Abstract
The shock exposure of the Santa Fe’s impact structure in New Mexico is evidenced by large human-size shatter cones. We discovered a new magnetic mechanism that allows a magnetic detection of plasma’s presence during the impact processes. Rock fragments from the impactites were once magnetized by a geomagnetic field. Our novel approach, based on Neel’s theory, revealed more than an order of magnitude lower magnetizations in the rocks that were exposed to the shockwave. Here we present a support for a newly proposed mechanism where the shock wave appearance can generate magnetic shielding that allow keeping the magnetic grains in a superparamagnetic-like state shortly after the shock’s exposure, and leaves the individual magnetized grains in random orientations, significantly lowering the overall magnetic intensity. Our data not only clarify how an impact process allows for a reduction of magnetic paleointensity but also inspire a new direction of effort to study impact sites, using paleointensity reduction as a new impact proxy.
Highlights
The advantage of the Santa Fe structure is that it is a deeply eroded structure that exposes the deep rocks that are not accessible in uneroded impact structures and provides a unique evidence of the exposed deep material to the shock pressure wave passing
There is an indication that shatter cones and planar deformation features, experiencing 5–30 GPa pressures dissipated from much higher-pressure fields, may be tied with unique magnetic properties
We argue that our observation of demagnetization of Santa Fe rocks by impact is the outcome of homogenizing the crystalline anisotropy, by modifying the outermost orbitals of the 3D electrons, allowing temporal crystalline isotropy
Summary
The advantage of the Santa Fe structure is that it is a deeply eroded structure that exposes the deep rocks that are not accessible in uneroded impact structures and provides a unique evidence of the exposed deep material to the shock pressure wave passing. The motivation of this study was to investigate the effect of impact pressure that produces shatter cones and planar deformation features (5–30 GPa) on Natural Remanent Magnetization (NRM). The classical work by Koenigsberger and the Thelliers soon after WWII laid out the generally accepted solution in terms of progressive double heating methods taking advantage of the law of partial TRM (pTRM)[21,22], named collectively as KTT). These KTT progressive double heating methods were developed to detect an effect of irreversible changes brought about by heating. Ogy have been the use of glasses, whose magnetic constituents do not alter on h eating[24] and of single plagioclase crystals with their included fine magnetite[25], which again does not alter on heating
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