Reconstructing the oxygen isotope composition of late Cambrian and Cretaceous hydrothermal vent fluid

摘要: Oxygen isotope analyses (δ18O) of 16 quartz–epidote pairs from late Cambrian (Betts Cove and Mings Bight, Newfoundland), Ordovician (Thetford Mines, Quebec, Canada) Cretaceous (Troodos, Cyprus) ophiolites are used to calculate the δ18O hydrothermal fluids which they crystallized. We combine these with 3 quartz-fluid inclusion measurements quartz–magnetite explore how range in submarine vent fluid has varied between Cambrian, today. The calculated values (−4 +7.4) is larger than that modern seafloor (0 +4). employ two numerical models ascertain whether this most consistent changes paleo-seawater or reactive flow path ancient systems. A static calculation oxygen composition as a function water–rock ratio suggests an ocean lower today, should be larger. Our data, however, show little evidence was much global ice-free value −1.2. dual porosity model for through fractured porous media relative evolution 87Sr/86Sr contact rock. epidotes suggest strontium concentration oceans may have been higher at present. data strikingly different younger samples, difficult unless fluid-rock interaction systems substantially different. It also possible some veins reset by obduction-related metamorphism. high calcium-to-sulfate early (and Cretaceous) seawater affected degree exchange, causing closer