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Unequilibrated assemblages of sulphide, metal and oxide in the fusion crusts of the enstatite chondrite meteorites

Published online by Cambridge University Press:  05 July 2018

M. J. Genge  and
M. M. Grady
M. J. Genge
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
M. M. Grady
Affiliation:
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
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Abstract

The fusion crusts of meteorites form due to heating during atmospheric entry and have mineralogies which are strongly influenced by changes in oxidation state. We have studied the fusion crusts of the most reduced primitive meteorite group, the enstatite chondrites, since they should demonstrate pronounced changes on oxidation. The fusion crusts are dominated by highly unequilibrated assemblages of sulphide, metal and oxide with compositions indicative of progressive oxidation by the reaction with atmospheric oxygen. Troilite becomes depleted in Ti, Cr and Mn, and enriched in Ni with increasing oxidation. Enrichments in the Ni-contents of kamacite and depletions in Si-content also occur with oxidation, although contemporaneous enrichments in Si within metal droplets occurs by partial melting. Assemblages dominated by Fe-oxide are found within fusion crusts as reaction rims on metal, as veins and within troilite-metal assemblages as droplets and formed by oxidation of metal during heating. Despite the evidence for large increases in redox state during heating, fusion crusts also contain lithophile sulphides indicating a high degree of disequilibrium during the atmospheric reprocessing of enstatite chondrite materials. Based on comparisons with experimental phase relations, ablation rates of 0.08–0.25 cm s−1 are predicted from the thermal gradients recorded in fusion crusts; these rates are broadly similar to those suggested for other meteorite groups.

Keywords

enstatite chondritesfusion crustoxidationalteration
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 4 , August 1999 , pp. 473 - 488
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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References

Benoit, P.H. Jull, A.J.T., McKeever, S.W.S. and Sears, D.W.G. (1993) The natural thermoluminescence and terrestrial ages of meteorites. Meteoritics, 28, 196–203.CrossRefGoogle Scholar
Bunch, T.E. and Rajan, R.S. (1988) Meteorite regolithic breccias. In Meteorites and the Early Solar System (Kerridge, J.F. and Matthews, M.S., eds), pp. 144–64. Univ. Arizona Press.Google Scholar
Genge, M.J. and Grady, M.M. (1999) The fusion crusts of the stony meteorites: Implications for the atmospheric reprocessing of extraterrestrial materials. Meteoritics Planet. Sci., 34, 341–56.CrossRefGoogle Scholar
Jarosewich, E. (1990) Chemical analyses of meteorites: A compilation of stony and iron meteorite analyses. Meteoritics, 25, 323–37.CrossRefGoogle Scholar
Keil, K. (1968) Mineralogical and chemical relationships among enstatite chondrites. J. Geophys. Res., 73, 6945–79.CrossRefGoogle Scholar
Krinov, E.L. (1960) Principles of Meteoritics. Pergamon, New York.Google Scholar
Ramdohr, P. (1967) Die schmelzkruste der meteoriten. Earth Planet. Sci. Lett., 2, 197–209.CrossRefGoogle Scholar
Ramdohr, P. (1973) The Opaque Minerals in Stony Meteorites. Elsevier, New York.Google Scholar
Leitch, C.A. and Smith, J.V. (1982) Petrography, mineral chemistry and origin of type I enstatite chondrites. Geochim. Cosmochim. Acta, 46, 2083–97.CrossRefGoogle Scholar
Naldrett, A.J. (1969) A portion of the system Fe-S-O between 900-1080°C and its application to sulfide ore magmas. J. Petrol., 10, 171–201.CrossRefGoogle Scholar
Öpik, E.J. (1958) Physics of Meteor Flight in the Atmosphere. Interscience, New York.Google Scholar
Rubin, A.E. (1997 a) Mineralogy of meteorite groups. Meteoritics Planet. Sci., 32, 231–48.CrossRefGoogle Scholar
Rubin, A.E. (1997 b) The Galim LL/EH polymict breccia: Evidence for impact-induced exchange between reduced and oxidized meteoritic material. Meteoritics Planet. Sci., 32, 489–92.CrossRefGoogle Scholar
Rubin, A.E. and Scott, E.R.D. (1997) Abee and related EH chondrite impact-melt breccias. Geochim. Cosmochim. Acta, 61, 425–35.CrossRefGoogle Scholar
Rubin, A.E., Fegley, B. and Brett, R. (1988) Oxidation state in chondrites. In Meteorites and the Early Solar System (Kerridge, J.F. and Matthews, M.S., eds), pp. 488–511. Univ. Arizona Press.Google Scholar
Sears, D.W. and Mills, A.A. (1972) Temperature gradients and atmospheric ablation rates for the Barwell meteorite. Nature Phys. Sci., 242, 25–6.CrossRefGoogle Scholar
Sears, D.W. and Mills, A.A. (1974) Thermoluminescence and the terrestrial age of meteorites. Meteoritics, 9, 47–67.CrossRefGoogle Scholar
Sears, D.W., Kallemeyn, G.W. and Wasson, J.T. (1982) The compositional classification of chondrites: II The enstatite chondrites. Geochim. Cosmochim. Acta, 46, 567–608.CrossRefGoogle Scholar
Skinner, B.J. and Luce, F.D. (1971) Solid solutions of the type (Ca, Mg, Mn, Fe)S and their use as geothermometers for the enstatite chondrites. Amer. Mineral., 56, 1269–96.Google Scholar
Van Schmus, W.R. and Wood, J.A. (1967) A chemical-petrologic classification for the chondritic meteorites. Geochim. Cosmochim. Acta, 31, 747–65.CrossRefGoogle Scholar
Weeks, K.S. and Sears, D.W.G. (1985) Chemical and physical studies of type 3 chondrites — V: The enstatite chondrites. Geochim. Cosmochim. Acta, 49, 1525–36.CrossRefGoogle Scholar