Metasomatism along fluid pathways in the ultra-high pressure Svartberget garnet-peridotite (Western Gneiss Region, Norway): Implications for the transport of slab-derived fluids within the mantle wedge

Garnet-peridotites often contain veins or layers of pyroxenite and eclogite of uncertain origin. We investigate the Svartberget garnetperidotite from the northernmost ultrahigh-pressure domain in the Western Gneiss Region (WGR) in Norway and show that the observed layering represents a sequence of metasomatic reaction zones developed along a fracture system. From the garnet-peridotite wall-rock to the fractures the following sequential reaction zones are recognized: clinohumite bearing garnet-peridotite, olivine-garnetwebsterite, garnet-websterite, orthopyroxene-phlogopite-garnetwebsterite, coarse-grained phlogopite-garnet-websterite, phlogopite- garnet-websterite, phlogopite-free garnet-websterite, inclusion-rich garnetite, garnetite, eclogite, retrograde omphacitite and felsic amphibole- pegmatite. TheMgO, FeOand CaOcontents generally decrease from the pristine peridotite towards the most metasomatized samples, with an associated increase in SiO