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Influence of Concurrent Brittle and Ductile Processes in a Fault Zone

Rachel Wells
Texas A&M University, Department of Geology and Geophysics College Station, TX; [email protected]

Fluid flow during or following faulting is influenced by the microscale structures developed during deformation. Recent studies show evidence for both brittle and ductile deformation in thrust faults of foreland fold-and-thrust belts. The goal of this research is to study how the competing effects of brittle and ductile (plastic and diffusional mass transfer) processes influence fluid flow. This study will focus on limestones and shales along the Hunter Valley and Copper Creek thrust faults in the foreland of the southern Appalachians. Previous studies, using transmission electron microscopy, have identified evidence for crystal plasticity in these rocks; however the spatial and temporal relations between microstructures resulting from crystal plastic, diffusive and brittle processes have not been fully investigated.

Field and laboratory studies will focus on the spatial and temporal relationships between brittle and ductile structures with emphasis on the relations between these structures and porosity. This study will make use of the scanning electron microscope to investigate the microstructures at a scale intermediate to previous investigations, and evidence for diffusive mass transfer will be evaluated by analyzing variations in chemical composition using an electron microprobe. This research will improve our understanding of how interactions between brittle and ductile deformation mechanisms in complex fault systems influence porosity and permeability, and will thus provide a more complete characterization of migration of fluids in the foreland of fold-and-thrust belts.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid