Elasticity and structure evolution of carbonates at upper mantle conditions

• Applicants: Dr. Sergio Speziale; Professor Dr. Björn Winkler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 242495784

In this project we focus on the precise and accurate experimental determination of the full elastic tensor of the main carbonate minerals from ambient to moderate high pressures and temperatures (15 GPa and and 800 K) and its relationship with compositional and structural parameters, which will be determined on the same samples. In addition, we will complement our experimental work with DFT-based computations and synchrotron x-ray thermal diffuse scattering (TDS) and inelastic x-ray scattering (IXS) for selected samples. Knowing the physical and chemical behaviour of carbonate minerals at pressure and temperature conditions of the lithosphere is a key factor in understanding the deep cycle of carbon in our planet. However, the current knowledge of the elastic properties of carbonates and their dependence on their structure and composition is still far from being complete. The overall objective of this proposal is to understand the p, T, x-dependence of the elastic stiffness tensor of carbonates up to mantle conditions. This aim will be achieved by a combination of Brillouin scattering, density functional theory calculations, thermal diffuse scattering experiments and inelastic x-ray scattering experiments. In order to achieve the objectives we will address the following topics: (a) perform complete samples characterization by single crystal diffraction, IR- and Raman spectroscopy, low temperature calorimetry, electron microprobe and dilatometry as required; (b) carry out Brillouin scattering measurements of compositionally and structurally well characterised synthetic and natural samples at ambient conditions up to pressures of 15 GPa. This will allow us to understand the dependence of the elastic tensor on pressure, composition and ordering state; (c) extend the elasticity systematics to pressures corresponding to the upper mantle and high temperatures by Brillouin scattering in the resistive-heated diamond anvil cell; (d) use synchrotron x-ray thermal diffuse scattering to extract elastic stiffnes coefficients from TDS for high temperatures and measure acoustic phonons by high resolution IXS; (e) complement the experimental studies by density functional theory based calculations, in order to establish the effect of anharmonicity, non-linear pressure dependencies, and ordering state to provide a benchmark for the TDS measurements.

• DFG Programme: Research Units
• Subproject of: FOR 2125: "Structures, properties and reactions of carbonates at high temperatures and pressures"
• Cooperation Partners: Wolfgang Morgenroth, Ph.D.; Privatdozent Hans Josef Reichmann, Ph.D.