Calcium Isotopic Fractionation and Compositions of Geochemical Reference Materials

Abstract

High‐precision calcium isotopic compositions of a set of geological reference materials from the IAG ( OU ‐6), ANRT ( UB ‐N), MPI ‐ DING , USGS and GSJ , relative to NIST SRM 915a, are reported here. Measurements were performed by thermal ionisation mass spectrometry (Triton instrument) using a 42 Ca– 43 Ca double spike. δ 44/40 Ca values of selected reference materials, mainly felsic rocks, are reported for the first time. Felsic rock values of δ 44/40 Ca ranged from 0.13‰ to 1.17‰, probably implying Ca isotopic fractionation could occur during magma evolution. δ 44/40 Ca values of ultramafic rocks, ranging from 0.74‰ to 1.51‰, were positively correlated with MgO and negatively with CaO contents, possibly owing to Ca isotopic fractionation during partial melting. δ 44/40 Ca of intermediate‐mafic rocks were around 0.78‰ and displayed limited variation, suggesting Ca isotopic fractionation is insignificant during magma evolution processes. As expected, δ 44/40 Ca of sedimentary and metamorphic rocks varied widely due to complex geological processes.