Magmowe skały zasadowe środkowej części Pomorza Zachodniego

Abstract

MAGMATIC ALKALINE ROCKS IN THE CENTRAL PART OF WEST POMERANIASummaryMagmatic, alkaline rocks have been found in bore holes Smoldzino 1, and Kurowo, located in the central part of the west Pomeranian area. The drillings have been made by the Enterprise for Petrloleum Prospectios at Piła. In bore hole Kurowo 2 a diabase dike occurs at a depth from 2147,0 to 2171,2  cutting the Cariboniferours formations. The relation of the diabase with the adjacent rocks has so far not been explained, mainly due to, a lack of cores from the contact zones here. Mineral composition (Table 1, Fig. 1), structure, texture (Fig. 2) and degree, of autometasomatic, alteration demonstrate that this is an asymmetric, distinctly tripartite formation. In the next bore hole Smołdzino 1 a 1amprophyre vein has been encountered.At a depth of 3418,6–3429,3 m it, cuts the Precambrian rocks at an angle of about 60°. The analysis of the mineral composition of this rocks (Table 2), and its structural and textural features show that this is the lamplophyre characterized by the kersantite composition, also of asymmetric structure. The high degree of autometasomatic, alteration of the lamprophyre does not allow any detailed mineralogical examinations to be carried out, however.The results of the chemical analyses of the magmatic alkaline rocks are presented in Table 3, and the results of the calculations made using A. N. Zawaricki and P. Nigglis methods are shown in Figs. 4 and 5. They point to some differences in the original composition of the individual parts of the diabase dike, mainly due to an irregular distribution of minerals in the dike. The bottom part of the dike is rich in plagioclase (Fig. 3), whereas the top part reveals abundant chlorite produced after the alteration of volcanic glass. The high K2O contents in the lamprophyre suggests the potassium nature of the volcanic glass, the increased CaO contents showing that the feldspar has previously been rich in anothite particles.In the samples under examination some main chemical components have been determined (Na2O, K2O, Fe2O3, FeO, CaO, MgO and TiO2) and then, together with the conversion into molecular values, presented in Tables 5 and 6. Table 7 shows the content of these components in the diabase from bore hole R-4. The contents of trace elements (Mn, Ba, Sr, Pb, V, Cr, Ni, CO and Cu) are presented in Table 9, 10 and 11. Both the geochemical analysis and the data from the petrographic examinations reveal considerable differences between the individual magmatic rocks from the bore holes Kurowo 2 and Smołdzino 1, and a heterogenity in the structure of these rooks in the section of the individual dikes.The differences in the geochemical composition between the diabase from bore hole Kurowo 2, lamprophyre from bore hole Smołdzino 1 and diabase from bore hole R-4 point to a relative sequence of the time development of the magmatic phenomena within one or several cycles.Comparisons and interpretation of the coefficients obtained (Figs. 6 and 7) indicate that probably the oldest generation is represented by the diabase from bore hole R-4, and the rocks from the bore holes Kurowo 2 and Smołdzino 1 belong, respectively, to the later ones.