This paper describes a two-limb single-pass modeling approach constrained by vent temperature, heat flow, vent geochemistry, active-source seismology, and seismically inferred circulation geometry to provide first-order constraints on crustal permeability, conductive boundary layer thickness, fluid residence times, and magma replenishment rates for the magma-hydrothermal system at the East Pacific Rise (EPR) near 9°50’N. Geochemical data from black smokers and nearby diffuse-flow patches, as well as an estimate of heat flow partitioning, suggest that nearly 90% of the heat output stems from heat supplied by the subaxial magma chamber, even though almost 90% of that output appears as diffuse flow at the seafloor. Estimates of magma replenishment rates are consistent with the evolution of lava chemistry over the eruption cycle between 1991–1992 and 2005–2006. If the recharge surface area is 105 m2, a one-dimensional model of hydrothermal recharge using EPR 9°50’N parameters gives rise to rapid sealing as a result of anhydrite precipitation; however, if the area of recharge widens at depth to ~ 106 m2, sealing by anhydrite precipitation may not significantly affect hydrothermal circulation.

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