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Colin R. Ward - One of the best experts on this subject based on the ideXlab platform.
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Comparison of elemental composition of macerals determined by Electron Microprobe to whole-coal ultimate analysis data
International Journal of Coal Geology, 2008Co-Authors: Colin R. WardAbstract:The elemental composition of the individual macerals in a suite of Australian coals has been determined in polished sections using light-element Electron Microprobe techniques. The analyses of the individual macerals in each coal were combined with data on maceral abundance to produce an inferred chemical composition for the organic matter of the respective whole-coal samples, and this was compared, for each sample, to the respective whole-coal ultimate analysis data, corrected to a dry, ash-free (daf) basis. Except for slightly lower values in some lower-rank coals, the inferred percentages of whole-coal C estimated from the Microprobe data were found to be very close to the respective whole-coal C percentages as determined by conventional ultimate analysis. The proportion of O in the coals indicated by the Microprobe study, however, appears to be as much as 2% higher than that derived from the ultimate analysis data, especially in the lower-rank coal samples. The difference it may represent errors in calculating the O percentages in ultimate analysis, errors in the Microprobe analysis due to difficulties in calibration or measurement, or increased proportions of O in the coals due to factors such as take-up with storage of the polished sections. The percentages of whole-coal N calculated from the Microprobe data are up to 0.5% (absolute) below the proportion of N determined directly by whole-coal ultimate analysis. This may reflect the inherent difficulty of dealing with a light element at low concentrations by the Microprobe technique, or it may indicate that some of the N occurs in the coals in mineral form. The percentages of whole-coal (organic) S calculated from the Microprobe study are close to the percentages of organic S determined for each sample by more conventional techniques. With the exception of (organic) O, which may be affected by other factors, and also possibly of N, the Electron Microprobe technique appears from the study to provide results that are consistent with ultimate analysis over a wide rank range.
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elemental composition of coal macerals in relation to vitrinite reflectance gunnedah basin australia as determined by Electron Microprobe analysis
International Journal of Coal Geology, 2000Co-Authors: Lila W. Gurba, Colin R. WardAbstract:Abstract The elemental composition of macerals in high-volatile bituminous coals from the Gunnedah Basin, New South Wales, Australia, has been analysed by light-element Electron Microprobe techniques. The results have been evaluated in relation to maximum vitrinite reflectance trends in vertical section, including the effects of marine influence and igneous intrusions on the coal-bearing sequence. Mean maximum vitrinite (telocollinite and desmocollinite) reflectance for the analysed samples ranges from 0.63% to 0.99%, and to 2.2% for coal affected by igneous intrusions. The carbon content of the vitrinite, as determined by Electron Microprobe, ranges from 79.74% to 86.07%, and up to 89.06% for the heat-affected coal studied. A simple relationship cannot be established between the reflectance of the vitrinite and its carbon content over this range of coal samples. Vitrinite in marine influenced coals (with suppressed reflectance) appears to have a slightly higher carbon content than vitrinite in isorank coals without marine influence. The increase in carbon may be due to incorporation of carbon and sulphur–rich lipoid material into the vitrinite component. Notwithstanding these differences, the carbon content of vitrinite (telocollinite) seems to be affected only slightly by the depositional changes that cause suppression of vitrinite reflectance in marine-influenced coals. Telocollinite carbon content may therefore be a useful alternative to vitrinite reflectance as a rank indicator in maturation studies. The carbon content of whole-coal samples, determined by ultimate analysis, shows in vertical section a trend intermediate between the carbon of the vitrinite determined by Electron Microprobe and that of the associated inertinite macerals. Whole-coal analysis data in this range depend on the relative proportions of the different macerals present, as well as the rank of the coal concerned. Coals affected by igneous intrusion show a different relationship between carbon and oxygen of vitrinite (telocollinite), relative to coals where the rank is determined by depth of burial alone. The difference in C–O relationships suggests that the short-term heating associated with intrusions produces chemical changes in macerals that are not paralleled in more normal rank advance.
