Hydrogen diffusion in clinopyroxene: dehydration experiments

Qun-ke, Xia; Chen, Daogong; Carpenter, Sandra L; Zhi, Xiefei; Wang, Rucheng; Hao, Changchun

doi:10.1007/bf02879499

Cited by 9 publications

(11 citation statements)

References 9 publications

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“…10). Although there are no experimental determinations of hydrogen diffusivity of mantle clinopyroxenes, estimates are now available for four clinopyroxenes with sufficiently high-Fe content to be reasonable proxies for mantle clinopyroxene: Jaipur diopside (Woods et al 2000 and this study), augite PMR-53 (this study), the Nüshan clinopyroxene (Xia et al 2000), and clinopyroxene from Fuego Volcano (Lloyd et al in revision). These studies provide a two orders of magnitude constraint on the diffusivity of hydrogen in mantle xenolith clinopyroxene (gray zone in Fig.…”

Section: Hydrogen Diffusivities In Mantle Xenolith Olivine and Pyroxementioning

confidence: 93%

“…A total of nine different clinopyroxenes have now been dehydrated experimentally to quantify hydrogen diffusivity: a synthetic Fe-free pure diopside (Sundvall et al 2009b), a synthetic diopside doped only with a small amount of Fe (Sundvall et al 2009a), Kunlun diopside (this study), Jaipur diopside (Woods et al 2000 and this study), a Russian diopside (Ingrin et al 1995), augite PMR-53 (this study), a megacryst from Nüshan, China, with highFe and very high-Al content (Xia et al 2000), and diopsides from Baikal and Malacacheta (Hercule 1996;Ingrin and Blanchard 2006). Attempts at hydration by exposure to H 2 gas have also been performed (Hercule and Ingrin 1999;Skogby 1994;Skogby and Rossman 1989;Sundvall and Skogby 2011;Sundvall et al 2009a;Weis et al 2015), but here, we focus only on published dehydration experiments.…”

Section: Comparison Of Peak-specific Hydrogen Diffusivities With Prevmentioning

confidence: 99%

“…on a log scale at 800 °C for Kunlun diopside (isotropic; dehydrated in CO/CO 2 gas mixture; this study), Jaipur diopside (fast directions approximately || a and c; dehydrated in CO/ CO 2 ; this study and Woods et al 2000), augite PMR-53 (dehydrated in CO/CO 2 ; this study), a Russian diopside (isotropic; dehydrated in air; Ingrin et al 1995), a high-Al megacryst (|| c only; dehydrated in CO/CO 2 ; Xia et al 2000), a phenocryst (Fuego; Lloyd et al in revision), and a synthetic Fe-bearing diopside (|| b only; dehydrated in air; Sundvall et al 2009a). Peak-specific diffusivities were estimated assuming consistent differences between bulk and peak diffusivities as a function of temperature.…”

Section: Fig 10mentioning

confidence: 99%

“…These differences are determined quantitatively for the Kunlun, Jaipur, and synthetic diopsides and augite PMR-53 (Table 4; Fig. 9), and estimated by visual inspection of the spectra in Ingrin et al (1995) and Xia et al (2000) The role of iron and redox reactions Hydrogen diffusivities in diopside increase with Fe content up to ~0.06 to 0.08 atoms per formula units (a.p.f.u.) or roughly 2 wt% FeO (Fig.…”

Section: Fig 10mentioning

confidence: 99%

“…Previous experimental efforts to measure hydrogen diffusion in clinopyroxene by heating at atmospheric pressure show order of magnitude variations in the diffusivity, even within the single end-member diopside, from 10 −10 m 2 /s at 1000 °C in a natural diopside from near Jaipur, India (Dyar et al 1996;Woods et al 2000), to 10 −14 m 2 /s at the same temperature in a synthetic Fe-doped diopside (Sundvall et al 2009a), with several studies providing intermediate values (Ingrin et al 1995;Sundvall et al 2009b;Xia et al 2000). These variations may be due to any or a combination of the following factors: significant imperfections (e.g., cracks or inclusions) in some samples used in previous experiments, differences in sample chemistry (particularly Fe 3+ and/or Al), and variations in hydrogen incorporation and diffusivity that depend on the specific mechanism for providing local charge-balance to hydrogen incorporated as a proton, H + .…”

Section: Introductionmentioning

confidence: 96%

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Site-specific hydrogen diffusion rates during clinopyroxene dehydration

