Vanadium micro-XANES determination of oxygen fugacity in olivine-hosted glass inclusion and groundmass glasses of martian primitive shergottite Yamato 980459

2020 ◽  
Vol 105 (11) ◽  
pp. 1695-1703
Author(s):  
Ryoichi Nakada ◽  
Tomohiro Usui ◽  
Masashi Ushioda ◽  
Yoshio Takahashi
Keyword(s):  
Oxygen Fugacity ◽  
Volcanic Rocks ◽  
Redox Condition ◽  
Magma Ascent ◽  
Glass Inclusion ◽  
Edge Structure ◽  
X Ray ◽  
Groundmass Glass ◽  
The Stability ◽  
Equilibrium Phases

Abstract The redox condition of magma determines the stability and composition of crystallizing and volatile phases in martian meteorites, reflecting the evolution of the martian interior. In the current study, direct analyses on the oxidation states of V, Cr, and Fe were performed based on the X-ray absorption near-edge structure (XANES) measurements equipped with a micro-sized X-ray beam. We first applied the micro-XANES (μ-XANES) technique to the olivine-hosted glass inclusion and groundmass glass of martian meteorite Yamato 980459 (Y98), which is interpreted as representing a primary melt composition. Mass-balance calculations and XANES spectra comparisons indicated that, while chromite and pyroxene affected Cr and Fe K-edge XANES spectra, the contribution of these minerals was minimal for V. The pre-edge peak intensity of V K-edge XANES enabled the estimation of the oxygen fugacity for inclusion and groundmass glasses. The calculated oxygen fugacity (fO2) of the glass inclusions was near the Iron-Wüstite (IW) buffer (IW-0.07 ± 0.32) for the glass inclusion, whereas it was 0.9 log units more oxidized (IW+0.93 ± 0.56) for the groundmass glasses. This result suggests that the redox condition of the parent magma of Y98 evolved during magma ascent and emplacement. Since Y98 is interpreted to have evolved in a closed system, our finding suggests that fractional crystallization and/or ascent of magma potentially induces the fO2 increase. This study shows that the μ-XANES technique enables us to determine the fO2 by only measuring a single phase of glassy compounds, and thus, it is useful to discuss the redox condition of volcanic rocks even if they do not crystallize out several equilibrium phases of minerals.

Generation of Calc-Alkaline Magmas During Crystallization at High Oxygen Fugacity: An Experimental and Petrologic Study of Tephras from Buldir Volcano, Western Aleutian Arc, Alaska, USA

2020 ◽  
Author(s):  
L E Waters ◽  
E Cottrell ◽  
M L Coombs ◽  
K A Kelley
Keyword(s):  
Oxygen Fugacity ◽  
Subduction Zones ◽  
Volcanic Rocks ◽  
High Oxygen ◽  
Calc Alkaline ◽  
Edge Structure ◽  
Liquidus Phase ◽  
High Oxygen Fugacity ◽  
Alkaline Volcanism ◽  
Aleutian Arc

