HR: 17:45h
AN: T44B-08    [Abstracts]
TI: Heterogeneity and Shear Localization in Natural Systems With Emphasis on the Interplay of Inelastic and Plastic Processes
AU: * White, J C
EM: clancy@unb.ca
AF: Dept. of Geology, University of New Brunswick, 2 Bailey Hall, Fredericton, NB E3B 2E6, Canada
AB: The ubiquity of transient (cyclic), heterogeneous deformation, notably shear localization, in the rock record is such as to characterize it as the anticipated 'normal' behaviour. The corollary is that steady, homogeneous deformation is rare, and where approached must reflect some special set of conditions that are not representative of the general case. An issue central to natural deformation is then not the existance of localized strain, but rather how the extant deformation processes scale over tectonic phenomena and in turn organize to enable a coherent descripion of earth deformation. The strain energy distributions which drive thermo- mechanical responses are in the first instance established at the grain-scale where the non-linear interaction of micromechanical processes introduces fundamental, heterogeneous behaviour described by various gradient theories, and evidenced by the defect microstructures of deformed rocks. Hence, the potential for non-uniform response is embedded within even quasi-uniform, monomineralic materials, as seen in the spatially discrete evolution of dynamic recrystallization. Despite the interest in the latter purely mechanical localization, the more common type of heterogeneity promoting localization comprises mechanically contrasting materials typical of most rocks. Natural shear localization commonly demonstrates a cyclic interplay between inelastic rupture and subsequent plastic material softening resulting from the concomitant introduction of exogenous material in the form of igneous melts, deformation-induced melts and fluid precipitates (veins). Together this 2-stage process reflects localization and stabilization of the shear phenomena. The cyclicity of this behavior indicates that material hardening and non-associated flow over some characteristic time is a precursor to localized instability, with stabliization of localized shear correlated with system softening tied to redistribution of strain energy dissipation within what is effectively a reconstituted material. The resultant spectrum of mechanical responses observed at all lithospheric levels has the effect of masking brittle (seismic?) records. Fluctuations in rock composition, pressure and temperature and fluid activity with crustal level produce 'windows of transience' which are particularly amenable to this behavior.
DE: 3902 Creep and deformation
DE: 3904 Defects
DE: 8012 High strain deformation zones
DE: 8030 Microstructures
DE: 8031 Rheology: crust and lithosphere (8159)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting