HR: 15:15h
AN: GP73A-06    [Abstracts]
TI: High-Temperature Magnetic Fabric Development from Deformation of Magnetite in Shear Experiments
AU: * Till, J L
EM: tillx010@umn.edu
AF: Institute for Rock Magnetism, Dept. of Geology and Geophysics, University of Minnesota, 100 Union St. SE, Minneapolis, MN 55455, United States
AU: Moskowitz, B M
EM: bmosk@umn.edu
AF: Institute for Rock Magnetism, Dept. of Geology and Geophysics, University of Minnesota, 100 Union St. SE, Minneapolis, MN 55455, United States
AU: Jackson, M
EM: irm@umn.edu
AF: Institute for Rock Magnetism, Dept. of Geology and Geophysics, University of Minnesota, 100 Union St. SE, Minneapolis, MN 55455, United States
AB: We present results from deformation experiments on synthetic shear zones deformed at high temperature (T=1000-1200°C) designed to study magnetic fabric development under plastic conditions. Samples composed of magnetite-plagioclase aggregates were synthesized by hot-pressing at 1200°C resulting in aluminum-substituted magnetite of composition Fe_3-xAl_xO₄ where x=0.2 (AM20). These samples were subsequently deformed in co-axial simple shear to shear strains of up to γ=3. Extremely large increases in magnetic anisotropy measured by both susceptibility and anhysteretic remanence (AMS and AARM) can be explained by increases in magnetic grain shape anisotropy, indicating internal strain in the magnetic grains. Weak crystalline preferred orientation of the magnetic grains in some samples indicates that dislocation creep may be active for some fraction of grains but does not predominate. Significant changes in acquisition of isothermal remanence and increases in coercivity after deformation are likely to be stress-induced and reflect increases in the internal stress state of the magnetic grains.
DE: 1518 Magnetic fabrics and anisotropy
DE: 3902 Creep and deformation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2009 Joint Assembly