Abstract Despite agreement that calc-alkaline volcanism occurs at subduction zones and is responsible for the genesis of continental landmasses, there is no consensus on the source of the Fe-depleted signature hallmark to calc-alkaline volcanism. In this study, we utilize mafic tephras collected from Buldir Volcano to address the genesis of strongly calc-alkaline volcanic rocks (those with a low Tholeiitic Index; ≤0.7) in a segment of the western Aleutian Arc to determine if the eruptions are plausibly part of a liquid line of descent, if they are mixtures of crustal melts and parental magmas, or if they are mixtures of melts of the mantle and the subducting slab. We conducted a series of H2O-saturated phase equilibrium experiments (1175–1000 °C; 100 MPa) in a rapid-quench cold-seal (MHC) apparatus on the most primitive natural lava from Buldir (9.34 wt% MgO) at oxidizing conditions near the Re-ReO2 buffer. We confirmed that all experiments equilibrated 0.3 ± 0.23 log units above the Re-ReO2 buffer (ΔQFM ∼ +2.8) using X-ray Absorption Near Edge Structure (XANES) spectroscopy. Chromite is the liquidus phase, followed by olivine, then plagioclase, then clinopyroxene, and finally hornblende. Once clinopyroxene saturates, spinel composition shifts to magnetite. We compared our experimental results to the major element geochemistry and petrology of six tephras (51.9–54.8 wt% SiO2) from Buldir collected during the 2015 field season of the GeoPRISMS shared platform. Tephras contain olivine + plagioclase + clinopyroxene + spinel ± hornblende; plagioclase comprises most of the crystalline volume, followed by either olivine or hornblende. Spinel is ubiquitous; with Cr- rich spinel inclusions in olivine and hornblende, and magnetite in the groundmass. Variations in phenocryst assemblages and compositions between samples can be attributed to differences in pre-eruptive temperatures, where hotter samples are devoid of hornblende, and contain Fo-rich olivine and plagioclase with lower An-contents, owing to the position of the mineral-in curves at fluid-saturated conditions. Experimental glasses match the depletion in FeOT observed in the tephra whole rock compositions. The continuous depletion in FeOT is attributable to saturation of spinel as a liquidus phase (initially as chromite) and continuous crystallization through the experimental series (changing to magnetite at colder temperatures). In contrast to the natural samples, the experiments show enrichment in TiO2 with decreasing MgO, suggesting that differentiation did not occur at 100 MPa on Buldir. The TiO2 depletion in volcanic rocks from Buldir can be accounted for if hornblende crystallization occurs close to the liquidus of a parental magma; a condition that is met at higher pressures and hydrous conditions. The emerging picture for Buldir Island is that (1) oxidizing conditions are required to drive the observed depletions in FeOT via crystallization of spinel, and (2) elevated H2O contents and high pressures are required to saturate hornblende close to the liquidus to reproduce the entire suite of major elements. Our study provides a mechanism to generate the calc-alkaline trends observed at Buldir without requiring mixing of slab and mantle melts. We conclude that calc-alkaline volcanic rocks with extremely low Tholeiitic Indices (0.7), like those from Buldir, cannot be generated in absence of high oxygen fugacity, even at high pressure and/or elevated water pressures.

scholarly journals Cation distribution and valence in synthetic Al–Mn–O and Fe–Mn–O spinels under varying conditions

2018 ◽  
Vol 82 (4) ◽  
pp. 975-992 ◽  
Author(s):  
Thomas N. Stokes ◽  
Geoffrey. D. Bromiley ◽  
G. Diego Gatta ◽  
Nicola Rotiroti ◽  
Nicola J. Potts ◽  
...  
Keyword(s):  
Oxygen Fugacity ◽  
Cation Distribution ◽  
Valence State ◽  
Ambient Pressure ◽  
Site Occupancy ◽  
Cation Site ◽  
Edge Structure ◽  
X Ray ◽  
Lack Of Information ◽  
Parental Melts

