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- Redaa, A., et al.
(författare)
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Testing Nano-Powder and Fused-Glass Mineral Reference Materials for In Situ Rb-Sr Dating of Glauconite, Phlogopite, Biotite and Feldspar via LA-ICP-MS/MS
- 2023
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Ingår i: Geostandards and Geoanalytical Research. - : Wiley. - 1639-4488 .- 1751-908X. ; 47:1, s. 23-48
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Tidskriftsartikel (refereegranskat)abstract
- Reference materials (RMs) with well-characterised composition are necessary for reliable quantification and quality control of isotopic analyses of geological samples. For in situ Rb-Sr analysis of silicate minerals via laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) with a collision/reaction cell, there is a general lack of mineral-specific and matrix-matched RMs, which limits wider application of this new laser-based dating technique to certain minerals. In this work, pressed nano-powder pellets (NP) of four RMs, GL-O (glauconite), Mica-Mg (phlogopite), Mica-Fe (biotite) and FK-N (K-feldspar), were analysed and tested for in situ Rb-Sr dating, complemented by isotope dilution (ID) MC-ICP-MS Rb-Sr analyses of GL-O and Mica-Mg. In addition, we attempted to develop alternative flux-free and fused 'mineral glasses' from the above RMs for in situ Rb-Sr dating applications. Overall, the results of this study showed that among the above RMs only two NP (Mica-Mg-NP and GL-O-NP) were suitable and robust for in situ dating applications. These two nano-powder reference materials, Mica-Mg-NP and GL-O-NP, were thus used as primary RMs to normalise and determine Rb-Sr ages for three natural minerals: MDC phlogopite and GL-O glauconite grains, and also Mica-Fe-NP (biotite). Our in situ analyses of the above RMs yielded Rb-Sr ages that are in good agreement (within 8%) of published ages, which suggests that both Mica-Mg-NP and GL-O-NP are suitable RMs for in situ Rb-Sr dating of phlogopite, glauconite and biotite. However, using secondary RMs is recommended to monitor the quality of the obtained ages.
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| 2. |
- Redaa, A., et al.
(författare)
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Assessment of elemental fractionation and matrix effects during in situ Rb-Sr dating of phlogopite by LA-ICP-MS/MS: implications for the accuracy and precision of mineral ages
- 2021
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 36:2, s. 322-344
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Tidskriftsartikel (refereegranskat)abstract
- Laser-ablation inductively-coupled plasma tandem mass-spectrometry (LA-ICP-MS/MS) allows for rapid and interference free analyses of Rb and Sr isotopes, permitting in situ Rb-Sr dating of minerals. However, the general lack of matrix matched reference materials remains one of its main obstacles, affecting both precision and accuracy. This study systematically investigates the impact of matrix effects and down-hole fractionation (DHF) on the in situ Rb-Sr ages of an igneous phlogopite mineral (MDC) analysed by an ICP-MS/MS using two different LA systems: (i) a RESOlution ArF (193 nm) excimer and (ii) a NWR (213 nm) Nd-YAG laser system. A phlogopite reference material (Mica-Mg), originating from the same location as the MDC, was prepared as a pressed nano-powder pellet (NP) and used in this study as a primary reference material. The results revealed that the accuracy of the Rb-Sr ages is typically within about 3% (for 70% of analysed samples), but occasionally higher ranging between 4 to 8% (ca. 30% of cases). We hypothesize that the above bias and uncertainty in the Rb-Sr ages are related to matrix effects between Mica-Mg-NP and MDC, due to their specific ablation characteristics and different physical properties. In addition, the elemental fractionation effects observed in this study for Rb-87/Sr-86 are also dependent on laser wavelength (i.e., 193 nm vs. 213 nm). Hence, developing an improved nano-powder reference material, or a mineral or glass with better matrix matching to natural phlogopite minerals would be desirable to further improve the accuracy of in situ Rb-Sr dating. Currently, regular monitoring of secondary and matrix-matched reference minerals such as the MDC phlogopite can be used to assess and evaluate the accuracy of in situ Rb-Sr dating of phlogopite, yielding ages within accuracy of ca. 3% or better.
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