Molybdenum isotope systematics in subduction zones

• We report δ98/95Moδ98/95Mo between −0.72 and +0.07‰+0.07‰ in different subduction zone lavas.
• Slab fluids lead to arc lavas with high δ98/95Moδ98/95Mo compared to the mantle.
• Melts from subducted sediments lead to arc lavas with lower δ98/95Moδ98/95Mo.
• The nature of the slab component controls δ98/95Moδ98/95Mo in arc lavas.

This study presents Mo isotope data for arc lavas from different subduction zones that range between δ98/95Mo=−0.72δ98/95Mo=−0.72 and +0.07‰+0.07‰. Heaviest isotope values are observed for the most slab fluid dominated samples. Isotopically lighter signatures are related to increasing relevance of terrigenous sediment subduction and sediment melt components. Our observation complements previous conclusions that an isotopically heavy Mo fluid flux likely mirrors selective incorporation of isotopically light Mo in secondary minerals within the subducting slab. Analogue to this interpretation, low δ98/95Moδ98/95Mo flux that coincides with terrigenous sediment subduction and sediment melting cannot be simply related to a recycled input signature. Instead, breakdown of the controlling secondary minerals during sediment melting may release the light component and lead to decreasing δ98/95Moδ98/95Mo influx into subarc mantle sources. The natural range between slab dehydration and hydrous sediment melting may thus cause a large spread of δ98/95Moδ98/95Mo in global subduction zone magmas.