A Highly dynamic hot hydrothermal system in the subduction environment: Geochemistry and geochronology of jadeitite and associated rocks of the Sierra del Convento mélange (eastern Cuba)

A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix melange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.