Experimental, plane strain deformations of plasticene and clay multilayers containing pre-cut ramps, have generated broad, flattopped to narrow, rounded fold geometries. Initial boundary conditions, including lubrication, end effects, and the ratio of mechanical unit to overburden rigidity determine proportions of translation and amplification which operate during the development of three main and two hybrid fold forms. Each fold geometry exhibits a unique strain pattern, but generally shows highest strains on overturned limbs, and above ramp regions. Lowest strains occur in footwall layers and between ramps. During folding, strain is produced by combinations of bending, rotation, flexural slip, and flexural flow. Layer parallel shortening strain transpires primarily before fold formation above ramps. Fold forms are dictated by the sequence of mechanisms, and proportional changes in strain mechanism magnitudes. Flexural slip predominates in flat-topped forms, while flexural flow prevails in rounded forms. Bending strain is minor in all geometries. Ellipse long-axis orientations define cleavage patterns which are more complex than proposed theoretical patterns due to variations in analogue lubrication and layer anisotropy. Analogue strain patterns may have potential for use in delineating subsurface folds and their history of development.
An investigation of strain and mesoscopic structure was undertaken in the Burkes Garden dome, located in the Narrows thrust sheet in southwest Virginia to delineate the dome's history of formation. The Burkes Garden dome is a broad, flat-topped structure containing two mesoscopifold sets trending N55E and N62W, subregional (N50E) and local (outlines dome shape) cleavage orientations, northwest and southeast dipping faults, and northwest and southeast verging folds. Strain values ( R = 1.1 - 1.5) are low and show little variance in the dome. Regional and mesoscopic structure, and strain values suggest dome development results from duplex formation in the Cambro-Ordovician dolomite/limestone package below the overlying Narrows thrust sheet. Duplex formation can be continued down strike by varying the number of horses and stable ramp position. Differential amounts of movement along the Saltville fault and/or lateral ramps at depth may have produced weak localized strike-parallel compression, resulting in northwest trending folds, and local cleavage orientations. Sheet lock-up probably occurred late during dome development producing northwest dipping faults, and southeast verging folds. / M.S.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106257 |
| Date | January 1983 |
| Creators | Bajak, Doris M. |
| Contributors | Geology |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | x, 120 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 10774008 |
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