HR: 1330h
AN: T42A-0278    [PDF]
TI: Damage and elastic recovery of calcite-rich rocks deformed in the cataclastic regime
AU: * Schubnel, A
EM: schubnel@geologie.ens.fr
AF: Lassonde Institute, 170 College Street, Toronto, ON M5S E3E Canada
AU: * Schubnel, A
EM: schubnel@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure de Paris, 24 rue Lhomond, Paris, 75005 France
AU: Fortin, J
EM: fortin@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure de Paris, 24 rue Lhomond, Paris, 75005 France
AU: Burlini, L
EM: lburlini@erdw.ethz.ch
AF: ETH Zurich, Sonnegstrasse 5, 8092 Zrich, SWITZERLAND, Zurich, 8092 Switzerland
AU: Gueguen, Y
EM: gueguen@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure de Paris, 24 rue Lhomond, Paris, 75005 France
AB: Both compressional and shear wave velocities have been measured during hydrostatic and triaxial experiments in Carrara marble and Solnhofen limestone at room temperature. During brittle-ductile transition, competition between dilatant deformation mechanisms (crack opening and propagation) and compaction mechanisms (pore-collapse, phase transition, pressure-solution) takes place and inhibits microcrack propagation and coalescence. As a consequence, elastic anisotropy due to cracks is less sharp which is an expected result from fracture mechanics. During cataclastic dilatancy, elastic wave velocities decreased quasi-isotropically due to diffuse cracking in the rock. In such a deformation regime, during some deviatoric stress relaxation tests (i.e. blocking the piston movement, so that some of the elastic strain was converted into permanent deformation), we consistently observed a slight but yet non-negligible increase of elastic wave velocities. Elastic recovery was faster when grainsize was smaller and could be complete within a few days. In such conditions, absence of a dead band in the stress space indicates that calcite friction coefficient is very low (0.1-0.2). Microstructure analysis confirms that dilatancy is due to grain boundary sliding, wheras compaction is due to plastic pore collapse and twinning activity of calcite monominerals. Competition between dilatant and compaction mechanisms seems to depend on the presence of fluids and on the strain rate. This experimental result could have important consequences for fault mechanics and is in agreement with macroscopical mechanisms invoked by Rice [1992] to explain the low friction coefficient of certain major faults, such as San Andreas.
DE: 3902 Creep and deformation
DE: 3909 Elasticity and anelasticity
DE: 5102 Acoustic properties
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
SC: Tectonophysics [T]
MN: 2003 Fall Meeting