In Situ Rb-Sr Dating Of Lunar Meteorites Using Laser Ablation MC-ICP-MS

Abstract

S Plagioclase, pyroxene and glass are the main component phases of different planetary materials. In situ Rb-Sr dating of these common phases thus would represent the timing of magmatic differentiation, effectively complementary to the rare, tiny U-Pb bearing phases that only form at a late stage. In this study, we selected lunar meteorites as examples to establish an in situ Rb-Sr dating method where plagioclase, pyroxene, ilmenite, and glasses were the laser-ablation (LA) targets. The accuracy of 87 Sr/ 86 Sr and 87 Rb/ 86 Sr measured by LA-MC-ICP-MS was better than 0.2 ‰ and 3 %, respectively, for samples with an 87 Rb/ 86 Sr ratio lower than 1. However, we found that the distributions of Rb and Sr in the natural materials were heterogeneous at the micrometer scale, leading to inaccurate 87 Rb/ 86 Sr ratio correction when calculated by normal data reduction methods. A new data reduction strategy of the smallest unit of isochron age (SUIA) was developed. Using the SUIA, the Rb-Sr isochron age of 2984 ± 43 Ma and 3149 ± 20 Ma was obtained for two lunar meteorites (NWA 10597 and NWA 6950, respectively). These results are identical within 1-2% deviation relative to the U-Pb dating ages for baddeleyite and apatite using SIMS. The present method may have broad applicability for determining the Rb-Sr isochron ages of other planetary samples. www.at-spectrosc.com/as/article/pdf/2022008 XXX At. Spectrosc. 2022, 43(X), XXX-XXX accuracy for 87 Sr/ 86 Sr isotope analysis as compared with ICP-MS/MS analysis. The MC-ICP-MS instrument with collision cell can resolve the interference of 87 Rb and provides excellent 87 Sr/ 86 Sr data. However, it is a new mass spectrometry system, very expensive, and thus increases the cost of analysis. Its popularity is still low in the global market.

A natural plagioclase reference material for microbeam Sr isotopic analysis

“…20; HNB, ref. 34) and K-feldspar (Tuyk, ref. 19) have been developed, only a few in-house plagioclase standards, such as JH56 (Sr content of ∼1000 μg g −1 , ref.…”

High-precision EPMA measurement of trace elements in ilmenite and reference material development

“…24,27,51 Higher accelerating voltage and beam current increase the ionization efficiency and electron flux, and increased counting time improves statistics for greater precision by increasing the total numbers of photons integrated. 52,53 Additionally, some engineered strategies are also implemented to lower detection limits, such as using larger Bragg analysis crystals to improve the geometric efficiency of the instrument, and using aggregate intensity counting software to improve counting statistics. 24,26,54 After detailed comparisons of Cameca SXFive EPMA conditions, the following approaches were set in this study: (1) a higher acceleration voltage of 20 kV was used to balance precision and spatial resolution (1–2 μm); (2) a higher beam current of 200 nA and longer peak counting time (20–120 s) were applied for trace elements to achieve a detection limit of around 10 μg g −1 (3 σ ); (3) three large (2 LLIF and 1 LPET) Bragg crystals and one normal (TAP) crystal were used for higher sensitivity and counting rates; (4) the software capacity of aggregate intensity counting was used, such as LLIF crystals in spectrometer 2 and 3 for Cr.…”

Preliminary Characterisation of New Reference Materials (CaW‐0, CaW‐1 and CaW‐3) for Microanalysis of Rare Earth Elements in Scheelite by Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry

“…This highlights the importance of accurately determining trace elements in scheelite, particularly for microanalysis, as it often comprises various mineral phases such as wolframite, quartz, muscovite and apatite (Zhang et al 2020). Numerous studies on microanalysis of REEs in scheelite have been conducted, utilising a range of techniques, including electron probe microanalysis (EPMA) (Fu et al 2017, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) (Zhao et al 2018) and laser ablation-inductively coupled plasmamass spectrometry (LA-ICP-MS) (Chen et al 2020, Ke et al 2019a, Ke et al 2019b, Li et al 2023, Lin et al 2020, Wang et al 2022, Zhang et al 2022a).…”