Hydrothermal alteration of basalt by seawater under seawater-dominated conditions

摘要: Fresh mid-ocean ridge basalt glass and diabase have been reacted with seawater at 150–300°C, 500 bar, water/rock mass ratios of 50, 62, 125, using experimental apparatus which allowed on-line sampling solution to monitor reaction progress. These experiments characterize under what we called “seawater-dominated” conditions hydrothermal alteration. In an experiment 300°C, undergoing alteration removed nearly all Mg2+ from amount 50 times its own mass. In the process, was converted entirely mixed-layer smectite-chlorite, anhydrite, minor hematite. Removal Mg occurred as a Mg(OH)2 component incorporated into secondary clay. This produced precipitous drop in pH early experiment, accompanied by dramatic increase concentrations Fe, Mn, Zn solution. As removal neared completion hydrolyzed, rose again heavy metal dropped. At 62 125 mineral assemblage similar that ratio 50. Solution chemistry, however, contrasted earlier were greater lower. caused significant leaching metals. At 300°C Na, Ca, Cu, Zn, CO2 most K, Ba, Sr, Mn leached silicates. H2S, Al, Si, possibly Co also significantly mobilized, whereas V, Cr, Ni not. Little or no sulfate reduced. Although submarine hot spring solutions sampled date along ridges clearly come rock-dominated systems, evidence ocean floor metabasalts heat flow studies indicates seawater-dominated prevail least locally both axial hightemperature systems flank lower temperatures.