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The diffusion behavior of hydrogen in plagioclase feldspar at 800-1000 C: Implications for re-equilibration of hydroxyl in volcanic phenocrysts by E. A. Johnson; G. R. Rossman is a scholarly article available to read on EtoBox.

What is The diffusion behavior of hydrogen in plagioclase feldspar at 800-1000 C: Implications for re-equilibration of hydroxyl in volcanic phenocrysts about?

To use structural hydroxyl (OH) concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption, it is first necessary to understand the diffusive behavior of hydrogen in plagioclase. In this study, diffusion coefficients for a natural OH-bearing plagioclase feldspar (Ab 66 An 31 Or 3 ) are determined from a series of integrated loss heating experiments performed at 800-1000 °C and 1 atm under air, nitrogen gas, and a CO 2 -H 2 mixture at the FMQ oxygen buffer. Hydrogen diffusion is found to be isotropic within analytical error. Using a one-dimensional diffusive loss model for an infinite slab, the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log D 0 = -1.62 ± 0.31 (m 2 /s) and E a = 266 ± 77 kJ/mol, and log D 0 = -0.97 ± 0.35 (m 2 /s) and E a = 278 ± 90 kJ/mol for experiments only conducted under nitrogen gas. Nearly complete (83-97%) loss of OH from the andesine was achieved in 900 and 1000 °C heating series, except for the 900 °C FMQ buffer experiment in which only 64% of the total OH was lost after 21.6 days of cumulative heating. The diffusion rates of hydrogen in the plagioclase after 800-1000

Author

E. A. Johnson; G. R. Rossman

Publisher

Mineralogical Society of America

Published

2013

Language

EN