Seismological constraints on core composition from Fe-O-S liquid immiscibility

Science

Volumn 306, Issue 5705, 2004, Pages 2239-2242

  Helffrich, George ^a   Kaneshima, Satoshi ^b  

^a UNIVERSITY OF BRISTOL   (United Kingdom)

^b TOKYO INSTITUTE OF TECHNOLOGY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

COMPOSITION; EARTH (PLANET); SEISMIC WAVES; SOLUBILITY; THERMODYNAMICS; WATER WAVE EFFECTS;

CORE COMPOSITION; IMMISCIBLE LIQUIDS; SEISMOLOGICAL CONSTRAINTS; WAVE SPEEDS;

SEISMOLOGY;

IRON; OXYGEN; SULFUR;

CHEMICAL COMPOSITION; CORE (PLANETARY); IMMISCIBILITY; IRON; OXYGEN; SEISMIC VELOCITY; SULFUR;

ARTICLE; CHEMICAL COMPOSITION; CRYSTAL STRUCTURE; DENSITY; LIQUID; MISCIBILITY; MOLECULAR WEIGHT; PRESSURE; PRIORITY JOURNAL; THERMODYNAMICS;

EID: 11144295210     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1101109     Document Type: Article

References (55)

1. F. Birch J. Geophys. Res. 57, 227 (1952).
2. D. J. Stevenson, Science 214, 611 (1981).
3. J.-P. Poirier, Phys. Earth Planet. Int. 85, 319 (1994).
4. B. J. Wood, Earth Planet. Sci. Lett. 117, 593 (1993).
5. K. C. Creager, Nature 356, 309 (1992).
6. D. E. Loper, Geophys. J. R. Astron. Soc. 54,398 (1978).
7. D. Gubbins, T. G. Masters, J. A. Jacobs, Geophys. J. R. Astron. Soc. 59, 57 (1979).
8. D. C. Hilty, W. Crafts, J. Metals, Trans. AIME 4, 1307 (1952).
9. V. Raghavan, Phase Diagrams of Ternary Iron Alloys, Part 2, Ternary Systems Containing Iron and Sulphur (Indian Institution of Metals, Calcutta, 1988).
10. T. Lay, C. J. Young, Geophys. Res. Lett. 17, 2001 (1990).
11. B. L. N. Kennett, E. R. Engdahl, and R. Buland, Geophys. J. Int. 126, 108 (1995).
12. The AK135 model is slower in the top 50 km of the outer core to account for the observed SKKS-SKS travel-time differences.
13. A. Souriau, M. Souriau, Geophys. J. Int. 98, 39 (1989).
14. P. M. Shearer, G. Masters, Geophys. J. Int. 102, 491 (1990).
15. G. Masters, D. Gubbins, Phys. Earth Planet. Int. 140, 159 (2003).
16. D. Alfè, G. D. Price, M. J. Gillan, Phys. Rev. B 65, 165118 (2002).
17. -3 (43). Layer thickness uncertainty from this value is ±0.2 km.
18. If the mass expelled only partially constitutes an immiscible liquid layer, the analysis becomes a question of what outer-core compositions do not lead to immiscibility as the inner core crystallizes. In any Fe-light element binary T-X (temperature-composition) diagram with a two-phase liquid region, inner-core crystallization will drive the outer core to less Fe-rich compositions, possibly crossing into the two-liquid field. This will always be from compositions with lower light-element concentrations, thereby yielding the conservative, lower bound that we seek.
19. V. Kress, Contrib. Mineral. Petrol. 139, 316 (2000).
20. The associated solution model uses the conservative assumption that the heat-capacity difference between different solution species is constant, which avoids unphysical behavior outside the model's calibration domain (4). The model supersedes an earlier asymmetric solution model (44) that describes the 1-atm Fe-O-S diagram of (8).
21. Y. Fei, J. Li, C. M. Bertka, C. T. Prewitt, Am. Mineral. 85, 1830 (2000).
