Ba and Sr isotopic patterns from step-leaching experiments on the pristine Aguas Zarcas CM2 meteorite

Abstract

Stepwise acid leaching experiments were performed on the pre-rain CM2 fall Aguas Zarcas to interrogate release patterns and isolate fractions with isotopic anomalies. Acid leachates and a bulk sample were analyzed for elemental abundances via solution ICP-MS, and Sr and Ba isotopic compositions were measured using TIMS. Isotopic systematics reveal diverse values for the bulk sample and leachates, interpreted to reflect the Aguas Zarcas parent body history. Compared with the NBS987 standard, μ⁸⁴Sr values for the bulk sample average + 90, while the leach fractions yield +326 to −2089, with the largest μ⁸⁴Sr depletions in the strongest acid leachates. For Ba isotopes, the bulk sample shows resolvable depletions (μ values) in ¹³⁰Ba (−210), ¹³⁵Ba (−64), ¹³⁷Ba (−73) and ¹³⁸Ba (−89). Early leachates show positive anomalies in ¹³⁰Ba (up to +2295), ¹³²Ba, ¹³⁵Ba, ¹³⁷Ba, and ¹³⁸Ba. In contrast, final leachates show strong depletions for the same nuclides (up to −60,000 ppm μ¹³⁰Ba). The Sr and Ba isotopic anomalies found in the earlier leachates suggest that nucleosynthetic signatures were redistributed to more soluble phases during parent body alteration. Moreover, contrasting p-nuclide Sr and Ba nucleosynthetic anomalies suggest that presolar contributions came from a variety of nucleosynthetic sources, including possibly a rotating massive star undergoing a core-collapse supernova or an electron capture supernova.