Primary carbonatite melt from deeply subducted oceanic crust

The geochemical and isotopic diversity observed in volcanic rocks at the Earth's surface is due in large part to partial melting in the Earth's mantle. Mineral inclusions in natural diamonds can provide a window into such deep mantle processes. Walter et al. provide experimental and geochemical observations showing that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. Such small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.