Evolution of Diamond-Forming Systems of the Mantle Transition Zone: Ringwoodite Peritectic Reaction (Mg,Fe)2SiO4 (Experiment at 20 GPa)

Abstract

Abstract—The peritectic reaction of ringwoodite (Mg,Fe)₂SiO₄ and silicate–carbonate melt with formation of magnesiowustite (Fe,Mg)O, stishovite SiO₂, and Mg, Na, Ca, K-carbonates is revealed by experimental study at 20 GPa of phase relations in the multicomponent diamond-forming MgO–FeO–SiO₂–Na₂CO₃–CaCO₃–K₂CO₃ system of the Earth mantle transition zone. An interaction of CaCO₃ and SiO₂ with a formation of Ca-perovskite CaSiO₃ is also detected. It is shown that the peritectic reaction of ringwoodite and melt with the formation of stishovite controls physicochemically the fractional ultrabasic-basic evolution of both magmatic and diamond-forming systems of deep horizons of the transition zone up to its boundary with the Earth lower mantle.