A HIGHLY DYNAMIC HOT HYDROTHERMAL SYSTEM IN THE SUBDUCTION ENVIRONMENT: GEOCHEMISTRY AND GEOCHRONOLOGY OF JADEITITE AND ASSOCIATED ROCKS OF THE SIERRA DEL CONVENTO MeLANGE (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.

Automated summary

This passage discusses the formation of jadeitites and related rocks in a subduction-related block in eastern Cuba. Through various geochemical data and fluid interactions, it explains the mineral composition and metamorphism within the rocks.