Problem genezy granodiorytów zawidowskich oraz gnejsów granodiorytowych z okolic Grabiszyc i Leśnej (Sudety Zachodnie)

Abstract

ORIGIN OF THE ZAWIDÓW GRANODIORITES AND OF GRANODIORITE GNEISSES FROM TBIE GRABASZYCE AND LEŚNA AREAS (WEST SUDETES)SummaryThe authors of the present paper substantiate the existence of a common original rock environment that has been responsible for the formation of granodiorite gnesses and, consequently, for the Zawidów granodiorites. Although M. Kozłowska-Koch (1965, p. 201) suggests a common original environment of these rocks, she is still of the option that the granodiorite gneisses (the so-called dark gneisses from Leśna) are dynamically altered Zawidów granodiorites.Moreover, the authors give a detailed petrological description of both the granodiorite gneisses and the Zawidów granodiorites, and ascertain that although these rocks are characterized by a common original environment, their alteration mode and genesis are different from those given by M. Kozłowska-Koch (1965, p. 201). According to the present authors, a geosynclinal clay-sand-greywacke formation existed in the area of the present Zawidów granodiorites and granodiorite gneisses, i.e. in a continuation of the third (in the lzera block) mica schist belt, eastwards and westwards, as well as north of it. The rocks of this formations underwent regional metamorphic processes, and gave rise to the granodiorite gneisses.In various parts of the area, metamorphosis was of various character. Studying the relicts, and comparing the mineral associations  found in them with those obtained by H. Winkler and H. v. Platen (1958, 1959, 1960, 1961) during an experimental metamorphosis of sedimentary rocks, the present authors have deduced a hypothetic lithological composition of original deposits. Furthermore, in the area here considered, they have ascertained the presence of the regional metamorphosis of greenstone facies and of higher facies, up to anatectic alterations inclusive (this latter has been responsible for the formation of granodiorite gneisses). In addition, they have observed the presence of strong post-crystalline deformations and of the later metasomatic regeneration of the dynamically altered formations. This process as expressed in the form of potassium and sodium features. Each of them is responsible for a regrouping in mineral composition of the altered rocks, appearing in various parts of the area with different intensity.Potassium metasomatos is gave the best effects in the eastern part of the area, causing alteration of gneisses into coarse-grained porphyraceous granites called by J. Oberc (1965) and M. Kozłowska-Koch (1965, p. 201) the Rumburk granites. Sodium invasion is best developed in the western part of the Izera block. It has been responsible for the alteration of gneisses into, the distinctly homogeneous Zawidów granodiorites.