Isotope geochemistry of volcanic rocks from the Barton Peninsula, King George Island, Antarctica

Abstract

C, O, H, S and Sr isotopes were investigated to characterize the isotopic composition of the Paleocene-Eocene volcanic rocks in Barton Peninsula, King George Island, Antarctica. The analyzed samples of volcanic rocks cover a range from basalt to andesite. The δ 13C and δ 18O values of calcite in volcanic rocks range from −7.5‰ to −3.2‰ and 0.4‰ to 5.1‰, respectively. The homogenous δ 13Ccal and depleted δ 18Ocal values relative to primary magmatic values reflect the effect of high temperature alteration of volcanic rocks. The δ 18O of volcanic rocks ranges from −1.1‰ to 7.2‰, and the majority of values are significantly lower than those of primary magmatic values. The low δ 18OWR values are compatible with high temperature alteration. The initial values of 87Sr/86Sr of volcanic rocks span a narrow range from 0.703 312 to 0.703 504 which belong to the present mid-oceanic ridge basalt. The values of 87Sr/86Sr of volcanics in the Barton Peninsula are similar to those determined in the Fildes Peninsula, King George Island. The δDWR and H2O contents of volcanic rocks range from −74‰ to −66‰ and 0.67 wt.% to 2.74 wt.%, respectively. The higher δDWR and H2O wt.% of volcanic rocks relative to fresh basalts also result from high temperature alteration. Sulfur isotope compositions of the volcanic rocks range from −12.5‰ to −7.0‰; these values may represent fractionation accompanying partial oxidation of magmatic S or incorporation of some bacteriogenic sulfide. The low S contents and negative correlation with C and H2O reflect the formation of calcite and breakdown of sulfide as a result of high temperature water-rock interaction.