Partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology

During subduction, oceanic lithosphere goes through a series of progressive dehydration and melting events. Initial dehydration of the slab occurs during low pressure metamorphism of the oceanic crust and involves significant dewatering and loss of labile elements. At depths of 80-120 km water release by the slab is believed to lead to partial melting of the oceanic crust. These melts, enriched in incompatible elements, fertilize the overlying mantle wedge and produce the enriched peridotitic sources of island arc basalts. Retention of Nb, Ta and Ti by a residual mineral in a refractory eclogitic lithology within the sinking slab are considered to cause their characteristic depletions in island arc basalts. These refractory eclogitic lithologies, enriched in Nb, Ta and Ti, accumulate at depth in the mantle. -from Author