VEGA 1/0029/10


Origin and age of megacrysts in alkali basalts of southern Slovakia

Principal investigator:
Vratislav Hurai
Investigators from institution:
Pavol Siman
Co-operating institutions and scientists:

Alkali basalts often contain megacrystals of rock-forming minerals, up to several cm in diameter. Alkali basalts of southern Slovakia contain amphibole, zircon, and K-feldspar megacrysts, which have not been studied until now. Origin of the megacrysts has not been satisfactorily explained. Amphiboles and K-spars are out of equilibrium with host basalts, but their composition is similar to that of rock-forming minerals of gabbros and syenites, originating during fractional crystallisation of alkali basalt in magmatic reservoirs. These processes may give rise to accumulations of PGE and REE. Main aim of the project was to elucidate the origin of megacrysts by means of trace elements, fluid and melt inclusions. Ar/Ar dating of the megacrysts will be combined with U-Pb-Th dating of zircon, monazite and titanite from the associated xenoliths with the aim to determine the age of basaltic volcanism in Southern Slovakia.