Possible fingerprints of low-intensity, multiple impacts in the magnetic fabric of some carbonaceous chondrites

The study of meteorites’ magnetic fabric may provide information on various stages of material evolution in the Solar System from accretion to planetesimal formation and so on. One of the key processes is collisions and (hypervelocity) impacts, supposedly resulting in the alteration of the petrofabric. Surprisingly, many of the carbonaceous chondrites are characterized by low shock-stage, in contrast to their magnetic fabric, which shows the influence of impacts. The study aimed to propose and test the hypothesis of nanoscale fragmentation as evidence for multiple low-intensity impacts, based on the characterization of the magnetic fabric. A pioneering application of a novel method on meteorites, the anisotropy of frequency-dependent magnetic susceptibility measurements may enable the identification of nanoscale mineral components and their orientation in meteorites, potentially indicating the presence of such processes. In addition, combined rock magnetic (including hysteresis, isothermal remanent magnetization, first-order reversal curve, and thermomagnetic experiments) and scanning electron microscopy were also conducted on three carbonaceous chondrites: Allende, Jbilet Winselwan, and Murchison. As the executed rock magnetic measurements revealed, FeNi alloys, iron sulphides (pyrrhotite), and magnetite were the main magnetic contributor minerals. The foliated magnetic fabric and the oblate susceptibility ellipsoid are likely the marks of asteroid impacts and collisions, even though the shock stage of the studied meteorites suggests unshocked or very weakly shocked petrofabric. Multiple, low-intensity impacts may explain such a paradox. Still, due to the lack of superparamagnetic contributors, no nano-scale superparamagnetic fabric could be recognized by the anisotropy of frequency-dependent magnetic susceptibility measurements. Along with the characterization of the magnetic fabric, our study provided essential information about the rock magnetic contributors of Jbilet Winselwan, whose magnetic characteristics have not yet been studied in detail.