154-1 Hot or not?: metamorphosed chondrules in CV chondrite Camel Donga 003 as evidence for varying degrees of metamorphism within the parent body

Session: Asteroid Observations, Return Missions, and Meteoritics: Interweaving Perspectives and Data (Posters)

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Abstract:

The CV carbonaceous chondrites are a group of primitive stony meteorites that record early solar-system evolution processes. They are typically of low metamorphic grade, though some metamorphosed CVs have recently been found. Camel Donga 003 (CD 003) is a CV chondrite breccia consisting of three lithologies, one of which – Lithology C – has been metamorphosed to petrologic type ~3.7. 

To further investigate the extent of metamorphism in CD 003, we examined a second thin section using microanalysis techniques, such as backscattered electron (BSE) imaging and energy dispersive spectroscopy (EDS) to identify all metamorphosed components within the sample. We identified 129 individual pieces of metamorphosed material, which we divided into seven groups: chondrules, chondrule fragments, matrix fragments, single mineral grains, clasts, and unclassified. The most abundant type of component is chondrules (n=56), 27 of which are present within clasts and 29 within the sample matrix. We then used EDS to analyze the mineral chemistry of silicates, metals, oxides, and sulfides, with a particular focus on the homogeneity of olivine, which is used to assess the extent of metamorphism. Chondrule olivine becomes more iron-rich and equilibrated during thermal metamorphism. 

Using average fayalite (Fa) contents and standard deviations of olivine, we divided all chondrules into two groups: equilibrated (n=35) and unequilibrated (n=21). Equilibrated chondrules are characterized by standard deviations ≤1; average compositions of olivine range from Fa_33-47. The unequilibrated group is characterized by average standard deviations >1 and average compositions of Fa_7-60. There are no significant differences between chondrule type or size within the unequilibrated and equilibrated populations. Additionally, the majority of chondrules found in clasts (74%) and in chondrules occurring outside of clasts (62%) are equilibrated, suggesting that all chondrules experienced the same range of temperature conditions. 

The less unequilibrated chondrules in our section of CD 003 are consistent with the chondrules in lithology C, which are all also unequilibrated (Fa_24±7 to Fa_34±4) with one exception (Fa_40±0.5). Unequilibrated chondrules experienced lower peak temperatures than equilibrated chondrules. Assuming a thermally stratified parent body, the two populations suggest that components were metamorphosed at different depths within the parent body and then mixed together during brecciation and reaccretion.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7652

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