¹Bennett J.K. Wilson, ²Kazuhide Nagashima, ^3,4Thomas J. Barrett, ⁵Veronica E. Di Cecco, ^5,6Kimberly T. Tait, ¹Michael G. Daly
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.12.046]
¹Center for Research in Earth and Space Science, York University, Toronto, ON, Canada
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, 1680 East-West Road, POST602, Honolulu HI96822, USA
³Department of Earth and Environmental Sciences, The University of Manchester, UK
⁴Center for Lunar Science and Exploration, Lunar and Planetary Institute, Houston, TX, USA
⁵Department of Natural History, Center for Applied Planetary Mineralogy, Royal Ontario Museum, Toronto, ON, Canada
⁶Department of Earth Science, University of Toronto, ON, Canada
Copyright Elsevier

The Tarda meteorite is a recently recovered C2-ungrouped carbonaceous chondrite that preserves evidence of early Solar System aqueous alteration. Tarda was found to share reflectance spectra with P-type asteroids, possibly enabling these elusive asteroids to be studied in the laboratory for the first time. Furthermore, Tarda has been shown to share many petrological and isotopic affinities with Tagish Lake – a pristine C2-ungrouped chondrite that is widely considered to source a D-type asteroid. Thus Tarda, Tagish Lake, and their respective spectral classes are probably genetically related, and potentially source a shared parent body. Despite their similarities, however, Tagish Lake hosts different lithologies and carbonate species than Tarda, suggesting distinct aqueous alteration histories between the two meteorites. Here, we present in-situ oxygen, carbon, and 53Mn–53Cr isotopic analyses of dolomite and magnetite in Tarda using Secondary Ion Mass Spectrometry to (i) investigate the conditions associated with aqueous alteration on the early Tarda parent body, and to (ii) compare our findings with Tagish Lake to assess heterogeneous aqueous alteration of their unique and likely shared parent body. For dolomite, we found that δ13C ranged from 55.8 ‰ to 72.9 ‰, while δ18O ranged from 23.3 ‰ to 28.8 ‰ with an average Δ17O of 0.1 ± 1.6. Dolomite additionally contained widespread 53Cr excesses that, if interpreted to have chronological significance, corresponds to a live [(53Mn/55Mn)0] value of (
. For magnetite, the δ18O values ranged from −5.5 ‰ to 5.8 ‰ with an average Δ17O of 2.4 ‰ ± 1.7. Oxygen isotope thermometry of a co-precipitating dolomite–magnetite pair indicates alteration temperatures of
°C. Compared to carbonates in Tagish Lake, dolomite in Tarda exhibits systematically lower δ17O, δ18O, and Δ17O signatures, but similar δ13C signatures. Temporally, the carbonates in both meteorites have identical ages within uncertainty. We conclude that Tarda has experienced greater aqueous alteration than Tagish Lake, likely due to increased water–rock interaction and/or higher temperatures.