The natural occurrence of hydroxide in olivine (original) (raw)
Related papers
Journal of Geophysical Research: Solid Earth, 2003
Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by 15 N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H 2 O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750-3100 cm À1 region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle-derived olivine analyzed to date contains 240 ppm wt. H 2 O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra.
Extrinsic and intrinsic mode of hydrogen occurrence in natural olivines: FTIR and TEM investigation
Physics and Chemistry of Minerals, 2001
Olivine crystals from two mantle nodules in kimberlites (pipe Udachnaya and pipe Obnazennaya, Yakutiya, Siberia) were investigated using EMP, TEM, AEM and FTIR techniques to determine the mode of hydrogen occurrence in olivine. Olivine contains three types of nanometer-sized inclusions:``large'' inclusions of hexagonal-like shape up to several hundred nm in size (1), lamellar defects (2) and small inclusions of hexagonlike shape up to several 10 nm in size (3). Lamellar defects and small inclusions are considered to be à`h ydrous'' olivine. All three types of inclusions contain OH) or water, but they are dierent with respect to their phase composition. In``large'' inclusions (1) hydrous magnesium silicates, such as serpentine + talc (``kerolite''?) and 10-A Ê phase + talc were identi®ed. Lamellar defects (2) and small inclusions (3) are depleted in Mg and Fe compared to the olivine matrix, while the silica content is the same as that of olivine. Modulations in the periodicity of the olivine structure are observed in SAED patterns and HREM images of (2) and (3). The superperiodicity can be referred to OH)-bearing point defect ordering in the olivine structure. If this is the case, the material of both lamellar defects and small inclusions can be assumed to be a``hydrous olivine'' Mg 2±x v x SiO 4 H 2x with a cation-de®cient olivine crystal structure. Thus, both an extrinsic mode of hydrogen occurrence in olivine, such as nanometer-sized inclusions of OH)-bearing magnesium silicates, and an intrinsic mode of hydrogen incorporation into the olivine structure, such as``hydrous olivine'' in itself, were found. The data obtained here show that the OH absorption bands observed in olivine spectra at 3704(3717) and 3683(3688) cm)1 can be unambiguously identi®ed with serpentine; the band at 3677(3676) cm)1 can be associated with talc. The absorption bands observed at 3591 and 3660 cm)1 in olivine match those of the 10-A Ê phase at 3594, 3662 and 3666 cm)1. Key words DHMS á Transmission electron microscopy (TEM) á Infrared spectroscopy á OH)-bearing point defects á 10-A Ê phase
Journal of Petrology, 2001
Hydrogen solubility and hydroxyl substitution mechanism in olivine INTRODUCTION at upper-mantle conditions are not only a function of pressure, Since the recognition about 30 years ago that nominally temperature, water fugacity and hydrogen fugacity, but are also anhydrous minerals (NAM) can incorporate hydrogen influenced by silica activity. Olivine synthesized in equilibrium in lattice defects (Beran, 1970; Wilkins & Sabine, 1973; with magnesiowüstite displays hydroxyl stretching bands in the Beran & Putnis, 1983; Aines & Rossman, 1984), conwavenumber range from 3640 to 3430 cm-1. In contrast, olivine siderable experimental and analytical effort has been in equilibrium with orthopyroxene shows absorption bands in a expended on estimating the OHstorage capacity of narrower wavenumber range from 3380 to 3285 cm-1. The two mantle minerals and determining the key factors confundamentally different spectra are assigned to hydroxyl in tetrahedral trolling OHsubstitution (e.g.
Hydration of mantle olivine under variable water and oxygen fugacity conditions
Contributions to Mineralogy and Petrology, 2014
The incorporation of H into olivine is influenced by a significant number of thermodynamic variables (pressure, temperature, oxygen fugacity, etc.). Given the strong influence that H has on the solidus temperature and rheological behavior of mantle peridotite, it is necessary to determine its solubility in olivine over the range of conditions found in the upper mantle. This study presents results from hydration experiments carried out to determine the effects of pressure, temperature, and the fugacities of H 2 O and O 2 on H solubility in San Carlos olivine at upper mantle conditions. Experiments were carried out at 1-2 GPa and 1,200°C using a piston-cylinder device. The fugacity of O 2 was controlled at the Fe 0 -FeO, FeO-Fe 3 O 4 , or Ni 0 -NiO buffer. Variable duration experiments indicate that equilibration is achieved within 6 h. Hydrogen contents of the experimental products were measured by secondary ion mass spectrometry, and relative changes to the point defect populations were investigated using Fourier transform infrared spectroscopy. Results from our experiments demonstrate that H solubility in San Carlos olivine is sensitive to pressure, the activity of SiO 2 , and the fugacities of H 2 O and O 2 . Of these variables, the fugacity of H 2 O has the strongest influence. The solubility of H in olivine increases with increasing SiO 2 activity, indicating incorporation into vacancies on octahedral lattice sites. The forsterite content of the olivine has no discernible effect on H solubility between 88.17 and 91.41, and there is no correlation between the concentrations of Ti and H. Further, in all but one of our experimentally hydrated olivines, the concentration of Ti is too low for H to be incorporated dominantly as a Ti-clinohumite-like defect. Our experimentally hydrated olivines are characterized by strong infrared absorption peaks at wavenumbers of 3,330, 3,356, 3,525, and 3,572 cm -1 . The heights of peaks at 3,330 and 3,356 cm -1 correlate positively with O 2 fugacity, while those at 3,525 and 3,572 cm -1 correlate with H 2 O fugacity.
