Alteration processes in the CV chondrite parent body based on analysis of NWA 2086 meteorite

Abstract

Analysis of the NWA 2086 CV3 chondrite showed a matrix/chondrule ratio of 52%, similar to Bali, Mokoia, and Grosanaja. Nearly twice as many chondrule fragments as intact ones demonstrate that an early fragmentation phase occurred prior to final accretion. After this event, no substantial mechanical change or redeposition is evident. Rims with double‐layered structures were identified around some chondrules, which, in at least one case, is attributed to an accretionary origin. The rim's outer parts with a diffuse appearance were formed by in situ chemical alteration. During this later process, Mg content decreased, Fe content increased, and olivine composition was homogenized, producing a rim composition close to that of the matrix. This alteration occasionally happened along fractures and at confined locations, and was probably produced by fluid interactions. Iron oxides are the best candidate for a small grain‐sized alteration product; however, technical limitations in the available equipment did not allow exact phase identification. These results suggest that NWA 2086 came from a location (possible more deeply buried) in the CV parent body than Mokoia or Bali, and suffered less impact effects—although there is no evidence of sustained thermal alteration. This meteorite may represent a sample of the CV parent asteroid interior and provide a useful basis for comparison with other CV meteorites in the future.

Possible melting produced chondrule destruction in NWA 6604 CK4 chondrite

“…No great difference was found regarding the Fe/Mg ratio in the less and more altered parts, in contrast opposite to several other CV3 meteorites (Kereszturi et al. ).…”

“…As the values do not align along a trendline, no substitution of Mg by Fe under a closed system likely occurred, in contrast to some other CV3 meteorites, such as NWA 2086 (Kereszturi et al. ). There is also no apparent difference between chondrule and matrix‐related olivine composition—although the range in the matrix is a bit smaller than in the chondrules.…”

Case study of chondrule alteration with IR spectroscopy in NWA 2086 CV3 meteorite

“…Detailed general analysis of the whole thin section of this NWA 2086 meteorite can be found in Kereszturi et al (2014). Here we Fig.…”

Nano‐FTIR Investigation of the CM Chondrite Allan Hills 83100

“…This suggests that the sample olivine is forsteritic in composition. However, chondrule rims and zones 4-15 μm from the rims of chondrules once subjected to aqueous alteration processes have been observed to have significant Mg depletion compared to the chondrule core (Kereszturi et al, 2014(Kereszturi et al, , 2015. A large body of both experimental and modeling work investigating the MIR spectral properties of the forsterite-fayallite olivine solid solution has been conducted (Burns & Huggins, 1972;Dorschner et al, 1995;Duke & Stephens, 1964;Dyar et al, 2009;Fabian et al, 2001;Hamilton, 2010;Lane et al, 2011).…”