Presentation Information
[R5-17]An attempt to identify mineral nanofragmentation as the mark of multiple low-intensity impacts in carbonaceous chondrites
*Balazs Bradak1, Yusuke Seto2, Sena Toyonaga1, Akos Kereszturi3, Martin Chadima4 (1. Kobe University, 2. Osaka Metropolitan University, 3. Hungarian Academy of Sciences, 4. AGICO)
Keywords:
anisotropy of frequency-dependent magnetic susceptibility,carbonaceous chondrites,magnetic minerals,hypervelocity impact,multiple low-intensity impacts
Combined rock magnetic, magnetic fabric studies, and scanning electron microscopy were conducted on three carbonaceous chondrites: Allende, Jbilet Winselwan, and Murchison. The study aimed to propose and test the hypothesis of nanoscale fragmentation as evidence for multiple low-intensity impacts by the characterization of the magnetic fabric. Using a novel method, anisotropy of frequency-dependent magnetic susceptibility measurements may allow the identification of nanoscale mineral components and their orientation in meteorites, possibly indicating such processes. As the executed rock magnetic measurements revealed, FeNi alloys, iron sulphides (pyrrhotite), and magnetite were the main magnetic contributor minerals. The foliated 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 fabric. 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. Besides such results, using the magnetic fabric parameters, some observations were made about the possible development and alteration of the fabric due to hypervelocity and multiple, low-intensity impacts. The former may cause more homogenic-, and the latter process results in a more scattered magnetic mineral (re-)distribution.