Influence of high marine Ca/SO4 ratio on alteration of submarine basalts at 2.41 Ga documented by triple O and Sr isotopes of epidote

Over the course of Earth’s history, marine sulfate concentrations have been increasing in response to long-term atmospheric oxygenation. In contrast modern oceans, where abundant precipitates hot oceanic crust as anhydrite, Precambrian oceans contained much less (~0–10 mM) sulfate, so that submarine hydrothermal systems were comparatively poor anhydrite. As a step towards exploring role chemical evolution seawater solutes, we investigate reaction between basalt and took place at ca. 2.43–2.41 Ga Vetreny Belt (Karelia craton, NW Russia) using fluid inclusion multi-isotope measurements complemented by reactive transport static aqueous-mineral equilibrium calculations. Using LA-ICP-MS, constrain Sr concentration least modified seawater-derived fluids address effect phase separation. Then, complement previous ?18O – ??17O datasets with new 87Sr/86Sr performed on 2.41 epidote from Belt, recent (0–6 Ma) Reykjanes, Iceland drilling site 504B eastern Pacific Ocean. The 87Sr/86Srinitial 0.7029–0.7042 –0.06 0.00‰ is best explained relatively high fraction (~90%) was delivered contemporaneous ? 0.7045, without significant removal early Monte-Carlo simulation dual-porosity model, range possible exchange trajectories based variability physical parameters (porosity, flow velocity, fracture spacing, recrystallization rates). Further, use series seawater-basalt calculations emphasis Ca/SO4 values Ga. Our demonstrate co-existing quartz absence feldspars represent less-evolved fluids. Consequently, assemblage provide an insightful archive for Sr. Based our modeling assumptions about Sr/Ca ratios, epidotes document initial 30 40 mM Ca 0–10 SO4, representing input data, suggest ratio (?1) low anhydrite promote higher be permanently stored silicates altered crust. contrast, depleted radiogenic due partitioning into which partly returns ocean upon cooling.