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dc.contributor.authorMehl, Luc  Concept link
dc.contributor.authorHirth, Greg  Concept link
dc.date.accessioned2010-06-16T19:32:23Z
dc.date.available2010-06-16T19:32:23Z
dc.date.issued2008-05-07
dc.identifier.citationJournal of Geophysical Research 113 (2008): B05202en_US
dc.identifier.urihttps://hdl.handle.net/1912/3662
dc.descriptionAuthor Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): B05202, doi:10.1029/2007JB005075.en_US
dc.description.abstractWe evaluate the applicability of plagioclase and gabbro flow laws by comparing predicted and observed deformation mechanisms in gabbroic shear zones. Gabbros and layered gabbro mylonites were collected from the Southwest Indian Ridge (SWIR), Ocean Drilling Program Hole 735B. Deformation temperatures are constrained by two-pyroxene thermometry, stress is estimated from grain size, and deformation mechanisms are analyzed by microstructure and the presence or absence of a lattice preferred orientation (LPO). Our analyses indicate that mylonite layers deformed at a strain rate in the range of 10−12 to 10−11 s−1, while coarse-grained gabbro deformed at a strain rate of approximately 10−14 to 10−13 s−1. Plagioclase in pure plagioclase mylonite layers exhibit strong LPOs indicating that they deformed by dislocation creep. Plagioclase grain size in mixed plagioclase-pyroxene mylonite layers is finer than in pure plagioclase layers and depends on the size and proportion of pyroxenes. Progressive mixing of pyroxene and plagioclase within gabbro mylonite layers is accompanied by weakening of the LPO, indicating that phase mixing promotes a transition to diffusion creep processes that involve grain boundary sliding. Our results indicate that experimental flow laws are accurate at geologic strain rates, although the strain rate for diffusion creep of fine-grained gabbro may be underestimated. At the conditions estimated for the SWIR crust, our calculations suggest that strain localization leads to a factor of 2–4 decrease in lower crustal viscosity. Away from shear zones, the viscosity of lower gabbroic crust is predicted to be similar to that of dry upper mantle.en_US
dc.description.sponsorshipThis work was supported with NSF grants EAR-0230267 and EAR-0409609.en_US
dc.format.mimetypetext/plain
dc.format.mimetypeapplication/postscript
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dc.language.isoen_USen_US
dc.publisherAmerican Geophysical Unionen_US
dc.relation.urihttps://doi.org/10.1029/2007JB005075
dc.subjectMyloniteen_US
dc.subjectRheologyen_US
dc.subjectFlow lawen_US
dc.titlePlagioclase preferred orientation in layered mylonites : evaluation of flow laws for the lower crusten_US
dc.typeArticleen_US
dc.identifier.doi10.1029/2007JB005075


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