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Science 17 December 1999:
Vol. 286. no. 5448, pp. 2323 - 2325
DOI: 10.1126/science.286.5448.2323
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Reports

Short-Lived Oxygen Diffusion During Hot, Deep-Seated Meteoric Alteration of Anorthosite

Claudia I. Mora, 1* Lee R. Riciputi, 2 David R. Cole 2

Heterogeneous oxygen isotope compositions of plagioclase from the Boehls Butte anorthosite include some of the most oxygen-18-depleted values (to -16 per mil) reported for plagioclase in meta-igneous rocks and indicate high-temperature (T > 500°C) isotopic exchange between plagioclase and nearly pristine meteoric fluid. Retrograde reaction-enhanced permeability assisted influx of meteoric-hydrothermal fluids into the deep-seated anorthosite. Isotopic gradients of about 14 per mil over 600 micrometers in single crystals require short-lived (about 104 years) diffusional exchange of oxygen and locally large effective water:rock ratios, followed by rapid loss of water and cessation of oxygen diffusion in the anorthosite.

1 Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA.
2 Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6365, USA.
*   To whom correspondence should be addressed. E-mail: cmora{at}utk.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Rates and Mechanisms of Isotopic Exchange.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)