Charakterystyka geochemiczna kwaśnych skał magmowych nadbałtyckiej części Pomorza

Abstract

GEOCHEMICAL CHARACTERISTICS OF THE ACID IGNEOUS ROCKS OF BALTIC PART OF THE WESTERN POMERANIASummaryAcid igneous rocks represented by early Permian porphyres were found in 10 boreholes from the Baltic part of the western Pomerania. Some of the main chemical components (Fe2O3, FeO, MgO, CaO, Na2O, K2O and TiO2) and trace-elements (Mn, Ba, Sr, Pb, V, Cr, Ni, Co and Cu) were determined. The analytical data obtained made it possible to differentiate four groups of porphyres (Table 2, Fig. 8). Average chemical composition and mean contents of trace elements for particular groups of porphyres are given in Tables 2 and 3, whilst the dependence of trace elements on some main chemical elements is illustrated in Figures 4–7.Intepretation of the values of the Mg/Fe2+ ratio (Fig. 2) and the position occupied by these groups in the differential triangle (Fig. 3) indicate that the groups correspond to four generations (I,II, III, IV); generation I is the oldest, IV – the youngest, and II and III represent transitional links. The porphyre generations (groups) distinguished here indicate relative time sequence of igneous phenomena within a single cycle or a few incomplete but supplementary volcanic cycles.The porphyres studied are mainly represented by potassium-sodium varietes; predominance of potassium over sodium is highly variable, being the clearest in the case of porphyres from conglomerates. Sodium-potassium porphyres (generation IV) are much less common. The value of the K/Na ratio generally increases along with depth of the profiles.