Differentiation of arc magmas and crustal growth: a Nd isotope perspective

Abstract

Abstract Arc magmas form new continental crust and are responsible for volcanic eruptions as well as for major metallic ore deposits. It is generally accepted that arc magmas are generated above subduction zones by partial melting of the mantle wedge and differentiate within the crust of the overriding plate through fractional crystallization, magma mixing and crustal assimilation. However, it is not clear in which proportions mantle and the above different intracrustal processes contribute to the broad geochemical variability of arc magmas. Here, using Nd isotope systematics and their geochemical modelling, I show that the thicker the crust of the overriding plate, the higher the assimilation rate of crustal rocks by mantle-derived magmas and the older the assimilated rocks. This highlights a systematic increase of crustal contribution to arc magma chemical and isotopic composition with the thickening of the overriding plate crust. The data presented are also consistent with growth and maturation of the continental crust through time by continuously increasing thickness, SiO2 content and Nd isotopically evolved composition.