The Molybdenum isotope subduction recycling conundrum: A case study from the Tongan subduction zone, Western Alps and Alpine Corsica

Molybdenum isotopes have emerged as novel tracers for high-temperature igneous and metamorphic processes. The debate remains to what extent different subducted slab lithologies, such oceanic crust marine sediments, contribute the Mo isotope signature of arc magmas and, hence, exert controls on terrestrial cycle. Here we investigate systematics from input output at Tongan subduction zone: Arc lavas islands, pelagic sediments altered (AOC) samples DSDP site 595/596 subducting Pacific plate. For complementary insights into fate its isotopic signatures during prograde metamorphism, also present data metasediments variably AOC-type eclogites Zermatt-Saas ophiolite, Switzerland Italy, Schistes Lustrés Complex in Alpine Corsica. Manganese oxide-rich show variable, depth-dependent Mo/Mn ratios compositions controlled by diagenetic reactions. As equivalents, Mn-rich eclogitic metapelites display lower contents ?98/95Mo compared their non-subducted protolith. This indicates prominent loss along with fractionation early metamorphism. In comparison unaltered MORB, low temperature seafloor alteration has shifted Mo/Ce studied AOC towards ratios, range most mafic published so far. However, some even AOC, likely due fluid-related upon preferential incorporation light residual rutile. Our document a isotopically heavy before metamorphism shallow depths forearc region. Moreover, when rutile crystallizes ~30 km depth, it fixes largest fraction material. creates an “arc Mo-conundrum” devolatization subarc is not able account fluid-mobile source responsible observed higher mantle. alternative scenario, mobilization slab-derived aqueous fluids stages mantle produces serpentinites enriched possible signature. Mechanical transport regions plausible recycling process accounting lavas. supported positive covariations elements As, Sb, Cs, which are thought be mostly released material subduction. We propose that multi-stage metasomatized can important possibly other elements.