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Calculated diffusion coefficients and the growth rate of olivine in a basalt magmaConcentration gradients in glass adjacent to skeletal olivines in a basalt have been examined by electron probe. The glass is depleted in Mg, Fe, and Cr and enriched in Si, Al, Na, and Ca relative to that far from olivine. Ionic diffusion coefficients for the glass compositions are calculated from temperature, ionic radius and melt viscosity, using the Stokes-Einstein relation. At 1170 C, the diffusion coefficient of Mg(2+) ions in the basalt is 4.5 billionths sq cm per sec. Comparison with measured diffusion coefficients in a mugearite suggests this value may be 16 times too small. The concentration gradient data and the diffusion coefficients are used to calculate instantaneous olivine growth rates. Growth necessarily preceded emplacement such that the composition of the crystals plus the enclosing glass need not be that of a melt. The computed olivine growth rates are compatible with the rate of crystallization deduced for the Skaegaard intrusion.
Document ID
19750063402
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Donaldson, C. H.
(Lunar Science Institute, Houston, Tex.; St. Andrews, University St. Andrews, United Kingdom)
Date Acquired
August 8, 2013
Publication Date
January 1, 1975
Publication Information
Publication: Lithos
Volume: 8
Subject Category
Geophysics
Accession Number
75A47474
Funding Number(s)
CONTRACT_GRANT: NSR-09-051-001
Distribution Limits
Public
Copyright
Other

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