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The Fe-C system at 5 GPa and implications for Earth’s core |
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| Authors: | Nancy L Chabot Andrew J Campbell David S Draper Munir Humayun Elizabeth Cottrell |
| Institution: | a Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA b Department of Geology, University of Maryland, College Park, MD 20742, USA c Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131-1126, USA d National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, Tallahassee, FL 32310, USA e Lawrence Livermore National Laboratory, 7000 East Avenue L-206, Livermore, CA 94550, USA f Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue, Washington, DC 20560, USA g University of Maryland, College Park, MD 20742, USA |
| Abstract: | Earth’s core may contain C, and it has been suggested that C in the core could stabilize the formation of a solid inner core composed of Fe3C. We experimentally examined the Fe-C system at a pressure of 5 GPa and determined the Fe-C phase diagram at this pressure. In addition, we measured solid metal/liquid metal partition coefficients for 17 trace elements and examined the partitioning behavior between Fe3C and liquid metal for 14 trace elements. Solid metal/liquid metal partition coefficients are similar to those found in one atmosphere studies, indicating that the effect of pressure to 5 GPa is negligible. All measured Fe3C/liquid metal partition coefficients investigated are less than one, such that all trace elements prefer the C-rich liquid to Fe3C. Fe3C/liquid metal partition coefficients tend to decrease with decreasing atomic radii within a given period. Of particular interest, our 5 GPa Fe-C phase diagram does not show any evidence that the Fe-Fe3C eutectic composition shifts to lower C contents with increasing pressure, which is central to the previous reasoning that the inner core may be composed of Fe3C. |
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