Fluid–metasedimentary rock interactions in subduction-zone mélange: Implications for the chemical composition of arc magmas

Elevated concentrations of certain large ion lithophile elements (LILE; e.g., Ba, K, Rb, , Ca, Sr), U, and Pb in arc magmas relative to high field strength elements (HFSE; e.g., , Th, Hf, Nb, Zr) are considered key indicators of fluid addition to arc magma source worldwide, but the fluid sources and processes of mass transfer are controversial. of downgoing slabs releases fluids that can flow through and react with metamorphosed -mafic rock packages in me´lange zones near slab-mantle interfaces. geochemical data from Syros, Greece, reveal that these fluids preferentially leach , U, and Pb when they infiltrate and react with subducted metasedimentary rocks. of these LILE-, U-, and Pb-enriched fluids to the mantle wedge at subarc depths directly trigger partial melting and generate magmas with elevated Ba/Th, Sr/Th, /Th, and U/Th, as well as radiogenic Sr. Alternatively, if fluid transfer occurs at shallower (e.g., Syros), the metasomatized mantle could be carried deeper by wedge flow to ultimately undergo partial melting in subarc regions.