Hydrogen Diffusion in Clinopyroxene at Low Temperatures (195°C–400°C) and Consequences for Subsurface Processes

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Author(s)Bissbort, Thilo
Author(s)Lynn, Kendra J.
Author(s)Becker, Hans-Werner
Author(s)Chakraborty, Sumit
Date Accessioned2023-02-09T15:33:42Z
Date Available2023-02-09T15:33:42Z
Publication Date2022-12-12
DescriptionThis article was originally published in Geochemistry, Geophysics, Geosystems. The version of record is available at: https://doi.org/10.1029/2022GC010520
AbstractStudying diffusion of hydrogen in nominally anhydrous minerals, like clinopyroxene, at low temperatures is a challenging task due to experimental and analytical difficulties. In this study, to overcome these problems we have produced H concentration gradients in single crystals of natural diopsidic clinopyroxene by ion implantation and measured the nanoscale profiles before and after diffusion anneals using Nuclear Resonance Reaction Analysis. These steps allowed us to conduct experiments at temperatures between 195°C and 400°C. Obtained diffusion rates show a consistent Arrhenius relation DH= 5.47(±13.98) · 10−8 · exp (−115.64(±11.5) kJ mol−1/RT) m2s−1. Notably, our results lie well within the range of extrapolations from high temperature experiments (≥600°C) of previous studies. This implies that fast diffusion of hydrogen (compared to other elements) extends to low temperatures. We used these results in a non-isothermal diffusion model that simulates the ascent of crystals (0.5, 1.0, and 2.0 mm) along two representative P-T-paths from 600°C to 100°C, to assess potential re-equilibration of H contents in clinopyroxene at low temperatures. Our model highlights the need to carefully consider boundary conditions, which are a function of P-T-fO2, that control the concentration gradient at the crystal's rim. The results from this model help to assess, as a function of crystal size and cooling rate, when re-equilibration must be considered. Key Points - Diffusion rates of hydrogen in clinopyroxene in the low temperature range (195°C–400°C) were quantified for the first time - Diffusion coefficients at low temperatures lie within the range of extrapolations from high temperature experiments - Non-isothermal modeling was applied to evaluate potential re-equilibration of clinopyroxene crystals at low temperatures
SponsorT. Bissbort thanks J. Primocerio for providing the EPMA data of clinopyroxene used in this study and C. Hirschle for Laue analysis for crystal orientation. He also thanks C. Beyer for his assistance in the lab. T. Bissbort expresses great gratitude for the operators and technical staff at the Dynamitron-Tandem-Laboratorium (RUBION). This work greatly benefited from the thoughtful reviews by J. Hermann and one anonymous reviewer. This research is funded by the DFG Project nos. BE 1307/5-1 and CH 166/20-1. Open Access funding enabled and organized by Projekt DEAL.
CitationBissbort, T., Lynn, K. J., Becker, H.-W., & Chakraborty, S. (2022). Hydrogen diffusion in clinopyroxene at low temperatures (195°C–400°C) and consequences for subsurface processes. Geochemistry, Geophysics, Geosystems, 23, e2022GC010520. https://doi.org/10.1029/2022GC010520
ISSN1525-2027
URLhttps://udspace.udel.edu/handle/19716/32256
Languageen_US
PublisherGeochemistry, Geophysics, Geosystems
Keywordsdiffusion
Keywordshydrogen
Keywordsclinopyroxene
Keywordsequilibration
Keywordslow-temperature
TitleHydrogen Diffusion in Clinopyroxene at Low Temperatures (195°C–400°C) and Consequences for Subsurface Processes
TypeArticle
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