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Chemical composition of macerals in bituminous coals of the Gunnedah Basin, Australia, using Electron Microprobe analysis techniques
International Journal of Coal Geology, 1999Co-Authors: Colin R. WardAbstract:Abstract The chemical composition of the organic matter in the principal macerals of high-volatile bituminous coals from the Gunnedah Basin, New South Wales (Rvmax of telocollinite between 0.6 and 1.1%) has been evaluated from polished section specimens using an Electron Microprobe technique. Highest proportions of carbon occur in the inertinite macerals, especially fusinite and secretinite (formerly resino-sclerotinite), as well as in sporinite; lowest proportions of carbon occur in the different macerals of the vitrinite group. Oxygen shows the reverse trend, being most abundant in vitrinite and least abundant in the inertinite components, whereas sulphur is lowest in the inertinites and highest in the liptinite (mainly sporinite) present. Evaluations of maceral composition, using the carbon content of telocollinite as a rank indicator, show that carbon is more abundant in both sporinite and semifusinite, relative to vitrinite, in low-rank high-volatile bituminous coals. The difference decreases with increasing rank, and the proportion of carbon in telocollinite becomes essentially the same as that in sporinite and semifusinite at carbon contents of about 89 and 91%, respectively. The carbon content of fusinite and secretinite, on the other hand, does not seem to vary appreciably with rank advance. No significant difference in composition occurs in the rank range studied between the three vitrinite varieties present, desmocollinite, telocollinite and a more highly reflecting telocollinite resembling pseudovitrinite. No evidence was found to indicate a higher hydrogen content, relative to telocollinite, for the vitrinite matrix of desmocollinite.
Michael J Jercinovic - One of the best experts on this subject based on the ideXlab platform.
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Electron Microprobe dating of monazite the story
Chemical Geology, 2017Co-Authors: Jeanmarc Montel, Alain Cocherie, Takenori Kato, Masaki Enami, Friedrich Finger, Michael L Williams, Michael J JercinovicAbstract:Abstract This paper is a testimony of how Electron Microprobe dating of monazite was developed in the early days of this technique, in the 90's. Five contributions have been collected from Nagoya, Clermont-Ferrand, Orleans, Salzburg, and Amherst. The technique was designed in Nagoya by Professor Suzuki, using an old JXA-5A JEOL Electron Microprobe. The first results were published in 1991, with great difficulty. Professor Suzuki also created the isochron-like Pb-Th* diagram to present the data. Progressive improvement of the method finally allowed the Nagoya team to date Cenozoic monazite. The technique was re-discovered in Clermont-Ferrand using a Cameca Camebax Microprobe. This team demonstrated the accuracy of the method, and proposed statistical tools to improve the precision and to handle multimodal populations. The first results were published in 1993. In Orleans, the French Geological Survey (BRGM) developed the method with a Cameca SX50 to support mapping projects. They developed a new method for calculating the age, and showed that this technique was very efficient for dating monazite in migmatites. In Salzburg, the first results were obtained in 1996, using a Jeol JX 8600. It proved to be very efficient in the Alps to distinguish Cadomian, Ordovician, Variscan and Alpine events. It allowed this team to directly date a monazite-allanite reaction they described for the first time. Finally, the Amherst team investigated in detail the technical issues of Electron Microprobe monazite dating. They showed that the best analytical procedures must include at least: detailed chemical mapping, several interference corrections and special care for background measurements. With the help of Cameca they designed a specific Microprobe for dating, named “Ultrachron”. With this machine, high precision ages can be obtained on well characterized individual grains in thin section, giving birth to a new era in geochronology of complex metamorphic rocks.
