MINERALS OF THE PSEUDOBINARY PEROVSKITE-BROWNMILLERITE SERIES FROM COMBUSTION METAMORPHIC LARNITE ROCKS OF THE HATRURIM FORMATION (Israel)
V.V. Sharygin a , E.V. Sokol a , Ye. Vapnik b
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel
Keywords: Perovskite; brownmillerite; larnite rocks; combustion metamorphism; Hatrurim
Pages: 709-726
Abstract
Brownmillerite, Fe-perovskite, and two intermediate phases (Ca3Ti(Fe,Al)2 O8 and Ca5Ti(Fe,Al)4 O13) were found in combustion metamorphic high-temperature larnite rocks of the Hatrurim Basin, Israel. This is the first finding evidencing the existence of the pseudobinary perovskite-brownmillerite series in nature. Fe-perovskite contains the Ca2 (Fe,Al)2 O5 end-member (up to 18 mole %), whereas brownmillerite Ca2 (Fe1-x Al x )2O5 with x = 0.15-0.55 is enriched in the CaTiO3 end-member (up to 15 mole %). The intermediate phases are Ca3Ti(Fe,Al)2 O8 (phase X) and Ca5Ti(Fe,Al)4 O13 (phase Y), which have synthetic analogs. In some larnite rocks, the phase X is the only member of the perovskite-brownmillerite series. It is clustered into two compositional groups, Ca3Ti(Fe 1.3Al0.7)O8 and Ca3Ti(Fe 1.6 Al0.4)O8. The phase Y is extremely rare and has the composition Ca5Ti(Fe 0.76 Al0.24)4O13. The presence of minor Si, Cr, Sr, Zr, and LREE is common for all minerals of the series. The Fe-perovskite + brownmillerite paragenesis was found in none of the studied rocks, which is consistent with the CaTiO3-Ca2Fe2O3 phase diagram. The rocks bear either one phase or two or three phases (Fe-perovskite + phase X; brownmillerite + phase X ± phase Y). According to the CaTiO3-Ca2Fe2O3 diagram, the minimum formation temperature for the Hatrurim larnite rocks estimated from the Fe-perovskite + phase X paragenesis is 1170-1200
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