Új módszer alkáli bazaltos magmák olivin- és klinopiroxén-frakcionációjának modellezésére

The generation and evolution of basaltic magmas which were the result of eruptions in monogenetic volcanic fields have recently been of interest worldwide in connection with volcanological studies. These magmas are of diverse temporal and spatial distribution, and there is considerable variety in their respective modal and chemical compositions, With respect to these facts, the Neogene–Quaternary monogenetic alkaline basaltic volcanic fields of the Carpathian–Pannonian region (CPR) can be considered as natural laboratories for basaltic magmas. A number of research studies have been published in the last three decades, but these were based on trace element modelling and were performed to characterise only the mantle source lithology or to calculate parental melt compositions. Furthermore, in this process primitive magma calculations were used, based on olivine fractionation or simply with olivine +/– clinopyroxene addition. The widely used parental melt calculations are less accurate if clinopyroxene fractionation occurred (or even if the source rock contained pyroxenite as well). This is because these are based on the major, or trace element compositions of olivine phyric ocean island basalts and peridotites. The principle of such calculations is to generate parental melt compositions through olivine addition. Based on some alkaline basaltic rocks from the CPR, for this study a new fractionation calculation method was carried out for olivine and/or clinopyroxene phyric intracontinental alkaline basalts. It was designed to calculate the amount of olivine ± clinopyroxene that fractionated from the parental basaltic melt using only the major elements and the Ni concentration of the basaltic rock, as well as the forsterite and Ni content of its olivine phenocrysts. Based on the degree of fractionation, the model is suitable for estimating the major element composition of the parental melt and its value.