Fluid-mediated element cycling in subducted oceanic lithosphere: The orogenic serpentinite perspective

Serpentinites are central to water (re)cycling in subduction zones and thus effect fluid-mediated element transfer between the hydrosphere Earth's mantle back into continental crust via calcalkaline magmatism. Diverse often controversial models exist on relevance of various source contributions budget fluid mobile elements hydrous peridotites how these evolve during cycle. This work offers novel constraints ongoing debates. We present a comprehensive bulk rock silicate mineral major trace study covering antigorite dehydration reaction based Cerro del Almirez antigorite-serpentinites chlorite-harzburgites, including systematics As, Sb, B, W, Li, In, Tl, Bi, Cd, Sn - so far unavailable for Almirez, there only few such data orogenic serpentinites general. integrate with reviewed literature develop general model geochemical subducting slab magmatic peridotite conditioning, enrichment upon oceanic hydration, compositional evolution progressive peak temperature dehydration, retrograde metasomatism exhumation. Pre-hydration processes produce strong variations centimetre metre kilometre scales. Serpentinisation seawater sediment-equilibrated pore fluids produces highly variable fluid-mobile (FME) enrichments Cs, ±Li, ±Bi, ±Pb, ±U exceeding primitive concentrations. Hydration numbers represent concept introduced this refine extent hydration-mediated FME enrichment. They measured ratio over fluid-immobile closely comparable compatibility normalised its corresponding abundance ratio. highest Sb As (up 650) lowest Ba Rb (down 0.06) data, quantifying fractions minimal (values >1) prograde loss <1). occurred primarily ocean floor trench shallow forearc settings where relevant, while addition from deeper sediment metamorphic is subordinate at best. Prominent Rb, Sr, Ba, Pb, Zn, Cl, Br, Na, K, Ca then lost serpentinite antigorite-out reaction. find no evidence support significant (e.g., Th, U, Ta, Li) as has been postulated by simple comparison Atg-serpentinite Chl-harzburgite coexisting Almirez. Magmatic preconditioning prior serpentinisation can account differences HFSE Chl-harzburgite, prominent retrogression serpentine talc demonstrated Sr adulterating certain FME. concludes that dominates imprint goes along successive loss. propose fluid-dominated, hybridised oxidised plate interface melange materials displaying spectacular sedimentary flavour distinctly overrepresented our sample record. Therefore, combined set Erro Tobbio may offer more representative estimate mass subducted serpentinite, be used modelling impact serpentinite-derived matter chemical cycling zones.