A genetic metasomatic link between eclogitic and peridotitic diamond inclusions

Abstract

Diamond inclusions sample the otherwise inaccessible archive of Earth's deep interior. The geochemical and petrological diversity of diamond inclusions reflects either pre-metasomatic upper mantle heterogeneity or metasomatism coeval with diamond formation. We focus on the origin of lithospheric garnet and clinopyroxene inclusions by simulating metasomatic reactions between eclogitic fluids and mantle peridotites at 5 GPa, 1000 C, and across a range of redox conditions (logfO2 = -1 to -6 ?FMQ). Our results demonstrate that fluid-rock interaction can result in the formation of eclogitic, websteritic, and peridotitic silicates from a single fluid during a single diamond-forming metasomatic event. Ergo, the petrogenesis of diamond and their inclusions can be syngenetic, and the petrological diversity of diamond inclusions can reflect metasomatism coeval with diamond formation. Furthermore, during the metasomatism, refractory peridotite can be converted to fertile websterite which could become a pyroxenitic mantle source for oceanic basalts.