Fluid-mediated alteration of eclogite lenses in subduction complexes: a case from the Leaota Massif (South Carpathians)

Abstract

AbstractLarge ion lithophile element enrichment is a feature of the lithologies affected by mass transfer owing to fluids from the subduction zones (Sorensen et al. 1997), well documented, for example, in mélanges of two subduction complexes: the Franciscan Complex (California) and Samana Metamorphic Complex (Dominican Republic). Here we illustrate a similar style of K–Ba–Rb alteration of various types of eclogites and their host rocks acquired during subduction zone metamorphism and subsequent inclusion in a metamorphosed subduction–accretion mélange complex in the Leaota Massif (South Carpathians). Textural evidence at different scales (knockers-with-rinds structures, phengite and atoll garnet overprints, open cavities) and thermobaric calculations document protracted fluid–rock interaction from near-peak conditions to the retrograde stages during detachment and ascension along the subduction channel. Fluids reverting to the surface along the subduction channel play an important part in the fluid budget of subduction zones.