Academic literature on the topic 'Nominally Anhydrous'

L'étude de l'eau contenue dans les minéraux nominalement anhydres et des paramètres influençant son incorporation est un sujet de recherche actif à cause de ses effets sur les propriétés physiques et chimiques du manteau. L'objectif de cette étude est de contraindre expérimentalement la solubilité de l'eau de l'olivine et de la wadsleyite à 410 km de profondeur (soit 14 GPa), en conditions saturées en eau, de 1200 °C à 1400 °C, à trois tampons de ƒO2, (Fe­FeO, Ni­NiO et Re­ReO2), et deux types de fluides différents (H2O et H2O+C2H2O4). Les expériences ont été réalisées en presse multi-enclumes en double capsules scellées pour préserver les fluides. Les échantillons ont ensuite été polis et analysés par MEB et microsonde électronique pour étudier leur composition. L'eau contenue dans les minéraux a été quantifiée par spectroscopie Raman, qui permet une résolution spatiale de l'ordre du micromètre, grâce à une méthode initiée pour l'olivine par Bolfan-Casanova et al. (2014) et continuée ici, puis étendue au cours de la présente étude à la wadsleyite (Martinek &amp; Bolfan-Casanova, 2019). Les erreurs associées à ces mesures ont été identifiées et quantifiées grâce à l'étude de monocristaux d'olivine et de wadsleyite, où les spectres Raman ont été acquis en fonction de l'orientation du minéral. L'objectif a été de permettre la distinction entre les différentes sources d'erreur de mesure et l'anisotropie naturelle de ces minéraux, et d'observer l'effet de deux méthodes de mesures différentes sur les erreurs. Les facteurs de conversion liant les rapports OH/Si mesurés par spectroscopie à la concentration en eau sont de 93108±24118 pour l'olivine, 250868±53827 pour la wadsleyite de composition Fo89, et de 57862±12487 pour une wadsleyite à Fo100 (facteurs en ppm en masse d'eau).Un important effet de la ƒO2 sur les températures de fusion a été observé dans les expériences sans carbone (baisse de 30 à 40 °C par unité log de ƒO2). Les teneurs en eau mesurées augmentent pour olivine et wadsleyite lorsque la température, ou la ƒO2, augmente, mais baissent drastiquement en présence de carbone ou de fusion, celle-ci étant favorisée par l'augmentation de température et de ƒO2. Les teneurs en eau mesurées s'échelonnent de 4600 à 18800 ppm pour la wadsleyite et de 350 à 2400 ppm pour l'olivine en absence de carbone, et de 1800 à 10900 ppm pour la wadsleyite et de 135 à 1030 ppm pour l'olivine en présence de carbone. Cette étude montre donc qu'en conditions réductrices ainsi que même en présence de carbone la teneur en eau aux conditions du bas du manteau supérieur reste substantielle<br>The study of the water content of nominally anhydrous minerals and the parameters influencing solubilities is an active research field because of its effects on the physical and chemical properties of the mantle. This study aims to experimentally constrain the water storage capacities of olivine and wadsleyite at a depth around 410 km (14 GPa) under water-saturated conditions, from 1200 °C to 1400 °C, with three different ƒO2 buffers (Fe­FeO, Ni­NiO et Re­ReO2) and two different fluid compositions (H2O et H2O+C2H2O4). Experiments have been conducted in the multi-anvil press, with sealed double capsules to preserve fluids. Samples were polished and analyzed by SEM and electron microprobe to study their composition. The water contents of minerals were measured by Raman spectroscopy with a method initiated for olivine by Bolfan-Casanova et al. (2014) continued here and extended to wadsleyite (Martinek &amp; Bolfan-Casanova, 2019). Errors related to this method have been quantified and identified with the study of two olivine and wadsleyite single-crystals with Raman spectra acquired as a function of the mineral's orientation. The goal was distinguishing the various measurement error sources from the natural anisotropy of the minerals, and observe the effect of two different measurement method on the errors. The conversion factors connecting the OH/Si measured by Raman spectroscopy to the water content are 93108±24118 for olivine, 250868±53827 for Fo89 wadsleyite, and 57862±12487 for Fo100 wadsleyite (factors in ppm weight of water).A significant effect of ƒO2 on the melting temperature has been observed in the carbon-free experiments (decreasing of 30 to 40 °C by ƒO2 log unit). The measured water contents for both olivine and wadsleyite increase with increasing temperature or ƒO2, but drop in the presence of carbon or melting, which benefits from higher temperature and ƒO2. The observed water contents vary from 4600 to 18800 ppm for wadsleyite and 350 to 2400 ppm for olivine in carbon-free experiments, and from 1800 to 10900 ppm for wadsleyite and 135 to 1030 ppm for olivine in carbon-bearing experiments. This study points out that even under reducing conditions and in the presence of carbon, the water content at the bottom of the upper mantles remains significant

