60-37 Constraining Piedmont Chronologies in Appalachia using Protolith Mineralogic Analyses

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

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Abstract:

Understanding the tectonic chronology of the Appalachian Piedmont province is crucial for our model of the development of North America. However, this timeline is complicated by shear zones like the Pleasant Grove - Huntingdon Valley (PGHV) Shear Zone, which could introduce up to 150 km of offset (Valentino et al. 1994). One way to assess the shear zone displacement is to compare neighboring units. In this study, we will do this with the Wissahickon Formation, a classic mica schist bedrock unit located in Pennsylvania, New Jersey, and Delaware. One hypothesis for transporting the Wissahickon onto Laurentia comes from Bosbyshell et al. (2016): the Rosemont Shear Zone and the PGHV Shear Zone transported the material southwest during the Alleghanian Orogeny. Another possibility is that the unit was obducted onto Laurentia and metamorphosed near its current location, named the Potomac Orogeny by Faill (1997). This project will use thin section analyses to assess the protolith compositions of the Wissahickon Formation and nearby Mount Cuba Wissahickon Formation, Peters Creek Formation, and Octoraro Creek Formation. Different protoliths may support the hypothesis from Bosbyshell et al. (2016) that the PGHV Shear Zone transported the Wissahickon from the northeast, while similar protoliths may indicate the Potomac Orogeny preceded the Taconic as proposed by Faill (1997).

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9319

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