Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments
Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δMo = −1.5 %, compared to the depleted mantle δMo = −0.2 %. Such light Mo isotope compositions reflect the redox-dependent aqueous mobility of isotopically heavy Mo associated with slab...
| Autores: | , , , , , , |
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| Tipo de documento: | artigo |
| Estado: | Versão publicada |
| Data de publicação: | 2022 |
| País: | España |
| Recursos: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositório: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/357196 |
| Acesso em linha: | http://hdl.handle.net/10261/357196 |
| Access Level: | Acceso aberto |
| Palavra-chave: | Atlantic Ocean Mid-Atlantic Ridge Anoxic conditions Glass Isotopic composition Isotopic fractionation Molybdenum Plume Proterozoic Sedimentation Subduction |
| Resumo: | Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δMo = −1.5 %, compared to the depleted mantle δMo = −0.2 %. Such light Mo isotope compositions reflect the redox-dependent aqueous mobility of isotopically heavy Mo associated with slab dehydration. Here we analysed basaltic glasses from the South-Mid Atlantic Ridge, whose parental melts are influenced by the enriched Discovery and Shona mantle plumes. We report increasingly higher δMo of up to −0.1 % from the most depleted samples towards those tapping more enriched mantle sources. δMo values correlate with radiogenic Sr and Nd isotopes, which indicates the recycling of Proterozoic sediments with a Mo isotopic composition that was not affected by subduction-related, oxic dehydration. We propose that the Mo isotope signatures were retained during subduction and reflect anoxic conditions during deep sea sedimentation in the mid-Proterozoic. Finally, Mo isotope fractionation between different terrestrial reservoirs likely depends on the slab redox budget, and therefore on the timing of subduction with regard to Earth’s surface oxygenation. |
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