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 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 δ O and δD 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 δ S values among sulfide minerals, both in the granodiorite stock and in nearby altered basaltic andesite. Broadly positive correlations of δ O-SiO 2 , δ O-( Sr/ Sr/ Sr) i , and Sr/ Sr/ Sr-SiO 2 can be established by siliceous fluids enriched in O as well as Sr. In addition, a positive relationship between (Sr. In addition, a positive relationship between ( Sr/ Sr/ Sr) i values and 1/Sr contents in basaltic andesites can result from mixing between fresh rocks and infiltrating fluids with different endmember Sr/ Sr/ Sr values and Sr contents. The hyperbolic variation of ( Sr/ Sr/ 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 O-and Sr-rich meteoric water circulating in the upper crust significantly contributed to hydrothermal activities in Barton Peninsula.

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

“…The values of 87 Sr/ 86 Sr of volcanics in the Barton Peninsula range from 0.703 314 to 0.703 504, which are similar to those determined in the Fildes Peninsula, King George Island (Machado et al, 2005). Shin et al (2009) reported that the Sr isotope …”

“…3c), significantly lower than the presumed original magmatic values of (-0.8±0.2)‰ (Sakai et al, 1982). Initial Sr isotopic compositions of the volcanic rocks span a narrow range from 0.703 312 to 0.703 504 which are similar to the less altered volcanic rocks reported by Shin et al (2009). These ( 87 Sr/ 86 Sr) i values of volcanic rocks belong to the present midoceanic ridge basalt (Dickin, 2005).…”

Lithium Isotope Geochemistry in the Barton Peninsula, King George Island, Antarctica

“…The 87 Sr/ 86 Sr ratios of meltwater, lake and seawater samples range from 0.704554 to 0.707716 with an average of 0.706004 (n = 26), from 0.706274 to 0.709006 with an average of 0.707822 (n = 5), and from 0.709025 to 0.709397 with an average of 0.709186 (n = 3), respectively (Table 1). Previous study showed that rock samples display the 87 Sr/ 86 Sr ratios, ranging from 0.703218 to 0.704620 with an average of 0.703685 (Shin et al, 2009).…”