白银厂矿区劈理成因的磁组构分析

MAGNETIC FABRIC ANALYSIS OF THE CLEAVAGES ORIGIN IN BAIYINCHANG MINING DISTRICT,GANSU

将磁性组构方法用于甘肃白银厂矿区的构造分析.结果表明该区岩石的磁性组构与岩石组构具有同一分布规律.岩石的磁线理与岩石的拉长线理L^a近于一致,磁面理与第一期劈理S_1基本平行,并垂直于岩石的磁化率椭球的最小主轴,也垂直于应变椭球的最短主轴方位,故推断第一期劈理S_1的成因主要属压扁成因.同时受到后期的多次变形与褶皱迭加影响.S_1轴面的优选面状分布发生变位不大,表明该区多次构造变形主要来自早期的同一主应力场作用所致.矿区岩石的磁面理与应变椭球拉长轴面或第一期劈理面S_1存在某些的角度差,表明该区岩石的劈理面由于受后期多次构造变形影响,可能发生剪切运动或旋转机制.

Magnetic fabric methods are used in the structure analysis in Baiyinchang mining district, Gansu. It is shown that the Magnetic fabric and pctrofabric possess coincident distribution characteristics. Magnetic lineations are coincident with stretched lineation (La 1) in rocks, and foliations of magnetic fabric are parallel to the first stage cleavage (S,), and are vertical to the directions of minimum axes of strain ellipsoids or the minium axes of susceptibility ellipsoids. It is deduced that the main origin of the first stage cleavages in rocks is oblated by compressive stress, and is affected by the superimpposition of the later metamorphism and structural deformation. The directions of preferred orientation of the axial plane of the first stage cleavages (S1) in rocks have got very little variation, it is shown that all metamorphism and structural deformation is arised from the early stage principal stress field in the district, but it is varied or rotated from the structural deformations of later stages in certain degree.