Plasma shielding removes prior magnetization record from impacted rocks near Santa Fe, New Mexico

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.

Effects of Pressure and Temperature Changes on Shock Remanence Acquisition for Single‐Domain Titanomagnetite‐Bearing Basalt

“…During the compression and decompression cycle, the microcoercivity of the titanomagnetite grain decreases due to the compression as $$3{\lambda }_{s}\sigma /{M}_{s}$$, and then, it increases to the original state: the blocking curve parallelly shifts to the high‐coercivity side and returns to the original curve on the Néel diagram, and the titanomagnetite particles between two curves acquires the remanence. Thus, the compression/decompression cycle in an applied field gives a remanence similar to an IRM (Dunlop et al., 1969; Kletetschka et al., 2021; Tikoo et al., 2015). The SRM stability with respect to the AFD treatment increased with increasing P peak values in this study (Figure 6b), which is consistent with the remanence acquisition associated with the change in pressure.…”

“…The effect of plasma generation at the time of the impact event was pointed out based on the simulations (Crawford, 2020) and has been proposed to remain in terrestrial (Kletetschka et al., 2021) and lunar (Tarduno et al., 2021) samples. The strength of the magnetic field owing to plasma generation was calculated to decrease with decreasing projectile radius (Crawford, 2020), and plasma‐induced magnetization was not detected in laboratory experiments (Funaki & Syono, 2008).…”