Séminaire CINaM - 4 mai 2017 - 14h00 - Salle R. Kern - Luminy - Marseille

Séminaire CINaM - jeudi 4 mai 2017 - 14h00 - Salle R. Kern - Luminy - Marseille

Theoretical investigation of equilibrium fractionation of stable isotopes: Mg isotopes in carbonate minerals par Marc Blanchard (Laboratoire Géosciences Environnement Toulouse (GET) - Observatoire Midi-Pyrénées (OMP) - Université Toulouse III, 14 avenue Edouard Belin, 31400 Toulouse, FRANCE)

The analysis of the mechanisms controlling the stable isotope composition of natural compounds and the use of these isotopic compositions to elucidate natural processes is a central field of geochemistry. An essential basis for interpreting isotopic compositions is to know the equilibrium isotopic fractionation factors. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between aqueous solutions and minerals. While for crystals, it is well established that equilibrium isotopic fractionation factors can be calculated using a statistical thermodynamic approach based on the vibrational properties, several theoretical methods are currently used to model ions in aqueous solution, such as finite-size molecular clusters or snapshots obtained from molecular dynamics simulations. In this talk, we will present a brief state of the art of this research field before focusing on the example of magnesium isotope fractionation between aqueous Mg2+ and carbonate minerals. Magnesium is a common impurity of calcium carbonate minerals and its isotopic composition could represent an important geochemical proxy of past oceans.