Calcium Isotope Ratios (δ<sup>44/40</sup>Ca) of Thirty‐Four Geological Chinese Reference Materials Measured by Thermal Ionisation Mass Spectrometry
Fang Liu, Xin Li, Zhaofeng Zhang, Jianghao Bai, Yajun An
Abstract
High‐precision calcium isotopic ratios of thirty‐four Chinese geological reference materials, including igneous, metamorphic and sedimentary rocks, river/marine sediments and soils, are reported. Measurements were conducted by thermal ionisation mass spectrometry (Triton TIMS) using a 42 Ca– 43 Ca double spike. These reference materials cover a wide range of chemical compositions with CaO ranging from 0.10 to 51.1% m / m . The δ 44/40 Ca variation of igneous rocks was up to 0.75‰, ranging from 0.61 ± 0.06‰ to 1.35 ± 0.04‰. Two metamorphic rocks yielded δ 44/40 Ca of 0.39 ± 0.02‰ and 0.86 ± 0.02‰, respectively. δ 44/40 Ca values of sedimentary rocks varied from −0.14 ± 0.09‰ to 0.98 ± 0.12‰, suggesting significant isotopic fractionation during low‐temperature processes. Like sedimentary rocks, river/marine sediments and soil displayed large Ca isotopic variations, with δ 44/40 Ca spanning from 0.12 ± 0.06‰ to 0.77 ± 0.03‰ and −0.09 ± 0.11‰ to 0.74 ± 0.08‰, respectively. The comprehensive data set reported in this study serves as a reference for quality assurance and inter‐laboratory comparison for high‐precision Ca isotopic studies.