Masters Theses

J. Bryan Paul

Date of Award

12-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Nicholas B. Woodward

Committee Members

Kenneth Walker, Don Byerly, Ranaye Dreier

Abstract

The Saltville fault is a regional thrust of the Valley and Ridge which extends approximately 550 km from Virginia to Georgia. The fault and its associated features are well exposed at Sharp Gap in Knoxville, Tennessee. At this location the fault zone is thick and local thrust geometries are complex. Four specific topics are investigated; (1) the structural geometries, (2) the morphology of the fault zone, (3) the deformation processes during thrusting, and (4) conditions within the fault zone during thrusting.

At Sharp Gap, exposures on 1-275 and Bruhin Road reveal at least three imbricates in the Rome Formation and Pumpkin Valley Shale of the Saltville sheet (hanging wall). On Bruhin Road the imbricates are upright and dip steeply southeast; on 1-275 the upper two imbricate slices are overturned, dipping northwest because of rotation related to folding of the Saltville thrust sheet.

Three folding events deformed the hanging wall at Sharp Gap. F1 folding, concurrent with formation of the upper imbricate; F2 fold ing, coaxial with F1 and concurrent with emplacement of the lower imbricate and presumably the Saltville sheet onto its Knox footwall; and F3 folding, with fold axes developed normal to thrust transport direction, concurrent with deformation that overturned the imbricate fan on 1-275 and only occurring locally.

The Saltville fault zone is thick, ranging from 7.4 m (1-275) to 10.2 m (Bruhin Road). The fault zone is divided into six separate subzones based on lithology and texture. The subzones are best developed on 1-275 and several also occur on Bruhin Road. Subzones A and B are composed of deformed Rome sediments. Subzone C is a footwall horse broken from the Knox during thrusting. Subzones D and E are composed of Rome dolomite and elastics, whereas subzone F is composed of deformed Rome sediments that are extremely strained. Cross-cutting relationships may be used to demonstrate that the lower five subzones were emplaced prior to uppermost subzone, subzone F. A gross distinction in the bulk fabric and textures also exists between the lower five subzones and subzone F. The lower subzones are described as random-fabric cataclasites, whereas subzone F is a foliated cataclasite. This difference in texture probably reflects differing conditions of formation.

Cataclasis and pressure solution were the deformation mechanisms within the fault zone during thrusting. Cataclasis is a sequential process of brittle fracture which ultimately leads to strain softening with grain size reduction. Cataclasis probably dominated deformation until grains became less than 100 μm. Pressure solution was the dominant deformation mechanism below 100 μm.

Two additional processes were recognized in the fault rocks: (1) Syntectonic dedolomitization, and (2) extension of the fault zone rocks by R1 Riedal shears. Dedolomitization of the cataclasite is enhanced by the brittle fracturing, the presence of clays, and pore fluids. The dedolomitization during thrusting may weaken the thrust plane significantly by changing the material properties of the deforming rock. Riedal shear deformation by brittle extension provides a mechanism for extending the fault zone during or after strain softening and ductile flow. The effects of this process could result in extension of the cataclasite lubricant at the base of thrust sheets over 100 times with 25 km displacement.

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