Geochemical evidence for mélange melting in global arcs

Abstract

Arc lavas form from melting of mélange rocks; sediment melts and slab-derived fluids are not major contributors.

Abstract

In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated.