HR: 1340h
AN: GP33A-0095    [Abstracts]
TI: Paleomagnetism of Vredefort: Plasma, Lightning, or ?
AU: Hart, R
EM: hart@schonlan.src.wits.ac.za
AF: University of Witwatersrand, Schonland Research Center, P. Bag 3, Johannesburg, Wits 2050 South Africa
AU: * Carporzen, L
EM: lcarpo@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de Paleomagnetisme, 4 place Jussieu, PARIS, 75005 France
AU: Gilder, S
EM: gilder@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de Paleomagnetisme, 4 place Jussieu, PARIS, 75005 France
AB: Our recent article (Carporzen et al., 2005) suggested that a turbulent plasma field created during the first few seconds of the ~10 km-diameter meteorite impact at Vredefort led to extremely strong and randomly oriented magnetic vectors in shocked granite-gneisses containing magnetite that formed during the impact event 2 billion years ago. Impact dykes and pseudotachylites that cooled days to years after the impact have coherent magnetization components with north-northeast declinations and downward (50°) inclinations, and with magnetic intensities similar to volcanic rocks that form today (1 A/m). These observations led us to propose a model explaining why meteorite impact craters on Mars are associated with negative magnetic anomalies. Our article was based on 127 paleomagnetic sites collected in 2002 and 2004. We have now more than tripled our paleomagnetic collection and have performed magnetic surveys with both Cesium vapor and triaxial magnetometers. Our latest results show that lightning contributes more significantly to the paleomagnetic records than we previously supposed, yet they remain inconsistent with a thermoremanent magnetization origin. Carporzen, L., Gilder, S. A. & Hart, R. J., Palaeomagnetism of the Vredefort meteorite crater and implications for craters on Mars. Nature 435, 198 - 201 (2005).
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 1518 Magnetic fabrics and anisotropy
DE: 1519 Magnetic mineralogy and petrology
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1533 Remagnetization
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005