Metamorphosed Plio-Pleistocene evaporites and the origins of hypersaline brines in the Salton Sea geothermal system, California: Fluid inclusion evidence

摘要: Abstract The Salton Sea geothermal system (SSGS) occurs in Plio-Pleistocene deltaic-lacustrine-evaporite sediments deposited the Trough, an active continental rift zone. Temperatures up to 365°C and hypersaline brines with 26 wt.% TDS are encountered at 1–3 km depth sediments, which undergoing greenschist facies hydrothermal metamorphism. Previous models for origins of Na-Ca-K-Cl have assumed that high salinities were derived mainly from downward percolation cold, dense formed by low-temperature dissolution shallow non-marine evaporites. New drillcores central part field contain metamorphosed, bedded evaporites 1 consisting largely hornfelsic anhydrite interbedded anhydrite-cemented solution-collapse shale breccias. Fluid inclusions trapped within breccia-cementing homogenize 300°C (identical measured downhole temperature) saline brines. Some 50 vol.% halite, sylvite carbonate crystals room temperature, some halite persist above upon laboratory heating. data consistent trapping halite-saturated fluids during metamorphism accompanying solution collapse shales. We conclude many salt residuum evaporitic was dissolved heated connate fluids. Therefore, situ halides CaSO 4 relatively deeply-buried lacustrine This fact places important constraints on modeling fluid-flow SSGS, as need not migrated over great distances. been further modified their present complex Na-Ca-K-Fe-Mn-Cl compositions on-going sediment water-rock interaction.