OXYGEN AND CARBON-ISOTOPE VARIATIONS OF CARBONATES AND SILICATES FROMTHE CARBONATITE MASSIF TIKSHEOZERO (NORTHERN KARELIA)

Carbon and oxygen isotope compositions have been determined for carbon ate minerals from different types of carbonatites (large carbonatite b odies, veins, eruptive breccia), as well as from different temperature classes of carbonatites (according to Samoilov [1]). It could be show n, that only high temperature carbonatites exhibit small variations of deltaO-18 and delta-C-13 falling in the range of ''high temperature m antle carbonates'', whereas low temperature calcites and dolomites sho w wide variations in deltaO-18. These changes in both isotope and mine ral compositions of low temperature carbonatites are interpreted as a result of repeated interaction with fluids. The oxygen isotope ratios in most of the eruptive breccia have been changed by secondary process es. The primary deep-seated isotope record has been preserved only in samples, in which carbonate occurs as fine-grained calcite groundmass. Preliminary results on oxygen isotope composition of different silica te minerals (amphibole, magnetite, biotite, albite, apatite) indicate isotope equilibrium for the mineral pair calcite-amphibole with isotop e temperatures representing superimposed processes.