Open AccessS, Sr, and Pb isotopic systematics of hydrothermal chimney precipitates from the Eastern Manus Basin, western Pacific: Evaluation of magmatic contribution to hydrothermal system
Author(s) -
Kim Jonguk,
Lee Insung,
Lee KyeongYong
Publication year - 2004
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2003jb002912
Subject(s) - geology , hydrothermal circulation , seawater , geochemistry , strontium , sulfur , δ34s , volcanogenic massive sulfide ore deposit , sulfate , mineralogy , seafloor spreading , pyrite , fluid inclusions , oceanography , sphalerite , chemistry , paleontology , organic chemistry
Sulfur, strontium, and lead isotopic analyses were performed on chimneys from the hydrothermal vent fields (the PACMANUS and Susu knolls) in the eastern Manus back arc basin. Lead isotope composition varies in a narrow range ( 206 Pb/ 204 Pb = 18.75–18.78, 207 Pb/ 204 Pb = 15.51–15.54, and 208 Pb/ 204 Pb = 38.31–38.40). Strontium isotopic ratios ( 87 Sr/ 86 Sr) of sulfate minerals vary from 0.7051 to 0.7077, falling between those of seawater (0.7090) and the hydrothermal fluid end‐member (0.7050). The δ 34 S values of the chimneys are −8.0 to −3.9‰ for the Susu knolls sulfide, +1.0 to +4.3‰ for the PACMANUS sulfides, and +7.4 to +20.6‰ for sulfate. The Susu knolls sulfides have the lowest values so far reported for volcanic‐hosted massive sulfides from modern seafloor. The low δ 34 S values of sulfates and sulfides cannot be explained by a simple seawater circulation model without an additional source of light sulfur. This is also supported by the presence of sulfate in hydrothermal end‐member fluid indicated by sulfur and strontium isotopic ratios in chimney sulfates. Biogenic sulfur and/or oxidation of H 2 S after boiling are excluded from the possible sources of light sulfur because of the lack of sediment cover and nonequilibrium in isotopic fractionation by boiling at seafloor. Disproportionation of magmatic SO 2, introduced into hydrothermal system through preeruptive degassing, is the most plausible mechanism for the observed low δ 34 S values. The lighter δ 34 S values and more radiogenic lead isotope compositions of the Susu knolls samples indicate that magmatic degassing was more vigorous at the Susu knolls than PACMANUS.