Demagnetization by shock

Abstract:

The impact structures are evidenced by either large shatter cones and/or planar deformation features. We discovered an additional new magnetic feature that supports formation by impact processes. Rock fragments from the impactites were once magnetized by a geomagnetic field. Paleointensity method on the rocks that were exposed to the shockwave by impact, reveal more than an order of magnitude lower geomagnetic field intensity. There is no known terrestrial rock demagnetization process capable of achieving such demagnetization while the rocks are exposed to a geomagnetic field during the impact. In addition, the magnetic orientations after the impact are scattered in multiple orientations. We show that the shock wave may have put the magnetic grains into a superparamagnetic-like state and left the individual magnetized grains in random orientations. Our data not only suggest that an impact could have caused reduction of magnetic paleointensity but also inspire a new direction of effort to study impact sites, using paleointensity as an approach, to answer new questions about physics of magnetic environment during the shock waves’ caused by hypervelocity impacts.