Sr-C-O isotopes in nephelinitic rocks and carbonatites, Gardiner Complex, Tertiary of East Greenland

The carbonatite-bearing Gardiner Complex in the Tertiary Magmatic Province of east Greenland formed during the opening of the North Atlantic. It is the core of a nephelinitic volcano. The magmatic liquids had initial ⁸⁷Sr⁸⁶Sr (Sr₀) of 0.7037 ± 4. Basement contaminated units are rare and confined to the marginal parts of the complex. The Sr0 of the magmatic liquids are similar to those of early tholeiites in the province and all could have formed from the same source. Calcites of few carbonatite dikes and late pegmatites show increasing δ¹⁸O and δ¹³C with inferred decreasing temperature, as a result of Rayleigh fractionation between the calcites and the coexisting vapour phase. No evidence of circulating meteoric water or pervasive metasomatic alteration has been observed in field relations, petrography or chemistry. The isotope results are readily interpreted in support of this view.