HR: 0830h
AN: GP21C-0041    [PDF]
TI: Shock and Anisotropy Related Magnetization in a Freshly Fallen LL Ordinary Chondrite
AU: * Gattacceca, J
EM: gattacceca@cerege.fr
AF: Cerege, BP 80, Aix-en-Provence, 13545 France
AU: Rochette, P
EM: rochette@cerege.fr
AF: Cerege, BP 80, Aix-en-Provence, 13545 France
AU: Denise, M
EM: denise@cimrs1.mnhn.fr
AF: MNHN, 61 rue Buffon, Paris Cedex 05, 75231 France
AB: We conducted a rock magnetic, magnetic anisotropy and paleomagnetic study of the brecciated LL6 bensour meteorite a few months after its fall on Earth. Magnetic properties, in particular hysteresis loops before and after heating, as well as high field anisotropy indicate that tetrataenite is the major magnetic mineral. A very strong coherent susceptibility and remanence anisotropy is evidenced and interpreted as due to the last large impact responsible for the post-metamorphic and post-brecciation compaction of this material. Demagnetization of mutually oriented sub-samples evidences three components of magnetization. Medium and high coercivity components carried by tetrataenite are randomly distributed down to a scale of 0.1 cc. They represent the magnetization acquired by tetrataenite during its formation by low-temperature atomic ordering of taenite, but the link with the original magnetization of taenite and kamacite grains, acquired during cooling of the parent body after metamorphism, is unknown. Alternatively this randomness may be due to a post-metamorphic thermoremanent magnetization subsequently randomized by brecciation. A non random low-coercivity component is also evidenced. We show that it clearly predates the fall of the meteorite on Earth and postdates the last major impact on the meteorite parent body. The coercivity spectrum of this component as well as the close relation with the impact-related petrofabric indicate that the low coercivity component is likely related to this major impact, possibly in quasi-absence of ambient magnetic field.
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 6240 Meteorites and tektites
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting