Selwsbergit z Ciechanowa – peralkaliczny sjenit hipabisalny

Abstract

SELWSBERGITE FROM CIECHANÓW –PERALKALIC HYPABYSSAL SYENITESummaryIn a bore hole at Ciechanów, crystalline rock, resembling macroscopically the pre-Cambrian granite of the crystalline basement of North-East Poland, has been found at a depth of 2494.0 m to occur under the Palaeozoic sedimentary rocks.Examinations of the rock from, Ciechanów have demonstrated that it is selwsbergite (peralkalic hypabysal syenite) that reveals holocrystalline, porphyritic texture with microgranular structure of rock matrix (Table 1, Fig. 4). Its chemical composition (Tables 1, 2, and 3), corresponds to that of peralkalic syenites where sodium character is expressed by the ratio of atomic numbers Na:K = 3: 1 (Figs. 2 and 3). The character of texture proves a hypabyssal form and stresses the lack of any relation to the older crystalline basement. An early completion of the drilling made at Ciechanów did not allow the authors to determine either the macrostructure of the rock body considered or its thickness. Petrographical examinations suggest a vein form here, and its chemical character and petrographic-structural features correspond to those of selwsbergirte (A. Johannsen, 1949).The genesis of the selwsbergite from Ciechanów should he referred to the Palaeozoic volcanic activity, where Na prevailed over K. Thus, we may draw a conclusion as to the comagmatic nature of the rock from Ciechanów as compared with other vein formations known from various stiratigraphical periods of Palaeozoic (M. Juskowiak, O. Juskowiak, W. Ryka, 1967; Z. Gumowska, M. Juskowiak, 1969).These formations developed due to the activity of the younger tectonic movements that affected and agitated the alkalic magma (O. Juskowiak, W. Ryka, 1967).The long-lived metamorphic-magmatic processes frequently end with sodium magmatic rocks. They are known to occur within the platform areas, where they constitute their younger structural elements, as for example in the area of Azof plate, Kola peninsula, Baltic shield and Scotland.