Numerical modeling of oceanic crustal hydrothermal systems

grantor: University of TorontoThe oceanic crust is a complex rock-mineral formation which extends up to several kilometers below the sea floor and covers laterally about two thirds of the planet. Hydrothermal circulation within the crust is driven by magmatic sources and carried by the fluid residing in pores and cracks. Hydrothermal advection transfers about one quarter of the Earth's total heat power from the interior. Marine sediments are believed to be the largest repositories of solid ice-like methane clathrate hydrates. The compliance technique is an important tool for assessment of this resource. It makes use of the oceanic surface gravity waves to induce pressure variations on the sea floor and measure the corresponding vertical deformation. This thesis deals with the convective heat and mass transfer within the oceanic crust, as a fractured porous medium, and the elastic, quasi-static response of hydrated marine sediments to gravity wave loading. Both generic and site-specific applications are considered. Most applications are tackled numerically in three spatial dimensions. The major results are as follows. Fractures can trigger and maintain hydrothermal circulation. The permeability-thickness product in the direction of flow is an adequate parameter to represent the fracture if convection is not vigorous. A new temperature homogenization mechanism for the off-axial convection is proposed which is due to quasi-lateral circulation within a permeable zone between sediment cover and basalt. It explains both the observed correlation between surface heat flux and sediment thickness, as well as regular heat flux variations when no buried topography is present. A hydrothermal model for the CoAxial Segment of the Juan de Fuca Ridge predicts ridge-parallel convection with the low-temperature vents spaced 1 'km' apart. The compliance approach is feasible for a non-layered medium. The average compliance response depends on the bulk hydrate content, but not on a particular connectivity pattern. However, the lateral variation in compliance correlates with the size of a typical lateral inhomogeneity.Ph.D