High‐Precision, High‐Accuracy Oxygen Isotope Measurements of Zircon Reference Materials with the SHRIMP‐SI

Abstract

Analytical protocols for SHRIMP‐SI oxygen isotope analysis (δ18O) of a suite of zircon reference materials (RMs) are presented. Data reduction involved a robust estimate of uncertainties associated with the individual spot as well as for groups where the spot data are combined. The repeatability of δ18O measurements is dependent on both the analytical conditions and the choice of the primary reference material. Under optimised conditions, repeatability was often better than 0.4‰ (2s) allowing sample uncertainties to be obtained to better than 0.2‰ (at 95% confidence limit). Single spot uncertainty combined the within‐spot precision with the scatter associated with repeated measurements of the primary zircon reference material during a measurement session. The uncertainty for individual spots measured under optimised conditions was between 0.3 and 0.4‰ (at 95% confidence). The analytical protocols described were used to assess a variety of zircon RMs that have been used for geochronology and for which laser fluorination oxygen isotope data are available (Temora 2, FC1, R33, QGNG and Plešovice), as well as zircons that have been used as RMs for trace element or other types of determination (Mud Tank, Monastery, 91500, AS57, AS3, KIM‐5, OG1, SL13, CZ3 and several other Sri Lankan zircons). Repeated analyses over nine sessions and seven different mounts show agreement within analytical uncertainty for Temora 2, FC1, R33, QGNG, Plešovice and 91500, when normalised to Mud Tank. For existing ion microprobe mounts with these materials, an appropriate δ18O can be determined. However, care should be taken when using zircons from the Duluth Complex (i.e., FC1, AS57 and AS3) as reference materials as our data indicated an excess scatter on δ18O values associated with low‐U zircon grains.

Chromite Reference Materials and Matrix Effects in SIMS Oxygen Isotope Measurements

“…2014, Ávila et al . 2020). The best of the test sample runs gives a spot‐to‐spot reproducibility (±0.3‰, 2 s ), better than that on the reference materials.…”

“…2014, Ávila et al . 2020). For example, a total impact energy of 20kV primary beam produces 20 μm diameter pits when using the CAMECA IMS‐1280, whereas SHRIMP analysis using a 15 kV primary beam results in 25 μm diameter pits.…”

“…2014, Ávila et al . 2020). A 15 kV Cs + primary beam was focused to approximately 25 μm diameter spot on the target surface.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…All eleven minerals were considered suitable as RMs. A calcite from the Oka carbonatite complex (Quebec, Canada) was presented 227 228 concluded that Temora 2 was a highly satisfactory RM for O isotope determinations if the provenance of the grains was well established. Repeated analyses over nine sessions and seven different mounts agreed within analytical uncertainty for zircons Temora 2, FC1, R33, QGNG, Plešovice and 91500 when normalised to Mud Tank zircon, which was regarded as a useful QC material with typical repeatability of #0.3& (2SD).…”

“…Homogeneity was demonstrated by hundreds of SIMS analyses and the recommended values of δ 13 C VPDB = −5.23 ± 0.06‰ and δ 18 O VPDB = −23.12 ± 0.15‰ were established by conventional IRMS. After measuring O isotope ratios in a range of zircon RMs with high-precision using SHRIMP, Avila et al 228 concluded that Temora 2 was a highly satisfactory RM for O isotope determinations if the provenance of the grains was well established. Repeated analyses over nine sessions and seven different mounts agreed within analytical uncertainty for zircons Temora 2, FC1, R33, QGNG, Plešovice and 91500 when normalised to Mud Tank zircon, which was regarded as a useful QC material with typical repeatability of ≤0.3‰ (2SD).…”