitic gneiss and late-stage granitic gneiss. The early-stage tonalitic gneiss formed at -1.8 Ga and the late-stage granitic gneiss formed approximately during the Paleozoic. The Bijigetai granodioritic gneiss complex is mainly composed of hornblende-plagioclase gneiss and biotite-plagioclase gneiss and the preliminary isotopic dating indicates that the main stage of this complex occurred in the Jinningian at 0.8-1 Ga.

关 键 词：阿拉善岩群 前寒武纪 再厘定 内蒙古阿拉善地区 

分 类 号：P534.1[天文地球—古生物学与地层学]