HR: 09:00h
AN: GP41C-05 INVITED     [Abstracts]
TI: Laboratory and Field Experiments to Better Understand Magnetic Anomalies of Meteorite Impacts
AU: * Gilder, S
EM: gilder@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
AU: Le Goff, M
EM: legoff@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
AU: Carporzen, L
EM: lcarp@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
AU: Hart, R J
EM: hart@schonlan.src.wits.ac.za
AF: University of the Witwatersrand, P. Bag 3 Wits, Johannesburg, 2050 South Africa
AU: Muundjua, M
EM: muundjua@schonlan.src.wits.ac.za
AF: University of the Witwatersrand, P. Bag 3 Wits, Johannesburg, 2050 South Africa
AU: Galdeano, A
EM: galdeano@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 05, IdF 75252 France
AB: The thermal and tectonic history of planets can be gleaned from the ancient magnetic fields recorded in their rock records. Because meteorite impacts alter the magnetic signals of rocks, one can hope to work out an approximate magnetic stratigraphy of a planet based on the relative timing of core dynamo activity versus the age of meteorite impact. Such is the common perception for Mars, whose giant impact craters, Hellas and Argyre, possess significantly lower magnetizations than surrounding regions. The typical assumption is that rocks in the craters were shock demagnetized in the absence of a core dynamo. To test these assumptions and to better understand the effects of stress on the remanent magnetizations of rocks, we have been carrying out both laboratory and field experiments. Here we report stress demagnetization experiments on single and multi-domain magnetite, the magnetic mineral most likely to carry the magnetic remanence on Mars. We also report paleomagnetic and geomagnetic measurements in the Vredefort crater, whose basement rocks carry magnetite as the remanence-bearing magnetic mineral. We conclude that magnetic fields fossilized in the rock record of meteorite impacts cannot be used to ascertain the presence or absence of a planet`s dynamo as previously assumed.
DE: 0654 Plasmas
DE: 0925 Magnetic and electrical methods (5109)
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 1540 Rock and mineral magnetism
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005