Date of Award
Honors Thesis (Open Access)
Colby College. Geology Dept.
Walter A. Sullivan
S-C mylonites form as a result of non-coaxial deformation in ductile shear zones. Planes of weakness develop and delineate two domains, the S and the C Each of these domains accommodates variable amounts of strain. Sample WMSZ-188 exhibits subgrain rotation (SGR) recrystallization in the C domains, and grain boundary migration (GBM) recrystallization in the S domains. This partitioning of recrystallization mechanisms indicates either: (1) strain-rate partitioning during a single deformation event; or (2) a second, lower-temperature deformation event that over-printed the C domains. This study tests these two hypotheses. Optical and EBSD analyses were used to look for evidence of a second phase of lower-temperature deformation in the S domains. The quartz grains in the S domains exhibit some areas of internal misorientation, however these zones are not interpreted as being a result of a SGR recrystallization overprint. High-temperature microstructures in feldspar and biotite also are preserved throughout the sample, indicating that no late-stage, low-temperature deformation over-printing occurred. These observations, in conjunction with optical analyses of samples from the region, indicate that these two recrystallization mechanisms are coeval. Because the sample does not record a syndeformational decrease in temperature and probably records nearly isobaric deformation due to its setting in a strike-slip fault system, the simultaneous generation of the recrystallization mechanisms is attributed to domainal strainrate partitioning during a single deformation event. One to three orders of magnitude of difference in strain-rate is required to transition from one recrystallization mechanism to another between the S and C domains. The implication of this domainal strain-rate partitioning is that caution must be exercised when using recrystallization mechanisms to determine deformation temperature.
Recommended CitationBeck, Emma N., "Examination of Spatial Variations in Recrystallization Mechanisms in Quartz" (2012). Honors Theses. Paper 654.
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