FOR 2125:  "Structures, properties and reactions of carbonates at high temperatures and pressures"

• Subject Area: Geosciences
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 242495784

Understanding the composition and physical properties of the Earth's transition zone and lower mantle and the processes governing their behavior is one of the grand challenges in modern Geoscience. One of the large gaps in our knowledge concerning the Earth's mantle is the role of carbonates. It is possible that > 90 % of the Earth's carbon is contained in the deep Earth and it is estimated that 0.9 - 1.8 Tmol carbon is subducted per year, mainly in the form of carbonates. Evidence for primary carbonate in magmas coming from depths > 150 km has long been available and diamonds formed at great depths (> 660 km) have been found. However, experimental support for the conclusions drawn from analyzing natural samples is very scarce, simply because the number of experiments in which structure-property relations of carbonates have been determined at pressures above 20 - 30 GPa and high temperatures is very small due to the significant technical difficulties which have to be overcome. The focus of the work carried out in the first funding period (2015-2017) of the Research Unit DFG-FOR2125 was to develop methods which will allow us to carry out experiments leading to a better understanding of phase relations, and the crystal chemistry and physical properties of carbonates at mantle conditions. In the second funding period, we will use these methods in the framework of nine interlinked projects to study reactions of carbonates with silicates and oxides, to understand and properties of carbonates with tetrahedrally coordinated carbon, and to investigate structural, electronic and physical properties of carbonates at mantle conditions. The research unit draws on the expertise and instrumentation available in groups in Frankfurt, Bayreuth, Berlin/Potsdam, Dortmund, Freiberg, Köln, and Hamburg/Schenefeld. which mutually complement each other.

• DFG Programme: Research Units

Projects

• Carbonates under shock compression: stability, phase transitions, and chemical reactions with silicates (Applicant Kroke, Edwin )
• Chemical reactions between carbonates and pyrolite mantle and the origin of ultra-deep diamonds (Applicant Dubrovinsky, Leonid )
• Coordination of the research unit 2125 (Applicant Winkler, Björn )
• Elastic properties of carbonates at high pressures and temperatures (Applicant McCammon, Catherine )
• Elasticity and structure evolution of carbonates at upper mantle conditions (Applicants Speziale, Sergio ;  Winkler, Björn )
• Electronic structure of Fe/Mg carbonates at conditions of the Earth's lower mantle: Implications for the formation of tetrahedrally coordinated carbon (Applicants Sternemann, Christian ;  Wilke, Max )
• Phase relations and melting in the system CaCO3 und MgCO3 at high pressures and temperatures (Applicants Koch-Müller, Monika ;  Reichmann, Ph.D., Hans Josef )
• Phase stabilities of carbonates and reaction between carbonates and mantle minerals at high pressures and temperatures studied in the LH-DAC by Raman and time-resolved laser fluorescence spectroscopy (Applicants Bayarjargal, Lkhamsuren ;  Winkler, Björn )
• Structural, electronic and thermodynamic properties of carbonates at high pressures and temperatures by in situ spectroscopy and atomic-scale simulations (Applicants Efthymiopoulos, Ilias ;  Jahn, Sandro ;  Koch-Müller, Monika )
• X-ray fluorescence and X-ray absorption spectroscopy studies of element redistribution processes between carbonates and mantle phases at lower mantle conditions (Applicants Appel, Karen ;  Wilke, Max )

• Spokesperson: Professor Dr. Björn Winkler