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Electron Microprobe petrochronology
Reviews in Mineralogy & Geochemistry, 2017Co-Authors: M Williams, Michael J Jercinovic, Kevin H Mahan, Gregory DumondAbstract:The term petrochronology has increasingly appeared in publications and presentations over the past decade. The term has been defined in a somewhat narrow sense as “the interpretation of isotopic dates in the light of complementary elemental or isotopic information from the same mineral(s)” (Kylander-Clark et al. 2013). Although complementary isotopic and elementary information are certainly a central and critical part of most, if not all, petrochronology studies, the range of recent studies that might use the term covers a much broader scope. The term “petrochronology” might alternatively be defined as the detailed incorporation of chronometer phases into the petrologic (and tectonic) evolution of their host rocks, in order to place direct age constraints on petrologic and structural processes. As noted by Kylander-Clark et al. (2013), the linkage between geochronology and petrology can involve a variety of data including mineral textures and fabrics, the distribution of mineral modes or volume proportions, compositional zoning, mineral inclusion relationships, and certainly major element, trace element, and isotopic composition of the chronometer and all other phases. Electron probe micro-analysis (EPMA) has a central and critical role to play in establishing the linkage between chronometer phases and their host assemblage. The basic instrument is an Electron microscope which can be used in either scanning or fixed beam modes, with integrated wavelength dispersive spectrometers (WDS), energy dispersive spectrometers (EDS), Electron detectors (to image secondary and backscattered signals) a light optical system, and optionally cathodoluminescence (CL) detection. The Electron Microprobe is used to investigate the distribution, composition, and compositional zonation of all mineral phases, the data that underpin thermobarometric analysis and modeling of P–T histories. The Microprobe, with μm-scale spatial resolution, can also characterize compositional zonation in very small accessory phases including monazite, xenotime, zircon, allanite, titanite, apatite, and others. This, as discussed below, can be a …
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Electron-Microprobe age mapping of monazite
American Mineralogist, 2005Co-Authors: Philippe Goncalves, Michael L Williams, Michael J JercinovicAbstract:High resolution X-ray maps of Th, U, Pb, and Y in monazite can be used to construct age maps, which reveal the continuous spatial distribution of ages in a single grain of monazite. The age mapping algorithm and three examples are presented to illustrate the capabilities and applications of this mapping technique, the insights it can provide into monazite geochronology in general, and its limitations compared to Electron Microprobe (EMP) quantitative dating and other in-situ geochronologic techniques. Age maps offer critical information for unraveling metamorphic and tectonic histories and for interpreting results from other geochronologic techniques, and they are a valuable aid for rigorously locating in-situ analytical points. Age mapping also can be used to better understand the behavior of the U-Th-Pb system in monazite during metamorphism, deformation, and s uid-circulation events. Age maps presented in this paper reveal unsuspected age heterogeneities on the micrometer scale, like a now-healed fracture not visible in back-scattered Electron (BSE) images or young domains less than 5 μm in width located inside an older core. In both cases, using age maps as a template for locating in-situ analysis points will minimize the peril of age mixing and erroneous geological interpretations. In addition to providing critical information for illustrating and interpreting the history of complex polygenetic monazite, age mapping may ultimately lead to a better understanding of the processes involved with monazite growth and recrystallization, and thus, even more powerful applications of the monazite geochronometer. The AgeMap program is available in a Windows version and can be downloaded from the internet at the following address: http://www.geo.umass.edu/probe/agemap.
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age mapping and dating of monazite on the Electron Microprobe deconvoluting multistage tectonic histories
Geology, 1999Co-Authors: Michael L Williams, Michael J Jercinovic, Michael P TerryAbstract:High-resolution X-ray mapping and dating of monazite on the Electron Microprobe are powerful geochronological tools for structural, metamorphic, and tectonic analysis. X-ray maps commonly show complex Th, U, and Pb zoning that reflects monazite growth and overgrowth events. Age maps constructed from the X-ray maps simplify the zoning and highlight age domains. Microprobe dating offers a rapid, in situ method for estimating ages of mapped domains. Application of these techniques has placed new constraints on the tectonic history of three areas. In western Canada, age mapping has revealed multiphase monazite, with older cores and younger rims, included in syntectonic garnet. Microprobe ages show that tectonism occurred ca. 1.9 Ga, 700 m.y. later than mylonitization in the adjacent Snowbird tectonic zone. In New Mexico, age mapping and dating show that the dominant fabric and triple-point metamorphism occurred during a 1.4 Ga reactivation, not during the 1.7 Ga Yavapai-Mazatzal orogeny. In Norway, monazite inclusions in garnet constrain high-pressure metamorphism to ca. 405 Ma, and older cores indicate a previously unrecognized component of ca. 1.0 Ga monazite. In all three areas, Microprobe dating and age mapping have provided a critical textural context for geochronologic data and a better understanding of the complex age spectra of these multistage orogenic belts.
