EGU22-11903, updated on 28 Mar 2022
https://doi.org/10.5194/egusphere-egu22-11903
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modern hotspot-influenced MORBs reveal anoxic conditions during deposition and subduction of recycled Proterozoic sediments in their source

Qasid Ahmad1, Martin Wille1, Carolina Rosca2, Jabrane Labidi3, Timothy Schmid1, Klaus Mezger1,4, and Stephan König5
Qasid Ahmad et al.
  • 1Institute of Geological Sciences, University of Bern, Bern, Switzerland (qasid.ahmad@geo.unibe.ch)
  • 2Isotope Geochemistry Group, Department of Geosciences, University of Tübingen, Tübingen, Germany
  • 3Université de Paris, Institut de physique du globe de Paris, CNRS, Paris, France
  • 4Center for Space and Habitability, University of Bern, Bern, Switzerland
  • 5Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC & UGR, Granada, Spain

Significant Mo mobility and isotope (δ98/95Mo) fractionation is induced during prograde metamorphism at present-day subduction zones. Depending on the redox conditions during early subduction and accompanied slab dehydration, isotopically heavy Mo is released towards the overlying mantle wedge, leaving behind a depleted, and isotopically light subducted slab. This isotopically light Mo signature has been detected in slab-melt influenced volcanic rocks and potentially will be traceable in ocean-island basalts, if their geochemical signatures are affected by previously subducted lithologies (i.e. slab and overlying sediments). Thus, the isotope composition of mantle plume-influenced volcanic rocks might reveal the nature of subducted and re-incorporated lithologies and possibly redox conditions during subduction.

In this study, we present new Mo isotope data for South-Mid Atlantic Ridge basalts that partly interacted with the enriched Discovery and Shona mantle plumes. Isotopically heavier Mo isotope ratios (δ98/95Mo > ambient depleted mantle) are observed in samples tapping a more enriched mantle source. Furthermore, δ98/95Mo correlates with radiogenic isotopes (Sr, Nd, Hf) indicating recycling of a Proterozoic sedimentary components with a Mo isotopic composition that was not modified during and before subduction by Mo mobility under oxidising conditions. Rather, the new Mo isotope data supports and expands on previous stable Se and S isotope evidence that suggests the incorporation of subducted anoxic Proterozoic deep-sea sediments into the mantle of the South-Mid Atlantic Ridge basalts.

How to cite: Ahmad, Q., Wille, M., Rosca, C., Labidi, J., Schmid, T., Mezger, K., and König, S.: Modern hotspot-influenced MORBs reveal anoxic conditions during deposition and subduction of recycled Proterozoic sediments in their source, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11903, https://doi.org/10.5194/egusphere-egu22-11903, 2022.

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