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Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores

Murrell, M. T. and Burnett, D. S. (1986) Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores. Journal of Geophysical Research B, 91 (B8). pp. 8126-8136. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20141106-134700232

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Abstract

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, D_U is 0.013 and D_K is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (D_K ≲ 10^(−4)). A typical value for D_U from a granitic silicate liquid at one atmosphere, 1150°C, and low f0_2 is about 0.02; D_(Th) is similar. At low f0_2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with D_U > 1. D_(Th) is less strongly affected. Because of the consistently low D_K/D_U, pressure effects near the core-mantle boundary would need to increase D_U by factors of ∼10^3 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements.


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http://dx.doi.org/10.1029/JB091iB08p08126DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/JB091iB08p08126/abstractPublisherArticle
Additional Information:Copyright 1986 by the American Geophysical Union. (Received June 10, 1985; revised February 3, 1986; accepted February 13, 1986) Paper number 5B5677. We thank J. Warner and Chevron Oil Field Research, La Habra, California, for access to their electron probe for the light element analyses. We also thank E. Stolper for the use of the piston-cylinder apparatus. We are especially grateful to Gerry Fine for his excellent help with the piston-cylinder runs and to W.R. Heuser for assistance with some of the early experiments. This work was supported by NASA grant NAG 9-94. Caltech Division of Geological and Planetary Sciences contribution number 4230.
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NASANAG 9-94
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Caltech Division of Geological and Planetary Sciences4230
Record Number:CaltechAUTHORS:20141106-134700232
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141106-134700232
Official Citation:Murrell, M. T., and D. S. Burnett (1986), Partitioning of K, U, and Th between sulfide and silicate liquids: Implications for radioactive heating of planetary cores, J. Geophys. Res., 91(B8), 8126–8136, doi:10.1029/JB091iB08p08126.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51384
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:06 Nov 2014 22:04
Last Modified:06 Nov 2014 22:04

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