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

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...

Supplemental Material: Unraveling the histories of Proterozoic shales through in situ Rb-Sr dating and trace element laser ablation analysis

“…This is approximately 4.4% younger than the published mean age of Mica-MG (519.4 ± 6.5 Ma; Hogmalm et al 2017). A discussion of the categorical differences and deviations between Mica-MG and MDC can be found in length within Redaa et al (2021). To summarise, the observed differences in elemental Rb/Sr fractionation between the nano-powder and natural mineral flakes of the same phlogopite are likely due to their different ablation properties (Redaa et al, 2021).…”

“…Laser analyses on samples and standards were carried out at Adelaide Microscopy, University of Adelaide using a laser ablation (RESOlution-LR ArF 193nm excimer laser) inductively couple-mass spectrometer (Agilent 8900x ICP-MS/MS) with the analytical parameters and tuning conditions following (Redaa et al, 2021) summarised in Table 1.…”

“…Ablating several clay-size minerals in one analysis have previously been done effectively using the same method to constrain fault reactivation histories in deep crystalline basements (Tillberg et al, 2020). In situ Rb-Sr dating of CRPG reference material Mica-MG (Govindaraju et al, 1994) prepared as a nano-powder pellet and a phlogopite mineral sample MDC sourced from the same quarry in Bekily, Madagascar were assumed to be of the same age (Armistead et al, 2020;Hogmalm et al, 2017;Li et al, 2020;Redaa et al, 2021) and were used as primary and secondary standards respectively. Furthermore, an independent illite pressed powdered pellet sample from Fithian, Illinois (Kralik, 1984) was also analyzed to determine whether the phlogopite nanopowder standard is suitable laser-ablation analysis of illite-rich granular shale samples.…”

“…A discussion of the categorical differences and deviations between Mica-MG and MDC can be found in length within Redaa et al (2021). To summarise, the observed differences in elemental Rb/Sr fractionation between the nano-powder and natural mineral flakes of the same phlogopite are likely due to their different ablation properties (Redaa et al, 2021). The granulated texture of the nanopowder material resulted in an irregular ablation characteristic that can be observed from the textures in the base of the laser-ablation pits (Fig.…”

Supplemental Material: Unraveling the histories of Proterozoic shales through in situ Rb-Sr dating and trace element laser ablation analysis

“…S3). Laser analyses on samples and standards were carried out at Adelaide Microscopy, University of Adelaide using a laser ablation (RESOlution-LR ArF 193nm excimer laser) inductively couple-mass spectrometer (Agilent 8900x ICP-MS/MS) with the analytical parameters and tuning conditions following (Redaa et al, 2021) summarised in Table 1.One spot analysis consisted of 20 seconds of gas background collected while the laser was not firing followed by 40 seconds of ablated signal. Strontium isotopes were measured in the oxidised molecule SrO.…”