Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Map in back pocket. Vita. Abstract. Includes bibliographical references (leaves 79-84). Also available via the Internet.

The Fries fault zone south of Riner, Virginia is marked by a ductile, greenschist-facies thrust that places Middle Proterozoic gneiss over deformed Late Proterozoic(?)—Early Paleozoic rocks of the western Blue Ridge province. This work presents an analysis of the field relationships and finite strain patterns within the fault zone, and further relates these features to an interpretation of its structural framework. A geologic map of the fault zone is provided, in addition to more detailed lithologic descriptions within the text. Noteworthy aspects of the field geology include: (1) the discovery of a reasonable protolith to the mylonitic Little River Gneiss, which could previously only be inferred; and (2) the recognition of a varied lithologic assemblage that is considered to be correlative with the Pilot Gneiss, which is exposed along strike within the Brush Creek anticlinorium. Kinematic analysis of tectonic fabrics within the Little River Gneiss, Pilot Gneiss, and Chilhowee Group suggest that the fault zone developed in response to southeast—northwest shortening, accommodated by general noncoaxial flow, which produced a top-to-the-northwest sense of shear at all scales of observation. However, it is evident that the original stratigraphic anisotropy within the Chilhowee Group effectively partitioned the coaxial and noncoaxial components of strain. Additional finite strain analyses within the Chilhowee Group, including the correlation of R_f/Ø data with quartz c-axis fabrics, indicate that there is considerable variation in the geometry of finite strain along the fault zone. Whereas flattening strains appear to predominate, it is evident that domains of constructional strain and plane strain are localized near the nose of the Brush Creek anticlinorium. These data are considered to support an interpretation in which the Pilot Gneiss and Chilhowee Group were metamorphosed and folded into a doubly-plunging antiform during the Taconic orogeny (ca. 480-435 Ma), and that progressive shortening of the Laurentian continental margin during this interval caused the Little River Gneiss to be uplifted along the Fries fault. The present structural framework of the Fries fault zone south of Riner, Virginia is thus considered to represent a northwest-vergent fold composed of Late Proterozoic—early Paleozoic strata, which is transected by the base of the Little River Gneiss. / Master of Science

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. / Master of Science