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Self-diffusion of magnesium in spinel and in equilibrium melts - Constraints on flash heating of silicatesAn isotopic tracer is used to measure Mg self-diffusion in spinel and coexisting melt at bulk chemical equilibrium. The diffusion coefficients were calculated from the measured isotope profiles using a model that includes the complementary diffusion of Mg-24, Mg-25, and Mg-26 in both phases with the constraint that the Mg content of each phase is constant. The activation energy and preexponential factor for Mg self-diffusion in spinel are, respectively, 384 +/- 7 kJ and 74.6 +/- 1.1 sq cm/s. These data indicate Mg diffusion in spinel is much slower than previous estimates. The activation energy for Mg self-diffusion in coexisting melt is 343 +/- 25 kJ and the preexponential factor is 7791.9 +/- 1.3 sq cm/s. These results are used to evaluate cooling rates of plagioclase-olivine inclusions (POIs) in the Allende meteorite. Given a maximum melting temperature for POIs of about 1500 C, these results show that a 1-micron radius spinel would equilibrate isotopically with a melt within about 60 min.
Document ID
19920062101
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Sheng, Y. J.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Wasserburg, G. J.
(NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Hutcheon, I. D.
(California Institute of Technology Pasadena, United States)
Date Acquired
August 15, 2013
Publication Date
June 1, 1992
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 56
Issue: 6 Ju
ISSN: 0016-7037
Subject Category
Lunar And Planetary Exploration
Accession Number
92A44725
Funding Number(s)
CONTRACT_GRANT: NAG9-43
CONTRACT_GRANT: DE-FG03-88ER-13851
Distribution Limits
Public
Copyright
Other

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