Crystal chemistry and reactivity of carbonate and hydrous minerals at Earth’s mantle conditions

The purpose of this work is to study the crystal structures, the stability field and their geologic relevance of carbonates and hydrous phases at Earth’s mantle conditions. In detail, we will focus on alkali carbonates. They are proposed as precursor of diamond formation and CO2 rich volcanism. The exact determination of high-pressure structures and density will allow completing a reference thermodynamic database for evaluation of mineral reaction involving carbonates in the mantle. The 2-years period of research, will allow also the completion of investigation of ultra-deep hydrous silicates. The recently discovered 11.5 Å phase and other DHAMS phases (dense hydrous aluminum magnesium silicates) can in-fact explain new features of the deep water and volatile cycles. Two key points will be clarified: the polymorphism and the stability of 11.5 Å and the extension of solid solution with iron endmembers. The simultaneous presence of Mg and Al in these DHAMS allow solid solution both with Fe2+ and Fe3+ end-members, therefore adapting to variable oxidation state of the mantle. The exact knowledge of the structure, density and stability of these phases, and the fluid release upon phase transformation, will allow an improved model for the deep water cycle, which, in turn, affect also carbon mobility.