Phase Diagrams of Iron Rich Alloys and Their Influence on the Chemical Structure of Planetary Cores

Details Phase Diagrams of Iron Rich Alloys and Their Influence on the Chemical Structure of Planetary Cores Phase Diagrams of Iron Rich Alloys and Their Influence on the Chemical Structure of Planetary Cores

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmmr31b..08c&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #MR31B-08

Other

1015 Composition Of The Core, 3630 Experimental Mineralogy And Petrology, 3924 High-Pressure Behavior, 5430 Interiors (8147)

Scientific paper

Many planetary bodies are thought to have metallic, iron rich cores, with a significant component of some 'light' alloying element(s). The identity of this light alloying component has a profound effect on the chemical properties of the core, including its melting/crystallization behavior, partitioning of minor and trace elements during core/mantle segregation and core crystallization, and other phase relations. Despite this importance, the light element component(s) of planetary bodies generally remain unknown, apart from those of a few iron meteorite parent bodies. Experimentally determined physical and chemical properties of iron-rich systems can be compared to observations and models of planetary interiors to constrain compositions of planetary cores. Here we summarize our recent high pressure, high temperature experiments on the phase diagrams of iron+light element (Fe-X) binaries, specifically iron-sulfide, iron-silicide, and iron-oxide systems. Melting as well as subsolidus phase relations have been determined in the laser heated diamond anvil cell, using either synchrotron X-ray diffraction or optical methods to establish phase boundaries. X-ray diffraction while laser heating the sample reveals the nature of structural transitions (including partial melting), and optical methods (such as temperature vs. emissivity and related methods) establish the phase boundaries with finer precision. Drawing on these and other recent experimental results, we compare and contrast the binary Fe-X phase diagrams to address such questions as: Which candidate light elements (S, Si, O, C) cause the largest melting point depression, and how does this change with pressure? Which can produce large density constrasts against crystallizing iron metal? and others. These results are compared to thermal and chemical models of terrestrial planet interiors (including Earth's), and important gaps and discrepancies in the available experimental data are highlighted.

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