| 1. |
- Cruz-Uribe, A. M., et al.
(författare)
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Trace element and isotopic zoning of garnetite veins in amphibolitized eclogite, Franciscan Complex, California, USA
- 2021
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 176:5
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Tidskriftsartikel (refereegranskat)abstract
- Here we present major element, trace element, and oxygen isotope data for garnet from an amphibolitized eclogite block from Ring Mountain, Franciscan Complex, California, USA. Garnetite veins 1-5 cm thick are laterally continuous up to 10 m within an Mg-rich blackwall zone of the eclogite block. Complex major and trace element zoning patterns reveal multiple stages of garnet growth in both the matrix and garnetite veins. Similarities in major and trace element zoning between matrix and vein garnet suggest that crystallization of the garnetite veins began toward the end of matrix garnet core growth, and continued throughout the garnet growth history of the rock. Oscillatory zoning in rare-earth elements suggests garnet growth in pulses, with matrix-diffusion-limited growth in between pulses. Oxygen isotope analyses of matrix and vein garnet have a range in delta O-18 values of 5.3-11.1 parts per thousand. Differences in delta O-18 values of up to similar to 4 parts per thousand between garnet core and rim are observed in both the matrix and vein; garnet cores range from 9.8 to 11.1 parts per thousand (median 10.4 parts per thousand), garnet mantles range from 8.3 to 10.0 parts per thousand (median 9.7 parts per thousand), and garnet rims range from 5.8 to 7.8 parts per thousand (median 6.7 parts per thousand). Late-stage vein crystallization appears as a garnet "cement" that fills in a network of small (typically 5-50 mu m) garnet cores, and likely crystallized from an amorphous phase. The low delta O-18 values of this latest stage of garnet growth are consistent with interaction with serpentinites, and likely represent the physical incorporation of the eclogite block into the serpentinite matrix melange.
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| 2. |
- Richter, M., et al.
(författare)
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Assessment of Five Monazite Reference Materials for U-Th/Pb Dating Using Laser-Ablation ICP-MS
- 2019
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Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- Monazite is a common accessory phosphate mineral that occurs under a wide range of pressure and temperature conditions in sedimentary, metamorphic and igneous rocks. Monazite contains high amounts of Th and U, rendering single monazite grains suitable for in-situ U-Th/Pb dating using laser ablation inductively-coupled mass spectrometry (LA-ICP-MS). Two key aspects of monazite dating that are critical for accurate age data with maximum precision are (i) optimized instrumental conditions to minimize analytical scatter and (ii) a well characterized reference material to ensure the accuracy of the obtained aged. Here, we analyzed five monazite reference materials (USGS 44069, 94-222, MAdel, Moacir and Thompson Mine Monazite) for their U-Th/Pb ages using LA-ICP-MS technique and applied a variety of laser spot diameters and repetition rates to find the best operational conditions to achieve accurate age data while maintaining maximum precision. We find that a spot diameter of 10 mu m and a repetition rate of 10 Hz yield the most precise ages with a deviation of +/- 2.0% from their respective high-precision U/Pb literature age data. Ages were reproduced in three different LA-ICP-MS laboratories using these parameters. Each reference material was tested for its suitability as a matrix-matched age reference material. For this, a rotating, iterative approach was adopted in which one reference monazite was used as calibration reference material against all others, which were treated as unknowns. The results reveal that USGS 44069, 94-222, Thompson Mine Monazite and MAdel all agree with their respective calculated ages and ID-TIMS reference ages and thus are suggested as suitable calibration reference materials. Moacir, however, appears slightly older than previously suggested (up to 4%), thus, caution is advised here when using Moacir as reference material for U-Th/Pb LA-ICP-MS dating in the absence of further absolute age calibration.
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| 3. |
- Soares, C. J., et al.
