Geometry, mechanisms, and mechanics of deformation in a Laramide thrust sheet.
| Main Author: | |
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1987.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | The Washakie thrust system consists of Precambrian-cored anticlines thrusted 8 to 12 km to the southwest along the EA and Black Mountain thrusts. The thrusts dip 20° to 30° to the northeast and may steepen at depth in the Precambrian rocks. The frontal fold of the thrust sheet developed ahead of a wide zone of northeast-dipping thrusts in the Precambrian rocks. This frontal fold may be a ramp anticline above a bend in the EA thrust or may be a monocline ahead of the EA and Black Mountain thrusts. Structures within the thrust sheet consist of thrusts which dip to the northeast, reverse faults which dip steeply to the southwest, folds which plunge to the northwest, and steep faults which strike north-south. Precambrian granitic gneisses in the thrust sheets deformed by faulting. Feldspars sustained most of the deformation by slip along cleavage fractures. Quartz fractured and experienced minor amounts of crystal-plastic mechanisms. Fluids aided in the healing of the quartz fractures and the syntectonic alteration of feldspars to phyllosilicates. Foliated cataclasite textures developed at temperatures under 350°C with water present. Theoretical models for deformation near a discrete shear crack and the bending and buckling of a layer above a thrust show that synthetic faults with shallow dips and antithetic faults with steep dips form near a thrust tip. Bending of a layer above a fault results in an asymmetric anticline-syncline pair or monoclinal flexure above reverse faults. A large amount of slip decreases fold asymmetry and decreases fold amplitude. Buckling of the bent layer only slightly modifies the fold shape when free slip at the base of the layer occurs, or when the substrate is much weaker than the layer. Thrusts in the footwall and hanging wall of the EA and Black Mountain thrusts may be sub-parallel synthetic faults, and the steeply dipping reverse faults in the hanging wall may be antithetic secondary faults associated with the underlying thrust. |
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| Item Description: | Typescript (photocopy). Vita. Nine maps on folded leaves in pocket. |
| Physical Description: | xiv, 217 leaves, 9 folded leaves of plates : illustrations, maps ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 182-190). |