Sr and Ba isotope composition of weathered eucrite
Stable strontium and barium isotopes are potential tracers for understanding planetary differentiation and the nature of the building blocks of terrestrial planets. Strontium and barium are fluid-mobile elements, but it remains unclear how terrestrial weathering affects the Sr-Ba isotopes compositio...
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| Language: | unknown |
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2024
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| Online Access: | http://nbn-resolving.org/urn:nbn:nl:ui:13-kg-dvwf https://easy.dans.knaw.nl/ui/datasets/id/easy-dataset:332134 |
| Summary: | Stable strontium and barium isotopes are potential tracers for understanding planetary differentiation and the nature of the building blocks of terrestrial planets. Strontium and barium are fluid-mobile elements, but it remains unclear how terrestrial weathering affects the Sr-Ba isotopes compositions in achondrites, thus hampering the utility of Sr-Ba isotopes in cosmochemistry. In this study, we conducted acetic acid leaching on three eucrites with varying weathering degrees (fall: Qiquanhu, hot desert find: Northwest Africa (NWA) 13583, and Antarctic find: Grove Mountains (GRV) 13001). Combined with detailed petrography observations and major and trace element analyses, we investigated the variations in Sr-Ba isotopes during terrestrial weathering. The degree of weathering follows an order of: NWA 13583>GRV 13001>Qiquanhu, evaluated based on several alteration signs, including: the presence of secondary carbonate, the enrichment of large ion lithophile elements (e.g., Sr, Ba, and U), and the Ce and Eu anomalies. The concentrations of Sr and Ba in the leachates of NWA 13583 show a good correlation with Ca, suggesting that the soluble Sr and Ba are derived from secondary carbonate. Differently, the concentrations of Sr and Ba in the leachates of Qiquanhu correlate with Al and Na, suggesting that the soluble Sr and Ba in Qiquanhu are derived from primary plagioclases. This also indicates that silicates dissolution may be inevitable in an acid leaching experiment for achondrites, even when using weak acetic acid. GRV 13001 shows no variation in Sr and Ba isotopes during leaching experiments. The δ138/134Ba in the leachate (0.26±0.02‰) of Qiquanhu is higher than that of the residue (0.04±0.03‰), reflecting that aqueous fluids preferentially uptake heavy Ba isotopes during plagioclase dissolution. Conversely, the leachate of NWA 13583 shows lower δ138/134Ba (-0.19±0.05‰) than that of residue (-0.10±0.03‰), reflecting the lighter Ba isotope composition in carbonate. Notably, the residue of NWA 13583 has ... |
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