The presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early Solar System; however, the process of aqueous alteration is still poorly understood. We investigated the oxygen isotopic compositions of secondary minerals in CR chondrites to constrain fluid conditions on the asteroidal parent body.
Calcite, dolomite, and magnetite are some of the aqueously-formed minerals frequently found in CR chondrites. Using secondary ion mass spectrometry (SIMS), we measured the oxygen isotopic composition of these minerals in situ. This technique is useful as it retains the petrographic context of the phases being measured.
The compositions of the secondary minerals track fluid evolution, showing that fluid chemistry was dominated by the formation of phyllosilicates. The fluid evolved from being O17,18-enriched to O16-enriched as aqueous alteration progresses on the parent body. Using well-established oxygen isotopic fractionation factors for calcite and magnetite formation, we determine that aqueous alteration on the CR parent body occurred at low temperatures of ~55-88 degrees celsius.
Check out our paper, “Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses“, now out in Geochimica et Cosmochimica Acta, for more details.
To download a pdf of the manuscript, click here.
Christie Jilly-Rehak 