Fluid-mediated alteration of eclogite lenses in subduction complexes: a case from the Leaota Massif (South Carpathians)
Elena Negulescu, Gavril Săbău, 2015. "Fluid-mediated alteration of eclogite lenses in subduction complexes: a case from the Leaota Massif (South Carpathians)", The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas, G. F. Zellmer, M. Edmonds, S. M. Straub
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Large 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.
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The subduction zone volatile cycle is key to understanding the petrogenesis, transport, storage and eruption of arc magmas. Volatiles control the flux of slab components into the mantle wedge, are responsible for melt generation through lowering the solidi of mantle materials and influence the crystallizing phase assemblages in the overriding crust. Further, the rates and extents of degassing during magma storage and decompression affect magma rheology, ultimately control eruption style and have consequences for the environmental impact of explosive arc volcanism. This book highlights recent progress in constraining the role of volatiles in magmatic processes.
Individual book sections are devoted to tracing volatiles from the subducting slab to the overriding crust, their role in subvolcanic processes and eruption triggering, as well as magmatic-hydrothermal systems and volcanic degassing. For the first time, all aspects of the overarching theme of volatile cycling are covered in detail within a single volume.