In situ Sr isotopic compositions of coexisting apatite and carbonate for carbonatites from the Sarfartoq alkaline complex, Greenland, have been determined by laser-ablation multicollector inductively coupled plasma mass spectrometry. This study is the first to examine the extent of Sr isotopic homogeneity among coexisting igneous minerals containing high Sr (>3000 ppm) and low Rb ( « 1 ppm) contents within a single ~ 50-µm-thin-section mount. This technique is capable of producing measured Sr/Sr values with analytical precision (~ 0.005%, 2s) approaching those obtained by thermal ionization mass spectrometry but in a much shorter interval of time (100 s vs.>1 h, respectively). The combined total analyses (n = 107) of apatite and carbonate yield Sr/Sr compositions ranging from ~ 0.7025 to ~ 0.7031. This relatively large variation in Sr isotopic compositions (~ 0.0006) is ~ 1 order of magnitude larger than the estimated external reproducibility (~ 0.00005,2s) of the method. The large range in Sr/Sr values suggests that apatite and carbonate precipitated predominantly under nonequilibrium conditions. The isotopic variations observed within individual hand specimens may therefore reflect larger (regional) scale open-system processes, possibly involving mixing of carbonatitic melts derived from distinct mantle sources or from a common isotopically heterogeneous mantle.
Geochimica Et Cosmochimica Acta, 2003, Vol 67, Issue 2, p. 289-302