Hydrothermal alteration and isotopic variations of igneous rocks in Barton Peninsula, King George Island, Antarctica

Abstract

O, H, S and Sr isotopes were investigated to charaterize the nature of hydrothermal fluids and alteration processes in volcanic and intrusive rocks in Barton Peninsula, King George Island. The oxygen and hydrogen isotope compositions of altered basaltic andesite and granodiorite are similar to each other. The oxygen and hydrogen isotopic values gradually decrease from altered basaltic andesite to altered dyke and quartz-veined volcaniclastic rocks. THe genetic linkage between hydrothermal fluid and granodiorite intrusion accounts for similar sulfur isotopic values among sulfide minerals, both in the granodiorite stock and in nearby altered basaltic andesite. The isotopic and trace element interelations suggest that meteoric water participated in hydrothermal activities via mixing with magmatic water, and the contribution of seawater was insignificant. All of the above results indicate that hydrothermal alteration was influenced by fluids related to granodiorite intrusion.