Modeling H, Na, and K diffusion in plagioclase feldspar by relating point defect parameters to bulk properties

Zhang, Baohua; Shan, Shuangming; Wu, Xiaoping

doi:10.1007/s00269-015-0782-5

Cited by 8 publications

(7 citation statements)

References 56 publications

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“…The preliminary equation is D H2O (m 2 /s) = 5.2 exp (-36,600/T) where T is inserted in K. The D H2O values are higher by 0.5 log units than data derived from dehydration of andesine (Johnson and Rossman 2013). The experimental data of Johnson and Rossman (2013) were reproduced by Zhang et al (2016) through a thermodynamic model that interconnects point defect parameters with bulk properties. A reason for the deviation of my data to those of Johnson and Rossman (2013) could be the higher water content of the andesine of 510 ± 90 ppm compared to the labradorite G2 (124 ± 15 ppm).…”

Section: Diffusion Of Hydrogen Species In Feldsparsmentioning

confidence: 99%

Hydrogen defects in feldspars: defect properties and implications for water solubility in feldspar

Behrens

2021

Phys Chem Minerals

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Hydrogen defects can strongly affect mechanical and chemical properties of feldspars. To get insight into the behavior of such defects, alkali feldspar and plagioclase of igneous origin were studied combining IR spectroscopy with heating experiments under well-controlled conditions. Near-infrared spectra show that OH groups are the predominant hydrous species in these feldspars but presence of minor amounts of molecular H2O cannot be excluded. Short-term annealing at 400–800 °C produces a small but significant irreversible change in the OH stretching vibration band which is attributed to relaxation of the feldspar structure. Polarized mid-infrared spectra of sanidine, adularia, and plagioclase recorded in situ at temperatures up to 600 °C show reversible shifts of maxima toward higher wavenumber and an overall decrease in integrated intensities. The pleochroic features of the OH vibration bands, i.e., the predominant orientation of OH dipoles along the crystallographic a axis in all feldspars and the additional band component perpendicular to the (010) plane in sanidine are still present in the high-temperature spectra. Different behavior during long-term annealing at high temperature was found for the alkali feldspars and the plagioclases. At 900–1000 °C, the Eifel sanidines rapidly lost about one quarter of the initial water content which is attributed to a weakly bound hydrogen species in the feldspar structure. The remaining hydrogen is very strongly bound and was still detectable in 0.7–0.9 mm thick sections after annealing for 108 days at 1000 °C in air dried by phosphorus pentoxide. In contrast, a 1-mm-thick section of plagioclase completely lost hydrogen during heating in air within 8 days at 1000 °C. After partial dehydration, the pleochroic behavior of the OH absorption bands of the feldspars was basically preserved except that the 3050 cm−1 band of the sanidine, oriented perpendicular to (010), becomes more pronounced than the 3400 cm−1 band, oriented parallel to the a direction. Annealing experiments at 1000 °C under controlled water pressures indicate equilibrium solubilities of several tens of ppm H2O in the plagioclases and more than 100 ppm H2O in the alkali feldspars already at 1 bar water pressure. The variation of the water content with H2O pressure and spectroscopic observations indicates that the water content in the feldspars is determined not only by the water pressure but also by already existing defects. Vacancies on alkali sites (VA1) may accommodate H2O molecules, possibly with subsequent hydrolysis of network bonds to minimize local stress. A likely explanation for the strongly bound hydrogen in the sanidine is a coupled substitution of H+ + Al3+ for Si4+ (AlOH defect) where the protons are located on interstitial sites. This incorporation model is supported by the complete recovery of the defects in H2O vapor after previous proton/alkali exchange in alkali chloride vapor at 1000 °C.

