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Experimental dehydration of natural obsidian and estimation of D_(H2O) at low water contents

Jambon, A. and Zhang, Youxue and Stolper, E. M. (1992) Experimental dehydration of natural obsidian and estimation of D_(H2O) at low water contents. Geochimica et Cosmochimica Acta, 56 (7). pp. 2931-2935. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20120821-111824383

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Abstract

Water diffusion experiments were carried out by dehydrating rhyolitic obsidian from Valles Caldera (New Mexico, USA) at 510–980°C. The starting glass wafers contained ~0.114 wt% total water, lower than any glasses previously investigated for water diffusion. Weight loss due to dehydration was measured as a function of experiment duration, which permits determination of mean bulk water diffusivity, D_w. These diffusivities are in the range of 2.6 to 18 × 10^(−14) m^2/s and can be fit with the following Arrhenius equation: In D_w(m^2/s) = -(25.10 ± 1.29)-(46,480 ± 11,400) (J/mol)/RT, except for two replicate runs at 510°C which give D_w values much lower than that defined by the above equation. When interpreted according to a model of water speciation in which molecular H_2O is the diffusing species with concentration-independent diffusivity while OH units do not contribute to the transport but react to provide H_2O, the data (except for the 510°C data) are in agreement with extrapolation from previous results and hence extend the previous data base and provide a test of the applicability of the model to very low water contents. Mean bulk water diffusivities are about two orders of magnitude less than molecular H_2O diffusivities because the fraction of molecular H_2O out of total water is very small at 0.114 wt% total water and less. The 510°C experimental results can be interpreted as due to slow kinetics of OH to H_2O interconversion at low temperature.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/0016-7037(92)90369-TDOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/001670379290369TPublisherUNSPECIFIED
Additional Information:© 1992 Pergamon Press. Received 3 December 1991. Accepted 10 April 1992. Available online 3 April 2003. We acknowledge the comments ofF. J. Ryerson, D. R. Baker, and two anonymous reviewers. YZ thanks J. Blank for help in C02 analyses. This research was supported by CNRS URA 736 to AJ and by NSF grant EAR-8916707 to EMS. Contribution 5034 of Division of Geological and Planetary Sciences, Cal tech. Editorial handling: G. Faure
Funders:
Funding AgencyGrant Number
Centre National de la Recherche Scientifique (CNRS)URA736
NSFEAR-8916707
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Caltech Division of Geological and Planetary Sciences5034
Record Number:CaltechAUTHORS:20120821-111824383
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120821-111824383
Official Citation:A Jambon, Youxue Zhang, E.M Stolper, Experimental dehydration of natural obsidian and estimation of DH2O at low water contents, Geochimica et Cosmochimica Acta, Volume 56, Issue 7, July 1992, Pages 2931-2935, ISSN 0016-7037, 10.1016/0016-7037(92)90369-T. (http://www.sciencedirect.com/science/article/pii/001670379290369T)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33401
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:21 Aug 2012 20:00
Last Modified:21 Aug 2012 20:00

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