Highly Reducing Conditions During Core Formation on Mercury: Implications for Internal Structure, the Distribution of Heat-Producing Elements and the Origin of a Magnetic Field

Details Highly Reducing Conditions During Core Formation on Mercury: Implications for Internal Structure, the Distribution of Heat-Producing Elements and the Origin of a Magnetic Field Highly Reducing Conditions During Core Formation on Mercury: Implications for Internal Structure, the Distribution of Heat-Producing Elements and the Origin of a Magnetic Field

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmmr31b..06m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #MR31B-06

Physics

1015 Composition Of The Core, 1025 Composition Of The Mantle, 1028 Composition Of Meteorites (3662, 6240), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008)

Scientific paper

According to previous models for the formation of Mercury, the estimated oxygen fugacity under which Mercurian core segregation took place was in the range 3 to 6 log units below the iron-wüstite buffer. These oxygen fugacities are in the same range as those suggested for enstatite meteorites. Based upon comparison with high pressure and high temperature experiments relevant to formation of enstatite meteorites, the core of Mercury may contain several wt% of Si, in addition to S. The presence of both Si and S is of importance as the ternary system Fe-S-Si has a vast immiscibility gap at low pressure, which is closed at high pressure (15 GPa-2000°C). It is possible that the Mercurian core has a shell structure comprising of: (i) an outer layer of Fe-S-Si liquid, rich in S; (ii) a middle layer of Fe-Si-S liquid, rich in Si; and (iii) an inner core of solid Fe-Si metal. We have explored the structure of the Mercurian mantle, assuming an EH-bulk composition, using the thermodynamic calculator p-MELTS. Quartz and orthopyroxene (opx) will be present throughout the Mercurian mantle, while garnet (gt) and cpx are only stable above 6GPa. Gt is the predicted liquidus phase at pressures > 6GPa, while it is Opx at pressures <6GPa. Both recently published metal/silicate partitioning data, as well as observations of U distribution in EH, suggest that this element behaves as a chalcophile element at low oxygen fugacity. We predict that U will be concentrated in the outer layer of the Mercurian core, and could thus act to maintain this part of Mercury's core molten, potentially contributing to the origin of Mercury's magnetic field.

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