ABSTRACT

The isotopic compositions of strontium in two suites of non-marine carbonate rocks from the Beacon Supergroup of the Transantarctic Mountains have been measured. Twelve samples of Permian age from the central sector of the Transantarctic Mountains and three samples of Upper Devonian age from southern Victoria Land all have significantly higher Sr⁸⁷/Sr⁸⁶ ratios than the oceans during Permian and Devonian times, respectively. The Sr⁸⁷/Sr⁸⁶ ratios of these carbonate rocks are independent of the distance to diabase intrusives of Jurassic age which caused local contact metamorphism of the country rock. However, a positive correlation between the insoluble residue content and the Sr⁸⁷/Sr⁸⁶ ratios of the carbonate rocks was ob erved. The average Sr⁸⁷/Sr⁸⁶ ratios, corrected by extrapolation to zero insoluble residue content, are: 0.7160 ± 0.0012 for the Permian suite and 0.7252 ± 0.0017 for the Devonian suite. The enrichment of these carbonate rocks in radiogenic Sr⁸⁷ is attributed to the provenance of dissolved strontium and sediment of the Beacon Supergroup. Reasonable estimates of the Rb/Sr ratios of the rocks in the drainage basins suggest that the Permian carbonates have a provenance whose present age is in the range 1.6 to 2.3 billion years, while the Devonian rocks were derived from terrain whose present age is of the order of 2.7 to 3.45 billion years. Rocks having ages in this range are known in the East Antarctic Shield and on the continents of the southe n hemisphere. These results suggest that the Sr⁸⁷/Sr⁸⁶ ratio may be a useful parameter for the study of non-marine carbonates elsewhere.