TY - JOUR
T1 - Strontium isotope analysis of apatite via SIMS
AU - Gillespie, Jack
AU - Nemchin, Alexander A.
AU - Kinny, Peter D.
AU - Martin, Laure
AU - Aleshin, Matvei
AU - Roberts, Malcolm P.
AU - Ireland, Trevor R.
AU - Whitehouse, Martin J.
AU - Jeon, Heejin
AU - Cavosie, Aaron J.
AU - Kirkland, Christopher L.
N1 - Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/1/5
Y1 - 2021/1/5
N2 - We report the development of a SIMS analytical method for in situ Sr isotope analysis of the mineral apatite at an analytical scale of 15 μm or less. Experiments were conducted on a series of reference apatites of widely differing Sr contents at three different mass resolution settings: low (3000), moderate (4200) and very high (16000), using a large-geometry CAMECA 1280 ion microprobe retrofitted with a HyperionTM oxygen plasma ion source. Peak-stripping algorithms tailored to the different mass-resolution settings were developed to correct for significant interferences on the target strontium isotope species in the mass spectra, namely Ca dimers, CaPO, Rb and SrH, and for instrumental mass fractionation. The most consistently accurate and precise 87Sr/86Sr ratios were achieved at the 3000 mass resolution setting with appropriate energy filtering and use of a cold trap. On average, corrected 87Sr/86Sr ratios by this method were elevated by ~0.8‰ above equivalent TIMS and solution ICPMS data, with consistent behaviour across the range of Sr concentrations. Individual spot precision of ± 0.001 to 0.004 (2SE) was achieved, depending on Sr content. The key advantages of SIMS analysis compared to existing LA-MC-ICP-MS methods are the high spatial resolution, low sample consumption, and the high mass resolution that allows for the elimination of problematic isobaric interferences. Our approach is particularly useful for the analysis of small or valuable targets, such as mineral inclusions or meteoric samples, and for apatite with high REE contents. However, the much larger volume of material consumed during LA-MC-ICP-MS analysis allows for substantially better precision than the SIMS method presented here. The highly variable trace element composition of natural apatites, involving both cationic and anionic substitutions, necessitates careful characterisation of prospective targets prior to any in situ analysis, in addition to matching to appropriate reference materials.
AB - We report the development of a SIMS analytical method for in situ Sr isotope analysis of the mineral apatite at an analytical scale of 15 μm or less. Experiments were conducted on a series of reference apatites of widely differing Sr contents at three different mass resolution settings: low (3000), moderate (4200) and very high (16000), using a large-geometry CAMECA 1280 ion microprobe retrofitted with a HyperionTM oxygen plasma ion source. Peak-stripping algorithms tailored to the different mass-resolution settings were developed to correct for significant interferences on the target strontium isotope species in the mass spectra, namely Ca dimers, CaPO, Rb and SrH, and for instrumental mass fractionation. The most consistently accurate and precise 87Sr/86Sr ratios were achieved at the 3000 mass resolution setting with appropriate energy filtering and use of a cold trap. On average, corrected 87Sr/86Sr ratios by this method were elevated by ~0.8‰ above equivalent TIMS and solution ICPMS data, with consistent behaviour across the range of Sr concentrations. Individual spot precision of ± 0.001 to 0.004 (2SE) was achieved, depending on Sr content. The key advantages of SIMS analysis compared to existing LA-MC-ICP-MS methods are the high spatial resolution, low sample consumption, and the high mass resolution that allows for the elimination of problematic isobaric interferences. Our approach is particularly useful for the analysis of small or valuable targets, such as mineral inclusions or meteoric samples, and for apatite with high REE contents. However, the much larger volume of material consumed during LA-MC-ICP-MS analysis allows for substantially better precision than the SIMS method presented here. The highly variable trace element composition of natural apatites, involving both cationic and anionic substitutions, necessitates careful characterisation of prospective targets prior to any in situ analysis, in addition to matching to appropriate reference materials.
UR - http://www.scopus.com/inward/record.url?scp=85096359972&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2020.119979
DO - 10.1016/j.chemgeo.2020.119979
M3 - Article
SN - 0009-2541
VL - 559
JO - Chemical Geology
JF - Chemical Geology
M1 - 119979
ER -