Lila W. Gurba - One of the best experts on this subject based on the ideXlab platform.
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determination of nitrogen in coal macerals using Electron Microprobe technique experimental procedure
International Journal of Coal Geology, 2001Co-Authors: Maria Mastalerz, Lila W. GurbaAbstract:This paper discusses nitrogen determination with the Cameca SX50 Electron Microprobe using PC0 as an analyzing crystal. A set of conditions using differing accelerating voltages, beam currents, beam sizes, and counting times were tested to determine parameters that would give the most reliable nitrogen determination. The results suggest that, for the instrumentation used, 10 kV, current 20 nA, and a counting time of 20 s provides the most reliable nitrogen determination, with a much lower detection limit than the typical concentration of this element in coal. The study demonstrates that the Electron Microprobe technique can be used to determine the nitrogen content of coal macerals successfully and accurately.
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elemental composition of coal macerals in relation to vitrinite reflectance gunnedah basin australia as determined by Electron Microprobe analysis
International Journal of Coal Geology, 2000Co-Authors: Lila W. Gurba, Colin R. WardAbstract:Abstract The elemental composition of macerals in high-volatile bituminous coals from the Gunnedah Basin, New South Wales, Australia, has been analysed by light-element Electron Microprobe techniques. The results have been evaluated in relation to maximum vitrinite reflectance trends in vertical section, including the effects of marine influence and igneous intrusions on the coal-bearing sequence. Mean maximum vitrinite (telocollinite and desmocollinite) reflectance for the analysed samples ranges from 0.63% to 0.99%, and to 2.2% for coal affected by igneous intrusions. The carbon content of the vitrinite, as determined by Electron Microprobe, ranges from 79.74% to 86.07%, and up to 89.06% for the heat-affected coal studied. A simple relationship cannot be established between the reflectance of the vitrinite and its carbon content over this range of coal samples. Vitrinite in marine influenced coals (with suppressed reflectance) appears to have a slightly higher carbon content than vitrinite in isorank coals without marine influence. The increase in carbon may be due to incorporation of carbon and sulphur–rich lipoid material into the vitrinite component. Notwithstanding these differences, the carbon content of vitrinite (telocollinite) seems to be affected only slightly by the depositional changes that cause suppression of vitrinite reflectance in marine-influenced coals. Telocollinite carbon content may therefore be a useful alternative to vitrinite reflectance as a rank indicator in maturation studies. The carbon content of whole-coal samples, determined by ultimate analysis, shows in vertical section a trend intermediate between the carbon of the vitrinite determined by Electron Microprobe and that of the associated inertinite macerals. Whole-coal analysis data in this range depend on the relative proportions of the different macerals present, as well as the rank of the coal concerned. Coals affected by igneous intrusion show a different relationship between carbon and oxygen of vitrinite (telocollinite), relative to coals where the rank is determined by depth of burial alone. The difference in C–O relationships suggests that the short-term heating associated with intrusions produces chemical changes in macerals that are not paralleled in more normal rank advance.
Frank C Hawthorne - One of the best experts on this subject based on the ideXlab platform.
