Self-diffusion of magnesium in spinel and in equilibrium melts - Constraints on flash heating of silicates

Details Self-diffusion of magnesium in spinel and in equilibrium melts - Constraints on flash heating of silicates Self-diffusion of magnesium in spinel and in equilibrium melts - Constraints on flash heating of silicates

Jun 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.2535s&link_type=abstract

Geochimica et Cosmochimica Acta (ISSN 0016-7037), vol. 56, no. 6, June 1992, p. 2535-2546.

Computer Science

15

Allende Meteorite, Magnesium, Self Diffusion (Solid State), Silicates, Spinel, Chemical Equilibrium, Melts (Crystal Growth), Temperature Dependence

Scientific paper

An 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.

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