Date of Award

2026

Document Type

Honors Thesis (Open Access)

Department

Colby College. Geology Dept.

Advisor(s)

Tasha Dunn

Second Advisor

Bill Sullivan

Third Advisor

Alan Rubin

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. Two CV chondrite breccias, Camel Donga 003 (CD 003) and Camel Donga 040 (CD 040) consist of multiple lithologies. CD 003 consists of three lithologies, one of which – Lithology C – has been metamorphosed to petrologic type ~3.7 (Alevy et al. 2025). CD 040 consists of two lithologies, one of which is metamorphosed to petrologic type 3.7 (Dunn and Alevy, 2024; Dunn et al. unpublished). Both samples contain metamorphosed components (i.e., chondrules, matrix fragments, clasts, etc.) mixed within the primitive lithologies. One hundred and twenty-seven metamorphosed components constitute ~32% of CD 003; ninety-nine metamorphosed components constitute ~27% of CD 040.

We examined thin sections using microanalysis techniques, such as backscattered electron (BSE) imaging and energy dispersive spectroscopy (EDS) to identify all metamorphosed components within the samples. Components were divided into seven groups: chondrules, chondrule fragments, matrix fragments, single mineral grains, clasts, and unclassified. In-situ microanalyses of each sample were carried out using Scanning Electron Microscopy (SEM) to characterize textures and mineralogy and we measured mineral chemistries of selected representative components using Electron Probe Microanalysis (EPMA). The extent of thermal metamorphism was determined by calculating compositions of olivine as mol% fayalite for each component.

Similar olivine compositions from all representative metamorphosed components suggest both samples experienced similar conditions within the CV parent body and are metamorphosed to roughly the same extent. Further comparisons can be made across the two samples as well as other metamorphosed CV chondrite breccias and the proposed CV4 NWA 8418 (MacPherson et al. 2023). CD 003 and CD 040 components are more metamorphosed than the clasts identified by Jogo et al. (2013; 2019), and representative chondrules and matrix in CD 003 and CD 040 have similar compositions to chondrules and matrix in NWA 8418. These findings suggest that components reflect varying degrees of thermal metamorphism experienced on the CV parent body prior to brecciation and reaccretion.

Keywords

Chondrites, Camel Donga, Thermal metamorphism, Meteorites

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