Water disequilibrium in olivines from Hawaiian peridotites: Recent metasomatism, H diffusion and magma ascent rates

Peslier, A. H.; Bizimis, Michael; Matney, Mark

doi:10.1016/j.gca.2015.01.030

Cited by 66 publications

(42 citation statements)

References 141 publications

(226 reference statements)

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“…Although some of the pyroxenes have spinel exsolutions, there is no difference in water content between pyroxene with and without exsolutions (Data Set S2), and, within exsolved pyroxene, between zone exsolution‐free and zones with exsolutions (supporting information S3). Olivine water contents, measured at the core of the olivine grains containing the highest amount of water in each sample range from 10 to 26 ppm H 2 O in SLC peridotites [ Peslier et al ., ]. Note that the one peridotite that contains trace amount of phlogopite, a hydrous mineral, has water contents for olivine and pyroxene that fall in the middle of the range of those for other samples (77SL‐420, Table ).…”

Section: Resultsmentioning

confidence: 99%

“…The obtained water content of 347 ppm H 2 O is within error of the one calculated with oriented β and γ spectra of one grain with no mineral exsolutions, 338 ppm H 2 O. The details of the calculations of the olivine water contents of these samples are discussed elsewhere [ Peslier et al ., ]. Because of the heterogeneous water content of the olivines, only the highest measured absorbance in α, β, and γ in any given sample is used here in each orientation for the water content calculation.…”

Section: Methodsmentioning

confidence: 99%

“…Our xenoliths are selected from well‐characterized samples for which major and trace element compositions of the minerals, as well as Sr, Nd, Hf, Os, and Fe isotopes are already available [ Bizimis et al ., ; Bizimis et al ., ; Williams and Bizimis , ]. Water content and distribution in olivine is reported in a separate paper [ Peslier et al ., ]. The harzburgites and lherzolites analyzed here are all spinel‐bearing with forsterite contents (Fo = olivine Mg/(Mg + ΣFe)) between 0.885 and 0.912 and spinel Cr numbers (Cr# = Cr/(Cr+Al)) between 0.066 and 0.154 (Data Set S1).…”

Section: Geological Context and Samplesmentioning

confidence: 99%

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Water in Hawaiian peridotite minerals: A case for a dry metasomatized oceanic mantle lithosphere

Peslier

Bizimis

2015

Geochem Geophys Geosyst

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The distribution of water concentrations in the oceanic upper mantle has drastic influence on its melting, rheology, and electrical and thermal conductivities and yet is primarily known indirectly from analyses of OIB and MORB. Here, actual mantle samples, eight peridotite xenoliths from Salt Lake Crater (SLC) and one from Pali in Oahu in Hawaii were analyzed by FTIR. Water contents of orthopyroxene, clinopyroxene, and the highest measured in olivine are 116-222, 246-442, and 10-26 ppm weight H 2 O, respectively. Although pyroxene water contents correlate with indices of partial melting, they are too high to be explained by simple melting modeling. Mantle-melt interaction modeling reproduces best the SLC data. These peridotites represent depleted oceanic mantle older than the Pacific lithosphere that has been refertilized by nephelinite melts containing <5 weight % H 2 O. Metasomatism in the Hawaiian peridotites resulted in an apparent decoupling of water and LREE that can be reconciled via assimilation and fractional crystallization. Calculated bulk-rock water contents for SLC (50-96 ppm H 2 O) are on the low side of that of the MORB source (50-200 ppm H 2 O). Preceding metasomatism, the SLC peridotites must have been even drier, with a water content similar to that of the Pali peridotite (45 ppm H 2 O), a relatively unmetasomatized fragment of the Pacific lithosphere. Moreover, our data show that the oceanic mantle lithosphere above plumes is not necessarily enriched in water. Calculated viscosities using olivine water contents allow to estimate the depth of the lithosphere-asthenosphere boundary beneath Hawaii at 90 km.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Geological Context and Samplesmentioning

confidence: 99%

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Water in Hawaiian peridotite minerals: A case for a dry metasomatized oceanic mantle lithosphere

