Experimental Modeling of the Formation of Zoned Magnesian Garnet at Various Starting Ca, Al, and Cr Concentrations Controlled by H2O-Rich Fluid

• Published in: Geochemistry international Vol. 59; no. 8; pp. 778 - 790
• Main Authors: Turkin, A. I., Chepurov, A. A., Zhimulev, E. I., Lin, V. V., Sobolev, N. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.08.2021; Springer Nature B.V
• Subjects: Carbon dioxide; Chromite; Corundum; Crystallization; Distribution; Earth and Environmental Science; Earth Sciences; Electron probe; Electron probe microanalysis; Garnet; Garnets; Geochemistry; Grains; Mineral assemblages; Peridotite; Recrystallization; Serpentine; chromium; calcium; experiment; garnet; aluminum; high pressure; peridotites
• ISSN: 0016-7029; 1556-1968
• DOI: 10.1134/S0016702921080097

— Natural serpentine was experimentally recrystallized in the presence of chromite, corundum, and carbonatite as sources of Cr, Al, and Ca, respectively, at P = 5 GPa and T = 1300°C using a BARS multi-anvil high-pressure apparatus. The experimental products contained synthesized mineral assemblages corresponding to those of natural garnet peridotites. Electron probe microanalysis (EPMA) of the garnet indicates that its grains are clearly zoned, first of all, in Ca distribution. The garnet grains exhibit a zoned distribution of #Ca = 100Ca/(Ca + Mg) of two types: (i) a systematic prograde increase from the cores of the seemingly homogeneous grains to their rims and (ii) a drastic change in Ca# with the transition from the darker to paler domains of the grains. The compositional zoning apparently resulted from quantitative changes in the Ca, Al and Cr quantitative proportions in the crystallization area under the effect of the H 2 O-rich (H 2 O/CO 2 > 65) fluid. The quantitative ratio of these elements is a key factor at the crystallization of peridotitic garnets typical of different peridotite varieties.