辽南小黑山地区太古宙构造变形序列

The Archaean Deformation Sequence in Xiaoheishan Area,Southern Liaoning,China

采用地质调查和显微镜下观察方法,研究了辽南小黑山区太古宙岩石组成和构造变形特征。小黑山区太古宙岩石包括上壳岩、古老片麻岩和变基性岩脉,它们在小黑山变质岩体中呈包体出现。上壳岩由黑云变粒岩、条带状闪石磁铁石英岩组成;古老片麻岩为条带状角闪黑云斜长片麻岩、条带状角闪斜长片麻岩,原岩为英云闪长岩;变基性岩脉为斜长角闪岩和角闪石岩。上壳岩堆积之后有英云闪长岩侵位,基性脉侵位于上壳岩和英云闪长岩(古老片麻岩)。小黑山区太古宙岩石经历了2幕变形:D1幕变形主要表现为褶皱构造(DF1)、与褶皱轴面平行的面理(DS1)、矿物线理(DL1);D2幕变形在叠加褶皱作用下形成斜歪倾伏褶皱(DF2),面理和线理不发育。小黑山区太古宙变质岩中发育的变形序列、构造特征、变形特征、变质条件表明,这2幕构造形迹群属于中部构造相。D1幕变形形成逆冲推覆构造,D2幕变形形成第Ⅲ型叠加褶皱,它们都是在同方向的水平挤压应力作用下的产物。

The components and deformation characteristics of Archaean rocks in Xiaoheishan area,southern Liaoning were studied through the field investigation and microscope observation.The Archaean rocks are composed of supracrustal rocks,gneisses and metamorphic mafic veins,which appears as enclaves in Xiaoheishan metamorphic plutons.The supracrustal rocks consist of biotite granulite and banding hornblende magnetite quartzite.The gneisses are composed of banding hornblende biotite plagioclase gneisses and banding hornblende plagioclase gneisses,their protolith was tonalite.Metamorphic mafic veins consist of plagioclase amphibolite and hornblendite.After supracrustal rocks deposited,into which the tonalite intruded,and then mafic veins intruded into the supracrustal rocks and tonalite（gneisses）.Plagioclase amphibolite contains enclaves of hornblendite.The Archaean rocks underwent two episodes of deformation.The first episode of deformation formed folds（DF1）,foliations（DS1） in parallel with axial-plane of the folds and lineations（DL1）.The second episode of deformation only formed inclined plunging folds（DF2） by superposed folding without foliations and lineations.Deformation sequence,features of structure and deformation in the Archaean metamorphic rocks show that the two episodes of the deformations should occurred in the setting of middle tectonic level.The first deformation formed nappe structures,and the second episode formed Ⅲ type superposed folds by horizontal compressing in the same direction.