Hydrogen incorporation in natural mantle olivines
Geophysical Monograph Series, 2006
Constraints on water storage capacity and actual content in the mantle must be derived not only from experimental studies, but also from investigation of natural samples. Olivine is one of the best-studied, OH-bearing "nominally anhydrous" minerals, yet there remain multiple hypotheses for the incorporation mechanism of hydrogen in this phase. Moreover, there is still debate as to whether the mechanism is the same in natural samples vs. experimental studies, where concentrations can reach very high values (up to ~o.6 wt% H 2 0) at high pressures and temperatures. We present new observations and review IR and TEM data from the literature that bear on this question. Hydrogen incorporation in natural olivine clearly occurs by multiple mechanisms, but in contrast to some previous assertions we find that there are strong similarities between the IR signatures of experimentally annealed olivines and most natural samples. At low pressures (lower than ~2 GPa) in both experiments and natural olivines, hydrogen incorporation might be dominated by a humite-type defect, but the nature of the defect may vary even within a single sample; possibilities include point defects, planar defects and optically detectable inclusions. IR bands between 3300 and 3400 cm-1 , ascribed previously to the influence of silica activity, are apparently related instead to increased oxygen fugacity. At higher pressures in experiments, the IR band structure changes and hydrogen is probably associated with disordered point defects. Similar IR spectra are seen in olivines from xenoliths derived from deeper parts of the mantle (below South Africa and the Colorado Plateau) as well as in olivines from the ultra-high pressure metamorphic province of the Western Gneiss Region in Norway.
Hydroxyl in mantle olivine xenocrysts from the Udachnaya kimberlite pipe
Physics and Chemistry of Minerals, 2006
The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to À180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730-3,330 cm À1. Bands at high energies (3,730-3,670 cm À1) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites
FTIR Spectrum of Phenocryst Olivine as an Indicator of Silica Saturation in Magmas
Journal of Petrology, 2004
Fourier Transform infrared (FTIR) absorption spectra of hydroxyl were measured on olivine phenocrysts from hydrous basaltic melts that originated in island-arc tectonic settings. The basaltic melts encompass a wide range of silica activities from orthopyroxene-saturated hypersthene-normative to nepheline-normative compositions. The intensities and wavenumber placement of hydroxyl absorption bands correlate with the degree of silica saturation of the parent melt from which the olivine crystallized. Olivines from silica-undersaturated nepheline-normative melts absorb IR radiation in the wavenumber range 3430-3590 cm À1 (Group 1). In contrast, olivines from orthopyroxene-saturated boninitic melts exhibit hydroxyl absorption bands in the wavenumber range 3285-3380 cm À1 (Group 2). Olivines crystallized at intermediate silica activities exhibit a combination of the two groups of hydroxyl IR bands, where the proportion of Group 2 bands increases with increasing silica saturation of the parent melt. The positions of hydroxyl absorption peaks observed here for natural samples are consistent with previous measurements on experimentally annealed olivines. Thus protonation experiments can be employed to make spectroscopically dry olivine structures visible by IR, yielding information on the silica saturation of the parental magmas. Hydroxyl concentrations in the studied olivines were estimated to be 1-2 ppm, corresponding to an olivine-melt partition coefficient of $(1Á0 AE 0Á3) Â 10 À4 .
Russian Journal of General Chemistry, 2011
Olivine is one of the most widespread minerals on the Earth, being the main component of the mantle in accordance with existing views. Olivine undergoes only minor alterations in going down to the depth of 350 km, but at deeper levels it can be transformed to β-modification (wadsleite) and, at the depth of 520 km, further to γ-modification (ringwoodite). Olivine occurs either as the main or auxiliary mineral for crust rocks (ultrabasites, basites, and kimberlites) and also as accessory mineral in acidic rocks. Depending on its genesis olivine contains isomorphous impurities of Cr, Ni, Ti, Mn, Ca, Co, etc. The composition of olivine and igneous inclusions entrapped during its growth constitutes important diagnostic criteria which identify the genesis of ore deposits. Regular variations of the content of basic end-members (forsterite and fayalite) and the availability and abundance of impurity elements make them suitable as indicators of ore formation process for various deposits. This point was exemplified by chromite-bearing massifs of the Polar Urals and platinumcopper-nickel deposits of Norilsk Ore Region. Olivine is commonly used as natural fireproof raw material.
Contributions to Mineralogy and Petrology, 2007
The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnetpyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxylstretching region. Two intense peaks were observed at 3,564 and 3,394 cm -1 , identical in energy to peaks in Ticlinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated.
American Mineralogist, 2004
Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by 15 N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H 2 O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750-3100 cm À1 region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle-derived olivine analyzed to date contains 240 ppm wt. H 2 O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra.