AAPG Foundation 2019 Grants-in-Aid Projects

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Deformation mechanism variation and CPO fabric development along the Willard thrust fault, Utah


The purpose of this project is to determine the extent of deformation mechanism variation along the Willard thrust fault, and to evaluate if the anticipated variation is related to variable fluid interaction. The goal is to identify any differences in the primary brittle-ductile deformation mechanisms in the fault, both across a strain gradient within each fault block and across the fault plane. Optical microstructures and crystallographic preferred orientation (CPO) fabrics will be analyzed to determine trends in the relative contributions of brittle fracturing, diffusional processes, and crystal-plasticity along with their possible relation to fluid interaction. This project also aims to better understand quartz CPO fabric development and to explore the relationships between CPO fabrics and variable temperature, slip systems, and fluid interaction. Each fault block of the Willard thrust fault will be studied to test the hypothesis that areas of higher strain, associated with increased fluid, have a stronger CPO fabric. Additionally, a relative vorticity estimate can be made from the CPOs, providing information on kinematic partitioning within the fault blocks. This project aims to provide a deeper understanding of the effect that fluids have on deformation mechanisms, CPO fabric development, and fault kinematics. Additionally, it intends to determine the role of the fault during fluid flow, particularly determining whether it acted as a conduit, channeling fluid flow; a barrier, preventing fluid to cross the fault plane; or some combination of the two. A better understanding of fluid flow across a fault can also increase our knowledge of secondary hydrocarbon migration along faults. The way fractures and fabrics in the fault zone influence hydrocarbon transportation is an important relationship to understand.