Trace element fractionation processes in the generation of island arc basalts

Abstract

Subduction-related magmas are characterized by distinctive minor and trace element ratios which are widely attributed to the introduction of a hydrous component from the subducted crust. Island arc rocks may usefully be subdivided into high and low Ce/Yb groups, and the latter are characterized by relatively restricted radiogenic isotope ratios. A local equilibrium model is developed in which the distinctive minor and trace element feature of arc rocks are the result of fluid percolation in the mantle wedge. It is argued that the degree of melting varies with crustal thickness, but not in any simple way with the magnitude of the fluid contribution. The observed range in Ce/Sm in the low Ce/Y..