CONTROLS ON DEEP GROUNDWATER CIRCULATION SYSTEMS

Understanding factors that control transport of fluids through the upper crust is of critical importance to elucidating potential pathways for movement of deep fluids to into shallow groundwater zones. Thermal springs provide a natural laboratory for study of such systems. While commonly associated with areas of elevated heat flow adjacent to igneous intrusive, thermal systems are also common in deformed sedimentary basins with relatively low heat flow. Here thermal waters obtain heat through deep circulation of meteoric water. Regional thermal gradients show circulation depths range up to 5 km depth adjacent to regions of active shale gas development. Along with deep circulation of meteoric waters, such sites can also be associated with discharge of deep thermogenic gas. While transport and discharge of fluids from such depths raise concerns for connection to surface environments, formation of such systems requires an ideal ‘permeability window’ where fluids are focused to surface. Such permeability windows are formed by unusual structural features, such as lateral ramps or intersecting fault structures.