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Numerical modeling of joint H2O-CO2 diffusion reveals decompression and cooling history: Application to the IDDP-1 borehole glass

Janine Birnbaum 1, Fabian B. Wadsworth1, Jackie E. Kendrick1, Ben Kennedy2, Paul A. Wallace1, Marize Muniz da Silva1, Yan Lavallée1

  • Affiliations: 1Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany 2School of Earth and Environment, University of Canterbury, Christchurch, New Zealand

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 95

  • Programme No: 3.16.22

  • Theme 3 > Session 16

Abstract

Numerical simulations of bubble growth have focused on the role of total water in vesiculation. We present a novel model that jointly solves for diffusion of molecular H2Oand CO2, along with reaction between OH-H2Omolecular in volcanic melts along specified pressure and temperature paths. The simulations produce outputs of bubble size, total vesicularity, water speciation and volatile content in the glass with distance from bubbles and the H2O/CO2 ratio of the vapor phase. This allows for comparison with multiple observables in natural samples. Combined with constraints provided by geophysical monitoring and geospeedometry, we can constrain possible decompression and cooling paths from source to surface. We apply the model to the IDDP-1 borehole at Krafla volcano, Iceland, which intersected a magma body at 2.1 km depth in 2009. Our model allows for reinterpretation of the cooling and decompression path experienced by the magma in the minutes following contact with drilling fluid, suggesting that storage may have been at higher pressure than previously thought (consistent with lithostatic load). We highlight the role of the different diffusivities of H2O and CO2 that 1) produce an apparent delay in bubble growth compared to a water-only system, 2) promote preferential resorption of water during cooling, resulting in a final non-equilibrium vapor phase, and 3) result in volatile profiles with distance that have little or no indication of resorption despite prevalent resorption due to cooling. The numerical model can be applied to many systems via a modular approach for e.g. viscosity, water and CO2 diffusivity and solubility.