Lightning remagnetization of the Vredefort impact crater: No evidence for impact-generated magnetic fields
Name
Wiess_Lightning remagnetization.pdf
Size
2.6 MB
Format
Adobe PDF
Checksum (MD5)
1cefd80ba412f29ccea68799d40a07b8
Author(s)
Carporzen, Laurent
Weiss, Benjamin P.
Gilder, Stuart A.
Pommier, Anne
Hart, Rodger J.
Date Issued
January 2012
Journal
Journal of Geophysical Research Planets
Publisher
American Geophysical Union (AGU)
Citation
Carporzen, Laurent et al. “Lightning Remagnetization of the Vredefort Impact Crater: No Evidence for Impact-generated Magnetic Fields.” Journal of Geophysical Research 117.E1 (2012). ©2012 American Geophysical Union
Version
Final published version
Abstract
The Vredefort impact crater in South Africa is one of the oldest and largest craters on Earth, making it a unique analog for planetary basins. Intense and randomly oriented remanent magnetization observed in surface samples at Vredefort has been attributed to impact-generated magnetic fields. This possibility has major implications for extraterrestrial paleomagnetism since impact-generated fields have been proposed as a key alternative to the dynamo hypothesis for magnetization on the Moon and asteroids. Furthermore, the presence of single-domain magnetite found along shock-generated planar deformation features in Vredefort granites has been widely attributed to the 2.02 Ga impact event. An alternative hypothesis is that the unusual magnetization and/or rock magnetic properties of Vredefort rocks are the products of recent lightning strikes. Lightning and impact-generated fields can be distinguished by measuring samples collected from below the present surface. Here we present a paleomagnetic and rock magnetic study of samples from two 10 m deep vertical boreholes. We show that the magnetization at depth is consistent with a thermoremanent magnetization acquired in the local geomagnetic field following the impact, while random, intense magnetization and some of the unusual rock magnetic properties observed in surface rocks are superficial phenomena produced by lightning. Because Vredefort is the only terrestrial crater that has been proposed to contain records of impact-generated fields, this removes a key piece of evidence in support of the hypothesis that paleomagnetism of the Moon and other extraterrestrial bodies is the product of impacts rather than past core dynamos.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1029/2011je003919