ABSTRACTThe spinel-group minerals, found in a range of igneous rocks, are resistant to weathering and can incorporate several multivalent elements, meaning they have the potential to provide insight into the redox conditions of parental magmas. Naturally occurring spinel can contain varying quantities of Mn, an element which occurs terrestrially and extra-terrestrially as Mn2+, Mn3+, Mn4+ and Mn5+. However, a lack of information on the effects of oxygen fugacity ($f_{{\rm O}_{\rm 2}}$) on: (1) Mn valence state and cation distribution; and (2) on spinel-melt partitioning means that the potential for a Mn-in-spinel oxy-barometer remains largely untested. Here, we use electron probe microanalysis, micro-focus X-ray Absorption Near Edge Structure (XANES) spectroscopy and single-crystal X-ray diffraction (SC-XRD) to investigate cation distribution and valence state in spinels in the Al–Mn–O and Fe–Mn–O systems synthesized at ambient pressure under varying $\hskip 2pt f_{{\rm O}_{\rm 2}}$ conditions. In contrast to previous studies, we find that the spectral resolution of the Mn K-edge XANES spectra is insufficient to provide quantitative data on Mn valence state and site occupancy, although it does verify that Mn is incorporated as both Mn2+ and Mn3+, distributed over tetrahedral and octahedral sites. Combination of data from XANES and SC-XRD refinements can, however, be used to model Mn, Al and Fe valence and site occupancy. It would be expected that Mn–Fe spinels have the potential to record $f_{{\rm O}_{\rm 2}}$ conditions in parental melts due to changes to the octahedral site under conditions that were more reducing. However, decoupling the effects of temperature and oxygen fugacity on the TFe3+–TMn2+ exchange in the Mn–Fe spinels remains challenging. In contrast, little variation is noted in Mn–Al spinels as a function of $\hskip 2pt f_{{\rm O}_{\rm 2}}$, implying that crystal chemistry and cation site geometry may significantly influence cation distribution, and by inference, crystal-melt partitioning, in spinel-group minerals.

scholarly journals The new X-ray absorption fine-structure beamline with sub-second time resolution at the Taiwan Photon Source

2021 ◽  
Vol 28 (3) ◽  
pp. 930-938
Author(s):  
Chih-Wen Pao ◽  
Jeng-Lung Chen ◽  
Jyh-Fu Lee ◽  
Meng-Che Tsai ◽  
Chi-Yi Huang ◽  
...  
Keyword(s):  
Fine Structure ◽  
Spectral Measurements ◽  
Edge Structure ◽  
X Ray ◽  
Xafs Spectroscopy ◽  
Absorption Fine ◽  
The Stability ◽  
X Ray Absorption ◽  
Photon Source

The new TPS 44A beamline at the Taiwan Photon Source, located at the National Synchrotron Radiation Research Center, is presented. This beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans (s-scans) and on-the-fly scans (q-scans) for X-ray absorption fine-structure (XAFS) spectroscopy experiments, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectral measurements. Ti and Te K-edge XAFS spectra were used to demonstrate the capability of collecting spectra at the limits of the working energy range. The Ni and Cu K-edge XAFS spectra for a Cu-doped Pt/Ni nanocomposite were acquired to test the performance of the newly commissioned beamline. Pt L 3- and Ru K-edge quick-scanning XAFS (QXAFS) spectra for standard Pt and Ru foils, respectively, revealed the stability of the q-scan technique. The results also demonstrated the beamline's ability to collect XAFS spectra on a sub-second timescale. Furthermore, a Zn(s)|Zn2+ (aq)|Cu(s) system was tested to indicate that the states of the Zn electrode could be observed in real time for charging and discharging conditions using an in situ/operando setup combined with QXAFS measurements.

Investigation of Organic Matter Entrapped in Synthetic Carbonates—A Multimethod Approach

2012 ◽  
Vol 19 (1) ◽  
pp. 132-144 ◽  
Author(s):  
Emilie Chalmin ◽  
Yves Perrette ◽  
Bernard Fanget ◽  
Jean Susini
Keyword(s):  
Organic Matter ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Edge Structure ◽  
X Ray ◽  
Multimethod Approach ◽  
The Stability ◽  
Log Linear ◽  
X Ray Absorption ◽  
Surface Changes

