Melt-peridotite interactions: Links between garnet pyroxenite and high-Mg# signature of continental crust

It has been hypothesized that continuous melt-rock reaction between a silicic melt and ultramafic country rock (lherzolite) can convert olivine to orthopyroxene, ultimately resulting in the formation of a high Mg# garnet pyroxenite, similar to what is seen in the Hannuoba garnet pyroxenite composite xenoliths. In addition, silicic melts that have reacted with mantle peridotite would be predicted to have anomalously high Mg#s and Ni contents (due to the strong buffering capacity of peridotite for Mg and Ni), producing melts having compositions similar to the intermediate-mafic granulite xenoliths in this study. It is thus possible that the Hannuoba garnet pyroxenites and intermediate-mafic granulites share a common petrogenetic origin. Such a link is further supported by the fact that the rare-earth element abundance patterns of melts calculated to be in equilibrium with the garnet pyroxenites roughly coincide with that of the intermediate granulites. It is concluded that the Hannuoba garnet pyroxenite-bearing composite xenoliths may present the first physical evidence for the hypothesized melt-rock reaction necessary for generating evolved magmas with high Mg# and hence, high-Mg# andesitic signature of the continental crust.