Liquidus karrooite stability and composition at reducing conditions |
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| Authors: | Email author" target="_blank">Alexander?BorisovEmail author Frank?Brenker Herbert?Palme |
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| Institution: | (1) Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetny 35, 109017 Moscow, Russia;(2) Institut für Mineralogie und Geochemie, Universität zu Köln, Zülpicher Strasse 49b, 50674 Köln, Germany |
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| Abstract: | We have determined the stability of rutile and karrooite on the liquidus of pseudobinary silicate melts of anorthite–diopside eutectic composition with, in addition, of up to 32 wt% TiO2 at one atm total pressure and at wide range of oxygen fugacities. At 1,300°C and at an fO2 below 10–11.2 atm rutile (TiO2) is replaced as liquidus phase by the pseudobrookite-type MgTi2O5–Ti3O5 solid solution with some Al in the crystal structure. The composition of karrooite was found to be strongly dependent on oxygen fugacity. Crystalline phases were identified by transmission electron microscopy (TEM). The results obtained in this study are relevant for understanding the chemistry of lunar armalcolites. Using  excess rutile solubility at reducing conditions, we estimated the Ti4+ /Ti3+ ratio in silicate melts at 1,300°C as function of fO2. |
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