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Poster De Conférence Année : 2023

Hydrogen diffusion in hydrous minerals: revised closure temperatures for isotopic exchange during fluid-rock interactions

B Reynard
  • Fonction : Auteur
J Jonfal
  • Fonction : Auteur
a -C Ganzhorn
  • Fonction : Auteur

Résumé

Interactions between aqueous fluids and rocks occur in a broad range of contexts ranging from hydrothermal alteration to regional metamorphism on Earth and parent body metamorphism in meteorites. 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 hydrous minerals. Deuterium-hydrogen exchange between amphibole (tremolite), vesuvianite minerals and deuterated gas (D2) was experimentally investigated in a furnace over the temperature range of 400-550°C at ambient pressure. D/(D+H) ratios in exchanged mineral grains were mapped using Raman spectroscopy. Deuterium hydrogen exchange proceeded by deuterium hydrogen lattice diffusion, and also along cleavage in amphibole. Arrhenius relations for deuterium-hydrogen lattice-diffusion coefficients were derived from the new dataset. Values of activation energy (E) is 198 ±11 (1s) kJ/mol and logD0 -3.0 ± 0.8 are obtained for vesuvianite, and 133 ± 13 kJ/mol, and -9.2 ± 0.9 for tremolite. Activation energy for tremolite is a minimum value and is likely higher and similar to those in the range 170-200 kJ/mol inferred for antigorite, chlorite and vesuvianite using similar methods. Diffusion coefficients obtained with bulk isotopic analysis for amphiboles and epidotezoisite are much higher and display lower apparent activation energy (<80 kJ/mol) than those inferred from spatially resolved diffusion profiles obtained using punctual methods (Raman, NanoSIMS). Overestimation of diffusion coefficients by bulk analysis is attributed to unverified assumptions on grain size for minerals presenting easy cleavage (amphiboles, epidote, ...) that decrease effective grain size and increase surface for diffusive exchange during the experiments. Minerals like vesuvianite and tourmaline that have no cleavage planes show low diffusion coefficients from both spatially resolved and bulk analytical methods. Extrapolation of these new diffusion laws to low temperatures yields closure temperature of hydrogen isotope diffusion in hydrous minerals that are much higher than previously estimated. Hydrous minerals may thus retain information on relatively high temperature metamorphism on parent bodies of carbonaceous chondrites, and could display hydrogen isotope zoning in terrestrial rocks that may record the history of metamorphic fluid interactions and volcanic eruptions.
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Dates et versions

hal-04123095 , version 1 (09-06-2023)

Identifiants

  • HAL Id : hal-04123095 , version 1

Citer

B Reynard, J Jonfal, a -C Ganzhorn, Jannick Ingrin. Hydrogen diffusion in hydrous minerals: revised closure temperatures for isotopic exchange during fluid-rock interactions. Experimental Mineralogy, Petroly and Geochemistry, Jun 2023, Milano, Italy. ⟨hal-04123095⟩
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