LAUSR

Fluid recharge and discharge between the deep ocean and the porous upper layer of off-axis oceanic crust tends to concentrate in small volumes of rock, such as seamounts and fractures, that are unimpeded by low-permeability sediments. Basement structure, sediment burial, heat flow, and other regional characteristics of off-axis hydrothermal systems appear to produce considerable diversity of circulation behaviors. Circulation of seawater and seawater-derived fluids controls the extent of fluid-rock interaction, resulting in significant geochemical impacts. However, the primary regional characteristics that control how seawater is distributed within upper oceanic crust are still poorly understood. In this paper we present the details of the two-dimensional (2D) BASALT numerical model (Basement Activity Simulated At Low Temperatures) of heat and fluid transport in an off-axis hydrothermal system. This model is designed to simulate a wide range of conditions in order to explore the dominant controls on circulation. We validate the BASALT model's ability to reproduce observations by configuring it to represent a thoroughly-studied transect of the Juan de Fuca Ridge eastern flank. The results demonstrate that including series of narrow, ridge-parallel fractures as sub-grid features produces a realistic circulation scenario at the validation site. In future projects, a full reactive-transport version of the validated BASALT model will be used to explore geochemical fluxes in a variety of off-axis hydrothermal environments.