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

Abstract

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 are usually performed on in-house standards. This contribution present a new reference material, ASH-15, a flowstone that is dated here by high-precision Isotope Dilution (ID) TIMS analysis using 36 sub-samples, 1–7 mg each. Age results presented here are slightly younger compared to previous ID dating of ASH-15, but in agreement with in-situ analyses (using WC1 as a 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 (2σ). 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, for example, zircon (

Absolute Age and Temperature Constraints on Deformation Along the Basal Décollement of the Jura Fold‐and‐Thrust Belt From Carbonate U‐Pb Dating and Clumped Isotopes

“…The analytical method and correction procedure follow Roberts et al (2017) using NIST 614 and WC-1 as primary reference materials and Guillong et al ( 2020) using a matched ablation crater aspect ratio for the primary reference materials and unknowns (in this study, spot sizes of 110 and 163 μm and repetition rates of 5.0 and 7.4 Hz, respectively, depending on the U content). In addition to the primary reference materials and samples, the secondary reference materials JT and ASH-15D (Guillong et al, 2020;Nuriel et al, 2020) were analyzed in each session to assess accuracy and repeatability. Correction for matrix effects with WC-1 was done by anchoring to a value of 0.85 common-lead, while samples and secondary reference materials were not anchored.…”

Near-surface Palaeocene fluid flow, mineralisation and faulting at Flamborough Head, UK: new field observations and U–Pb calcite dating constraints

“…1b). The chalk at Flamborough Head is amongst the youngest exposed in Yorkshire and comprises the Burnham Chalk Formation (late Coniacian to early Santonian) and the overlying Flamborough Chalk Formation (Santonian) (see Whitham, 1993;Mortimore, 2019).…”

“…Calcite is an extremely abundant mineral fill in brittle fractures and faults of wideranging host lithologies. It has been shown to be an effective chronometer that can be linked to the timing of hydrothermal mineralisation, fault slip and fold development Ring and Gerdes, 2016;Goodfellow et al, 2017;Nuriel et al, , 2019Beaudoin et al, 2018;Hansman et al, 2018;Holdsworth et al, 2019Holdsworth et al, , 2020Parrish et al, 2018;Smeraglia et al, 2019;Roberts et al, 2020).…”

Expanding the limits of laser-ablation U–Pb calcite geochronology

“…Similar to that of the 207 Pb / 206 Pb ratio, this correction encompasses offset due to both mass bias and detector efficiency differences (i.e., there is no prior gain calibration for the Daly detector array). Using this method, we retrieved ages of 3.01 ± 0.15 (MSWD = 1.3; n = 30) and 65.9±1.1 (MSWD = 1.2; n = 40) for secondary RMs ASH15 (2.96 Ma; Nuriel et al, 2020) and Duff Brown Tank (64 Ma; Hill et al, 2016), respectively. Because the purpose of this study is to gain a better understanding of the analytical equipment uncertainties associated with the standards (e.g., upper intercept of WC-1, 207 Pb / 206 Pb value of NIST614) were not propagated into the uncertainties of unknown analyses.…”