Noble gas and stable isotope geochemistry of thermal fluids from Deception Island, Antarctica

• Published in: Antarctic Science
• Main Authors: Kusakabe, Minoru, Nagao, Keisuke, Ohba, Takeshi, Seo, Jung Hun, Park, Sung-Hyun, Lee, Jong Ik, Park, Byong-Kwon
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2009
• Subjects: Antarc*; Antarctic Science; Antarctica; Deception Island
• Online Access: http://dx.doi.org/10.1017/s0954102009001783; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102009001783

Abstract New stable isotope and noble gas data obtained from fumarolic and bubbling gases and hot spring waters sampled from Deception Island, Antarctica, were analysed to constrain the geochemical features of the island's active hydrothermal system and magmatism in the Bransfield back-arc basin. The 3 He/ 4 He ratios of the gases (< 9.8 × 10 -6 ), which are slightly lower than typical MORB values, suggest that the Deception Island magma was generated in the mantle wedge of a MORB-type source but the signature was influenced by the addition of radiogenic 4 He derived from subducted components in the former Phoenix Plate. The N 2 /He ratios of fumarolic gas are higher than those of typical mantle-derived gases suggesting that N 2 was added during decomposition of sediments in the subducting slab. The δ 13 C values of -5 to -6‰ for CO 2 also indicate degassing from a MORB-type mantle source. The H 2 /Ar- and SiO 2 geothermometers indicate that the temperatures in the hydrothermal system below Deception Island range from ~150°C to ~300°C. The δD and δ 18 O values measured from fumarolic gas and hot spring waters do not indicate any contribution of magmatic water to the samples. The major ionic components and δD-δ 18 O-δ 34 S values indicate that hot spring waters are a mixture of local meteoric water and seawater. Mn and SiO 2 in spring waters were enriched relative to seawater reflecting water-rock interaction at depth.