83-3 Deciphering redox histories of aqueously altered carbonaceous asteroids with X-ray spectroscopy

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

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The chemical evolution of asteroids in the early Solar System is considered central to molecular studies of the origin of life and early Earth conditions. Carbonaceous chondrites widely contain minerals, such as carbonates, phyllosilicates, and sulfides, interpreted to have formed during progressive aqueous alteration from multiple instances of ice melting on their asteroidal parent bodies. These minerals hold keys to understanding the evolution of redox conditions on carbonaceous chondrite parent bodies. We used synchrotron X-ray microprobe fluorescence (μXRF) and X-ray Absorption Near-Edge Spectroscopy (XANES) at beam line 2-3 at SSRL to characterize valence states of Fe in CM carbonaceous chondrites having a range of aqueous alteration degrees. We focused on characterizing trace Fe in carbonate minerals, as well as Fe in phyllosilicate matrix. In successive generations of carbonate minerals (calcite and dolomite) with formation order inferred from petrographic relationships and Mn abundance, we find that early-forming, Mn-poor carbonate is associated with greater Fe valence number. This finding appears to support the view, in agreement with existing models and analytical results, that there may have been a transition toward more reducing conditions as aqueous alteration progressed on the CM parent body. This hypothesis is further supported by XANES measurements of the phyllosilicate matrix of a suite of CM chondrites that underwent varying degrees of aqueous alteration.

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

doi: 10.1130/abs/2025AM-9677

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