AbstractOrganic matter (OM) entrapped in calcite is regularly used for environmental studies; however, insertion mechanisms and types of interaction remain poorly understood. The present study used a new methodology to investigate interactions between OM and the calcite matrix during crystallization processes with humic acid (HA) entrapment. A multimethod approach confirmed that HA is both adsorbed onto the calcite surface and incorporated into the calcite lattice during crystallization. Our results also confirm the log-linear correlation between fluorescence intensity and calcite matrix HA concentration. Fourier transform infrared spectroscopy showed that HA in colloidal conformation is adsorbed onto the calcite surface as a result of the structure of the OH stretching band. We also developed a new method based on synchrotron analysis that uses sulfur as a tracer element for entrapped HA and that localizes the OM electrostatically adsorbed onto the calcite surface. Changes in the sulfur environment, determined using X-ray absorption near-edge structure spectroscopy, indicated more complex insertion mechanisms than simple adsorption of HA during calcite crystallization. Desorption experiments revealed the stability of the OM atomic structure and its layered nature. These results allowed us to draw up a general model of OM insertion in calcite.

scholarly journals Self-Fluxing Mechanism in Geopolymerization for Low-Sintering Temperature of Ceramic

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1325
Author(s):  
Noorina Hidayu Jamil ◽  
Mohd. Mustafa Al Bakri Abdullah ◽  
Faizul Che Pa ◽  
Hasmaliza Mohamad ◽  
Wan Mohd Arif W. Ibrahim ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Sintering Temperature ◽  
Edge Structure ◽  
X Ray ◽  
Granulated Blast Furnace Slag ◽  
Different Temperatures ◽  
Low Sintering Temperature ◽  
The Difference ◽  
Pre Treatment ◽  
The Stability

Kaolin, theoretically known as having low reactivity during geopolymerization, was used as a source of aluminosilicate materials in this study. Due to this concern, it is challenging to directly produce kaolin geopolymers without pre-treatment. The addition of ground granulated blast furnace slag (GGBS) accelerated the geopolymerization process. Kaolin–GGBS geopolymer ceramic was prepared at a low sintering temperature due to the reaction of the chemical composition during the initial stage of geopolymerization. The objective of this work was to study the influence of the chemical composition towards sintering temperature of sintered kaolin–GGBS geopolymer. Kaolin–GGBS geopolymer was prepared with a ratio of solid to liquid 2:1 and cured at 60 °C for 14 days. The cured geopolymer was sintered at different temperatures: 800, 900, 1000, and 1100 °C. Sintering at 900 °C resulted in the highest compressive strength due to the formation of densified microstructure, while higher sintering temperature led to the formation of interconnected pores. The difference in the X-ray absorption near edge structure (XANES) spectra was related to the phases obtained from the X-ray diffraction analysis, such as akermanite and anothite. Thermal analysis indicated the stability of sintered kaolin–GGBS geopolymer when exposed to 1100 °C, proving that kaolin can be directly used without heat treatment in geopolymers. The geopolymerization process facilitates the stability of cured samples when directly sintered, as well as plays a significant role as a self-fluxing agent to reduce the sintering temperature when producing sintered kaolin–GGBS geopolymers.

Experimental investigation of FeCO3 (siderite) stability in Earth's lower mantle using XANES spectroscopy

2019 ◽  
Vol 104 (8) ◽  
pp. 1083-1091 ◽  
Author(s):  
Valerio Cerantola ◽  
Max Wilke ◽  
Innokenty Kantor ◽  
Leyla Ismailova ◽  
Ilya Kupenko ◽  
...  
Keyword(s):  
High Spin ◽  
Lower Mantle ◽  
Spin Crossover ◽  
High Spin State ◽  
Xanes Spectroscopy ◽  
Edge Structure ◽  
X Ray ◽  
Edge Features ◽  
The Stability ◽  
X Ray Absorption

Abstract We studied FeCO3 using Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy at pressures up to 54 GPa and temperatures above 2000 K. First-principles calculations of Fe at the K-edge in FeCO3 were performed to support the interpretation of the XANES spectra. The variation of iron absorption edge features with pressure and temperature in FeCO3 matches well with recently reported observations on FeCO3 at extreme conditions, and provides new insight into the stability of Fe-carbonates in Earth's mantle. Here we show that at conditions of the mid-lower mantle, ~50 GPa and ~2200 K, FeCO3 melts and partially decomposes to high-pressure Fe3O4. Carbon (diamond) and oxygen are also inferred products of the reaction. We constrained the thermodynamic phase boundary between crystalline FeCO3 and melt to be at 51(1) GPa and ~1850 K. We observe that at 54(1) GPa, temperature-induced spin crossover of Fe2+ takes place from low to high spin such that at 1735(100) K, all iron in FeCO3 is in the high-spin state. A comparison between experiment and theory provides a more detailed understanding of FeCO3 decomposition observed in X-ray absorption spectra and helps to explain spectral changes due to pressure-induced spin crossover in FeCO3 at ambient temperature.

