Calculated diffusion coefficients and the growth rate of olivine in a basalt magma

Author(s): Donaldson, Colin H.
Volume Title: Lithos (Oslo)
Source: Lithos (Oslo), 8(2), p.163-174. Publisher: Elsevier, Amsterdam, International. ISSN: 0024-4937 CODEN: LITHAN
Note: In English. Lunar Sci. Inst., Contrib.; illus.
Summary: Concentration gradients in glass adjacent to skeletal olivines in a DSDP 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 Mg2+ ions in the basalt is 4-5-10-9 cm2/s. 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 of 2-6-10-7 cm/s. This is too slow for olivine to have grown in situ during quenching. 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.
Year of Publication: 1975
Research Program: DSDP Deep Sea Drilling Project
Key Words: 01 Mineralogy and Crystallography; Basalts; Calculation; Coefficients; Crystal growth; Crystallization; Diffusion; Diffusion coefficients; Genesis; Geochemistry; Igneous rocks; Magmas; Minerals; Models; Nesosilicates; Olivine; Olivine group; Orthosilicates; Processes; Rates; Silicates; Temperature; Theoretical studies; Volcanic rocks
Record ID: 1975024699
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from U. S. Geological Survey, Hawaiian Volcano Observatory, United States

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