Podział B-lineacji tektonicznej na podstawie badań w Sudetach

Józef Oberc, Jerzy Kotowski

Abstract


Classification of tectonic B-lineation based on studies in the Sudety Mts.

No comprehensive classification of B-lineation has been presented hitherto in the geological literature (see references). The present authors propose the first 'classification of the B-lineation, based upon their observations in the Sudetes Mts. This classification takes into account the following features: geometric form (Fig. 1), size, time-relation to movement (Fig. 5) material (Fig. 8), geometric relation to foliation surfaces (Fig. 9), intersection of various S-surfaces (Fig. 11) and origin (Fig. 12). The classification distinguishes furthermore: mono-B-lineation. poli-B-lineation (composite), and superimposed B lineation (Fig. 13). A detailed explanation of some new proposed terms is given below. Various types of Imeations are designated by symbols shown on schematic diagrams. The symbols are derived from English terminology. They can be useful for detailed descriptions of tectonic phenomena. Post-dieformational elongated rock bodies (neo-enclaves, or recrystallization enclaves) with long axes (r) concordant with the direction of the background, are produced by reorystallization in rocks forming in parakinematic conditions. J. Obere and J. Kotowski (1969, p. 124). interpreted such bodies of the Rumburg granite within the Izera Mts gneisses, as farmed by reorystallization which was most active along. B-lineation of older tectonites (Fig. 6). Relics of older tectonites within the recrystallized rock bodies are elongated according to B-lineation (Fag. 7 Polish text) and their internal structure is consistent with analogous lineation in mantle rocks of the recrystallized bodies. The lineation consists of linear elements. The authors consider as a linear element single elongated forms, more or less distinctly delimited from the background, and consisting of single mineral grains or of mineral aggregates. The linear elements can be simple — when they consist of a grain or of grains of one mineral species, or composite — when they consist of various mineral species. Thus the lineation is set of linear elements having the same orientation in space, and occurring most frequently side- by side. Edges (p) farmed by intersection of S-surfaces of various types (Fig. 11) are considered as linear elements. A set of such edges concordant with the coordinate should be considered as B-lineation. The so-called copied lineation (co) is a hitherto unknown type of B- -lineation. It was observed in the Zawidów granodiorite at Zawidów. Mesoscopic enclaves of shists occurring in thiis metamorphio granodiorite display in some cases distinct crenulation on the surfaces. The surfaces separating the mesoscopieally isotropic granodiorite from the schists show a lineation which is a copy of the crenulation on the surface on the schists. (Fig. 10 Polish text). Mono-B-lineation (mBl) is defined by the present authors as a single- -type lineation, produced during one phase of deformation. This type of lineation is present chiefly 'in sedimentary rocks, as crenulation and mesoand macroscopic folds. Poli-B-lineation (pBl composite) is present usually in metamorphic rocks. This term designates several types of B-lineation within a bed, produced 'during one phase of deformation and arranged parallel (Fig. 14 Polish text). Superimposed B-lineation (sBl) represents an assemblage of lineations within a bed of a definite rock type, formed during two or more phases of evolution. Two cases are possible: the lineations of different age are either parallel or oblique, and in extreme cases, even perpendicular to each other. Other terms used in the diagrams are known generally and need no special explanations.

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