Document Type

Thesis

Abstract

The contact between Mesoproterozoic granitoid gneisses and metasedimentary rocks of the Neoproterozoic Lynchburg Group on the southeastern flank of the Blue Ridge anticlinorium in central and northern Virginia has traditionally been interpreted as a southeast dipping unconformity. To test this I mapped approximately 20 km” in the eastern Blue Ridge near the Tye River in Nelson County, Virginia. The Lynchburg Group consists of metamorphosed arkosic sandstone, greywacke, siltstone, and cobble conglomerate deposited in an alluvial to deep-water rift setting. The basement-cover contact dips steeply to the northwest and places basement rocks structurally above the Lynchburg Group. At the contact, bedding in metasiltstone and fine-grained metasandstone dips steeply to the northwest, parallel to the contact. Sedimentary structures and regional patterns suggest that bedding is overturned throughout the region. Greenschist facies mylonite zones occur within the basement, near the contact, dip steeply to the northwest, have down-dip mineral elongations and display top-to-the southeast (reverse) kinematic indicators. Although, these observations are consistent with a northwest dipping reverse fault, rocks directly at the contact are unconformable and not in fault contact. The overall structure of the Lynchburg Group is an overturned homocline with beds consistently dipping steeply to the northwest. The stratigraphy, as mapped by Wehr (1985), in northern Virginia extends as far south as the Tye River. The steeply dipping basement-cover contact along the Tye River in Nelson County is interpreted to be an unconformity although regional patterns the eastern Blue Ridge may be more complex.

Date Awarded

2003

Department

Geology

Advisor 1

Christopher M. Bailey

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