Unraveling the simultaneous shock magnetization and demagnetization of rocks

Gattacceca, Julie C. and Boustie, M. and Lima, E. and Weiss, B.P. and de Resseguier, T. and Cuq-Lelandais, J.P. (2010) Unraveling the simultaneous shock magnetization and demagnetization of rocks. Physics of the Earth and Planetary Interiors, 182 (1-2). pp. 42-49. DOI 10.1016/j.pepi.2010.06.009

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Abstract

In the natural case of a hypervelocity impact on a planetary or asteroidal surface, two competing phenomena occur: partial or complete shock demagnetization of pre-existing remanence and acquisition of shock remanent magnetization (SRM). In this paper, to better understand the effects of shock on the magnetic history of rocks, we simulate this natural case through laser shock experiments in controlled magnetic field. As previously shown, SRM is strictly proportional to the ambient field at the time of impact and parallel to the ambient field. Moreover, there is no directional or intensity heterogeneity of the SRM down to the scale of ∼0.2 mm3. We also show that the intensity of SRM is independent of the initial remanence state of the rock. Shock demagnetization and magnetization appear to be distinct phenomena that do not necessarily affect identical populations of grains. As such, shock demagnetization is not a limiting case of shock magnetization in zero field. As a consequence, when it can be recognized in a rock, SRM must be considered as a reliable record of the direction and intensity of the ambient magnetic field at the time of impact. The natural process of hypervelocity impact where a rock carrying a remanent magnetization is shocked in the presence of an ambient field can be studied as the simple superimposition of shock demagnetization and shock magnetization. For this there are now a variety of techniques that allow experimental study of both phenomena separately or simultaneously as in this study. These results have potential implications for the paleomagnetic study of meteorites, and lunar rocks, and for the understanding of the magnetic signature (as studied through paleomagnetism and/or magnetic anomalies) of terrestrial, lunar and Martian impact craters.

Item Type: Article
Uncontrolled Keywords: NILAREP
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Physics of the Earth and Planetary Interiors
Volume: 182
Page Range: pp. 42-49
Identification Number: 10.1016/j.pepi.2010.06.009
Depositing User: Sarah Humbert
Date Deposited: 06 Feb 2012 19:01
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2358

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