The Fries Fault near Riner, Virginia: an example of a polydeformed, ductile deformation zone

The Fries Fault, a 1.2-2.3 km wide zone near Riner, is a major tectonic discontinuity in the Blue Ridge geologic province, characterized by progressive stages of continuous ductile deformation. Trending northeast with a shallow to moderate southeast dip, this fault juxtaposes Little River Gneiss on the southeast against Pilot Gneiss and the Chilhowee Formation to the northwest. A 0.8-1.2 km wide subzone of protomylonite within the Little River Gneiss grades into a 0.5-1.0 km wide mylonite subzone, the latter containing narrow bands of phyllotactic ultramylonite ranging in width from centimeters to tens of meters. Mylonitization is reflected by a marked reduction in grain size, elongation of quartz and fracturing of feldspar, all concomitant with the development of a mylonitic foliation (S_m). Ductile deformation processes involving grain elongation, recovery and recrystallization, combined with chemical processes (primarily pressure solution), are the dominant strain-accommodation mechanisms in the formation of S_m. Rocks within the fault zone have undergone four phases of Paleozoic deformation. An early S₁ foliation has been nearly completely transposed by S_m(S₂), which dominates across most of the area. The development of S_m was accompanied by a retrogressive metamorphism that altered basement rocks from lower amphibolite to greenschist facies. Chilhowee Group rocks remained at lower greenschist facies. Post-faulting deformation produced an S₃ crenulation cleavage associated with northeast trending, overturned F₃ folds. Subsequent refolding produced open, northwest trending F₄ folds. Although the bulk deformation is progressive simple shear, flattening is increasingly dominant during the later stages of deformation.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Geological Sciences

Department dc:contributor.department

Geological Sciences

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1979

Author dc:creator

• Kaygi, Patti Boyd

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/53821

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/53821