(författare)
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Characterisation of Apatites as Potential Uranium Reference Materials for Fission-track Dating by LA-ICP-MS
- 2015
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Ingår i: Geostandards and Geoanalytical Research. - 1639-4488. ; 39:3, s. 305-313
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Tidskriftsartikel (refereegranskat)abstract
- k crystal (6.9gg(-1)U). The relative standard deviation (1 RSD) of the U concentration determined by ID-ICP-MS of both apatite crystals was 1.5%, whereas 1 RSD for the We report homogeneity tests on large natural apatite crystals to evaluate their potential as U reference materials for apatite fission-track (AFT) thermochronology by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The homogeneity tests include the measurements of major element concentrations by electron probe microanalysis (EPMA), whereas for U concentration, isotope dilution (ID) ICP-MS and laser ablation (LA) ICP-MS were employed. Two apatite crystals are potential reference materials for LA-ICP-MS analysis: a 1cm(3) fraction of a Durango crystal (7.5gg(-1)U) and a 1cm(3) Mud TanLA-ICP-MS results was better than 4%, providing sufficient homogeneity for fission-track dating. The results on the U homogeneity for two different apatite samples are an important step towards establishing in situ dating routines for AFT analysis by LA-ICP-MS. Nous restituons des tests d'homogeneite sur des grands cristaux d'apatite naturelle afin d'evaluer leur potentiel en tant que materiaux de reference pour l'U en vue d'une application dans le domaine de la thermochronologie par traces de fission sur apatite (AFT) par spectrometrie de masse a plasma induit couplee a l'ablation laser (LA-ICP-MS). Les tests d'homogeneite incluent des mesures des concentrations en elements majeurs par microsonde electronique (EPMA), alors que pour la concentration en U, la dilution isotopique (ID) ainsi que l'ablation laser (LA) ICP-MS ont ete employees. Deux cristaux d'apatite sont des materiaux de reference possibles pour les analyses LA-ICP-MS: une fraction d'1 cm(3) d'un cristal de Durango (7,5 mu gg(-1)U) et un cristal d'1cm(3) de Mud Tank (6,9 mu gg(-1)U). L'ecart type relatif (1RSD) de la concentration en U determinee par ID-ICP-MS des deux cristaux d'apatite est 1,5%, tandis que celui pour les resultats LA-ICP-MS est inferieur a 4%, offrant ainsi une homogeneite suffisante pour les datations par la methode des traces de fission sur apatite. Les resultats concernant l'homogeneite de l'U pour deux echantillons differents d'apatite sont une etape importante vers la possibilite d'envisager des datations AFT in situ en routine par LA-ICP-MS.
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| 4. |
- Soares, CJ, et al.
(författare)
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Novel calibration for LA-ICP-MS-based fission-track thermochronology
- 2014
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Ingår i: Physics and chemistry of minerals. - : Springer Science and Business Media LLC. - 0342-1791 .- 1432-2021. ; 41:1, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel age-equation calibration for fission-track age determinations by laser ablation inductively coupled plasma mass spectrometry. This new calibration incorporates the efficiency factor of an internal surface, [ηq]is, which is obtained by measuring the projected fission-track length, allowing the determination of FT ages directly using the recommended spontaneous fission decay constant. Also, the uranium concentrations in apatite samples are determined using a Durango (Dur-2, 7.44 μg/g U) crystal and a Mud Tank (MT-7, 6.88 μg/g U) crystal as uranium reference materials. The use of matrix-matched reference materials allows a reduction in the uncertainty of the uranium measurements to those related to counting statistics, which are ca. 1 % taking into account that no extra source of uncertainty has to be considered. The equations as well as the matrix-matched reference materials are evaluated using well-dated samples from Durango, Fish Canyon Tuff, and Limberg as unknown samples. The results compare well with their respective published ages determined through other dating methods. Additionally, the results agree with traditional fission-track ages using both the zeta approach and the absolute approach, suggesting that the calibration presented in this work can be robustly applied in geological context. Furthermore, considering that fission-track ages can be determined without an age standard sample, the fission-track thermochronology approach presented here is assumed to be a valuable dating tool.
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