CM chondrite aqueous alteration examined by geochemical modelling and laboratory experiments

Haller, Robin L.I. (2026) CM chondrite aqueous alteration examined by geochemical modelling and laboratory experiments. PhD thesis, University of Glasgow.

Abstract

Mighei-like (CM) meteorites are the most abundant group of carbonaceous chondrites and have been aqueously altered on their parent body/bodies to various degrees. As such, their study is key to understanding the evolution of the early Solar System and the delivery of water to Earth. However, the CM chondrites in our collection still sample only a small portion of the asteroids in our Solar System and questions such as under what conditions CM chondrites have been altered or how long did the aqueous alteration require are difficult to answer through meteoritical studies alone. Hence, this thesis was created to complement and expand on knowledge about the aqueous alteration of CM chondrites through geochemical modelling and laboratory experiments. As there is to date relatively little mineralogical information available on unaltered CM chondrites of petrologic type 3 (CM3s), the pristine CO3.00 Dominion Range 08006 was chosen as starting composition and was reacted with an aqueous fluid with additional CO2, NH3 and HCl based on cometary abundances and other modelling studies. Equilibrium models with variations in temperature, water/rock (W/R) ratio (by mass), CO2 concentration and other parameters such as pressure were built to provide an overview of possible alteration conditions in CM chondrites. Based on the results of these models, kinetic models were built to simulate the evolution of aqueous alteration with the trade-off of fewer parameters (fixed CO2 concentration in the aqueous fluid) and a simplified mineralogy. The models suggest that CM chondrites could form for a wide range of temperature, W/R ratio and CO2 concentration with more altered CM1 chondrites forming generally at higher temperatures than CM2s. All CM chondrites could have formed in different areas of a single parent after several years of aqueous alteration, although the exact duration depends heavily on the temperature. The laboratory experiments simulated a parent body alteration of DOM 08006 chips for which significant amounts of calcite formed after 30 days with a carbonated fluid but not with pure water, suggesting that the formation of early calcite in CM chondrites likely required the accretion of C-bearing ice, meaning that the CM parent body/bodies likely accreted beyond the CO2 snowline.

Terrestrially altered CM chondrites usually build little rust due to their low abundance of iron metal; nonetheless, terrestrial weathering can still have a profound impact on the mineralogy and isotopic composition, as shown by previous studies and experiments with pristine samples returned form asteroids Ryugu and Bennu. To evaluate the effect of terrestrial weathering on CM chondrites of different petrologic type, laboratory experiments were conducted with chips of Chwichiya 002 (a C3.00- ung but with similarities to CM chondrites), Murchison, Kolang and LaPaz Icefield 02277 reacting with artificial rainwater under oxidising conditions. The reacted chips, together with complementary kinetic models, suggest that Fe-sulphides, calcite and unknown Na-K chlorides are highly susceptible to terrestrial weathering and can potentially dissolve within less than 30 days. In less altered CM chondrites, metal and amorphous silicates also alter very quickly. Oxidising conditions result mainly in goethite and talc whereas under more reducing conditions, alteration products bear similarities to parent body alteration. Especially for CM3 chondrites, this style of alteration could decrease their petrologic type and could be the reason for the scarcity of CM3 chondrites in meteorite collections. Better models and broader and more sophisticated laboratory experiments are needed to better study and understand the aqueous alteration of CM chondrites.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Meteoritical Society.
• Subjects: G Geography. Anthropology. Recreation > GB Physical geography; Q Science > QB Astronomy; Q Science > QE Geology
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Funder's Name: Meteoritical Society
• Supervisor's Name: Lee, Professor Martin
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86227
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 15 Sep 2026 11:26
• Last Modified: 17 Sep 2026 11:33
• Thesis DOI: 10.5525/gla.thesis.86227
• URI: https://theses.gla.ac.uk/id/eprint/86227

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