Document Type
Thesis
Abstract
The Neoproterozoic Swift Run Formation is a metasedimentary unit that unconformably overlies Mesoproterozoic granitoid basement in the western Blue Ridge in central Virginia. Metabasalts of the 570-550 Ma Catoctin Formation conformably overlie the Swift Run Formation. The unit is composed of metasiltstone/phyllite, matrixsupported arkosic phyllite, arkosic metasandstone and metaconglomerate, and minor metabasalt. The mineralogy, texture, and sedimentary structures are consistent with fluvial, lacustrine and alluvial depositional environments in a mechanical weatheringdominated setting. The Swift Run Formation’s thickness is highly variable, changing from 0 to ~300 m over distances of a few km. Neoproterozoic topographic highs are preserved where the Swift Run Formation is locally absent. Locally, the Swift Run Formation was deposited in half grabens bounded by NE-striking normal faults. To the east of the main basement-cover unconformity the Swift Run Formation crops out in a series of outliers 3-11 km long and <0.7 km wide. Previous workers have interpreted these outliers to by synclinal infolds or tectonic windows through a supposed Rockfish Valley thrust sheet. Field data is consistent with reverse faults bounding these structures on the SE and unconformities on the NW contacts of these outliers. In this model, NWtranslation of the hanging walls occurred either ductily during greenschist-facies deformation and/or brittlely during the Blue Ridge thrust event. The Swift Run Formation developed a pervasive SE-dipping foliation of moderate to mylonitic intensity during greenschist facies deformation and metamorphism that also caused pervasive NEtrending folds and reactivation of original normal faults. * ar/?Ar ages from syntectonic white mica yield ages from 340-320 Ma, consistent with early Alleghanian deformation. Paleomagnetic analysis for paleolatitude information was inconclusive.
Date Awarded
2008
Department
Geology
Advisor 1
Christopher M. Bailey
Recommended Citation
Gattuso, Adam, "Tectonic Significance of the Late Neoproterozic Swift Run Formation and Basement-Cover Unconformity in the Virginia Blue Ridge" (2008). Geology Senior Theses. William & Mary. Paper 196.
https://scholarworks.wm.edu/geologyseniors/196
