USING GEOCHEMICAL ALTERATION OF SEAFLOOR BASALTS AS A PROXY FOR FLUID-FLOW FLUXES THROUGH THE OCEAN CRUST

Circulation of seawater through the seafloor plays a vital role in the exchange of heat, fluid, and chemical species between the oceanic lithosphere and the hydrosphere. Seawater circulates through the ocean crust at mid-ocean ridges, ridge flanks, seamounts, and subduction zones. Understanding how these fluids evolve and modify their environments is necessary for understanding how the fluids affect not only the chemical budgets of the oceanic crust and ocean but those of other marine systems as well. While a significant amount of research has been conducted regarding heat and chemical fluxes, the quantification of fluid fluxes through the ocean floor in these different regimes has remained elusive. We are using numerical geochemical models and laboratory experiments in an attempt to quantify these fluxes. We have used numerical reactive transport models to predict basalt/seawater interaction at a variety of temperatures and fluxes that span the spectrum of seafloor environments. Unaltered basalt was collected from the axial ridge of the East Pacific Rise and analyzed using SEM, XRF, and XRD. This basalt will eventually be used in the laboratory experiments and its composition served as the initial composition in the numerical models. The results of these numerical experiments have been used to generate the hypotheses that we will test in laboratory experiments and will allow us to compare observed changes in mineralogy and fluid composition with thermodynamically predicted changes. We will present: (1) the results of our petrologic analyses, (2) the results of our numerical modeling, and (3) the hypotheses we will test in our lab experiments. Eventually, a continuum model of the fluid interactions between the different seafloor environments will provide the insight necessary to understand the geochemical links between them.