Unusual mixed silica-carbonate deposits from magmatic-hydrothermal hot springs, Savo, Solomon Islands

作者：Smith D J^*; Jenkin G R T; Petterson M G; Naden J; Fielder S; Toba T; Chenery S R N

来源：Journal of the Geological Society, 2011, 168(6): 1297-1310.

DOI：10.1144/0016-76492011-003

The volcanic island of Savo, Solomon Islands, hosts an active hydrothermal system discharging unusual alkaline (pH 7-8) sulphate-rich, chloride-poor fluid, with variable admixtures of Ca-Mg-HCO(3)(-)-rich fluid. Hot springs and their outflow streams precipitate a variety of deposits, including travertine, silica sinter and unusual mixed silica-carbonate rocks. Travertine fabrics are dominated by ray-crystal calcite, associated with rapid abiotic precipitation from a supersaturated solution. Sinter is produced by evaporation of thermal waters, and downstream samples contain preserved traces of micro-organisms, which potentially acted as templates for precipitation. Trace element chemistry of sinters and travertines includes anomalously high levels of Te, indicating a magmatic origin for a component fluid in the hydrothermal system. Springs are close to or at saturation with both calcite and amorphous silica. Increased contributions from the Ca-Mg-HCO(3)-end-member favours calcite formation; this fluid is of low-temperature origin, and as such is favoured by high rainfall. Mixed samples show cyclical changes between silica and carbonate precipitation, potentially as a result of seasonal variation in rainfall.

• 出版日期2011-12