Semester

Spring

Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Jaime Toro.

Abstract

Near the Allegheny Structural boundary between the Appalachian Plateau and the Valley and Ridge Province of the West Virginian Appalachians lie four major thrust faults: the Pulaski, Saltville, Narrows, and the St. Clair all of which are associated with the Alleghenian Orogeny. Of these major thrusts, the St. Clair thrust fault represents the boundary of the Allegheny Structural Front and is one of the few major thrust faults that are exposed at the surface in the Appalachians of West Virginia.;The St. Clair thrust fault represents an example of fault-propagation folding. Within fault-propagation folding, trishear deformation and fault-bend folding can be linked to deformation. Kinematic modeling was conducted using Midland Valley's 2DMove software package to recreate the geometry of the fault and its associated fold. Modeling software was also used to determine the effects of individual parameters within trishear deformation. The parameters examined include the propagation-to-slip ratio, trishear apex angle, trishear angle, angular shear, and the number of trishear zones. Of these parameters, the propagation-to-slip ratio has the most impact on the geometry of the footwall fold. The propagation-to-slip ratio determines how much the fault propagates through the strata and also dictates what type of fold develops. A P:S ratio that is zero results in the formation of a detachment fold, a small P:S ratio results in a trishear fault-propagation fold, and a large P:S ratio results in the development of a fault-bend fold.;Through surficial mapping and kinematic modeling, it has been concluded that the St. Clair thrust fault formed in two steps involving fault-propagation folding. The overturned syncline in the footwall, the Glen Lyn Syncline, was formed by trishear deformation, with a propagation-to-slip ratio of approximately 0.25, as the fault slowly propagated through the strata. Then, the fault broke through to the surface due to an increase in the P:S ratio and a second mode of deformation occurred, fault-bend folding. This combination of trishear deformation and fault-bend folding created the present-day geometry of the St. Clair thrust fault and its associated structures.;By recreating the sequential cross-sections, it was possible to determine the amount of displacement needed for each cross-section. The southwestern most cross-section was modeled and a minimum displacement value of approximately 2300 meters was needed. Erosion has removed the hanging wall cut-off; therefore the total displacement is not constrained.;Two additional cross-sections to the northeast show evidence of an anticline in the hanging wall. The values of deformation in these cross-sections are more representative of the actual amount of displacement needed. Displacement values decreased from 7500 meters to 6700 meters toward the northeast, or by about 10%.

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