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^(18)O/^(16)O homogenization of the middle crust during anatexis: The Thor-Odin metamorphic core complex, British Columbia

Holk, Gregory J. and Taylor, Hugh P., Jr. (1997) ^(18)O/^(16)O homogenization of the middle crust during anatexis: The Thor-Odin metamorphic core complex, British Columbia. Geology, 25 (1). pp. 31-34. ISSN 0091-7613. doi:10.1130/0091-7613(1997)025<0031:OOHOTM>2.3.CO;2.

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The occurrence of isotopically uniform quartz (δ^(18)O = 12.5‰ ± 0.5‰) and feldspar (10.9‰ ± 0.7‰) throughout different rock types indicates that much of a 6-km-thick section of the mid-crustal Selkirk allochthon underwent internally buffered ^(18)O/^(16)O homogenization during Paleocene melting and decompression as it moved up the Monashee thrust ramp. Areas of uniform δ^(18)O are those with the most leucogranite or those subjected to severe anatexis. Only locally, in the most impermeable (or refractory) zones did ^(18)O exchange among the rocks, leucogranite melts, and aqueous fluids fail to go to completion (i.e., in the deepest parts of the section, in a marble-rich zone, around some thick amphibolites, and in most garnets). Evidence for ^(18)O/^(16)O heterogeneity in the protoliths of these rocks is observed in stratigraphically correlative lower-grade units elsewhere in British Columbia, as well as in garnets that coexist with isotopically homogeneous quartz. In our model, ^(18)O/^(16)O homogenization accompanied muscovite dehydration and partial melting of pelites with only minor influx of external H_2O, followed by release of magmatic H_2O from these melts (triggering further melting of adjacent feldspathic assemblages) as they were uplifted 20 km during thrusting just prior to onset of detachment faulting. Locally, low δ^(18)O in feldspar (down to −3.8) and profound quartz-feldspar ^(18)O/^(16)O disequilibrium were imprinted at shallow levels during meteoric-hydrothermal alteration associated with Eocene detachment faulting.

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Additional Information:© 1997 Geological Society of America. Manuscript received May 30, 1996. Revised manuscript received September 16, 1996. Manuscript accepted October 8, 1996. This research was supported by National Science Foundation grant EAR 93-17036 and Geological Society of America grant 4951-92. We thank S. Carr, P. Larson, B. Nesbitt, M. Palin, R. Parrish, M. Peters, L. Silver, B. Wernicke, S. Wickham, and P. Wyllie for discussions, and J. Holk for field assistance. Reviews by A. Grunder, Z. Sharp, and S.Wickham substantially improved the manuscript. Division of Geological and Planetary Sciences, California Institute of Technology, Contribution 5609.
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NSFEAR 93-17036
Geological Society of America4951-92
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Caltech Division of Geological and Planetary Sciences5609
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Official Citation: Gregory J. Holk and Hugh P. Taylor, Jr 18O/16O homogenization of the middle crust during anatexis: The Thor-Odin metamorphic core complex, British Columbia Geology, January, 1997, v. 25, p. 31-34, doi:10.1130/0091-7613(1997)025<0031:OOHOTM>2.3.CO;2
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ID Code:38431
Deposited By: Ruth Sustaita
Deposited On:10 May 2013 22:32
Last Modified:09 Nov 2021 23:37

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