Fluid circulation in the oceanic crust: Contrast between volcanic and plutonic regimes
Additional Document Info
Vein carbonates from a variety of ocean crust environments have been analyzed for Sr contents and Sr and oxygen isotopic compositions. Veins from upper crustal lithologies typically have low formation temperatures (<100-degrees-C) and from within 10-15 m.y. after crust formation, from solutions containing a basaltic component of very high Ca/Sr (>30 times that of hot smoker vent fluids). Veins from the gabbro lithologies at site 735B show both high (>150-degrees-C) and very low (<10-degrees-C) formation temperatures. The high-temperature carbonate veins have a large basaltic component (low Sr-87/Sr-86) with low Ca/Sr and probably formed before unroofing of this deep crustal block. The low-temperature veins have only a minor basaltic component, and formed after unroofing, but within 0-40 m.y. of crust formation. Hot smoker vent fluids represent the low Ca/Sr limit of fluids recorded by carbonate veins and thus cannot describe the totality of the seawater-ocean crust Ca/Sr exchange budget.