22. In contrast to earlier high-pressure experiments in the Fe-FeS system, recent experiments indicate lower Fe-FeS eutectic temperatures at high pressure (45-47).
23. R. Boehler, Earth Planet. Sci. Lett. 111, 217 (1992).
24. R. Boehler, Nature 363, 534 (1993).
25. 3S eutectic experiments requires volume-mixing nonideality and leads to significant differences in Fe-rich liquid densities if neglected. Compositional uncertainty ≃ ± 1 wt %.
26. C. E. Harvie, J. P. Greenberg, J. H. Weare, Geochim. Cosmochim. Acta 51, 1045 (1987).
27. A. Dziewonski, D. L. Anderson, Phys. Earth Planet. Int. 25, 297 (1981).
28. The calculated core liquid densities and wave speeds within ±2% of PREM that we consider to be feasible match the outer-core properties.
29. A. Zerr, A. Diegler, R. Boehler, Science 281,243 (1998).
30. J-Array Group, J. Geomagn. Geoelec. 45, 1265 (1993).
31. J. E. Vidale, H. M. Benz, Mature 356, 678 (1992).
32. S. Kaneshima, G. Helffrich, J. Geophys. Res. 103, 4825 (1998).
33. D. J. Stevenson, Geophys. J. R. Astron. Soc. 88, 311 (1987).
34. -1, eliminating any topography on the boundary between the liquids.
35. A. Morelli, A. M. Dziewonski, Geophys. J. Int. 112, 178 (1993).
36. -3 (75).
37. K. Holland, T. J. Ahrens, Science 275, 1623 (1997).
38. S. Urakawa, M. Kato, M. Kumazawa, in High-Pressure Research in Mineral Physics, M. Manghnani, Y. Syono, Eds. (American Geophysical Union, Washington, DC, 1987), pp. 95-111.
39. T. Okuchi, Science 278, 1781 (1997).
40. V. S. Solomatov, D. J. Stevenson, J Geophys. Res. 98, 5375 (1993).
41. 9 years. Parameter values are from (49), A rotating spherical geometry modifies the analysis, but appears to reduce the likelihood of entrainment (50).
42. D. C. Rubie, C. K. Gessmann, D. J. Frost, Mature 429, 58 (2004).
43. F. D. Stacey, C. H. B. Stacey, Phys. Earth Planet. Int. 110, 83 (1999).
44. V. Kress, Contrib. Mineral. Petrol. 127, 127 (1997).
45. T. M. Usselman, Am. J. Sci. 275, 278 (1975).
46. Y. Fei, C. M. Bertka, L. W. Finger, Science 275, 1621 (1997).
47. J. Li, Y. Fei, H.-K. Mao, K. Hirose, S. R. Shieh, Earth Planet. Sci. Lett. 193, 509 (2001).
48. Y. Fei, C. T. Prewitt, H.-K. Mao, C. M. Bertka, Science 268, 1892 (1995).
49. S. Labrosse, J.-P. Poirier, J.-L Le Mouël, Phys. Earth Planet. Int. 99, 1 (1997).
50. J. R. Lister, B. A. Buffett, Phys. Earth Planet. Int. 105, 5 (1998).
51. M. Schimmel, H. Paulssen, Geophys. J. Int. 130, 497 (1997).
52. J. Park, V. Levin, Bull. Seismol. Soc. Am. 90, 1507 (2000).
53. We used this cross-correlation method for the deconvolution with a 2-Hz cutoff. To window the arrivals in the linear stacks, we used the phase function for the phase-weighted stack (51), forcing it to be smooth in the neighborhood of the arrival by fitting it to a Lorenzian and tapering.
54. R. Kind, J. Geophys. 42, 191 (1976).
55. We thank the Japan Society for the Promotion of Science for support; V. Kress for clarifications about the liquid thermodynamic model; C. Houseman, B. Wood, and the referees for suggestions that substantially improved the manuscript; and J. Jacobs for inspiration to learn more about the core.