Phase Relations in the Model System SiO2–MgO–Cr2O3: Evidence from the Results of Experiments in Petrologically Significant Sections at 12–24 GPa and 1600°C
- 39 Downloads
The new results of an experimental study of the majorite MgSiO3–magnesiochromite MgCr2O4 model section are discussed, and general topology of the SiO2–MgO–Cr2O3 system is analyzed. Despite the absence of some petrogenic components (CaO, FeO, Al2O3, Na2O, K2O, and others) in this system, our study, performed in wide pressure range (10–24 GPa), allows us to consider all of the most important phase transformations (in this case, magnesium silicates and oxides) in the upper mantle, transition zone, and uppermost lower mantle. Addition of Cr shows the influence of a minor element on the phase transition parameters. New data on the solubility of Cr in deep minerals (garnet, olivine, wadsleyite, ringwoodite, and bridgmanite) were obtained, which allowed us to determine the influence of Cr on the structural patterns of the major mantle phases. It is shown that addition of 1 wt % Cr2O3 shifts the boundaries of phase transformations by 50 km (olivine/wadsleyite) and 10 km (wadsleyite/ringwoodite) to a lower-pressure domain in comparison with Cr-free systems. In a first approximation, the results of experimental study of phase relations in pseudobinary sections of the SiO2–MgO–Cr2O3 system simulate the phase composition of the restitic part of the upper mantle, transition zone, and uppermost lower mantle under partial melting conditions. It is shown that the Cr concentration in mantle phases is significantly controlled by the Cr/Al ratio in the protolith.
Keywords:mantle majorite knorringite magnesiochromite experiment
The experimental and structural study was supported by the Russian Science Foundation, project no. 17-17-01169. In this study, we used the author’s database of high-pressure phase associations, created with the support of Program 8P no. 0137-2018-0043.
This study was supported by the Russian Science Foundation, project no. 17-17-01169.
- 1.Akaogi, M., Phase transitions of minerals in the transition zone and upper part of the lower mantle, Geol. Soc. Am., Sp. Pap., 2007, vol. 421, pp. 1–13.Google Scholar
- 3.Andrault, D., Properties of lower–mantle Al-(Mg,Fe)SiO3 perovskite, Geol. Soc. Am., Sp. Pap., 007, vol. 421, pp. 15–36.Google Scholar
- 5.Bulatov, V., Brey, G.P., and Foley, S.F., Origin of low-Ca, high-Cr garnets by recrystallization of low-pressure harzburgites, Extended Abstracts of 5th International Kimberlite Conference, Araxa, Brazil, 1991, CPRM Sp. Publ. 2/91, 29–31 (1999).Google Scholar
- 11.Harte, B., Harris, J.W., Hutchison, M.T., et al., Lower mantle mineral associations in diamonds from Sao Luiz, Brazil, Mantle Petrology: Field Observations and High Pressure Experimentation: A Tribute to Francis R. (Joe) Boyd, Houston: The Geochemical Society, 1999, no. 6, pp. 125–153.Google Scholar
- 18.Ishii, T., Kojitani, H., Fujino, K., et al., High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultra-high pressure chromitites in ophiolites, Am. Mineral., 2015, vol. 100, pp. 59–65.CrossRefGoogle Scholar
- 24.Liang, F., Yang, J., Xu, Z., and Zhao, J., Moissanite and chromium-rich olivine in the Luobusa mantle peridotite and chromitite, Tibet: deep mantle origin implication, J. Himal. Earth Sci., 2014, spec. vol., p. 103.Google Scholar
- 25.Malinovskii, I.Yu., Doroshev, A.M., Ran, and E.N., Stability of chromoium-bearing garnets of the pyrope–knorringite series, Eksperimental’nye issledovaniya po mineralogii (1974–1975) (Experimental Studies on Mineralogy (1974–1975)), Sobolev, V.S. and Godovikov, A.A., et al., Novosibirsk: In-t geologii i geofiziki SO AN SSSR, 1975, pp. 110–115.Google Scholar
- 30.Ringwood, A.E., The Chemical Composition and Origin of the Earth, Hurley, P.M., Ed., Advances in Earth Science, Cambridge: M.I.T. Press, 1966.Google Scholar
- 31.Ringwood, A.E. and Major, A., The system Mg2SiO4–Fe2SiO4 at high pressures and temperatures, Phys. Earth Planet. Inter., 1970, vol. 89, p. 3.Google Scholar
- 33.Ryabchikov, I.D., Mechanisms and conditions of magma formation in mantle plumes, Petrology, 2003, vol. 11, no. 6, pp. 496–503.Google Scholar
- 35.Ryabchikov, I.D., Brey, G.P., and Bulatov, V.K., Carbonate melts in equilibrium with mantle peridototes at 50 kbar, Petrologiya, 1993, vol. 1, no. 2, pp. 189–194.Google Scholar
- 36.Ryabchikov, I.D., Ionov, D.A., Kogarko, L.N., and Kovalenko, V.I., Chemical variations in mantle peridotites as result of different degree of partial melting of primitive mantle, Dokl. Akad. Nauk SSSR, 1987, vol. 295, no. 1, pp. 185–189.Google Scholar
- 39.Sirotkina, E.A., Bindi, L., Bobrov, A.V., et al., Synthesis and crystal structure of chromium-bearing anhydrous wadsleyite, Phys. Chem. Mineral., 2018b, p. 1–6. doi 10.1007/s00269-017-0926-xGoogle Scholar
- 40.Sobolev, N.V., Diamond parageneses and the problem of deep-seated mineral formation, Zap. Vsesoyuz. Mineral. O-va, 1983, no. 4, pp. 389–397.Google Scholar