Other
Scientific paper
Apr 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005gecoa..69.2141c&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 69, Issue 8, p. 2141-2151.
Other
36
Scientific paper
The abundances of Ni and Co in the Earth’s mantle are depleted relative to chondrites due to terrestrial core formation. Recently, the observed mantle depletions of these elements have been explained by liquid metal-liquid silicate equilibrium during core formation in a high pressure, high temperature magma ocean on the early Earth. However, different magma ocean models, which would be expected to give consistent results, have proposed vastly different pressures (24 to 59 GPa), temperatures (2200 to >4000 K) and oxygen fugacities (-0.15 to -2.4 ΔIW) for the Earth’s magma ocean. In an attempt to resolve the contradictory results from different magma ocean models and determine the thermodynamic conditions appropriate for core formation in the Earth, experiments were conducted to better constrain the influences of temperature and C on the partitioning behaviors of Ni and Co. Results of experiments at 7 GPa with temperatures of 1923 2673 K show that the metal-silicate partition coefficients for both Ni and Co decrease with increasing temperature, with the effect being more significant for Ni. Little change in the partitioning behaviors of either Ni or Co with varying C-content of the metallic liquid was found. By combining the new temperature data with previous results from pressure and oxygen fugacity studies, we parameterized the partitioning behavior of Ni and Co and applied the parameterizations to core formation in a terrestrial magma ocean. Multiple combinations of pressure, temperature, and oxygen fugacity can explain the observed mantle depletions of Ni and Co, and all of the very different previously proposed magma ocean conditions are generally consistent with valid solutions. By using the FeO content of the Earth’s mantle as an additional constraint on the oxygen fugacity, magma ocean conditions of 30 60 GPa, > 2000 K, and -2.2 ΔIW are suggested. Similar systematic approaches and studies of other moderately siderophile elements could further constrain the magma ocean conditions on the early Earth.
Agee Carl B.
Chabot Nancy Lynne
Draper David S.
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