STRONTIUM AND NEODYMIUM ISOTOPE COMPOSITION IN QUARTERNARY LAVAS OF THE GREAT CAUCASUS IN VIEW OF ITS PETROGENESIS

Data have been given and discussed on strontium and neodymium isotope composition in the products of newest andesite volcanism of the Great Caucasus. Composition of the starting melts of Quartermary volcanic ro cks have been formed mainly by mantle material contaminated remarkably by crust component. The significant variations of Sr isotope composit ion show different degree of crust matter role in formation and evolut ion of the magmas. Strontium isotope composition analysis of the lava complexes together with the data on its petrographic composition show that the contamination is the leading process responsible for the enri chment of calc-alkali and subalkali magmas in radiogenic strontium for the Great Caucasus volcanism considered. Two different mechanisms of melt contamination by crust material have been stated. In the first ca se crust material (sialic melting) inflow occurred during the melt dif ferentiation, whereas in the second case -no crust component inflow oc curred before and during the differentiation.