Chemical reactions between carbonates and pyrolite mantle and the origin of ultra-deep diamonds

• Applicant: Professor Dr. Leonid Dubrovinsky
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 242495784

Despite the number of studies performed at conditions of the Earth's mantle, very little (if something at all) is known about the carbon solubility and/or carbon-silicon substitution in major lower mantle silicates - bridgmanite (the most abundant mineral in the Earth) and CaSiO3 perovskite. Our and other groups investigations (in framework of the first funding period) of carbonate's behaviour at high pressures and temperatures reveal the formation of numerous compounds containing CO4-units. These works pointed out drastic changes in the crystal chemistry of carbonates above approximately 70 GPa and 2000 K. The novel observations on silica and carbon-bearing systems strongly suggest carbon may possibly be incorporated in Mg-, Fe-, Al-bearing or Ca-silicate perovskites, or even form silicate-carbonate phase(s) in the lowermost part of the lower mantle, and maybe in other regions of the Earth in its earlier stages of formation, when temperatures were higher. One of the major aims of this project is therefore the experimental investigation of possible carbon incorporation in (Mg,Fe)(Si,Al)O3 (bridgmanite) and CaSiO3 perovskite and/or the formation of complex compounds, containing both CO4 and SiO6 groups, at conditions of Earth's lower mantle. If carbon can really dissolve into silicate perovskites, it would have a major impact on our understanding of the deep carbon cycle, possible deep carbon reservoirs, and processes which may be capable of recycling a big amount of carbon deep inside the Earth.

• DFG Programme: Research Units
• Subproject of: FOR 2125: "Structures, properties and reactions of carbonates at high temperatures and pressures"
• Co-Investigator: Professorin Dr. Natalia Dubrovinskaia