Fluids in Continental Fault Zones: Evidence From Neomineralized Clays

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Newly-grown clays in fault rock preserve the isotopic signature of fluids that were present during faulting, and will be used to constrain the plumbing of shallow fault systems and the dominant source of fluids. Examining fluid infiltration and circulation of crustal fault systems tests the hypothesis that fluids originating at the surface are the dominant phase in strike-slip fault and normal fault systems. This research project will use paired oxygen and hydrogen isotopic measurements on newly-grown illite from a suite of detachment (normal) fault systems in southwestern United States and continental strike-slip faults (San Andreas Fault, Alpine Fault, North Anatolian Fault). These faults contain neomineralized clays and are well-studied examples of major continental fault systems. The field approach utilizes surface sampling and recent drill core, while the laboratory works involves stable and radiogenic analyses, supported by various sample characterization studies.Studying fluid circulation in natural fault systems is fundamental to understanding the role of fluids within the upper crust, which has major implications for the strength and seismogenesis of faults, and the formation of economic deposits. The approach in this study can be applied to many fault systems around the world to examine the relative contributions of metamorphic (deep) and meteoric (surface) fluids, so it has excellent potential for broad application. This field and laboratory project includes graduate and undergraduate students at the University of Michigan, and involves international collaboration with several field and laboratory experts. The training of young scientists contributes significantly to tomorrow's needs for human capital in science, math and engineering fields. Results will be published in the professional literature and inserted in appropriate public outreach and teaching setting, as well as scientific presentations by team members.