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Some two-dimensional kinematic analyses of the drape-fold concept

David M. Weinberg
David M. Weinberg
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January 01, 1978

The vertical basement-block movements and overlying folds in the sedimentary veneer that characterize the deformation style of the Wyoming province are amenable to simple two-dimensional kinematic analyses. These analyses examine the lateral transport needed when no thickness change of the folded sedimentary rocks occurs, and they are based on simple geometric constructions that approximate the folded shape of the uppermost bedding surfaces of the Mesozoic and Paleozoic sections (about 3,900-m total thickness). Lateral-displacement requirements of these rocks are significantly different, and this difference implies that the rocks on the downthrown basement block are put into a state of shear. Additionally, these differences suggest that significant volume problems are created within the fold during the folding process. The first models show that, within the Paleozoic carbonate section (450 m thick), lateral displacements of the top and bottom bedding surfaces differ by nearly 100% at one point during folding but are nearly identical at other times. Refinements of the simple models indicate that some stratigraphic horizons in folds with 1,200 m or less displacement over vertical faults in the basement may not require large lateral movements. If several bedding-plane detachments were present in the Paleozoic carbonate blocks, volume problems within the hinge zones could be significantly reduced.

Geometrically scaled laboratory specimens were experimentally deformed, and their final geometry is comparable to that of natural counterparts. Comparison of calculated and observed lateral displacements agree within 7%, based on the simplest analytical model, but only agree within 50% for another model.

It is concluded that the kinematic approach to drape folding is useful, because it provides information about the required lateral displacements of large rock masses during folding. It also illuminates other problems that must be investigated before a better understanding of drape-fold structures is possible.

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Figures & Tables


GSA Memoirs

Laramide Folding Associated with Basement Block Faulting in the Western United States

Vincent Matthews, III
Vincent Matthews, III
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Geological Society of America
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Publication date:
January 01, 1978




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