Different modes of alteration in carbonaceous chondrites: timelines and processes

There are many unknowns when it comes to understanding our Solar System, one of them being the alteration processes that meteorites undergo. Meteorites represent a point in time from which they were extracted from the prevailing Solar System processes, therefore their microstructures, microtextures and composition provide invaluable evidence to the role of volatiles and early Solar System processes. This study examines three carbonaceous chondrites; NWA 3118, a CV and two CMs - Murchison and Sutter's Mill. These samples were analysed using SEM-EBSD and FEI Teneo Lovac FEG-SEM with dual Bruker Series 6 detectors (also referred to as NanoMin), each method presented various advantages and disadvantages. The observed microstructures enable the development of a timeline, where it is inferred whether the chondrites preserve primary formation or secondary alteration processes. From discussing and interpreting these microtextures, it was inferred that NWA 3118 provides an insight into predominantly primary formation features. In comparison, the microstructures seen in this Murchison sample indicate alteration on its parent body and multiple additions to the chondrite. Sutter's Mill underwent the same early processes as Murchison; however, its highly unusual lithology is attributed to potential asteroidal mixing. These findings are then linked to the role of volatiles, therefore gaining an insight into early Solar System processes.