Free Energy Minimization Calculations Of Lizardite At Variable Pressures and Temperatures

HR: 0800h
AN: V51B-1477 [Abstracts]
TI: Free Energy Minimization Calculations Of Lizardite At Variable Pressures and Temperatures
AU: Pellenq, R J
EM: pellenq@crmcn.univ-mrs.fr
AF: Centre de Recherche en Matiere Condensee et Nanosciences, CNRS, Campus de Luminy, case 913, Marseille, 13288 France
AU: * Auzende, A
EM: auzende@impmc.jussieu.fr
AF: Centre de Recherche en Matiere Condensee et Nanosciences, CNRS, Campus de Luminy, case 913, Marseille, 13288 France
AU: * Auzende, A
EM: auzende@impmc.jussieu.fr
AF: Institut de Mineralogie et de Physique des Milieux Condenses, Institut de Physique du Globe de Paris, Campus Boucicaut, Batiment 7, Paris, 75015 France
AU: Devouard, B
EM: b.devouard@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, Observatoire de Physique du Globe de Clermont-Ferrand, 5, rue Kessler, Clermont-Ferrand, 63038 France
AU: Baronnet, A
EM: baronnet@crmcn.univ-mrs.fr
AF: Centre de Recherche en Matiere Condensee et Nanosciences, CNRS, Campus de Luminy, case 913, Marseille, 13288 France
AU: Grauby, O
V51B-1477 AF: Centre de Recherche en Matiere Condensee et Nanosciences, CNRS, Campus de Luminy, case 913, Marseille, 13288 France
AB: Serpentine minerals are mainly forming by hydrothermal alteration of the oceanic lithosphere. This hydration process mainly produces lizardite, the flat 1:1 variety, after magnesian silicates and largely changes the mechanical proprieties of the lithosphere. Investigations of the structure-properties relationships of lizardite by an atomistic simulation method based on transferable semi-empirical interatomic potentials provides data pertinent to geophysical models. The lizardite structure was first relaxed at room temperature and 1 atmosphere. The minimum free energy is obtained for an equilibrium unit-cell volume V₀ = 184Å³, close to the experimental one. The fit of the energy well around V₀ by an equation of state (Birch-Murnaghan) combined to the analyses of the elastic constant tensor provide an average bulk modulus B₀ of lizardite around 60 GPa. The cohesion energy between two successive layers was calculated as 0.33 eV (i.e., 0.11 eV per OH bond) which is compatible with hydrogen bonding and with recent ab initio calculations. These results show that the chosen set of interatomic potentials provide a reasonable description of lizardite. Upon pressure and temperature variations, we evidenced that structural changes are mainly pressure-induced. Pressure is mainly accommodated by a decrease of the c parameter up to 10 GPa due to the reduction of the interlayer space. The transition observed in the evolution of the c parameter occurring around 2 GPa can be explained by the bending of the surface hydroxyl groups lying in the interlayer space above this pressure. These results are in good agreement with experimental results. The extension of such simulations work to antigorite, the high pressure, modulated variety of serpentine, is currently in progress.
DE: 3617 Alteration and weathering processes (1039)
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 5194 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005