The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic... more The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic intrusive rocks (deposit composition) or by partial melting experiments on carbonated lherzolites (source composition). Pervasively altered, degassed and contaminated material preclude the determination of the primitive melt composition. Here we present data on melt compositions trapped in unaltered olivine cracks that have been healed and overgrown prior
ABSTRACT A natural smoky quartz crystal from Shandong province, China, was characterised by laser... more ABSTRACT A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP-MS, electron probe microanalysis (EPMA), and solution ICP-MS to determine the concentration of twenty-four trace and ultratrace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium-in-quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA-ICP-MS laboratories, three EPMA laboratories, and one solution-ICP-MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 μg g−1), Al (154 ± 15 μg g−1), Li (30 ± 2 μg g−1), Fe (2.2 ± 0.3 μg g−1), Mn (0.34 ± 0.04 μg g−1), Ge (1.7 ± 0.2 μg g−1) and Ga (0.020 ± 0.002 μg g−1), and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. Concentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.This article is protected by copyright. All rights reserved.
... microanalysis and x-ray reflectivity data Tran M. Phung,1 Jacob M. Jensen,1 David C. Johnson,... more ... microanalysis and x-ray reflectivity data Tran M. Phung,1 Jacob M. Jensen,1 David C. Johnson,1∗ John J. Donovan2 and Brian G. McBurnett3 ... Symp. Proc. 1992; 238: 119. 25. Labar JL. Microbeam Analysis (23rd edn) San Francisco Press: San Francisco, CA, 1988; 253. 26. ...
We find no physical basis for traditional mass-fraction weighted averaging of X-ray continuum mea... more We find no physical basis for traditional mass-fraction weighted averaging of X-ray continuum measured in pure elements to estimate continuum production from compounds. Measurements of continuum from pairs of stable isotopes demonstrate that mass alone (the presence of more or fewer neutrons) has no effect on continuum production in electron probe microanalysis. Electron-fraction weighted averaging, which is based on the relative contribution of each constituent element to the electron (or proton) composition of a compound, proved superior to mass-fraction weighted averaging, in predicting the continuum of a compound from the measured continuum of its elements.
Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate corre... more Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate correction for the X-ray continuum (or background) created by the Bremsstrahlung effect from the primary electron beam. This X-ray continuum, as measured on a wavelength-dispersive spectrometer at any particular wavelength, is primarily a function of the mean atomic number of the material being analyzed. One can calibrate the dependence of the continuum on mean atomic number by measuring and curve fitting the X-ray intensities at the analytical peak in pure elements, oxides, and binary compound standards that do not contain any of the analyte or any interfering elements and use that calibration to calculate the X-ray background correction. For unknown samples, the mean atomic number is determined from the elemental concentrations calculated by the ZAF or φ(ρz) matrix correction, and the fit regression coefficients are used iteratively to calculate the actual background correction. Over a larg...
We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs)... more We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using ...
Fundamental physical law informs that neutrons play no role in electron probe microanalysis, and ... more Fundamental physical law informs that neutrons play no role in electron probe microanalysis, and therefore, mass-based models follow an improper route to data reduction. Castaing's mass-based first approximation inappropriately remains the starting point-see any microprobe textbook-for development of quantitative electron probe microanalysis. By incorrectly relating intensity of characteristic x rays to mass rather than to charge, such conventional models demand an isotope (mass) effect; our robust experiments detected none.
Dakhleh Glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occ... more Dakhleh Glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occur over an area of ca. 400km2 in and around the Dakhleh Oasis in central western Egypt. Previous studies establish a meteorite impact origin for the Dakhleh Glass. No impact crater has yet been found, suggesting an airburst origin. The Dakhleh Glass-forming impact event occurred during the
The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic... more The chemical composition of kimberlite melts has previously been estimated by measuring aphanitic intrusive rocks (deposit composition) or by partial melting experiments on carbonated lherzolites (source composition). Pervasively altered, degassed and contaminated material preclude the determination of the primitive melt composition. Here we present data on melt compositions trapped in unaltered olivine cracks that have been healed and overgrown prior
ABSTRACT A natural smoky quartz crystal from Shandong province, China, was characterised by laser... more ABSTRACT A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP-MS, electron probe microanalysis (EPMA), and solution ICP-MS to determine the concentration of twenty-four trace and ultratrace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium-in-quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA-ICP-MS laboratories, three EPMA laboratories, and one solution-ICP-MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 μg g−1), Al (154 ± 15 μg g−1), Li (30 ± 2 μg g−1), Fe (2.2 ± 0.3 μg g−1), Mn (0.34 ± 0.04 μg g−1), Ge (1.7 ± 0.2 μg g−1) and Ga (0.020 ± 0.002 μg g−1), and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. Concentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.This article is protected by copyright. All rights reserved.
... microanalysis and x-ray reflectivity data Tran M. Phung,1 Jacob M. Jensen,1 David C. Johnson,... more ... microanalysis and x-ray reflectivity data Tran M. Phung,1 Jacob M. Jensen,1 David C. Johnson,1∗ John J. Donovan2 and Brian G. McBurnett3 ... Symp. Proc. 1992; 238: 119. 25. Labar JL. Microbeam Analysis (23rd edn) San Francisco Press: San Francisco, CA, 1988; 253. 26. ...
We find no physical basis for traditional mass-fraction weighted averaging of X-ray continuum mea... more We find no physical basis for traditional mass-fraction weighted averaging of X-ray continuum measured in pure elements to estimate continuum production from compounds. Measurements of continuum from pairs of stable isotopes demonstrate that mass alone (the presence of more or fewer neutrons) has no effect on continuum production in electron probe microanalysis. Electron-fraction weighted averaging, which is based on the relative contribution of each constituent element to the electron (or proton) composition of a compound, proved superior to mass-fraction weighted averaging, in predicting the continuum of a compound from the measured continuum of its elements.
Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate corre... more Quantitative EPMA (electron probe microanalysis) intensity measurements require an accurate correction for the X-ray continuum (or background) created by the Bremsstrahlung effect from the primary electron beam. This X-ray continuum, as measured on a wavelength-dispersive spectrometer at any particular wavelength, is primarily a function of the mean atomic number of the material being analyzed. One can calibrate the dependence of the continuum on mean atomic number by measuring and curve fitting the X-ray intensities at the analytical peak in pure elements, oxides, and binary compound standards that do not contain any of the analyte or any interfering elements and use that calibration to calculate the X-ray background correction. For unknown samples, the mean atomic number is determined from the elemental concentrations calculated by the ZAF or φ(ρz) matrix correction, and the fit regression coefficients are used iteratively to calculate the actual background correction. Over a larg...
We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs)... more We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using ...
Fundamental physical law informs that neutrons play no role in electron probe microanalysis, and ... more Fundamental physical law informs that neutrons play no role in electron probe microanalysis, and therefore, mass-based models follow an improper route to data reduction. Castaing's mass-based first approximation inappropriately remains the starting point-see any microprobe textbook-for development of quantitative electron probe microanalysis. By incorrectly relating intensity of characteristic x rays to mass rather than to charge, such conventional models demand an isotope (mass) effect; our robust experiments detected none.
Dakhleh Glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occ... more Dakhleh Glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occur over an area of ca. 400km2 in and around the Dakhleh Oasis in central western Egypt. Previous studies establish a meteorite impact origin for the Dakhleh Glass. No impact crater has yet been found, suggesting an airburst origin. The Dakhleh Glass-forming impact event occurred during the
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