<p>Systematic infrared and nuclear magnetic resonance investigations of common crustal minerals were undertaken to better understand the geologic significance of minor components of structural hydrous species within these nominally anhydrous minerals.</p> <p>The absolute hydrogen concentration in three alkali feldspars and eight plagioclase samples was measured with ¹H nuclear magnetic resonance spectroscopy. The mid-infrared integral absorption coefficient was determined to be 15.3 ± 0.7 ppm⁻¹cm⁻², allowing quantitative analysis of OH and H₂O in feldspars with infrared spectroscopy. A survey of hydrous species in igneous feldspars found that feldspars contain structural OH (0-512 ppm H₂O), H₂O (0-1350 ppm H₂O), and NH₄⁺ (0-1500 ppm NH₄⁺) groups as well as fluid inclusions and alteration products. Composition and crystal structure influence the type of hydrous species that can be incorporated into feldspars, but the concentration and speciation of structural hydrogen is at least partially determined by the geologic environment. The diffusivity of H in OH-bearing plagioclase was determined at 800-1000°C (D0=5.7±2.5x10⁻⁴ m²/sec and Q=224±33 kJ/mol). A millimeter-sized volcanic feldspar phenocryst would be expected to lose a significant proportion of its OH concentration on the timescale of a typical eruption (hours to weeks).</p> <p>The structures and compositions of low albite and ussingite, Na₂AlSi₃O₈(OH), are similar. The strong hydrogen bonding in ussingite is found to be fundamentally different from the hydrogen bonding environment of OH in feldspars. Comparison of the infrared spectra of structural isomorphs reedmergnerite, NaBSi₃O₈, and low albite suggest that OH is incorporated in both structures through protonation of the most underbonded oxygen site.</p> <p>The concentration of structural OH in diopside was determined for four granulite facies siliceous marble samples from the Adirondacks, New York. Diopside OH concentration increases monotonically with increasing estimated water fugacity for each outcrop.</p> <p>Hydrogen concentration is correlated to Ti concentration in zoned grossular skarn garnets from Birch Creek, CA. Decrease of Ti and H from garnet cores to rims may be related to the solubility of Ti in the skarn-forming fluid. Skarn garnets from an Adirondacks, NY, wollastonite ore deposit exhibit a large range of OH concentrations broadly related to rock type that are due to recrystallization and partial dehydration.</p>

abstract: Hydrogen isotope compositions of the martian atmosphere and crustal materials can provide unique insights into the hydrological and geological evolution of Mars. While the present-day deuterium-to-hydrogen ratio (D/H) of the Mars atmosphere is well constrained (~6 times that of terrestrial ocean water), that of its deep silicate interior (specifically, the mantle) is less so. In fact, the hydrogen isotope composition of the primordial martian mantle is of great interest since it has implications for the origin and abundance of water on that planet. Martian meteorites could provide key constraints in this regard, since they crystallized from melts originating from the martian mantle and contain phases that potentially record the evolution of the H2O content and isotopic composition of the interior of the planet over time. Examined here are the hydrogen isotopic compositions of Nominally Anhydrous Phases (NAPs) in eight martian meteorites (five shergottites and three nakhlites) using Secondary Ion Mass Spectrometry (SIMS). This study presents a total of 113 individual analyses of H2O contents and hydrogen isotopic compositions of NAPs in the shergottites Zagami, Los Angeles, QUE 94201, SaU 005, and Tissint, and the nakhlites Nakhla, Lafayette, and Yamato 000593. The hydrogen isotopic variation between and within meteorites may be due to one or more processes including: interaction with the martian atmosphere, magmatic degassing, subsolidus alteration (including shock), and/or terrestrial contamination. Taking into consideration the effects of these processes, the hydrogen isotope composition of the martian mantle may be similar to that of the Earth. Additionally, this study calculated upper limits on the H2O contents of the shergottite and nakhlite parent melts based on the measured minimum H2O abundances in their maskelynites and pyroxenes, respectively. These calculations, along with some petrogenetic assumptions based on previous studies, were subsequently used to infer the H2O contents of the mantle source reservoirs of the depleted shergottites (200-700 ppm) and the nakhlites (10-100 ppm). This suggests that mantle source of the nakhlites is systematically drier than that of the depleted shergottites, and the upper mantle of Mars may have preserved significant heterogeneity in its H2O content. Additionally, this range of H2O contents is not dissimilar to the range observed for the Earth’s upper mantle.<br>Dissertation/Thesis<br>Masters Thesis Geological Sciences 2015

