Evidence for mantle metasomatism by hydrous silicic melts derived from subducted oceanic crust.

Shows that the melting of basalt under both water-added and low-temperature conditions can yield extremely alkali-rich silicic liquids. Properties of the liquids; Similarity to glasses preserved in mantle xenoliths found in subduction zones and to veins in exhumed metamorphic terranes of fossil convergent zones; Interaction with mantle olivine, which produces modal mineralogies identical to those observed in metasomatized Alpine-type peridotites; Suggestion that mantle metasomatism by slab-derived melt is more common than believed.