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Section: Diffusion Of Hydrogen Species In Feldsparsmentioning

confidence: 99%

Hydrogen defects in feldspars: defect properties and implications for water solubility in feldspar

Behrens

2021

Phys Chem Minerals

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“…The cBΩ model has been successfully implemented in diverse types of materials, including solid solutions and minerals [121][122][123][124]. Some recent examples of geophysical interest include the diffusion of He in olivine studied in the framework of the cBΩ model by Vallianatos and Saltas [53] and the work by Zhang and his coworkers who have studied self-and hetero-diffusion in (Mg,Fe) 2 SiO 4 polymorphs, as well as hetero-diffusion (H, Na, K) in plagioclase feldspar [122][123][124]. In the latter case [124], the cBΩ model underestimates the electrical conductivity but gives some constraints to the reported experimental results.…”

Section: Some Remarks On the Evaluation Of The Electrical Conductivitmentioning

confidence: 99%

An Overview of the Experimental Studies on the Electrical Conductivity of Major Minerals in the Upper Mantle and Transition Zone

Dai

Jiang

et al. 2020

Materials

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In this paper, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle and mantle transition zone of Earth, namely, olivine, pyroxene, garnet, wadsleyite and ringwoodite. The main influence factors, such as temperature, pressure, water content, oxygen fugacity, and anisotropy are discussed in detail. The dominant conduction mechanisms of Fe-bearing silicate minerals involve the iron-related small polaron with a relatively large activation enthalpy and the hydrogen-related defect with lower activation enthalpy. Specifically, we mainly focus on the variation of oxygen fugacity on the electrical conductivity of anhydrous and hydrous mantle minerals, which exhibit clearly different charge transport processes. In representative temperature and pressure environments, the hydrogen of nominally anhydrous minerals can tremendously enhance the electrical conductivity of the upper mantle and transition zone, and the influence of trace structural water (or hydrogen) is substantial. In combination with the geophysical data of magnetotelluric surveys, the laboratory-based electrical conductivity measurements can provide significant constraints to the water distribution in Earth’s interior.

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“…A hygrometer based on Al* would potentially bear the advantages of: (a) wide applicability due to the ubiquitous presence of plagioclase in most igneous rocks, (b) ease of measurement with standard-based wavelength dispersive X-ray spectrometry (WDS) attached to an electron-probe micro-analyser (EPMA), (c) good preservation potential due to slow diffusion of Al, Ca, and Na compared to H (e.g. 32 – 35 ), and (d) potential to resolve changing concentrations recorded in mineral zoning. Therefore, the scope of this study is to test, if the incorporation of Al* in plagioclase can be developed into a geo-hygrometer, using both natural samples from a range of environments and experimentally-grown plagioclase crystals precipitated from melts with contrasting water contents.…”

Section: Importance and Estimation Of Pre-eruptive Water Concentratiomentioning

confidence: 99%

The influence of water in silicate melt on aluminium excess in plagioclase as a potential hygrometer

Fiedrich¹,

Martin²,

Storck³

et al. 2018

Sci Rep

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Measuring water contents of magmas is fundamental to resolving a number of geological questions, such as the mechanisms of silicic magma evolution, the triggering of volcanic eruptions, and the formation of porphyry copper deposits. This study focuses on the correlation between apparent deviations from stoichiometry of plagioclase crystals and high water concentration in the magmatic melt from which they grew. We considered this relationship as a potential geo-hygrometer (water activity indicator). To test and potentially calibrate this new technique, a range of natural and experimental plagioclase crystals were analysed, with particular care taken to identify and avoid analytical bias and artefacts. In contrast to recently published material, we found no systematic aluminium excess in plagioclase, irrespective of the water concentration of the silicate melt it crystallised from. This suggests that aluminium excess in plagioclase cannot serve as a geo-hygrometer. The high likelihood of misinterpreting analytical artefacts (due to alkali migration and imprecise standardisation) as small deviations from stoichiometry, also requires its application as a mineral exploration tool to be treated with caution.

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Modeling H, Na, and K diffusion in plagioclase feldspar by relating point defect parameters to bulk properties

Cited by 8 publications

References 56 publications

Hydrogen defects in feldspars: defect properties and implications for water solubility in feldspar

Hydrogen defects in feldspars: defect properties and implications for water solubility in feldspar

An Overview of the Experimental Studies on the Electrical Conductivity of Major Minerals in the Upper Mantle and Transition Zone

The influence of water in silicate melt on aluminium excess in plagioclase as a potential hygrometer

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