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1 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet 2 Univ. du Quebec a Montréal 3 De Beers GeoScience Center 4 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet
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. Copyright © 2003 Elsevier Science Ltd.
Geochimica Et Cosmochimica Acta, 2003, Vol 67, Issue 2, p. 289-302
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