Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 385, Issue -, Pages 79-88Publisher
ELSEVIER
DOI: 10.1016/j.epsl.2013.10.026
Keywords
cosmochronology; chondrites; magma residence time
Categories
Funding
- NASA [NNX09AB-93G]
- NSF [EAR03-19230, EAR07-44079, EAR10-53466]
- Division Of Earth Sciences
- Directorate For Geosciences [1053466, 1355590] Funding Source: National Science Foundation
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Experimental data are reported on Mg diffusion in plagioclase crystals with a range of anorthite content (x(An)), at temperatures between 800 and 1150 degrees C. Oriented and polished single crystals of anorthite (x(An) = 0.93), labradorite (x(An) = 0.67), andesine (x(An) = 0.43) and oligoclase (x(An) = 0.23) were each embedded in powered source material enriched in natural MgO or (MgO)-Mg-25 and suspended in a furnace at constant temperature. Diffusion profiles in quenched samples were measured from the polished surface using SIMS depth profiling. The diffusion coefficient does not depend significantly on the Mg concentration gradient, and little anisotropy is observed between the b and c directions in labradorite. Diffusion coefficients increase systematically with decreasing x(An), and the entire data set is described by ln D = (-6.06 +/- 1.10) - (7.96 +/- 0.42)x(An) - 287 +/- 10 kJ/mol/RT, where R is the gas constant, T is absolute temperature, and the diffusion coefficient D is in m(2)/s. Al-26-Mg-26 ages in albite-rich plagioclase are much more easily reset than in anorthite, with closure temperatures up to 120-150 K lower. (C) 2013 Elsevier B.V. All rights reserved.
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