Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth

Abstract

The structural and chemical changes to which carbon dioxide is subjected with increasing pressure and temperature are discussed here with the purpose of following the modifications of this important geochemical material on proceeding from the Earth's surface down to the core-mantle boundary. The relevance of metastabilities, and then of kinetic controlled transformations, is evidenced in the P-T ranges characteristic of both molecular phases and extended covalently bonded structures. From a chemical point of view, this analysis highlights how the characterization of the melting of the extended structures would represent an important step to understand the role of this compound in the chemistry of the Earth's mantle.

Carbon Dioxide under Earth Mantle Conditions: From a Molecular Liquid through a Reactive Fluid to Polymeric Regimes

“…Both experiments and calculations have shown that carbon dioxide exhibits several polymeric structures at pressures corresponding to those geological conditions. They notably include two crystalline phases, one featuring a three-dimensional networkCO 2 -Vand the other a layered formCO 2 -VI. − After extensive controversy about the structures of CO 2 -V, , the crystalline phase whose reported stability region is most likely to intersect the geotherm, presently, the issue appears to be clarified in favor of the β-cristobalite structure ( I 4̅2 d ) .…”