Origin of Cl-bearing silica-rich melt inclusions in diamonds: Experimental evidence for an eclogite connection

Melting phase relations of a model chloridefiand carbonate-bearing eclogite have been studied at 7.0-10.5 GPa and 1200-1675 °C. The mineral assemblage coexisting with partial melts is garnet, omphacite, kyanite, and coesite or stishovite. At temperatures of 1200-1400 °C, the partial melt has an SiO²-poor, Cl-bearing carbonatite composition. With increasing temperature, it becomes progressively SiO² rich, and at temperatures of 1500-1700 °C contains as much as 53 wt% SiO². The compositions of the melts are comparable with those of silicic end members of inclusions in fibrous and/or cloudy diamonds worldwide, implying that they may be produced via chemical reactions of alkalic chloride-carbonate liquids with mantle eclogites. Our experiments reproduced the trends of the compositional variations of the fluid or melt inclusions within eclogitic diamonds, and thus suggest a reliable model for their origin.