Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmgp43a0883l&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #GP43A-0883
Physics
1533 Remagnetization, 1540 Rock And Mineral Magnetism
Scientific paper
The effects of shock waves on the natural remanent magnetization (NRM) and the intrinsic magnetic properties of solar system materials remains poorly known. Still, hypervelocity impacts are phenomena are of primary importance in the evolution of many extraterrestrial bodies. Hence, the interpretation of the paleomagnetic signal of most meteorites is blurred by the effects of impacts. Similarly, the remagnetization patterns associated to impact basins on Mars, the Moon or asteroids cannot be interpreted with certainty. We present new experiments in which four different terrestrial rocks (with different magnetic mineralogy) were impacted using detonators containing 0.8 g of the high-order explosive penthrite. Maximum pressure is about 10 GPa at the detonator contact (O 6 mm). The shock wave was modeled numerically and we studied the effects on the preexisting NRM as well as on the intrinsic magnetic properties of the shocked rocks. We show that in each case, the intrinsic magnetic properties of the rock are permanently modified by the shock wave. Magnetite-, titanomagnetite- and pyrrhotite-bearing rocks show a noticeable increase of their coercivity, whereas a hematite-bearing rock displays a lower coercivity after impact. These changes are not annealed even at high temperature (580 °C). Though most of the original NRM is not affected by the shock wave, we observe, in the low-coercivity component of the (titano)magnetite bearing rocks a shock demagnetization and a remagnetization. The direction of this remagnetization is poorly defined but does not seem closely related to the ambient field at the time of impact.
Boustie Michel
Gattacceca Jérôme
Lamali A.
Rochette Pierre
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