HR: 0800h
AN: GP21A-0120 [Abstracts]
TI: Development of Magnetic Fabrics in Experimental Shear Zones During Plastic Deformation
AU: * Till, J L
EM: tillx010@umn.edu
AF: University of Minnesota
Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0128, United States
AU: Jackson, M
EM: irm@umn.edu
AF: University of Minnesota
Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0128, United States
AU: Zimmerman, M E
EM: zimme030@umn.edu
AF: University of Minnesota
Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0128, United States
AU: Moskowitz, B M
EM: bmosk@umn.edu
AF: University of Minnesota
Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455-0128, United States
AB:
Magnetite-bearing rock analogues were synthesized and deformed in simple shear to observe the development
of magnetic fabrics under metamorphic conditions. Deformation was carried out using a gas-medium pressure
apparatus at elevated temperatures (500 ° C) and confining pressures around 300 MPa in order to achieve
plastic deformation. Samples composed of 2-micron, high-blocking-temperature (TB > 500 ° C)
magnetite in a calcite matrix were pressed and annealed under isostatic conditions so as to produce a nearly
isotropic starting fabric. The samples were then given weak-field thermoremanent magnetizations (TRM)
perpendicular to the shear plane and deformed below the blocking temperature of pseudo-single domain
magnetite. Intensity of post-deformation magnetic anisotropy as determined by AMS and AARM increases
systematically with amount of shear strain. In all deformation experiments, intermediate-coercivity overprints
were acquired with variable orientations and magnitudes, and the initial magnetization direction was preserved
as a stable, high-coercivity component. The original TRM therefore withstands differential stresses up to 300
MPa and indicates that no systematic rotation of the magnetite grains takes place during shear, yet the magnetic
fabric ellipsoid produced by deformation is oriented oblique to the shearing direction.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1540 Rock and mineral magnetism
DE: 3625 Petrography, microstructures, and textures
DE: 3902 Creep and deformation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting