Title:Numerical Simulations of Submarine and Subaerial Magmatic Hydrothermal Systems

Magmatism at mid-ocean-ridges is predominantly basaltic and acts as a heat source for hydrothermal convection cells. Seawater percolates through the ocean floor into the subsurface, is heated near the magma chamber, travels upward, and vents at the ocean floor, eventually forming black smoker fields. Numerical simulations in 3D with pure water and a homogeneous permeability have shown that the system naturally forms regularly-spaced pipe-like upflow zones which is well-supported by measurements and observations. These simulations further revealed that most of the downflow occurs in the immediate vicinity of the upflow zone where fluids are heated to about 200 C. Introducing geological structures to the model geometry adds further complexity to the system but preserves the first order principle described above. Convection at a mid-ocean ridge system with a deeper gabbroic part overlain by a basaltic layer of higher permeability develop a secondary convection cell establishes within the highly permeable basalt layer resulting in a more efficient cooling of the upper part of the upflow zone. Normal faults within the oceanic crust near the ridge axis are often referred to as conduits for enhanced up- or downflow. First numerical simulations introducing normal faults as heterogeneities within the permeability structure of the model geometry show that downflow velocities similar to the ones described above only develop in relatively wide normal faults (50m) that have a high permeability contrast to the surrounding rock (up to two orders of magnitude) and are located very close to the ridge axis.