HR: 11:30h
AN: T51H-05 INVITED     [PDF]
TI: Lattice Preferred Orientations in Naturally Deformed Peridotites: A Link from the Lab to Mantle Dynamics
AU: * Hirth, G
EM: ghirth@whoi.edu
AF: Woods Hole Oceanographic Institution, MS#8, Woods Hole, MA 02543 United States
AB: Our understanding of the rheological behavior of the Earth's mantle has been greatly enhanced by microstructural observations of both naturally and experimentally deformed rocks. The analysis of microstructures in naturally deformed rocks provides a critical link between theoretical and experimental studies and large-scale geologic processes. A current limitation in the application of both experimental observations on the development of lattice preferred orientations (LPO) in mantle rocks, and theoretical studies that are tested using the same data, is that the experiments are conducted at considerably higher stresses (or temperatures) than those experienced during deformation in the asthenosphere (or lithosphere). However, since specific deformation processes produce diagnostic microstructures, analyses of textures preserved in rocks can be used to constrain the applicability of experimental flow laws. In this talk I will present our new data obtained using EBSD (Electron Backscatter Diffraction) on LPOs in naturally deformed mantle rocks with well-constrained deformation histories. I will (1) discuss how the evolution of LPO with increasing strain in natural shear zones (Singletary and Hirth, in prep) compares with that determined experimentally (e.g., Zhang et al., 2000; Bystricky et al., 2000) and theoretically (e.g., Wenk and Tome, 1999; Kaminski and Ribe, 2001). (2) Illustrate the possible effects of grain boundary sliding (GBS) on the development of LPO (Braun, Hirth and Kelemen, in prep) and describe microstructural evidence that a transition from dislocation creep to diffusion creep can result in randomization of a pre-existing LPO and promote strain localization in the mantle lithosphere (Warren and Hirth, in prep). Throughout the talk I will compare the interpretations provided by the microstructural observations to predictions based on the extrapolation of experimentally determined flow laws for olivine aggregates (e.g., Hirth and Kohsltedt, 2003) and discuss their implications for the dynamics of the oceanic upper mantle.
DE: 3902 Creep and deformation
DE: 5120 Plasticity, diffusion, and creep
DE: 8030 Microstructures
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8162 Rheology--mantle
SC: Tectonophysics [T]
MN: 2003 Fall Meeting