In this study, we take a numerical modeling approach to investigate crustal-scale fluid flow in areas of crustal extension subjected to normal and/or detachment faulting. In areas subjected to continental extension, brittle normal faulting of the upper crust leads to steep topographic gradients that provide the driving force (head gradient) and pathways (fractures) to groundwater flow. Ductile extension in the lower crust is characterized by high heat fluxes, granitic intrusion, and migmatitic gneiss domes. When downward fluid flow reaches the detachment shear zone that separates the upper and lower crust, high heat flux combined with magmatic/metamorphic fluids cause density inversions leading to buoyancy-driven upward flow. Therefore, mid-crustal shear zones represent crustal-scale hydrothermal systems characterized by buoyancy-driven fluids convection. Several geochemical studies of North American core complexes show that circulation of meteoric fluids during the development of the detachment shear zone is ubiquitous. The circulation of fluids at lower crustal levels is the result of the interplay between rock type, temperature, porosity and permeability, and fluid pathways.
We present the results of finite-element numerical models using ABAQUS/Standard that simulate groundwater flow in an idealized cross-section of a metamorphic core complex. The simulations investigate the effects of (1) crust and fault permeability and porosity, (2) width of the faults, (3) depth of the faults and shear zone, and (4) topography (head gradient) on groundwater flow. Our results show that fluid migration to mid- to lower-crustal levels is significantly fault-controlled and depends primarily on the permeability contrast between the fault zone and the crustal rock as well as the presence of a permeable shear zone, and additionally, our simulations reveal that higher fault/crust permeability contrast leads to channelized flow in the fault zone and shear zone, while lower contrast allow leakage of the fluids in the crust.
|Commitee:||Morra, Gabriele, Zhang, Rui|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 56/05M(E), Masters Abstracts International|
|Subjects:||Geology, Hydrologic sciences, Theoretical Mathematics|
|Keywords:||Detachment system, Fluid flow, Numerical modeling, Python|
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