A study in extensional tectonics /
| Main Author: | |
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1989.
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| Subjects: | |
| Online Access: | Link to ProQuest copy Link to OAKTrust copy ProQuest, Abstract |
| Abstract: | Boudin wavelength to thickness ratios are determined by: (1) the value of the power-law exponent in the layer, (2) the ratio of layer strength to confining medium strength; and (3) the ease of slip on the layer-medium interfaces. Equant boudins may form in layers with large power-law exponents while boudins with wavelength to thickness ratios of 5 or more may form in layers bounded by weak surfaces. Normal faults in a siltstone layer, bounded above and below by detachments, show a transition from a symmetric reflection pattern to an extensional duplex. Portions cut by normal faults alternate laterally with portions cut by thrusts. Variations in slip on the detachments may have caused alternating extension and shortening. A model of a viscous layer bounded on both sides by weak faults with asperities, confirms this. Where extension was layer-parallel, faults and fault zones form a symmetric reflection pattern. Where extension was non-layer-parallel, this pattern yeilds to an extensional duplex. Theoretical models of shear bands in a Mohr-Coulomb layer show a similar transition. A model of strain softening or strain hardening plastic layers shows that hardening favors long wavelength necks while softening favors shear zones. A model of deep, frictionless, moderate angle ramps on both normal faults (normal ramps) and thrust faults (thrust ramps) shows that ramps migrate in the direction of hanging-wall flow, but do not change shape. Footwall stresses have the same magnitude as hanging-wall stresses but footwall strain-rates may be reduced. A normal ramp causes vertical extension and horizontal shortening in the hanging-wall and the footwall. Both a hanging-wall syncline and a footwall anticline form. Local fracturing is favored at the ramp. A thrust ramp causes stresses and strain-rates of the opposite sign. Both a hanging wall anticline and a footwall syncline form. Local fracturing is favored on flats adjacent to the ramp. An old geometric model of flexural folding above a listric normal fault implied simple shear in one direction coupled with layer-parallel shortening and produced large area balance errors. A new model assumes shear parallel to a marker bed that folds during deformation and elliminates the error. |
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| Item Description: | "Major subject: Geology." Typescript (photocopy). Vita. |
| Physical Description: | xiv, 200 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |