Solving the paradox of the Fe-O system to understand the mineralogy of deep planetary interiors

• Applicant: Professorin Dr. Elena Bykova
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497931379

Processes on the surfaces of rocky planets, such as Earth, are directly connected to the chemistry and dynamics of their interiors. The presence of an atmosphere and its composition, the formation and function of a geodynamo, plate tectonics – the most important conditions for a planet’s habitability – are all directly linked to mineral physics and geochemistry of the bulk planet. The key minerals constituting the Earth’s mantle and many phases proposed for mantles of the extra-terrestrial rocky planets are isostructural to iron oxides (e.g. ringwoodite is isostructural to Fe3O4, akimotoite has the same crystal structure as hematite, Fe2O3, and periclase and wuestite are also isostructural). The extreme p,T-conditions generally required for the synthesis of non-quenchable high-p,T-silicates are currently preventing a deeper understanding of their structure-property relations at Mbar-conditions. Unlike their silicate counterparts, the corresponding iron oxides generally can be synthesized at much milder, but still challenging, conditions, making them perfect model compounds for studying complex phases and chemical transformations of planetary mantle minerals at high p,T. However, for more than a dozen iron oxides that have been discovered at high pressures in the last few years, no silicate analogs have been reported yet. This so-called “Fe-O system paradox” is unexpected and surprising and requires an explanation. Currently, we cannot exclude that the behavior of the Fe-O system and silicates might be indeed fundamentally different or that conditions within the Earths or super-Earths might prevent complex silicates to form, but this is highly improbable. Instead, the working hypothesis of the current proposal is that the experimental methods used so far, and the p,T conditions explored up to now were inappropriate for the detection of complex phases. A major bottleneck in finding the correct answer for “Fe-O system paradox” is the lack of experimental data concerning the behavior of planetary materials at their mantle and core conditions i.e. pressures above 100 GPa and temperatures above 2500 K. A key parameter – their crystal structure – is unknown for most of the compounds thought to form e.g. the interior of Super-Earths. Single-crystal X-ray diffraction (SCXRD) in diamond anvil cells, which I and co-workers have been actively developing, opens the way to determine not only the crystal structures of compounds at truly extreme conditions, but also allows to refine their chemical composition. In the frame of the project I’m going to develop technologies for collecting SCXRD both at high-p and high-T conditions and explore the ways to extend the current limits of the method beyond 250 GPa. I’m going to apply the developed techniques to resolve the “Fe-O system paradox”, and study the chemistry and crystal chemistry of geo- and planetary materials (mainly in the Fe-Mg-Al-Si-O system) at pressures above 100 GPa and temperatures above 2500 K.

• DFG Programme: Independent Junior Research Groups
• International Connection: Sweden
• Major Instrumentation: fast speed gated CCD camera ; set of high-accuracy motors with controllers
• Instrumentation Group: 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek) ; 6930 Elektrische Steuergeräte und Anlagen
• Cooperation Partner: Professor Dr. Igor Abrikosov