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Mass‐Independent and Mass‐Dependent Ca Isotopic Compositions of Thirteen Geological Reference Materials Measured by Thermal Ionisation Mass Spectrometry
Author(s) -
He Yongsheng,
Wang Yang,
Zhu Chuanwei,
Huang Shichun,
Li Shuguang
Publication year - 2017
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12153
Subject(s) - radiogenic nuclide , igneous rock , isotope , thermal ionization mass spectrometry , mass spectrometry , analytical chemistry (journal) , geology , mineralogy , seawater , fractionation , chemistry , geochemistry , environmental chemistry , ionization , ion , chromatography , mantle (geology) , physics , oceanography , organic chemistry , quantum mechanics
We report mass‐independent and mass‐dependent Ca isotopic compositions for thirteen geological reference materials, including carbonates ( NIST SRM 915a and 915b), Atlantic seawater as well as ten rock reference materials ranging from peridotite to sandstone, using traditional ε and δ values relative to NIST SRM 915a, respectively. Isotope ratio determinations were conducted by independent unspiked and 43 Ca‐ 48 Ca double‐spiked measurements using a customised Triton Plus TIMS . The mean of twelve measurement results gave ε 40/44 Ca values within ± 1.1, except for GSP ‐2 that had ε 40/44 Ca = 4.04 ± 0.15 (2 SE ). Significant radiogenic 40 Ca enrichment was evident in some high K/Ca samples. At an uncertainty level of ± 0.6, all reference materials had the same ε 43/44 Ca and ε 48/44 Ca values. We suggest the use of δ 44/42 Ca to report mass‐dependent Ca isotopic compositions. The precision under intermediate measurement conditions for δ 44/42 Ca over eight months in our laboratory was ± 0.03‰ (with n ≥ 8 repeat measurements). Measured igneous reference materials gave δ 44/42 Ca values ranging from 0.27‰ to 0.54‰. Significant Ca isotope fractionation may occur during magmatic and metasomatism processes. Studied reference materials with higher (Dy n /Yb n ) tend to have lower δ 44/42 Ca, implying a potential role of garnet in producing magmas with low δ 44/42 Ca. Sandstone GBW 07106 had a δ 44/42 Ca value of 0.22‰, lower than all igneous rocks studied so far.