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Shock compression of KFeS_2 and the question of potassium in the core

Somerville, Malcolm and Ahrens, Thomas J. (1980) Shock compression of KFeS_2 and the question of potassium in the core. Journal of Geophysical Research B, 85 (B12). pp. 7016-7024. ISSN 0148-0227. doi:10.1029/JB085iB12p07016.

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The Hugoniot equation of state of KFeS_2 (initial density 2.663 g/cm^3) has been determined for pressures up to 110 GPa. The Hugoniot data demonstrate a transformation at 13±1 GPa to a phase with an apparent zero-pressure density of 3.7±0.2 g/cm^3. A comparison of the inferred isentrope of KFeS_2 (high-pressure phase) with those of Fe, FeS_(0.9), and FeS_2 indicates that the atomic volume of potassium in KFeS_2 is approximately twice that of iron at 75 GPa. In the temperature and pressure range of the experiments, potassium fails to meet the empirical Hume-Rothery and Raynor (HRR) criterion for solubility of an element in iron, namely, that the molar volume of the element should not exceed that of iron by a factor greater than ∼1.4. However, both the applicability of the HRR solubility criterion and the inferred isentrope of KFeS_2 at high pressure are uncertain. Thermochemical calculations of the partitioning of K between a sulfide and silicate phase (e.g., KFeS_2 and KAlSiO_4 or KAlSi_3O_8 (hollandite)) indicate that pressure does not have a pronounced effect on the relative stability of solid KFeS_2 and potassium aluminosilicate high-pressure phases. The calculations suggest that the high-pressure phase of KFeS_2 would not be stable in relation to KAlSiO_4 (kalsilite) in the upper mantle, or in relation to KAlSi_3O_8 (hollandite) in the lower mantle. However, the calculations do not bear directly on the question of partitioning of K into an iron sulfide melt from lower mantle aluminosilicate phases. Although the present results cannot absolutely rule out the hypothesis that a large fraction of the terrestrial potassium budget has dissolved into a molten iron sulfide-bearing core, the present analysis of the pressure-volume relation for potassium, iron, iron sulfides, potassium aluminosilicate, and potassium iron sulfide yields no evidence in support of this hypothesis.

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Alternate Title:Shock compression of KFeS2 and the question of potassium in the core
Additional Information:Copyright 1980 by the American Geophysical Union. (Received January 29, 1980; revised August 11, 1980; accepted August 15, 1980.) Paper number 80B1165. We are indebted to James R. Long, Epaprodito Gelle, Ronald Smith, and Michael Long for the careful operation of the shock wave facility in the Helen and Roland Lindhurst Laboratory of Experimental Geophysics. We thank R. F. Wendlandt for a constructive review of an earlier manuscript and for forwarding an important paper (Wendlandt and Eggler, 1980) prior to publication. We appreciate the advice on sample materials proffered by K. Goettel, the contribution of Sally Hill in characterizing our samples, and useful discussions with E. M. Stolper. This work was supported by NSF grant EAR77-23156. Contribution 3378, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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NSFEAR 77-23156
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Caltech Division of Geological and Planetary Sciences3378
Issue or Number:B12
Record Number:CaltechAUTHORS:20141104-145449462
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Official Citation:Somerville, M., and T. J. Ahrens (1980), Shock compression of KFeS2 and the question of potassium in the core, J. Geophys. Res., 85(B12), 7016–7024, doi:10.1029/JB085iB12p07016.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51255
Deposited By: George Porter
Deposited On:04 Nov 2014 23:10
Last Modified:10 Nov 2021 19:08

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