HR: 17:00h
AN: S22E-05    [PDF]
TI: On the Strength Contrast Between Naturally Deformed Crust and Mantle Rocks.
AU: * Drury, M R
EM: martynd@geo.uu.nl
AF: Department of Earth Science, Utrecht University, PO Box 80.021, Utrecht, 3508TA Netherlands
AU: van Roermund, H L
EM: hermanvr@geo.uu.nl
AF: Department of Earth Science, Utrecht University, PO Box 80.021, Utrecht, 3508TA Netherlands
AB: Field studies on upper mantle peridotite bodies provide information on deformation processes and mechanical strength of continental upper mantle rocks. Microstructures and lattice preferred orientations (LPO) in many continental peridotites indicate that dislocation creep is often the dominant deformation process in medium to coarse-grained rocks. Such coarse, dry, mantle rocks are expected to be much stronger than continental crust. In this contribution an example is described where, grain-size sensitive creep was the dominant deformation mechanism resulting in a low strength contrast between crust and mantle rocks. The example is from hydrated ultra-high-pressure peridotites from W. Norway. The geometry of folded compositional layers and the foliation refraction across layers implies that fine-grained olivine and pyroxene rocks are weaker than coarse-grained rocks. The structures are consistent with a granular flow process, like diffusion creep, with a limited viscosity contrast between the compositional layers. Some of the fold generations in the mantle rocks were formed after the mantle peridotites were emplaced into the continental crust. The intense post-emplacement deformation in the mantle rocks is consistent with a limited strength contrast between the hydrated mantle rocks and the surrounding quartzo-feldspathic crustal rocks.
DE: 3902 Creep and deformation
DE: 5120 Plasticity, diffusion, and creep
SC: Seismology [S]
MN: 2003 Fall Meeting