Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.v51b..09c&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #V51B-09
Physics
6250 Moon (1221), 1015 Composition Of The Core, 1025 Composition Of The Mantle, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 1065 Trace Elements (3670)
Scientific paper
The mantles of the Earth and Moon are similarly depleted in V, Cr, and Mn relative to the concentrations of these elements in chondritic meteorites [1,2]. The similar depletions have been suggested to be due to a common genesis of the Earth and Moon, with the Moon inheriting its mantle, complete with V, Cr, and Mn depletions, from the Earth during the impact-induced formation of the Moon. We have conducted multi-anvil experiments that systematically examined the effects of pressure, temperature, and silicate and metallic compositions on liquid metal-liquid silicate partitioning of V, Cr, and Mn. Increasing temperature is found to significantly increase the metal-silicate partition coefficients for all three elements. Increasing the S or C content of the metallic liquid also causes the partition coefficients to increase. Silicate composition has an effect consistent with Cr and Mn being divalent and V being trivalent. Over our experimental range of 3-14 GPa, the partitioning behavior of V, Cr, and Mn did not vary with pressure. With the effects of oxygen fugacity, metallic and silicate compositions, temperature and pressure understood, the partition coefficient for each element was expressed as a function of these thermodynamic variables and applied to different core formation scenarios. Our new metal-silicate experimental partitioning data can explain the mantle depletions of V, Cr, and Mn by core formation in a high temperature magma ocean under oxygen fugacity conditions two log units below the iron-wuestite buffer, conditions similar to those proposed by [3] from their metal-magnesiowuestite study. In contrast, more oxidizing conditions proposed in recent core formation models [4] cannot account for the V, Cr, and Mn depletions. Additionally, because we observe little or no pressure effect on V, Cr, and Mn partitioning in our experiments, we conclude that the mantle depletions of these elements during core formation are not dependent on planet size. Accordingly, the V, Cr, and Mn depletions in the lunar mantle could have been derived from a body much smaller than the Earth, such as the impactor in a giant impact scenario, if that body had been hot enough and reducing enough during its core formation. With this current understanding, our data do not require the mantle of the Moon to be derived from the Earth's mantle [1] A. E. Ringwood, in Advances in Earth Science, P. Hurley, Ed. (MIT Press, Boston, 1966), pp. 357-398. [2] G. Dreibus, H. Wanke, Lunar Planet. Sci. 10, 315 (1979). [3] C. K. Gessmann, D. C. Rubie, Earth Planet. Sci. Lett. 184, 95 (2000). [4] K. Righter, M. J. Drake, Earth Planet. Sci. Lett. 171, 383 (1999).
Agee Carl B.
Chabot Nancy Lynne
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