HR: 1340h
AN: MR23C-0078    [Abstracts]
TI: Solubility of Minerals in HP-HT Aqueous Fluids: Results and Potentials of in situ Synchrotron X-Ray Fluorescence
AU: * Daniel, I
EM: Isabelle.Daniel@univ-lyon1.fr
AF: Laboratoire de Sciences de la Terre, UMR 5570 CNRS-ENS Lyon-UCB Lyon1, Bat geode 43 bd du 11 novembre 1918, Villeurbanne, 69622 France
AU: Sanchez Valle, C
EM: csanchez@ens-lyon.fr
AF: Dpt of Geology, U. of Illinois - Urbana Champaign, nat hist bdg 1301 w green st., Urbana, Il 61801 United States
AU: Reynard, B
EM: Bruno.Reynard@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR 5570 CNRS-ENS Lyon-UCB Lyon1, Bat geode 43 bd du 11 novembre 1918, Villeurbanne, 69622 France
AU: Martinez, I
EM: martinez@ipgp.jussieu.fr
AF: aboratoire de Physique et Chimie des Interactions G‚ologiques : UMR 7579 CNRS-IPGP-Paris7, 2 pl Jussieu, Paris, 75251 France
AU: Simionovici, A S
EM: Alexandre.Simionovici@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR 5570 CNRS-ENS Lyon-UCB Lyon1, Bat geode 43 bd du 11 novembre 1918, Villeurbanne, 69622 France
AB: CO₂-rich saline aqueous fluids are liberated into the mantle when the altered oceanic crust is subducted, leading to the important geochemical phenomena of mantle wedge metasomatism and arc magmatism. To better understand these processes, knowledge of mineral-fluid equilibria and mineral solubility in high pressure-high temperature crustal fluids is thus required. We report here in situ measurements on the solubility of strontianite (SrCO₃) and GeO₂-rutile at P (up to 6.6 GPa) and T (up to 400°C) relevant for cold subducted slabs. The composition of the fluid surrounding the crystal, loaded in an externally heated diamond-anvil cell, was analysed in situ by monitoring the X-ray fluorescence of Sr²⁺ and Ge⁴⁺ cations, respectively, until chemical equilibrium was reached. Experiments were carried out at the ESRF (ID22 beamline) using a high-resolution monochromatic beam (2x5 μm² and 18 keV), and a collection geometry at 30° from the transmitted beam. This results in quantitative analysis of the solution down to the 20 ppm level. In the case of strontianite, kinetic data of the dissolution reaction showed instantaneous equilibration times at 400°C. Measured dissolution rates are essentially compatible with a first-order reaction mechanism and allow to retrieve the activation energy (E_A) for the dissolution of SrCO₃ at HP-HT conditions. Taking into account activity coefficients, measured Sr²⁺ concentrations are used to determine the solubility constant (K_s) of SrCO₃ at HP-HT conditions, allowing further thermodynamic modelling of carbonate dissolution. In the case of GeO₂-rutile, we observed a gradient of the Ge concentration in the fluid. Hence, on the top of solubility measurements, it also allows to calculate the diffusion coefficients of Ge in high P-T aqueous fluids. This experiment thus shows the suitability of the SXRF technique for the in situ study of elemental diffusion in aqueous systems under high P-T conditions. Such data are essential for the modeling of diffusive transport of elements and its influence on the growth and dissolution of minerals.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3924 High-pressure behavior
DE: 3939 Physical thermodynamics
DE: 3994 Instruments and techniques
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005