Diffusion kinetics of Fe 2+ and Mg in aluminous spinel: experimental determination and applications

Details Diffusion kinetics of Fe 2+ and Mg in aluminous spinel: experimental determination and applications Diffusion kinetics of Fe 2+ and Mg in aluminous spinel: experimental determination and applications

Sep 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002gecoa..66.2903l&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 66, Issue 16, pp.2903-2913

Computer Science

23

Scientific paper

The diffusion coefficients of Fe 2+ and Mg in aluminous spinel at ~20 kb, 950 to 1325°C, and at 30 kb, 1125°C have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles. The oxygen fugacity, fO 2 , was constrained by graphite encapsulating materials. The retrieved self-diffusion coefficients of Fe 2+ and Mg at ~20 kb, 950 to 1325°C, fit well the Arrhenian relation, D = D 0 exp(-Q/RT), where Q is the activation energy, with D 0 (Fe) = 1.8 (±2.8) × 10 -5 , D 0 (Mg) = 1.9 (±1.4) × 10 -5 cm 2 /s, Q(Fe) = 198 ± 19, and Q(Mg) = 202 ± 8 kJ/mol. Comparison with the data at 30 kb suggests an activation volume of ~5 cm 3 /mol. From analysis of compositional zoning in natural olivine-spinel assemblages in ultramafic rocks, previous reports concluded that D(Fe-Mg) in spinel with Cr/(Cr + Al) 0.5 is ~10 times that in olivine. The diffusion data in spinel and olivine have been applied to the problems of preservation of Mg isotopic inhomogeneity in spinel within the plagioclase-olivine inclusions in Allende meteorite and cooling rates of terrestrial ultramafic rocks.

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