Trace element models for mantle melting: application to volcanic arc petrogenesis

Abstract

Understanding mantle melting above subduction zones requires an evaluation of the behaviour of elements for which the mantle contribution greatly exceeds any subduction contribution. In this paper we present a compilation of partition coefficients for a suite of these elements (Nb, Zr, Y, Yb, Ca, Al, Ga, V, Sc, Fe, Mn, Co, Cr, Mg, Ni) for temperatures of 1200–1300°C, oxygen fugacities of QFM ± 1 and sub-alkaline compositions. These coefficients yield good-fit mantle depletion trends for abyssal, orogenic and trench-wall peridotites. Modelling of pooled melts from mantle melting columns, presented as FMM (fertile MORB mantle) normalized patterns, give signatures of the composition and degree of melting of the mantle wedge that are generally independent of the subduction component. In particular, patterns formed from melting of fertile mantle exhibit normalized element abundances in the order VHI > HI > MI (VHI = very highly incompatible, HI = highly incompatible and MI = moderately incompatible) at low degrees of melting, becoming VHI = HI = MI at high degrees of melting. With derivation from progressively depleted sources, the patterns for moderate degrees of melting change to VHI < HI = MI at moderate degrees of depletion and VHI < HI < MI at high degrees of depletion.