Date Thesis Awarded

5-2009

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Geology

Advisor

Christopher M. Bailey

Committee Member

Brent Edward Owens

Committee Member

Scott Southworth

Committee Member

Stuart Hamilton

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, matrix-supported 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 weathering-dominated 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, NW-translation 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 NE-trending folds and reactivation of original normal faults. 40Ar/39Ar ages from syntectonic white mica yield ages from 340-320 Ma, consistent with early Alleghanian deformation. Paleomagnetic analysis for paleolatitude information was inconclusive.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

Comments

Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.

GattusoAdam2009-Plate.pdf (58956 kB)
Plate -- Geologic Map of Central Western Albemarle County, Virginia

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