Mantle melting in equilibrium with an Iron–Wüstite–Graphite buffered COH-fluid |
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| Authors: | Sigurdur Jakobsson John R Holloway |
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| Institution: | (1) Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland;(2) School of Earth and Space Exploration and Department of Chemistry and Biochemistry, Arizona State University, Tempe, USA |
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| Abstract: | Partial melting experiments on a San Carlos peridotite were done in a Walker type multi-anvil press at pressures from 5 to
12.5 GPa. Experiments were done in the presence of a COH-fluid and at oxygen fugacity controlled by the Fe–FeO buffer. Olivine,
clinopyroxene, garnet and orthopyroxene are stable in all but the highest temperature 10 GPa experiments where olivine and
garnet coexist, and the highest temperature 5 GPa experiments where olivine is the single crystalline phase. The solidus at
5 GPa was found to be at approximately 1,200°C and the liquidus was estimated to be at 1,325°C, which is ∼500°C lower than
has been reported for dry melting of peridotite. The aluminum concentration of the melts decreases with increasing melt fraction
and decreases also with increasing pressure. At 5 GPa the melts have a CaO/Al2O3-ratio of 0.85–1.0, which is similar to that of undepleted komatiites; major element concentrations are also identical to
those of undepleted komatiites such as the Munro komatiites. At 10 and 12.5 GPa the partial melts have CaO/Al2O3-ratios above 1.5 and major element composition almost identical to aluminum depleted komatiites such as the Barberton komatiites.
We therefore conclude that in the presence of a reducing COH-fluid both aluminum-depleted and -undepleted komatiites could
have formed at temperatures much lower than generally accepted. |
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| Keywords: | Melting Peridotite Komatiite COH-fluid |
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