Olivine–spinel geothermometry—Indicator of formation identity of rocks and a basis for geodynamic reconstructions in Antarctica

The article reports studies on composition of rock-forming and accessory minerals from various mafites and ultramafites. Spotlight is on olivines and Cr spinel which are one of the first crystallization stages informing on chemical and thermodynamic characteristics of mantle sources and thermobaric regime in the course of magma generation. The temperatures of rock formation were calculated and analyzed using four classic versions of olivine–spinel geothermometer: Jackson–Irvine–Reder, Ono, Fabry and O’Neil–Wall–Ballhous–Berry–Green (O’NWBBG) for different ultramafites and mantle xenolites as the case-studies of Antarctica, Mongolia, Ural and some other regions. It is mentioned that olivine–spinel equilibrium temperatures are comparable in ophiolites and in zoned and stratified rock masses, and are higher than the temperature of mantle xenolites. It is concluded on applicability of the main versions of olivine–spinel geothermometers in calculation of temperatures in mafites and ultramafites with a view to reconstructing geodynamic formation conditions for different blocks in the Earth crust. Furthermore, the authors analyze some typomorphic indicators of a formation identity of rocks, namely, the Ni:M ratio in olivine and the ferrum content f of Cr spinel. It is found that the ratio of Ni:Mn > 2 in olivine is typical of ophiolites and mantle xenolites, and is much lower in other formations. The rocks from zoned and stratified formations feature the higher values of f (0.6–0.7) in Cr spinel, while ophiolites and mantle xenolites display the minimum values of this parameter (0.3–0.4). The results are important for better and penetrative understanding of formation and evolution of mantle systems, including their geodynamics. Such approach is crucial in investigation of inaccessible and non-outcropping areas of the Earth crust as conventional analytical techniques are inexecutable in full measure in this case. The study was carried out under the state contract with the Ministry of Science and Higher Education of the Russian Federation, Contract No. FSRW-2024-0003. Basic and Inter-Disciplinary Research of Geological Formations at Vostok Station in Antarctica.