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 mélange (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.
We are grateful for Alfred Kroner's inspiration and advice. We also wish to thank the reviewers Samuel Angiboust, Tatsuki Tsujimori and Kennet Flores for their thorough and accurate suggestions and comments. This research was funded by Spanish projects CGL2009-12446, CGL2015-65824 and PID2019-105625RB-C21 granted by MICINN and MINECO and a FPI Ph.D. grant to J.C-P. by MICINN. YRA acknowledge support from DFG project RO4174/3-3 and from the SYNTHESYS program (http://www.synthesys.info/), Projects 312253/GB-TAF-4245 and 226506/GB-TAF-2342, funded by European Community Research Infrastructure Action under the FP7 "Capacities" Program. Support for field campaigns from the Cuban Institute of Geology and Paleontology and analyses at CIC from the University of Granada is acknowledged. The authors thank the staff of the University of Granada