摘要
内蒙古大青山地区是华北克拉通北缘早前寒武纪变质杂岩发育地区，也是高级变质地层发育地区。多年来，对该区早前寒武纪变质地层的组成和划分一直存在着争议。近几年来，作者以相同或相似的岩性组合为基本填图单位，以变形变质作用特征的研究为主线，结合岩浆活动作用、原岩建造等方面的研究，通过对内蒙古大青山地区的６幅 １∶５万区域地质调查，提出自该区早前寒武纪变质地层自下而上可划分为古太古代兴和岩群、中太古代乌拉山岩群和古元古代美岱召岩群３个岩群，并进一步划分为８个岩组。其中兴和岩群和乌拉山岩群均遭受了麻粒岩相－高角闪岩相条件下的多期强烈的变形变质作用改造，并相互参差交错地共生在一起。详细地构造解析结果表明，兴和岩群和乌拉山岩群均遭受到一期下地壳麻粒岩相环境下的近水平剪切变形和高角闪岩相条件下的近南北向和近东西向纵向构造置换作用的改造。早期近水平剪切导致乌拉山岩群的各个地层单元以透镜状岩片叠置于兴和岩群之上，后期纵向构造置换作用导致兴和岩群和鸟拉山岩群的不同地层单元沿现存叶理相互穿插，造成以现存叶理为标志的“假互层”或“假夹层”。美岱召岩群为一套浅变质的碎屑沉积岩系，仅遭受绿片岩相变质，变形特征也不同于乌拉山岩群。
Early Precambrian metamorphic complex and also high - grade metamorphic strata are well - developed in Daqingshan area in the northern margin of North China craton. But the composition and division of the early Precambrian metamorphic strata have been disput-ing for many years. In recent five years, 1∶ 50 000 geological mapping with mapping uint of the same or similar rocks reveals that the early Precambrian metamorphic strata may be divided into Palaeoarchean Xinghe rock group, Mesoarchean Wulashan rock group and Palaeoprotero-zoic Meidaizhao rock group from lower to upper, of which Xinghe rock group and Wulashan rock group were overlapped and paragenesised by strongly poly - deformation and metamor-phism under granulite - high amphibolite facies. All the Xinghe Rock group and Wulashan rock group are deformed by an early near horizontal and bedding parallel ductile shearing and later near N - S trending and near E - W trending deformation. The deformation results in a stratigraphic sequence charac teried by 'stratigraphic breaking, contact and intercalation of different uints'. Meidaizhao rock group is a series of clastic rocks lowly metamorphismed with green-schist facies and unconformatially overlies on the high grade metamorphic complex composed of Xinghe rock group Wulashan rock group and metamorphosed plutonic intrusions into the supracrustal rocks above.
出处
《世界地质》
CAS
CSCD
2001年第3期209-218,共10页
World Geology
关键词
大青山地区
早前寒武纪
变质地层
内蒙古
变质作用
Daqingshan area
early Precambrian
metamorphic strata
near horizontal shearing
