Phase relations of a carbonaceous chondrite at lower mantle conditions

Details Phase relations of a carbonaceous chondrite at lower mantle conditions Phase relations of a carbonaceous chondrite at lower mantle conditions

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.v72b1307a&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #V72B-1307

Physics

Geophysics

1010 Chemical Evolution, 1025 Composition Of The Mantle, 1749 Volcanology, Geochemistry, And Petrology, 3630 Experimental Mineralogy And Petrology

Scientific paper

The refractory element ratios of Earth's mantle are close to carbonaceous chondrite values. One of the ideas on Earth's bulk composition is that the Earth is made of carbonaceous chondrite-like materials, but the redox state of Earth is closer to that of Enstatite chondrite than carbonaceous chondrite. We do not know exactly when and how the reduction event was occurred at proto Earth. Therefore, it is important to considering differentiation process of early earth that the phase relations of mantle composition are investigated under variable Fe/FeO conditions at high pressures. Allende meteorite (CV chondrite) is applicable to one of the oxidized model of the proto earth, whereas the most reduced model is Peridotite and Metal. We report the phase relations of Allende meteorite in the pressure range from 22 to 30 GPa, at 1600-2300 °C. We use natural Allende meteorite as starting material. The Kawai type multianvil apparatus was used for the present experiments. The truncated edge length of the anvil was 2 mm. We use two kinds of heating element, LaCrO3 and Re. LaCrO3 heater was used for subsolidus experiments, and Re heater was used for melting experiments. Pressure calibrations were made at high temperatures using il-pv phase transition, Al2 O3 content of Pv determined by in situ X-ray diffraction measurements with the Jamieson's Gold scale [1]. The micro-area X-ray diffractometer and EPMA were used for phase identification and compositional analysis of run products. The liquidus phase changed from garnet to Mg-perovskite at about 24.5 GPa, and magnesiowustite remained second liquidus phase. The solubility of mafic components in Ca-perovskite in Allende composition is higher than that reported on Peridotite bulk composition. The Ca/(Ca+Mg+Fe) ratio of Ca-perovskite is 0.6 in Allende experiments, whereas that is 0.9 in Peridotite experiments [2]. Our result suggests that chemical differentiation process could change with FeO contents of magma ocean.
References [1] Jamieson et al., in high-Pressure Research in Geophysics, edited by S. Akimoto and M. H. Manghanani, pp. 27-48, CAPJ, Tokyo, 1982. [2] Hirose, K., J. Geophys. Res., 107, 2002.

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