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The oxygen isotope anatomy of a slowly cooled metamorphic rock

Eiler, J. M. and Valley, J. W. and Baumgartner, L. P. and Graham, C. M. (1994) The oxygen isotope anatomy of a slowly cooled metamorphic rock. Abstracts with Programs - Geological Society of America, 26 (7). p. 43. ISSN 0016-7592.

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Laser-probe and ion microprobe analyses of δ^(18)O in magnetite from a granulite facies rock (Adirondack Mts., NY) document gradients over two scales: 10-100 µm within grains and 5-10 mm across a polygranular matrix. Analyses focus on layer of magnetite grains (5-10 mm wide) bounded by alkali feldspar on one side and garnet on the other. Ion microprobe analyses of magnetite adjacent to alkali feldspar document a depletion in δ^(18)O of up to 3‰, in the outer 100 µm of individual grains, steepening toward magnetite-feldspar grain boundaries. The magnitude, direction and shape of this zonation are in agreement with model predictions for diffusive exchange between magnetite and adjacent alkali feldspar during cooling. The same pattern of zonation is found in magnetite grains adjacent to garnet. However, slow rates of oxygen self diffusion in garnet prohibit such gradients forming by interdiffusion between magnetite and garnet. The presence of gradients requires that magnetite underwent exchange with another phase through grain boundaries.

Item Type:Article
Additional Information:© 1994 Geological Society of America.
Issue or Number:7
Record Number:CaltechAUTHORS:20130809-103022270
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39835
Deposited By: Tony Diaz
Deposited On:09 Aug 2013 20:32
Last Modified:03 Oct 2019 05:11

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