abstract: The transport of hydrogen to the Earth’s deep interior remains uncertain. The upper mantle minerals have very low hydrogen solubilities (hundreds of ppm). The hydrogen storage capability in the transition zone minerals (2 wt%) is high compared to those of the upper mantle. The hydrogen storage in the lower mantle is not well known. The main minerals in the lower mantle bridgmanite and ferropericlase have very low hydrogen storage capacities (less than 20 ppm). In order to further understand the hydrogen storage in the lower mantle, a series of experiments had been conducted to simulate the environment similar to the Earth’s mantle. The experiments with hydrous Mg2SiO4 ringwoodite (Rw) show that it converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2(mStv), containing ∼1 wt% H2O together with bridgmanite (Brd) and MgO at the pressure-temperature conditions expected for lower mantle depths between approximately 660 to 1600 km. Brd would break down partially to dense hydrous silica (6–25 mol%) and(Mg,Fe)O in mid-mantle regions with 0.05–0.27 wt% H2O. The hydrous stishovite has a CaCl2 structure, which is common among hydrous minerals in the lower mantle. Based on this observation, I hypothesize the existence of hydrous phases in the lower mantle. The experiments found a new hexagonal iron hydroxide (η-Fe12O18+x/2Hx) between the stability fields of the epsilon and pyrite-type FeOOH at 60–80 GPa and high temperature. The new phase contains less H2O, limiting the H2O transport from the shallow to the deep mantle in the Fe–O–H system. Possible hydrogen storage in Ca-perovskite was studied. CaPv could contain 0.5–1 wt% water and the water in CaPv could distort the crystal structure of CaPv from cubic to tetragonal structure. In conclusion, hydrogen can be stored in hydrous stishovite in the shallower depth of the lower mantle. At greater depth, the new η phase and pyrite-type phase would take over the hydrogen storage. The role of CaPv in deep water storage needs to be considered in future studies.<br>Dissertation/Thesis<br>Doctoral Dissertation Natural Science 2019

abstract: Fluorine (F) is a volatile constituent of magmas and hydrous mantle minerals. Compared to other volatile species, F is highly soluble in silicate melts, allowing F to remain in the melt during magma differentiation and rendering F less subject to disturbance during degassing upon magma ascent. Hence, the association between fluorine in basalts and fluorine in the mantle source region is more robust than for other volatile species. The ionic radius of F- is similar to that of OH- and O2-, and F may substitute for hydroxyl and oxygen in silicate minerals and melt. Fluorine is also incorporated at trace levels within nominally anhydrous minerals (NAMs) such as olivine, clinopyroxene, and plagioclase. Investigating the geochemical behavior of F in NAMs provides a means to estimate the pre-eruptive F contents of degassed magmas and to better understand the degassing behavior of H. The partition coefficients of F were determined for clinopyroxene, olivine, plagioclase, and hornblende within melts of olivine-minette, augite-minette, basaltic andesite, and latite compositions. The samples analyzed were run products from previously-published phase-equilibria experiments. Fluorine was measured by secondary ion mass spectrometry (SIMS) using an 16O- primary beam and detection of negative secondary ions (19F-, 18O-, 28Si-). SIMS ion intensities are converted to concentrations by analyzing matrix-matched microanalytical reference materials and constructing calibration curves. For robust F calibration standards, five basaltic glasses (termed Fba glasses) were synthesized in-house using a natural tholeiite mixed with variable amounts of CaF2. The Fba glasses were characterized for F content and homogeneity, using both SIMS and electron-probe microanalysis (EPMA), and used as F standards. The partition coefficients for clinopyroxene (0.04-028) and olivine (0.01-0.16) varied with melt composition such that DF (olivine-minette) < DF (augite-minette) < DF (basaltic andesite) < DF (latite). Crystal chemical controls were found to influence the incorporation of F into clinopyroxene, but none were found that affected olivine. Fluorine partitioning was compared with that of OH within clinopyroxenes, and the alumina content of clinopyroxene was shown to be a strong influence on the incorporation of both anions. Fluorine substitution into both olivine and clinopyroxene was found to be strongly controlled by melt viscosity and degree of melt polymerization.<br>Dissertation/Thesis<br>Ph.D. Geological Sciences 2012