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

O, H, S and Sr isotopes were investigated to characterize 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 delta(18)O and delta D values gradually decrease from altered basaltic andesite to altered dyke and quartz-veined volcaniclastic rock. The genetic linkage between hydrothermal fluid and granodiorite intrusion accounts for similar delta(34)S values among sulfide minerals, both in the granodiorite stock and in nearby altered basaltic andesite. Broadly positive correlations of delta(18)O-SiO(2), delta(18)O-((87)Sr/(86)Sr)i, and (87)Sr/(86)Sr-SiO(2) can be established by siliceous fluids enriched in (18)O as well as (87)Sr. In addition, a positive relationship between ((87)Sr/(86)Sr)(i) values and 1/Sr contents in basaltic andesites can result from mixing between fresh rocks and infiltrating fluids with different endmember (87)Sr/(86)Sr values and Sr contents. The hyperbolic variation of ((87)Sr/(86)Sr)(i)-K/Rb suggests 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, and (18)O- and (87)Sr-rich meteoric water circulating in the upper crust significantly contributed to hydrothermal activities in Barton Peninsula.