HR: 0800h
AN: GP21A-13    [Abstracts]
TI: Compositional, thermal, and orientation dependency of olivine magnetic properties
AU: * Belley, F
EM: fanfan24@siu.edu
AF: Department of Geology, Southern Illinois University, Carbondale, IL 62901, United States
AU: Ferré, E C
EM: eferre@geo.siu.edu
AF: Department of Geology, Southern Illinois University, Carbondale, IL 62901, United States
AU: Martín-Hernández, F
EM: fatima@geo.uu.nl
AF: Paleomagnetic Laboratory ‘Fort Hoofddijk', Utrecht University, Utrecht, 3584 CD, Netherlands
AU: Jackson, M J
EM: irm@umn.edu
AF: Institute for Rock Magnetism, University of Minnesota, Minneapolis, MN 55455, United States
AU: Dyar, M D
EM: mddyar@amherst.edu
AF: Mount Holyoke College, Clapp 320, 50 College Street, South Hadley, MA 01075, United States
AU: Catlos, E J
EM: catlos@okstate.edu
AF: Oklahoma State University, School of Geology, 105 Noble Research Centre, Stillwater, OK 74078, United States
AB: Olivine is an orthosilicate solid solution between forsterite Mg₂SiO₄ (Fo₁₀₀) and fayalite Fe2SiO4 (Fo₀). Cations such as Si⁴⁺ and Mg²⁺ are responsible for the diamagnetic behavior, whereas Fe²⁺ and other cations, present as defects in the lattice, such as Fe³⁺, Cr²⁺, and Mn²⁺, contributes to the paramagnetic behavior of the olivine. Yet, most natural and even synthetic olivines contain ferromagnetic iron oxide exsolutions similar to those commonly reported in other mafic silicates. Olivine is one of the most abundant constituents in the upper mantle of rocky planets, in meteorites, and in cosmic dust. Olivines with composition ranging form Fo₁₀₀ to Fo₀ are then exposed to temperatures that vary widely from about 5 K, away from the Sun in space, to about 1773 K at the 410 km olivine-wadsleyite transition. Below the Néel temperature (T_N< 65 K), natural and synthetic fayalites exhibit a magnetic transition interpreted as the change from paramagnetic to antiferromagnetic behavior. A second low-temperature transition has been described around 20 K in fayalite and was attributed to a change from collinear to canted antiferromagnetic state. The magnetic properties of fayalite are also varying with crystal orientation. At decreasing temperature, just below T_N, the magnetic susceptibility along the b axis stops following the Curie-Weiss law and begins to decrease. This drastic change is a clear indication of the antiferromagnetic behavior. The variation of magnetic susceptibility as a function of decreasing temperature along the two other axes, a and c, remains practically constant through the Néel transition. At the second low temperature transition (Tt), around 23 K, the variation of magnetic susceptibility with temperature changes along the c axis whereas no changes are noted along a and b. Experiments were performed on natural and synthetic ferromagnesian olivines of various iron contents between 4 and 300 K to further investigate their magnetic properties, regarding low-temperature transitions, compositional dependency, and magnetic anisotropy. Measurements were carried out in high magnetic fields, above the saturation of the ferromagnetic exsolutions to get access to the paramagnetic or diamagnetic properties of olivine.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 3900 MINERAL PHYSICS
DE: 5400 PLANETARY SCIENCES: SOLID SURFACE PLANETS
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly