Alkali Addition as a Factor of Variability of Natural Picrite and Basite Melts

The petrochemical modeling indicates a possibility of alkali (e.g., Na2O) “assimilation” by a basite “normal” melt from a now of deep-seated fluids as it follows from comparing calculated and real alkaline compositions, the subsequently appeared fractions being undergone “alkalization” at the cost of initial non-alkaline picritoid melt. The role of a large depth and low melting degree in the formation of alkaline basite-ultrabasite melts being not denied, an important correction to this concept should be taken into account, namely, for the possibility of alkali addition to the magmatic system from an outward stable source (i.e., alkali “mobility” in the system). This makes the genetical conception of “alkalization” under consideration to be most probably in the application to the most widespread alkaline basites, especially in volcanic regions of riftogenesis and related now of depth-seated fluids.