Ferriss

Plank

Walker

2016

Contrib Mineral Petrol

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peaks at 3620, 3550, 3460, and 3355 cm −1 in the thickness direction at 800 °C. Bulk hydrogen diffusivity in the Jaipur diopside is consistent with previous work, and hydrogen diffusivity in augite PMR-53 is slightly lower than the fast direction diffusivities measured || [100] and [001]* in Jaipur diopside. Both diopsides show 1-2 orders of magnitude differences in the peaks-specific diffusivities, with the fastest diffusivities at 3450 cm −1 and the slowest at 3645 cm −1 . However, the hydrogen diffusivities in Jaipur diopside are 2-4 orders of magnitude higher than those in Kunlun diopside for bulk hydrogen and all peaks. Thus, peak-specific differences cannot by themselves adequately explain the 5 orders of magnitude range in hydrogen diffusivities observed experimentally in different diopsides. The results are broadly consistent with a previously proposed increase in hydrogen diffusivity in diopside with Fe up to 0.6-0.8 a.p.f.u., although there may be an opposing relationship with Al(IV). The results of this study and others predict high water diffusivities in Fe-bearing mantle xenolith clinopyroxene, on the order of ~10 −9 to 10 −11 m 2 /s at 1000 °C. The common observation of hydrogen zonation in mantle xenolith olivine, but not in clinopyroxene implies that hydrogen diffusion is much faster in olivine than in pyroxene, which then requires the operation of the fastest diffusion mechanism quantified in olivine and diffusivities in clinopyroxene at the lower end of this 2 orders of magnitude range. Such high diffusivities strongly suggest that water in mantle xenoliths has at least partially equilibrated with the host magma, and that the diffusion profiles observed in mantle xenolith olivine reflect only the final stage of ascent after water begins to exsolve. AbstractThe rate of hydrogen diffusion in clinopyroxene is relevant to interpreting hydrogen ("water") concentrations in xenoliths, phenocrysts, and clinopyroxene-hosted melt inclusions to provide insight into the deep-earth water cycle and volcanic explosivity. Here, we determine bulk and site-specific hydrogen diffusivities in two diopsides and an augite by heating initially homogeneous water-bearing samples in a 1-atm CO/CO 2 gas-mixing furnace at 800-1000 °C and oxygen fugacity at the quartz-fayalite-magnetite buffer and observing H-loss profiles. The O-H stretching range between wavenumbers 3000 and 4000 cm −1 in FTIR spectra is resolved into 4-6 peaks, each of which is assumed to represent a distinct defect site for the hydrogen, to determine peakspecific diffusivities using our previously published whole-block method. For the diopside from the Kunlun Mts. in China, Arrhenius relations are reported for peaks at 3645, 3617, 3540, 3443, and 3355 cm −1 based on measurements at 816, 904, and 1000 °C. Bulk and sitespecific diffusivities are determined for the same set of peaks at 904 °C for the second diopside (Jaipur). The augite (PMR-53) was a triangular thin slab, and hydrogen diffusivities were determined for bulk hydrogen and Communicated by Gor...

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Section: Hydrogen Diffusivities In Mantle Xenolith Olivine and Pyroxementioning

confidence: 93%

Section: Comparison Of Peak-specific Hydrogen Diffusivities With Prevmentioning

confidence: 99%

Section: Fig 10mentioning

confidence: 99%

Section: Fig 10mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

See 3 more Smart Citations

Site-specific hydrogen diffusion rates during clinopyroxene dehydration

Ferriss

Plank

Walker

2016

Contrib Mineral Petrol

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Reconciling the discrepancy between the dehydration rates in mantle olivine and pyroxene during xenolith emplacement

Tang

Hui

et al. 2019

Geochimica et Cosmochimica Acta

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Hydrogen concentration profiles through olivine and pyroxene in peridotite xenoliths carried in rift basalts from northern Tanzania (Lashaine, Eledoi, and Kisite localities) show bell-shaped distributions, indicating that diffusive hydrogen loss has occurred in all minerals. Homogeneous major element concentrations and equilibration of hydrogen between the cores of olivine and coexisting pyroxene suggest that hydrogen loss resulted from diffusive degassing during host magma emplacement. For these samples, hydrogen diffusivities in olivine and coexisting pyroxene must be within the same order of magnitude, similar to experimentally determined diffusivities, but in contrast to previous observations made on xenolithic peridotites. We demonstrate here, for the first time using natural samples, that significant differences in activation energy is likely the primary parameter that causes the discrepancy between hydrogen diffusion in olivine and pyroxene observed in different suites of mantle xenoliths. Because hydrogen diffuses faster in olivine than in pyroxene as temperature increases, hydrogen loss in the Tanzanian mantle xenoliths must have occurred at relatively low temperatures ($750 to $900°C), whereas hydrogen loss observed in previous xenolith studies likely occurred at higher temperatures ($950 to >1200°C). Thus, the diffusive loss of hydrogen in the Tanzanian mantle xenoliths may have occurred at shallow depths or at the Earth's surface.

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