Role of mechanical anisotropy in the internal evolution of a thrust sheet /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1992.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | A planar mechanical anisotropy may be caused by stratigraphic layering, imbricate faulting, or other uniformly oriented and distributed planar deformation features within thrust sheets. The structural style of the Absaroka thrust sheet, Wyoming, varies with magnitude of shortening, stacking sequence of strata, proximity to the basal thrust surface, and position. The stratigraphic section within the hanging wall is divided into two main structural lithic units. Where only the upper unit is present, shortening was achieved by imbricate thrust faulting with little associated folding. Where both units are present, large magnitude shortening was achieved by duplex development in the lower unit and large-amplitude, long-wavelength folding in the upper unit. Imbrication, fault-propagation folding, and duplex development are interpreted to have primarily occurred during late stages of motion on the Absaroka thrust fault. Field observations and mechanical model results suggest that the main imbricate faults formed in a break-back sequence as the thrust sheet was emplaced, but that individual duplexes formed in a break-forward sequence. Geometric models of simple fault-propagation folds have been extended to included the case in which folding initiates above a thrust ramp of constant dip. This model can describe fault propagation folding in inhomogeneous anisotropic strata that involves the formation of isolated contraction faults in the stronger units that link during fold growth. A mechanical model of fault-bend folding in an anisotropic viscous thrust sheet demonstrates that narrow, elongate bands of stress concentration oriented parallel and perpendicular to the planar anisotropy emanate from the ramp regions during thrust sheet motion. Material in the hanging wall experiences layer parallel and layer perpendicular maximum principal stress as it moves over a thrust ramp consistent with the stress/strain history inferred for natural thrust sheets. Stress conditions favorable for brittle, contractional faulting develop above the flats adjacent to the thrust ramps. Kink-like fault bend folds develop in anisotropic thrust sheets if the fault surface contains isolated, planar ramps with locally rounded ramp-flat comers. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Geology." Includes 2 folded plates in back pocket. |
| Physical Description: | xiii, 153 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |