Three-dimensional kinematics and geometries of thrust-related folds
Wilkerson, Marlon Scott
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https://hdl.handle.net/2142/19711
Description
Title
Three-dimensional kinematics and geometries of thrust-related folds
Author(s)
Wilkerson, Marlon Scott
Issue Date
1991
Doctoral Committee Chair(s)
Marshak, Stephen
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Language
eng
Abstract
This dissertation examines three-dimensional kinematics and geometries associated with the development of thrust-related folds. First, the complex relationship between fold geometry and along-strike changes in fault displacement and fault shape was considered by extending equations describing conventional two-dimensional folding models into the third dimension. Graphs of these equations predict relationships between fold axial-surface angles in map view and fault-ramp dip and fault displacement in cross section. Differences in model structure-contour map patterns are sufficient to distinguish between model fold types. Second, the along-strike geometrical changes of a blind duplex in the frontal Ouachita fold-thrust belt, Oklahoma were studied. Subsurface mapping based on interpretations of seismic-reflection and well data indicates that the duplex is substantially larger than previously thought. Changes in three-dimensional geometry of folds associated with this duplex occur due to modification by lateral and oblique fault ramps and a tear fault. The spatial rate of change in displacement based on interpretations from this duplex and other non-metamorphic fold-thrust belts is expressed by ($\Psi$), the angle of differential transport. I find that a value of $\Psi$ = 32$\sp\circ$ is the empirical limit of differential transport a non-metamorphic thrust sheet can accommodate before it loses coherency and becomes segmented by tear faults. Third, computerized tomographic (CT) images through sand models were used to investigate strain patterns that form in response to movement over oblique fault ramps. Map-view deflections of initially straight marker lines within sand layers suggest that layers truncated by the right-stepping oblique ramp systematically deflect counter-clockwise, whereas marker lines in overlying layers radially diverge from the model center. These differences in displacement most likely reflect variations in vertical stress and imply that actual thrust sheets may display different displacement trajectories depending on vertical position within the thrust sheet. In support of this concept, a model describing the maximum shear stress vector on an oblique fault ramp illustrates a similar depth dependence.
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