New Reference Materials and Assessment of Matrix Effects for SIMS Measurements of Oxygen Isotopes in Garnet

Abstract

Accurate ion microprobe analysis of oxygen isotope ratios in garnet requires appropriate reference materials to correct for instrumental mass fractionation that partly depends on the garnet chemistry (matrix effect). The matrix effect correlated with grossular, spessartine and andradite components was characterised for the Cameca IMS 1280HR at the SwissSIMS laboratory based on 17 reference garnet samples. The correlations fit a second degree polynomial with maximum bias of ca. 4‰, 2‰ and 8‰ respectively. While the grossular composition range 0 -25% is adequately covered by available reference materials, there is a paucity of them for intermediate compositions. We characterize three new garnet reference materials GRS2, GRS-JH2 and CAP02 with a grossular content of 88.3 ± 1.2% (2sd), 83.3 ± 0.8% and 32.5 ± 3.0% respectively. Their microscale homogeneity in oxygen isotope composition was evaluated by multiple SIMS sessions. The reference δ 18 O value was determined by CO2 laser fluorination (δ 18 OLF). GRS2 has δ 18 OLF = 8.01 ± 0.10‰ (2sd) and repeatability within each SIMS session of 0.30 -0.60‰ (2sd), GRS-JH2 has δ 18 OLF

Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

“…Count rates on the 16 O peak were between 1.2 and 2.0 × 10 9 counts per second. An off-line matrix bias correction based on the grossular and spessartine contents of garnet was applied using the equation given in (Vho et al 2020c). In every session, the secondary garnet reference material GRS-JH2 (X grs = 0.833 ± 0.008; Vho et al 2020b) was analyzed to check the validity of the matrix bias calibration (Online Resource 2).…”

A Method for Secondary Ion Mass Spectrometry Measurement of Lithium Isotopes in Garnet: The Utility of Glass Reference Materials

“…The absence of a significant compositional IMF due to Ca for measurements of Li isotopes in garnet is notable in that Ca is identified as a major source of IMF for oxygen isotope measurements in garnet by SIMS (e.g., Vielzeuf et al 2005, Page et al 2010, Ickert and Stern 2013, Martin et al 2014, Vho et al 2020. However, the compositional IMF due to Fe and Mn observed here for Li isotopes is also proposed by several studies of oxygen isotopes in aluminosilicate garnets (Fe 2+ : Vielzeuf et al 2005;Mn: Vielzeuf et al 2005, Martin et al 2014, Vho et al 2020. Thus, although there is some commonality between compositional IMF for Li and oxygen isotopes measured in aluminosilicate garnet, distinct dominant elements suggest a difference in the IMF for these two measurements.…”

“…2010, Ickert and Stern 2013, Vho et al . 2020). Well‐characterised natural minerals are used as RMs in most studies of mineral isotopic compositions by SIMS (e.g., Valley and Kita 2009).…”

High‐spatial‐resolution measurements of iron isotopes in pyrites by secondary ion mass spectrometry using the new Hyperion‐II radio‐frequency plasma source

“…54,55 It results from various processes occurring during secondary atom ionization, extraction, secondary ion transmission and detection. 55 The IMF is known to be highly dependent on sample characteristics (mineralogy, chemical composition and crystallographic orientation [55][56][57] 58,59 as well as δ 34 S measurements in Fe-Ni sulfides, 56,60,61 and Mg and Si isotopes in silicates (e.g. olivine, glass, pyroxene) with an IMF depending on their Mg content.…”

“…This effect is corrected by measuring reference material (same mineral, crystallography and major element chemical compositions) and samples in the same analytical conditions. The IMF variations occur in various isotopic systems, for example, the δ 18 O measurements of garnets are strongly affected by their Ca-Fe-Mg content 58,59 , as well as δ 34 S in Fe-Ni sulfides 56,60,61 , and Mg and Si isotopes in silicates (e.g. olivine, glass, pyroxene) with an IMF depending on their Mg content 43,62 .…”