Peslier

Bizimis

2015

Geochem Geophys Geosyst

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“…In contrast to the fast dehydration kinetics of olivine (Mackwell and Kohlstedt, 1990), which may lead to decompression-induced water loss as documented by olivine grains with hydrogen contents decreasing from core to rim (Peslier and Luhr, 2006;Peslier et al, 2015), loss of hydrogen in pyroxenes is generally slower (Ingrin et al, 1995;Stalder and Skogby, 2002). Although the oxidation of iron serves as an important hydrogen extraction mechanism (Skogby and Rossman, 1989), other trivalent cations such as aluminum and chromium, which are abundant in natural orthopyroxenes, reduce hydrogen mobility considerably, such that hydrogen diffusion presumably depends on the ratio of these trivalent elements (Stalder and Behrens, 2006).…”

Section: Introductionmentioning

confidence: 91%

Water in orthopyroxene from abyssal spinel peridotites of the East Pacific Rise (ODP Leg 147: Hess Deep)

Hesse

Gose

Stalder

et al. 2015

Lithos

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“…Concurrent mixing and crystallisation should produce suites of melt inclusions with approximately constant H 2 O/Ce regardless of melt La/Yb or host olivine composition.The observed H 2 O/Ce variability in the EVZ inclusions is best explained by the diffusion of H 2 O into or out of the melt inclusions as they equilibrate with their carrier melts. Hydrogen diffusion in olivine is complex and occurs via several mechanisms: protons may exchange with Mg vacancies (denoted [Mg]); Si or Ti vacancies, ([Si], [Ti]); trivalent cations; electronic defects (protonpolaron exchange, denoted 'PP'); or a combination of these mechanisms (e.g Padrón-Navarta et al, 2014;Peslier et al, 2015)…”

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confidence: 99%

Diffusive over-hydration of olivine-hosted melt inclusions

Hartley

Neave

Maclennan

et al. 2015

Earth and Planetary Science Letters

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Editor: B. Marty Keywords: melt inclusion melt mixing diffusion water olivine IcelandThe pre-eruptive water content of magma is often estimated using crystal-hosted melt inclusions. However, olivine-hosted melt inclusions are prone to post-entrapment modification by H + diffusion as they re-equilibrate with their external environment. This effect is well established for the case of H + loss from olivine-hosted inclusions that have cooled slowly in degassed magma. Here we present evidence for the opposite effect: the addition of H + into inclusions that are held in melts that are enriched in H 2 O with respect to the trapped melts. The compositional variability in a suite of 211 olivine-hosted inclusions from the Laki and Skuggafjöll eruptions in Iceland's Eastern Volcanic Zone indicates that diffusive H + gain governs the H 2 O content of incompatible trace element depleted inclusions. Individual eruptive units contain olivine-hosted inclusions with widely varying incompatible element concentrations but near-constant H 2 O. Furthermore, over 40% of the inclusions have H 2 O/Ce > 380, significantly higher than the H 2 O/Ce expected in primary Icelandic melts or mid-ocean ridge basalts (150-280). The fact that the highest H 2 O/Ce ratios are found in the most incompatible element depleted inclusions indicates that hydration is a consequence of the concurrent mixing and crystallisation of compositionally diverse primary melts. Hydration occurs when olivines containing depleted inclusions with low H 2 O contents are juxtaposed against more hydrous melts during mixing. Melt inclusions from a single eruption may preserve evidence of both diffusive H + loss and H + gain. Trace element data are therefore vital for determining H 2 O contents of melt inclusions at the time of inclusion trapping and, ultimately, the H 2 O content of the mantle source regions. Crown

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Water disequilibrium in olivines from Hawaiian peridotites: Recent metasomatism, H diffusion and magma ascent rates

Cited by 66 publications

References 141 publications

Water in Hawaiian peridotite minerals: A case for a dry metasomatized oceanic mantle lithosphere

Water in Hawaiian peridotite minerals: A case for a dry metasomatized oceanic mantle lithosphere

Water in orthopyroxene from abyssal spinel peridotites of the East Pacific Rise (ODP Leg 147: Hess Deep)

Diffusive over-hydration of olivine-hosted melt inclusions

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