Molybdenumisotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments Ahmad, Q. König, S. Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δ98/95Mo = −1.5 ‰, compared to the depleted mantle δ98/95Mo = −0.2 ‰. Such light Mo isotope compositions reflect the redoxdependent 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 δ98/95Mo of up to −0.1‰from the most depleted samples towards those tapping more enriched mantle sources. δ98/95Mo 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. 2022-11-18T11:39:01Z 2022-11-18T11:39:01Z 2022-10-12 journal article Ahmad, Q... [et al.] (2022) Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments. Geochem. Persp. Let. 23, 43–48. [https://doi.org/10.7185/geochemlet.2236] https://hdl.handle.net/10481/78039 10.7185/geochemlet.2236 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional European Association of Geochemistry