Abstract
The typochemical features of spinels forming continuous series from Al–Cr spinels to Ti-magnetite and ulvöshpinel from basic-ultrabasic rocks of the North Siberian platform are considered. Their comparative characteristics are carried out with similar minerals of alkaline basalts of oceanic islands and Lunar marine basalts on the modified 3D-diagram Al–Cr–(Fe3+ + 2Ti)–Fe2+ proposed by the author. The identification of a continuous isomorphous series from chromian spinel to ulvöspinel is one of the mineralogical indicators of a possible paragenetic relationship between picrite-basalt, alkaline olivine-basalt, alkaline-ultrabasic, and kimberlite formations in the North Siberian platform. Using the Ballhaus-Berry-Green olivine-chromespinel oxythermobarometer, it was shown that for the studied rocks of the North Siberian platform, the oxygen volatility lg fO2 is 2–4 orders of magnitude higher than that specified by the fayalite-magnetite-quartz (FMQ) buffer and corresponds to the oxidation state of platinum-bearing dunite-clinopyroxenite associations of rocks of the Ural-Alaskan and Aldan types.