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druse clinopyroxene in d orbigny angritic meteorite studied by single crystal x ray diffraction Electron Microprobe analysis and mossbauer spectroscopy
Meteoritics & Planetary Science, 2009Co-Authors: Yassir A Abdu, R B Scorzelli, Maria Eugenia Varela, G Kurat, Izabel De Souza Azevedo, S J Stewart, Frank C HawthorneAbstract:The crystal structure of druse clinopyroxene from the D'Orbigny angrite, (Ca0.944 Fe 2+ 0.042 Mg0.010Mn0.004) (Mg0.469Fe 2+ 0.317Fe 3+ 0.035Al0.125Cr0.010Ti0.044) (Si1.742Al0.258) O6, a = 9.7684(2), b = 8.9124(2), c = 5.2859(1) A, β = 105.903(1)°, V = 442.58 A 3 , space group C2/c, Z = 2, has been refined to an R1 index of 1.92% using single-crystal X-ray diffraction data. The unit formula, calculated from Electron Microprobe analysis, and the refined site scattering values were used to assign site populations. The distribution of Fe 2+ and Mg over the M1 and M2 sites suggests a closure temperature of 1000 °C. Mossbauer spectroscopy measurements were done at room temperature on a single crystal and a powdered sample. The spectra are adequately fit by a Voigt-based quadrupole-splitting distribution model having two generalized sites, one for Fe 2+ with two Gaussian components and one for Fe 3+ with one Gaussian component. The two ferrous components are assigned to Fe 2+ at the M1 site, and arise from two different next-nearest-neighbor configurations of Ca and Fe cations at the M2 site: (3Ca,0Fe) and (2Ca,1Fe). The Fe 3+ /Fetot ratio determined by Mossbauer spectroscopy is in agreement with that calculated from the Electron Microprobe analysis. The results are discussed in connection with the redox and thermal history of D'Orbigny.
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identification of normal and anomalous compositions of minerals by Electron Microprobe analysis k rich feldspar as a case study
Canadian Mineralogist, 1998Co-Authors: David K Teertstra, Frank C Hawthorne, Petr CernyAbstract:The precision of Electron-Microprobe (EMP) measurements at a 4sigma level of confidence is about 1%. By using internally consistent standards with compositions compatible with stoichiometries of the structural formulae, minerals with a generally similar matrix may be analyzed with < or =2% accuracy. Systematic analytical error of a standard may be greatly reduced by examination of the results of analysis of closely related unknown minerals. If a standard is compositionally and structurally well characterized, the accuracy of analysis of samples of near-identical composition may then approach 1% absolute. The bulk of the results, which give the expected stoichiometry of the structure, may be classified as normal. Anomalous measurements, which do not conform to ideal stoichiometry of feldspar, were used to identify analytical overlap with hematite micro-inclusions, light-element substitution, and a compositional trend toward []Si 4 O 8 in adularia from granitic pegmatites.
Abbie Lindeberg - One of the best experts on this subject based on the ideXlab platform.
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quantifying crystallization and devitrification of rhyolites by means of x ray diffraction and Electron Microprobe analysis
American Mineralogist, 2012Co-Authors: Michael C Rowe, Ben S Ellis, Abbie LindebergAbstract:Devitrification of silicic volcanic rocks is a relatively common process, resulting in the production of microcrystalline silica and feldspar components. Here we investigate how the products of pervasive devitrification may be characterized using the combined techniques of X-ray powder diffraction, Electron Microprobe analysis, and X-ray fluorescence analysis to provide a new calibrated approach to calculating the crystallinity and mineral modes in both glassy vitrophyre and devitrified volcanics. Using the integrated areas of the X-ray diffraction peaks associated with both the crystalline and amorphous components, the relative proportions of groundmass crystallites and amorphous material from both glassy and devitrified material can be calculated. A detailed calibration indicates a linear relationship among the ratio of the integrated counts and bulk crystallinity. Mineral proportions are also calculated from X-ray fluorescence measurements of whole-rock and groundmass separates and are well correlated to crystallinities calculated from both X-ray diffraction and Electron Microprobe image analysis for vitrophyre samples. Devitrification products in a pervasively devitrified sample are tridymite, quartz, sanidine, and a Ca-rich aluminosilicate component. Mineral analysis and X-ray mapping by Electron Microprobe analysis indicates that the Ca-rich aluminosilicate component appears to be the dominant metastable or amorphous phase in the devitrified sample with proportions calculated from X-ray mapping (~32%) in reasonable agreement with the calculated proportion of amorphous material determined by means of X-ray diffraction (~38%). These results demonstrate the robustness of this combined X-ray diffraction and Electron Microprobe imagery technique for quantifying and characterizing crystallization in complex samples.