Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp33b..02l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #GP33B-02
Physics
1540 Rock And Mineral Magnetism, 5420 Impact Phenomena, Cratering (6022, 8136), 6225 Mars
Scientific paper
Renewed interest in the effects of impact-generated shocks on magnetic materials has been fueled by satellite observations of magnetic crustal remanence on Mars, new dynamic and static pressure experiments on rocks and pure minerals, and paleomagnetic studies of terrestrial craters. Attempts have been made to infer the magnetic carriers in planets and asteroids based on the experimental response of minerals to dynamic and static pressure. For example, unmagnetized crust surrounding impact basins on Mars has been attributed to low pressure (a few GPa) shock demagnetization. Dynamic and static experiments at low pressures (<1GPa) show that remanence decreases after the application of stress. The reduction of magnetic moment is accompanied by permanent changes in the magnetic properties. Recent experiments have expanded the pressure range of both static and dynamic experiments (up to 10-20 GPa), as well as the compositions of minerals investigated. Our compilation of the total body of data reveals universal trends, which include a decrease in magnetic remanence and an increase in bulk coercivity with increasing pressure. However, at low pressures (< a few GPa), the demagnetization trends are not unique for different minerals and compositions. Furthermore, at moderate shock pressures (~10 GPa), unusual features occur in specific phases, e.g. the remanence of pyrrhotite may increase as a result of permanent changes in its magnetic properties. Residual remanence is an unreliable measure of peak shock pressure; whereas, the changes in bulk magnetic properties are better correlated with pressure and a more robust "shock barometer." Unfortunately, the complex behavior of magnetic minerals to shock prevents the straightforward interpretation of magnetic carriers on Mars based on remote measurements of crustal remanence. At present, the nature of the intensely magnetized crust on Mars remains enigmatic.
Louzada Karin L.
Stewart Sarah T.
Weiss Benjamin P.
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