Mechanics of thrust-ramp spacing /
| Main Author: | |
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1990.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Data measured from published cross sections and maps show that the spacing of major structures in some fold-and-thrust belts is systematic. In thrust belts the spacing between frontal ramps decreases to the foreland. In fold belts there is a more regular spacing of folds regardless of position. This contrast in spacing may be in part attributable to differences in stratigraphy, sequence of deformation, and strength of the decollement. Utilizing these observations, along with the recognition of a continuum between the contrasting styles of fold belts and thrust belts leads to a hypothesis that folding instability during the earliest shortening in a foreland belt will localize faulting. To support this study, I have identified and characterized the structural lithic members and units of the Idaho-Wyoming-Utah thrust belt. The identification of structural units is based primarily on field work from within the Absaroka, Darby, and Prospect thrust sheets. Each thrust sheet is divided into two or three structural units: a lower weak decollement zone, and a middle strong unit-upper cover unit. A model for the development of a folding instability in a layered sequence suggests that the thrust sheets studied is best modelled as two units, and the decollement zone may be much weaker then expected. The thermal and compaction history of the decollement horizon may account for variations in strength between the thrust sheets. Additionally, there may not be a one-to-one correspondence of fold wavelength and thrust-ramp spacing. To investigate the effect of emplacing a thrust sheet, I have developed elastic, plane strain models of the state of stress in the footwall beneath the last formed, or most forward thrust ramp. These models include the load of an overriding thrust sheet and a synorogenic sedimentary wedge. The location of failure in the footwall occurs where there is a favorable tradeoff between the spatial rates at which mean stress and differential stress decrease toward the foreland. The model predicts that faults nucleate above the basal decollement and that fault trajectories should have a flat-and-ramp geometry. Pore pressures may affect the location of failure under some conditions. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Geology." |
| Physical Description: | xii, 116 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |