Restite entrainment in S-type granites: A systematic review

Abstract

S-type granites show linear correlations for major elements and some trace elements in bivariate diagrams against maficity (FeO_t + MgO), with negative trends for major incompatible elements and positive trends for major compatible elements, extending beyond the usual composition of experimental and anatectic melts. Although several petrogenetic processes have been suggested, restite entrainment has been prominently proposed to explain that compositional feature. Restite entrainment implies that melt leaves the partially melted source rocks containing variable amounts of the solid phases present in the melting volume, which are generally Ca-Fe-Mg-Ti-richer and Si-Na-K-poorer than the melt. The entrainment of these phases will consequently produce the described compositional trends. In this manuscript I provide a review of this process based on my personal experience with thermodynamic modelling of the partial melting of metasedimentary sources and on conclusions published by other authors. In particular, I review what constitutes restite, the factors that control the entrainment of minerals, the proposed types of restite entrainment, the evidence in favor of (or against) this process, and other related aspects.