Paper No. 170-6
Presentation Time: 9:00 AM-6:30 PM
TESTING KINEMATIC MODELS OF DEFORMATION SEQUENCE IN THE BEAR VALLEY STRIP MINE, EAST-CENTRAL PENNSYLVANIA: A FAULT KINEMATIC AND ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS) ANALYSIS
As part of a broader multidisciplinary study on fold form and 3-D strain distribution of the well-exposed fold train in the Bear Valley Strip Mine of east-central Pennsylvania, we report here some preliminary kinematic and geometric tests on the deformation sequence previously reported from this classic outcrop. The “Whaleback” Anticline in the Bear Valley Strip Mine (BVSM) is a unique locale to test the relationship between general fold form and secondary deformation that results from folding. Strip mining for coal exposed the fold in exquisite detail early in the last century. Modern techniques enable the rapid collection of high-resolution three-dimensional spatial data to produce detailed digital surface models, from which quantitative analysis can be extracted. This abstract focuses on the several generations of mesoscale structures with a well-established chronology that record strain before, during and after BVSM folding. Finally, AMS analyses will hopefully illuminate grain-scale distributed strain in the folded layer, which will be linked to deformation history. Kinematic information was collected from a large population of minor faults, with a focus on constraining cross-cutting and geometric relationships between fault families. Fault populations include sets of conjugate wrench faults and low-angle thrusts (with respect to paleo-horizontal) that appear to be early, and associated with layer parallel shortening (LPS); and conjugate extensional fault systems that produce roughly strike-parallel and transverse grabens that are seemingly developed late, associated with fold tightening. Kinematic fault slip analysis is done on grouped data from locations throughout the mine to invert for shortening direction. These data can then be used to establish a progressive shortening direction history that can be compared to inferred pale-stress/strain axes from proximal AMS sites. Our preliminary data broadly support early models of structural development in this area of the Alleghany Orogeny of early LPS, followed by kink folding, and finally fold tightening. These data will ultimately be mapped on our 3-D model of the BVSM fold system to test relationships between measured strain and fault kinematics with deformation fields predicted by curvature models of the present-day fold form.