Fractionation of polymethylene chains: An electron crystallographic investigation

1986 ◽  
Vol 44 ◽  
pp. 794-795
Author(s):  
Douglas L. Dorset
Keyword(s):  
Cross Section ◽  
Binary Systems ◽  
Linear Chain ◽  
Pure Component ◽  
Organic Substrates ◽  
Crystallographic Investigation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molecular Sizes ◽  
The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

Chemical and orientational imaging of polymeric samples

1994 ◽  
Vol 52 ◽  
pp. 68-69
Author(s):  
H. Ade ◽  
B. Hsiao ◽  
G. Mitchell ◽  
E. Rightor ◽  
A. P. Smith ◽  
...  
Keyword(s):  
Ethylene Terephthalate ◽  
National Laboratory ◽  
Brookhaven National Laboratory ◽  
Carbonyl Groups ◽  
Aromatic Rings ◽  
Edge Structure ◽  
X Ray ◽  
Scanning Transmission ◽  
Polymeric Samples ◽  
X Ray Absorption

We have used the Scanning Transmission X-ray Microscope at beamline X1A (X1-STXM) at Brookhaven National Laboratory (BNL) to acquire high resolution, chemical and orientation sensitive images of polymeric samples as well as point spectra from 0.1 μm areas. This sensitivity is achieved by exploiting the X-ray Absorption Near Edge Structure (XANES) of the carbon K edge. One of the most illustrative example of the chemical sensitivity achievable is provided by images of a polycarbonate/pol(ethylene terephthalate) (70/30 PC/PET) blend. Contrast reversal at high overall contrast is observed between images acquired at 285.36 and 285.69 eV (Fig. 1). Contrast in these images is achieved by exploring subtle differences between resonances associated with the π bonds (sp hybridization) of the aromatic groups of each polymer. PET has a split peak associated with these aromatic groups, due to the proximity of its carbonyl groups to its aromatic rings, whereas PC has only a single peak.

Interactions of Ge Atoms with High- ê Oxide Dielectric Surfaces

2005 ◽  
Vol 879 ◽  
Author(s):  
Scott K. Stanley ◽  
John G. Ekerdt
Keyword(s):  
Oxide Layer ◽  
Photoelectron Spectroscopy ◽  
Chemical Vapor ◽  
Temperature Programmed Desorption ◽  
Tungsten Filament ◽  
X Ray ◽  
Dielectric Surfaces ◽  
Temperature Programmed ◽  
The Stability ◽  
Ge Nanocrystals

AbstractGe is deposited on HfO2 surfaces by chemical vapor deposition (CVD) with GeH4. 0.7-1.0 ML GeHx (x = 0-3) is deposited by thermally cracking GeH4 on a hot tungsten filament. Ge oxidation and bonding are studied at 300-1000 K with X-ray photoelectron spectroscopy (XPS). Ge, GeH, GeO, and GeO2 desorption are measured with temperature programmed desorption (TPD) at 400-1000 K. Ge initially reacts with the dielectric forming an oxide layer followed by Ge deposition and formation of nanocrystals in CVD at 870 K. 0.7-1.0 ML GeHx deposited by cracking rapidly forms a contacting oxide layer on HfO2 that is stable from 300-800 K. Ge is fully removed from the HfO2 surface after annealing to 1000 K. These results help explain the stability of Ge nanocrystals in contact with HfO2.

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