| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4739528 | Russian Geology and Geophysics | 2008 | 18 Pages |
Brownmillerite, Fe-perovskite, and two intermediate phases (Ca3Ti(Fe,Al)2O8 and Ca5Ti(Fe,Al)4O13) were found in combustion metamorphichigh-temperature larnite rocks of the Hatrurim Basin, Israel. This is the first finding evidencing the existence of the pseudobinaryperovskite-brownmillerite series in nature. Fe-perovskite contains the Ca2(Fe,Al)2O5 end-member (up to 18 mole %), whereas brownmilleriteCa2(Fe1−xAlx)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)2O8(phase X) and Ca5Ti(Fe,Al)4O13 (phase Y), which have synthetic analogs. In some larnite rocks, the phase X is the only member of theperovskite-brownmillerite series. It is clustered into two compositional groups, Ca3Ti(Fe1.3Al0.7)O8 and Ca3Ti(Fe1.6Al0.4)O8. The phase Y isextremely rare and has the composition Ca5Ti(Fe0.76Al0.24)4O13. The presence of minor Si, Cr, Sr, Zr, and LREE is common for all mineralsof the series. The Fe-perovskite + brownmillerite paragenesis was found in none of the studied rocks, which is consistent with theCaTiO3–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 fromthe Fe-perovskite + phase X paragenesis is 1170–1200 °C. This paragenesis is proposed as a new thermometer for metacarbonate rocks ofthe high-temperature region of the spurrite-merwinite facies.
