The potential for aqueous fluid-rock and silicate melt-rock interactions to re-equilibrate hydrogen in peridotite nominally anhydrous minerals

Abstract

This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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

“…However, slow cooling or dwelling at temperatures that are typical for serpentinization (∼300°C, Guillot et al, 2015) can erase a mantle signature in large crystals (2 mm) in a few thousand years (Figure 9, left). Results from modeling hydrogen diffusion in clinopyroxene at 300°C illustrate the development of the hydrogen distribution at temperatures associated with serpentinization, a process that was first suggested by Lynn and Warren (2021) and is supported by the newly obtained low-temperature diffusivity constraints here. In general, differences in the degree of re-equilibration between crystals of the same size but that traveled along different geotherms are smaller for larger crystals.…”

“…However, a legitimate question that remains is whether hydrogen concentrations that are measured in NAMs collected on Earth's surface really represent the original H contents established in the mantle, or if these contents were modified at some later stage for example, by alteration, metasomatism (Kilgore et al., 2020; Peslier et al., 2015; Tang et al., 2020) or mineral‐melt interaction (Le Roux et al., 2021; Lynn & Warren, 2021). In spite of the growing number of experimental studies that reveal new details on hydrogen in NAMs and systematic studies about hydrogen contents in these minerals (Kumamoto et al., 2019; Warren & Hauri, 2014), studies that treat natural mantle xenoliths seem to yield contrasting results in terms of what the hydrogen content actually recorded (Gose et al., 2011; Wang et al., 2021).…”

“…Since diffusion controls the redistribution of hydrogen in a crystal it is crucial to determine rates of diffusive transport as a function of various parameters (e.g., temperature, pressure, f O 2 , or mineral composition) to assess potential modifications of hydrogen contents at different conditions. These quantities are known only by extrapolation of high temperature data because most experimental data for H diffusion in NAMs have been collected only over a limited range of high temperatures (800°C–1200°C for olivine, 600°C–1000°C for pyroxenes; e.g., Demouchy & Mackwell, 2006; Demouchy et al., 2016; Ferriss et al., 2016, 2018; Hercule & Ingrin, 1999; Ingrin et al., 1995; Mackwell & Kohlstedt, 1990; Stalder & Behrens, 2006; Stalder & Skogby, 2003; Woods et al., 2000) and may lead to large uncertainties on extrapolation (Lynn & Warren, 2021).…”

3D Diffusion of Water in Melt Inclusion‐Bearing Olivine Phenocrysts

“…The mesh point spacing was determined to be 60 times smaller than the length of the [001] axis from the center of the crystal. This resulted in mesh resolutions of 4-12.5 μm, which is comparable to other 3D modeling efforts that have explored H + diffusion in olivine (Lynn & Warren, 2021). The mesh resolution in the melt inclusion was determined to be one twelfth of the melt inclusion radius, which resulted in mesh resolutions of 0.8-8.3 μm.…”

Postmelting hydrogen enrichment in the oceanic lithosphere

“…In addition, no large core to rim variations are observed, inconsistent with transient serpentinization. Last, hydrogen diffusivities at serpentinization temperatures may be too low to affect primary H 2 O abundances in pyroxenes, although this is still debated (37).…”