从五台山下前寒武系变形特征论某些构造形迹的运动学意义

分布在五台山区的早前寒武纪五台群和滹沱群,遭受了多期变形和变质,小型构造发育。层理配置反映变形性质和程度;片理(劈理)为早世代挤压-剪切褶皱的轴面片理,又成为晚世代弯滑褶皱的滑动面;线理(压扁拉长的砾石、杏仁体和矿物集合体)垂直于早世代褶皱枢纽,为a线理;这一运动学特征在显微组构中亦有反映。本区发现了“折射变位”、“非共面反射变位”和“共面反射变位”等褶皱枢纽变位轨迹。上述构造形迹可为运动学分析提供依据,可对造山带的重要性质获得广泛的理解。

ON KINEMATIC SIGNIFICANCE OF SOME STRUCTURAL FEATURES IN VIEW OF DEFORMATION FEATURE OF THE LOWER PRECAMBRIAN IN WUTAI MOUNTAIN

The early Precambrian Wutai Group and Hutuo Group of the Wutai Mountain region underwent multiple deformation and polymetamorphism; from subgreenschist fades to amphibolite fades. Small-scale structures (planar and linear fabrics and minor folds) are developed there as those preserved in the deformed and metamorphosed early Precambrian terrains elsewhere.The bedding furnishes an internal marker whose geometric confinguration reflects the nature and degree of deformation. The cleavage and schistosity acted as an axial plane role in the early generation of compressed shear fold, and changed into a slip plane in the later generation of flexural slip fold. The kinematic significance of some linear fabrics, such as elongated pebbles and mineral streaks, is still under discussion, In the Wutai Group, the flattened and elongated pebbles from the metaconglomerate, the amygdales from meta-basalt and some mineral aggregates are all perpendicular or nearly perpendicular to the hinge of early generation minor fold, indicating that these linea-tions display the a-axis of kinematic coordinate in the early deformation of each tectonic stage. This property is reflected more or less in the microscopic fabrics.Some new types of displacing path of fold hinge are discovered in the Wutain Mountain region, including "refracted displacement", "non-planar reflected displacement" and "co-planar reflected displacement".All these features can ben used as evidences of kinematic analysis.Apparently correct understanding and interpertation of small-scale structural features can help us to get a much more comprehensive understanding of major features of an orogenic belt.A thorough investigation of structural features provides foundamental gro-ds for kinematic analysis.