HR: 1330h
AN: S22A-0424    [PDF]
TI: Windows of Transient Creep and Rupture in Continental Lithosphere
AU: * White, J C
EM: clancy@unb.ca
AF: Department of Geology University of New Brunswick, Box 4400, Fredericton, NB E3B 5A3 Canada
AB: Factors influencing variations of mechanical strength with depth include the geothermal gradient (T, P), lithology and fluids, amongst others. In stratified models of the lithosphere, gross variations in lithology control partitioning of mechanical behaviour into strong versus weak rheologies as a function of the latter factors. In exhumed crustal section there exist large volumes of both highly deformed and relatively undeformed continental lithosphere that nonetheless record similar crustal conditions in their metamorphic mineral assemblages. This spatial and temporal heterogeneity of lithospheric deformation means that data on strength in nature come from rocks weak enough to deform, while those that remain undeformed must be inter alia strong. Field-based studies record deformation styles that are repeated within any large-scale variation in crustal lithology. These `windows of transient deformation' are commonly associated with localization (fast strain rate, high-strength transient) and veins or melts (fluid input) that argue against steady-state behaviour. Comparison of experimentally imposed bounds with strength-related microstructures suggests that background ambient low stress/low strain rate response (bulk rheology) has imposed on it cyclic hardening and softening. These observations belie simple descriptions of P/T-related depth variations in strength and instead, deformation mechanisms appear to be critically sensitive to outwardly subtle variations in deformation environment. Such cycles of transient behaviour, including brittle deformation, are observed at all levels of the continental crust, and at least into the upper mantle.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 7218 Lithosphere and upper mantle
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting