Deuterium-hydrogen inter-diffusion in chlorite

作者：Ganzhorn Anne Celine^*; Pilorge Helene; Le Floch Sylvie; Montagnac Gilles; Cardon Herve; Reynard Bruno

来源：Chemical Geology, 2018, 493: 518-524.

DOI：10.1016/j.chemgeo.2018.07.010

• Diffusion
• Chlorite
• Subduction zone

Interactions between aqueous fluids and rocks occur in a broad range of contexts ranging from hydrothermal alteration veins to regional metamorphism. Tracking these processes and understanding their reaction kinetics require a precise knowledge of the diffusion of water in rocks, and of isotope fractionation in major minerals, such as chlorite. Deuterium-hydrogen exchange between Mg-rich chlorite and water (D2O) was experimentally investigated using a belt press over the temperature range of 315-650 degrees C at pressures of 1.5 GPa and 3 GPa. Both chloritite chip and chlorite powder were used. D/(D + H) ratios in chlorite grains were mapped using Raman spectroscopy. Deuterium-hydrogen exchange proceeded by deuterium-hydrogen inter-diffusion in chlorite (lattice diffusion). As chlorite is a phyllosilicate, i.e. an anisotropic mineral, diffusion coefficients were determined for crystallographic directions parallel and perpendicular to the silicate layers (perpendicular and parallel to the c* axis, respectively). Arrhenius relations for deuterium-hydrogen inter-diffusion coefficients were derived from the new dataset. Activation energy (E) is comprised between 215 +/- 21 (1 sigma) kJ/mol (perpendicular to the c* axis) and 194 +/- 21 kJ/mol (parallel to the c* axis). Log(10)(D-0) is -2.2 +/- 1.3m(2)/s for diffusion in the direction perpendicular to the c* axis and -4.5 +/- 1.3m(2)/s for diffusion parallel to it. The bulk diffusion law derived from a combination of our data with data from Graham et al. (1987) yields E = 176 +/- 8 kJ/mol and log(10)(D-0)=-5.1 +/- 0.4m(2)/s.

• 出版日期2018-8-20