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Grain boundary diffusion rates in high-grade metamorphic rocks

Eiler, J. M. and Valley, J. W. and Baumgartner, L. P. and Graham, C. M. (1993) Grain boundary diffusion rates in high-grade metamorphic rocks. Abstracts with Programs - Geological Society of America, 25 (6). p. 326. ISSN 0016-7592. http://resolver.caltech.edu/CaltechAUTHORS:20130809-101403107

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Abstract

The rate of grain boundary diffusion has a strong influence on the mechanisms and scales kinetics in rocks. Grain boundary diffusion rates for oxygen isotopes have been previously estimated by grain coarsening or diffusive penetration experiments. We have combined ion microprobe and laser-based stable isotope analysis with numerical modeling to estimate the grain boundary diffusivity of oxygen isotopes in a granulite from the Adirondack Mnts., N.Y. The sample studied is a slab (ca. 20x30x50 cm) of gneiss from the Lyon Mnt. magnetite mine. This sample contains a sharp contact between nearly pure magnetite ore and the magnetite bearing, quartzo-feldspathic host-rock. Laser analysis of traverses across the contact reveal a 2.5‰/1.6 cm gradient between magnetite from within the ore (6.0‰) and accessory magnetite in the host (3.5‰), with an asymmetric, sigmoidal profile between the two extremes. The inflection in this profile is at the contact and the larger, steeper half is in the magnetite ore. The profile in the ore has a curvature characteristic of diffusion, and a penetration distance of 6-7mm. Ion microprobe analysis of individual magnetite grains (ca. 1-2mm) at the contact reveals that gradients of 2.3‰ are found on a scale of 500 um. Stable Isotope thermometry within mm-scale domains on both sides of the contact agree with the predictions of "Fast Grain Boundary" diffusion modeling (Eiler et al. 1992, CMP) for "dry" retrogression. The zonation of individual grains at the contact is also in agreement with Fast Grain Boundary modeling.


Item Type:Article
Additional Information:© 1993 Geological Society of America.
Record Number:CaltechAUTHORS:20130809-101403107
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130809-101403107
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39833
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Aug 2013 21:13
Last Modified:19 Aug 2013 21:13

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