Iron and zinc stable isotope evidence for open-system high-pressure dehydration of antigorite serpentinite in subduction zones

Subducted serpentinites have the potential to control exchange of volatile and redox sensitive elements (e.g., Fe, S, C, N) between slab, mantle wedge deep mantle. Here we examine mobility iron zinc in serpentinite-derived fluids by using their stable isotopes (δ56Fe δ66Zn) high-pressure subducted meta-serpentinites from Cerro del Almirez massif (Spain). This preserves a metamorphic front antigorite (Atg-serpentinite) antigorite-olivine-orthopyroxene (transitional lithologies) -bearing serpentinites, chlorite-bearing harzburgite (Chl-harzburgite), displaying granofels, spinifex fine-grained recrystallized textures. Those rocks were formed at eclogite facies conditions (1.6–1.9 GPa 680–710 °C). The mean δ56Fe all (+0.05 ± 0.01‰) is identical within an error that primitive (+0.03 0.03‰). A positive correlation indices peridotite protolith fertility Al2O3/SiO2) suggests values samples predominantly reflect compositional variations, likely produced prior episodes melt extraction. In contrast, Zn concentrations ([Zn] = 34–67 ppm) isotope signatures (δ66Zn +0.18 – +0.55‰) show broad range values, distinct those 54 ppm; δ66Zn +0.16 0.06‰). Atg-serpentinites 34–46 +0.23 0.06‰) display similar [Zn] slab other meta-ophiolites. Both increase transitional lithologies 45–67 +0.30 Chl-harzburgites with granofels 38–59 +0.33 0.04‰) or 48–66 +0.43 0.09‰) Importantly, abnormally high relative abyssal peridotites (29–45 exists δ66Zn. interpreted mobilization subduction zone pressures temperatures coupled significant fractionation. An Atg-serpentinite Chl-harzburgite associated U/Yb, Sr/Y, Ba/Ce Rb/Ce, suggesting both record interaction had equilibrated metasedimentary rocks. Quantitative models metasediment derived can isotopically heavy as consequence sediment carbonate dissolution subsequent complexation species released [ZnHCO3(H2O)5+] [ZnCO3(H2O)3]). Our further demonstrate reduced carbon cannot produce signature hence explain variations observed Chl-harzburgites. most straightforward explanation for thus serpentinite dehydration accompanied open system infiltration oxidized, carbonate-rich sediment-derived during prograde subduction-related metamorphism.