The effects of back-arc spreading on arc magmatism

Abstract

Mantle flow is a key feature that can affect melt production and composition in and around subduction zones. In this study, I use three-dimensional numerical models to investigate the role of mantle flow on subduction-related volcanism during back-arc extension. Results show that for a time interval of about 10-15 Myr during back-arc basin formation and spreading a wide convection cell brings mantle that has already partially depleted at the back-arc to the mantle wedge. Before and after this phase, the mantle reaching the sub-arc melting region is fertile. Thus, changes in back-arc activity and mantle flow pattern can be responsible for changes in magmatic composition and the amount of magmatism at the arc. These results are consistent with many examples of present-day subduction zones, in which phases of actively spreading back-arc correspond to a gap or a decrease of the arc volcanic activity.