Analiza mezoskopowa lineacji biotytu w gnejsach izerskich
Abstract
Mesoscopic analysis of lineation of biotites in the Izera gneisses
A B-lineation of biotite is one of mesoscopic features observed at the surfaces of gneisses resulted from parakinematic giranitization within metamorphic complex of the Izera Mts. (Lower Silesia). It is developed in the form of equilineair accumulates of plates (fig. 1) corresponding to poly-B-lineation (Oberc, Kotowski , 1971). The latter consists of several partial lineations of biotite. Special orientation of partial lineations is different when related to coordination system. It is resulted from translation displacements mainly in the ab surface. Equilinear biotite accumulates are oriented parallel with other parakinematic lineations represented by anastomosic feldspar-quartz and feldspar aggregates. Biotite accumulates occurring at the margins of discoidal feldspar grains display irregular orientation. They are curvilinear. Partial lineation resulted from translation shows differentiated relative displacement of biotite plates. These displacements display variable directions in regard with lineation (fig. 3). Biotite plates occurring near linear feldspar poiphyroblasts on the foliation planes show different displacement paths (fig. 4). In gneisses containing discoidal feldspars partial lineation of biotite exhibits radial distribution (fig. 6, 7 and 8). Partial lineation of biotite shows some features of A-lineation, characterized by ^considerable directional dispersion.
A B-lineation of biotite is one of mesoscopic features observed at the surfaces of gneisses resulted from parakinematic giranitization within metamorphic complex of the Izera Mts. (Lower Silesia). It is developed in the form of equilineair accumulates of plates (fig. 1) corresponding to poly-B-lineation (Oberc, Kotowski , 1971). The latter consists of several partial lineations of biotite. Special orientation of partial lineations is different when related to coordination system. It is resulted from translation displacements mainly in the ab surface. Equilinear biotite accumulates are oriented parallel with other parakinematic lineations represented by anastomosic feldspar-quartz and feldspar aggregates. Biotite accumulates occurring at the margins of discoidal feldspar grains display irregular orientation. They are curvilinear. Partial lineation resulted from translation shows differentiated relative displacement of biotite plates. These displacements display variable directions in regard with lineation (fig. 3). Biotite plates occurring near linear feldspar poiphyroblasts on the foliation planes show different displacement paths (fig. 4). In gneisses containing discoidal feldspars partial lineation of biotite exhibits radial distribution (fig. 6, 7 and 8). Partial lineation of biotite shows some features of A-lineation, characterized by ^considerable directional dispersion.