Hydrothermal convection and crustal accretion at fast spreading ridges – insights from numerical modeling

Hydrothermal systems at mid-ocean ridges have a major control on the thermal and chemical evolution of the young oceanic crust, they have created hydrothermal ore deposits that are economically interesting and they sustain unique ecosystems near the vent sites. To better understand how hydrothermal systems work it is important to quantify the mass and energy transport by hydrothermal flow and to constrain the lateral and vertical extend of the hydrothermal circulation within the oceanic crust. The depth extend of hydrothermal cooling, for instance, is not well constrained. From geochemistry we find that fluids equilibrate with the host rock near the axial melt lens, which suggests shallow hydrothermal convection above the melt lens. The crustal temperature structure inferred from seismic tomography, however, points at deeper hydrothermal circulation within the lower gabbros. Directly linked to the depth extend of hydrothermal cooling is the question whether oceanic crust at fast-spreading ridges accretes predominantly in-situ ("many sills model") or crystalizes in the axial melt lens ("gabbro glacier model"). Numerical modeling is a powerful tool to shed more light on these processes. I will present new results of our 2D numerical model solving for crustal accretion in the presence of hydrothermal cooling. These results support crustal-scale hydrothermal flow and also place a limit on the amount of oceanic curst that can crystallize in-situ. In addition we use a our 3D hydrothermal flow model to quantify the mass and energy fluxes within upper and lower crust and to look in detail at the hydrothermal flow patterns on shorter time scales. Furthermore I will provide some insight into the numerical techniques that we develop and improve in our group.