EPR spectroscopy of endogenous carbonates from the regions of trap and alkaline-ultrabasic magmatism (Siberian Platform)

EPR spectrscopy was used to study specific features of distribution of para magnetic admixtures in endogenous carbonates formed in the zones of contact of trap and alkaline-ultrabasic intrusions with deposits of the Siberian P latform cover. It was established that the main paramagnetic centers in the studied samples area a) ions Mn2+, isomorphously replacing Ca2+ and Mg2+, b) ions Fe3+, forming oxide or hydroxide clusters 100-1000 Angstrom and mor e in size, and c) radiation centers, originated from natural ionizing radia tion. Using indicator features of spectra, it was established that carbonat es from magnesian-skarn associations are a solid solution of calcite with d olomite and ankerite. Compared with carbonatites, calcites from the contact s with traps have a lower Fe content and low concentrations of Fe3+ cluster s. Radiation centers were detected in Fe-free calcites accompanying apatite . The number of paramagnetic ions Mn2+ decreases in low-temperature generat ions of calcite. All genetic groups have a tendency to replacement of struc turally inhomogeneous high-temperature solid solutions of carbonates by sto ichiometric calcites, dolomites, ankerites, and siderites.