Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmgp23a..07g&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #GP23A-07
Physics
1540 Rock And Mineral Magnetism, 1595 Planetary Magnetism: All Frequencies And Wavelengths, 5420 Impact Phenomena, Cratering (6022, 8136)
Scientific paper
The source of magnetic fields on extraterrestrial bodies is largely unknown. There is particularly little information about magnetic fields on asteroids and the Moon for the last 3 billion years because most samples from these bodies predate this time. An exception is the small amount of impact-melt which has been continuously created by hypervelocity impactors over most of solar system history. Impact melt can be used to test the controversial hypothesis that magnetic fields on extraterrestrial bodies were predominantly the product of impact-produced plasmas rather than of core dynamos. However, to date only a small amount of impact melt has been analyzed paleomagnetically. To assess the quality of impact melts as recorders of magnetic fields, in January 2004 and January 2005 we collected thousands of samples of basaltic glass from the perimeter of Lonar Crater, a 1.8 km diameter impact crater which formed approximately 50,000 years ago in the Deccan Traps in Maharashtra, India. Lonar crater is a unique extraterrestrial analog because it is the only fresh impact crater on the Earth in a basaltic target. Most glass samples have rounded features and are between 0.01 and 1 cm in size, indicating that they are fladen and impact spherules (microtektites) formed from molten ejecta that cooled in mid-air while subject to rotational and aerodynamic forces. We have found that both types of glasses are strongly magnetic (saturation remanence of ~2 A m-1), contain ferromagnetic crystals that are predominantly single domain in size, and have no significant remanence anisotropy. The glasses also carry a natural remanent magnetization (NRM) presumably acquired just after the impact. However, alternating field demagnetization results in large directional changes of the magnetic moment, with little decrease in moment intensity. We interpret this unusual behavior as progressive removal of different coercivity components that cooled while the orientation of the spinning glasses changed relative to the paleofield. We are currently working to determine whether Lonar glasses accurately record the paleofield intensity in which they cooled. Because the glasses acquired their NRM during the first tens of seconds after crater formation, a comparison of paleointensities derived from glass that cooled while rotating in mid-air and glass that cooled while stationary, may also allow us to determine if an impact at Lonar Crater amplified the ambient magnetic field.
Garrick-Bethell Ian
Louzada Karin L.
Maloof Adam C.
Soule Adam S.
Stewart Sarah T.
No associations
LandOfFree
Paleomagnetism of Lonar Crater Impact Glass does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Paleomagnetism of Lonar Crater Impact Glass, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Paleomagnetism of Lonar Crater Impact Glass will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-963679