Towards &amp;lt;i&amp;gt;in-situ&amp;lt;/i&amp;gt; U–Pb dating of dolomites

Elisha, Bar; Nuriel, Perach; Kylander‐Clark, Andrew; Weinberger, R.

doi:10.5194/gchron-2020-19

Cited by 5 publications

(4 citation statements)

References 20 publications

(26 reference statements)

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“…210 µm for the HK13 fluorite (see Table A5). To correct for DF, a matrixmatch primary RM can be used if laser ablation generates similar crater aspect ratios between the reference material and unknown samples (Elisha et al, 2020;Guillong et al, 2020). Such a matrix-match RM is not yet available for fluorite U-Pb geochronology (Piccione et al, 2019).…”

Section: In Situ La-icp-ms U-pb Datingmentioning

confidence: 99%

Uranium incorporation in fluorite and exploration of U–Pb dating

et al. 2021

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Abstract. The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U–Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). The uranium distribution within fluorite is mapped using induced fission-track and synchrotron radiation X-ray fluorescence nano-imaging, showing that higher U content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr, implies that neither solid-state diffusion nor dissolution–recrystallization occurred. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of −23.6 ± 0.4 ‰V-CDT. We propose that the U incorporation in the fluorite lattice results from the development of a redox front during bacterial sulfate reduction. Flog generation sampled and analyzed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) on four different crystals provides identical U–Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0 ± 1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U–Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy.

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Section: In Situ La-icp-ms U-pb Datingmentioning

confidence: 99%

Uranium incorporation in fluorite and exploration of U–Pb dating

et al. 2021

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“…Finding the right matrix-matched reference material (RM) is a major hurdle for LA analyses of carbonates because of the variety of mineralogy (calcite, dolomite, and aragonite), textures, composition (e.g., high-magnesium calcite, high common lead), and ages (e.g., low radiogenic lead in young samples). Textural differences such as microcrystalline, fine-and coarse-grained material, between the unknown and RMs can contribute to high uncertainties due to differences in ablation efficiency, down-hole fractionation, and differences in crater morphology (e.g., Guillong et al, 2020;Elisha et al, 2020). Observed deviations are potentially up to 20 % of the final intercept age depending on the degree of crater geometry mismatch and are related either to downhole fractionation and/or matrix effects (Guillong et al, 2020).…”

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confidence: 99%

The use of ASH-15 flowstone as a matrix-matched reference material for laser-ablation U − Pb geochronology of calcite

et al. 2021

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Abstract. Latest advances in laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) allow for accurate in situ U−Pb dating of carbonate material, with final age uncertainties usually >3 % 2σ. Cross-laboratory reference materials (RMs) used for sample-bracketing are currently limited to WC1 calcite with an age of 254.4±6.5 (2σ). The minimum uncertainty on any age determination with the LA-ICPMS method is therefore ≥2.5 %, and validation by secondary RMs is usually performed on in-house standards. This contribution presents a new reference material, ASH-15, a flowstone that is dated here by isotope dilution (ID) thermal ionization mass spectrometry (TIMS) analysis using 37 sub-samples, 1–7 mg each. Age results presented here are slightly younger compared to previous ID isotope ratio mass spectrometry (IRMS) U−Pb dates of ASH-15 but within uncertainties and in agreement with in situ analyses using WC1 as the primary RM. We provide new correction parameters to be used as primary or secondary standardization. The suggested 238U∕206Pb apparent age, not corrected for disequilibrium and without common-lead anchoring, is 2.965±0.011 Ma (uncertainties are 95 % confidence intervals). The new results could improve the propagated uncertainties on the final age with a minimal value of 0.4 %, which is approaching the uncertainty of typical ID analysis on higher-U materials such as zircon. We show that although LA-ICPMS spot analyses of ASH-15 exhibit significant scatter in their isotopic ratios, the down-hole fractionation of ASH-15 is similar to that of other reference materials. This high-U (≈1 ppm) and low-Pb (<0.01 ppm) calcite is most appropriate as a reference material for other speleothem-type carbonates but requires more-sensitive ICP-MS instruments such as the new generation of single-collector and multi-collector ICP-MS. Reference materials with high-Pb and low-U or both low-U and low-Pb compositions are still needed to fully cover the compositional range of carbonate material but may introduce analytical challenges.

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“…The total crater depths, including the material excluded for analysis during the 7s "pre-ablation" vary from 97 to 153 µm in Pierre-Perthuis fluorite samples and from 231 to 266 µm for the HK13 fluorite (see Table A3 of Appendix A). To correct for DF, a matrix-match primary RM can be used if laser ablation generates similar crater aspect ratios between the reference material and unknown samples (Elisha et al, 2020;Guillong et al, 2020). Such a matrix-match RM is not yet available for fluorite U-Pb geochronology (Piccione et al, 2019).…”

Section: Msmentioning

confidence: 99%

Uranium incorporation in fluorite and exploration of U-Pb dating

Lenoir¹,

Blaise²,

Somogyì³

et al. 2020

Preprint

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Abstract. The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U-Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). Uranium distribution within fluorite is mapped using induced fission-track and Synchrotron radiation X-Ray Fluorescence nano-imaging, showing that higher uranium content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr implies that neither solid-state diffusion nor dissolution-recrystallization did occur. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of −23.6 ± 0.4 ‰ V-CDT. We propose that the U incorporation in the fluorite lattice results from its reduction mediated by H2S release during bacterial sulphate reduction. Flog generation sampled and analyzed by LA-ICP-MS on four different crystals provides identical U-Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0 ± 1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U-Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy.

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Towards <i>in-situ</i> U–Pb dating of dolomites

Cited by 5 publications

References 20 publications

Uranium incorporation in fluorite and exploration of U–Pb dating

Uranium incorporation in fluorite and exploration of U–Pb dating

The use of ASH-15 flowstone as a matrix-matched reference material for laser-ablation U − Pb geochronology of calcite

Uranium incorporation in fluorite and exploration of U-Pb dating

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