S- and Sr-isotopic compositions in barite–silica chimney from the Franklin Seamount, Woodlark Basin, Papua New Guinea: constraints on genesis and temporal variability of hydrothermal fluid

• Published in: International journal of earth sciences : Geologische Rundschau 2017-07, Vol.106 (5), p.1723-1733
• Main Authors: Ray, Durbar, Banerjee, Ranadip, Balakrishnan, S., Paropkari, Anil L., Mukhopadhyay, Subir
• Format: Article
• Language: English
• Subjects: Atmospheric precipitations; Barite; Basins; Chemical analysis; Components; Earth and Environmental Science; Earth Sciences; Enrichment; Geochemistry; Geology; Geophysics/Geodesy; Growth; Hydrologic cycle; Isotope composition; Isotopes; Lava; Leaching; Magma; Mineral Resources; Mineralization; Ocean floor; Original Paper; Precipitation; Ratios; Seamounts; Seawater; Sedimentology; Silica; Silicon dioxide; Strontium; Strontium isotopes; Structural Geology; Sulfur; Sulfur dioxide; Sulphur; Temporal variability; Temporal variations; Thermal energy; Thickening; Variability; Water analysis
• ISSN: 1437-3254; 1437-3262
• DOI: 10.1007/s00531-016-1381-5

Isotopic ratios of strontium and sulfur in six layers across a horizontal section of a hydrothermal barite–silica chimney from Franklin Seamount of western Woodlark Basin have been investigated. Sr-isotopic ratios in barite samples ( 87 Sr/ 86 Sr = 0.70478–0.70493) are less radiogenic than seawater ( 87 Sr/ 86 Sr = 0.70917) indicating that substantial leaching of sub-seafloor magma was involved in the genesis of hydrothermal fluid. The SO 2 of magma likely contributed a considerable amount of lighter S-isotope in fluid and responsible for the formation of barite, which is isotopically lighter (δ 34 S = 19.4–20.5 ‰) than modern seawater (δ 34 S ~ 21 ‰). The systematic changes in isotopic compositions across the chimney wall suggest temporal changes in the mode of mineral formation during the growth of the chimney. Enrichment of heavy S- and Sr-isotopes (δ 34 S = 20.58 ‰; 87 Sr/ 86 Sr = 0.70493) in the outermost periphery of the chimney indicates that, at the initial stage of chimney development, there was a significant contribution of seawater sulfate during barite mineralization. Thereafter, thickening of chimney wall occurred due to precipitation of fluid carrying more magmatic components relative to seawater. This led to a gradual enrichment of lighter isotopes (δ 34 S = 20.42–19.48 ‰; 87 Sr/ 86 Sr = 0.70491–0.704787) toward the inner portion of the chimney wall. In contrast, the innermost layer surrounding the fluid conduit is characterized by heavier and more radiogenic isotopes (δ 34 S = 20.3 ‰; 87 Sr/ 86 Sr = 0.7049). This suggests there was increasing influence of percolating seawater on the mineral paragenesis at the waning phase of the chimney development.