Doctoral Dissertations

Date of Award

6-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Dietrich Roeder

Abstract

An interpretation of a COCORP seismic reflection profile indicates that the Great Smoky thrust, cropping out in Southeast Tennessee, has a slip of about 140 km. Eight structure sections, drawn to the base of Paleozoic deformation, straddle the trace of the thrust and cover an area of about 12,000 square km. The sections show that the Great Smoky thrust cuts the most internal (southeasterly) structures of the Valley and Ridge thrust system, but was in place prior to movement of the Saltville fault in that system.
The section suggests that several thrusts internal to the Great Smoky fault (Miller Cove, Dunn Creek, Brushy Mountain, and others) belong to a sled runner thrust complex (COCORP thrust system) similar to the Valley and Ridge. The basal detachment in this complex was the Great Smoky fault, and, in Northeast Tennessee, the Pulaski fault.

The CGCORP thrust system differs from the more external Valley and Ridge thrust system in that it dismembers structures formed by polyphase, at least partly early Paleozoic, deformation. Pre-, syn-, and post- foliation structures are cut obliquely (map view) and discordantly (cross section) by elements of the COCORP thrust system along its external limit of outcrop.

In the internal portion of the western Blue Ridge, relations of folds to COCORP thrusting are poorly documented, but several tectonic events are broadly synchronous with regional metamorphism. In particular, the Greenbrier fault, considered premetamorphic because it does not affect metamorphic isograds, postdates two phases of major folding. The dominant foliation in the area is axial planar to the earlier of these folding phases. In the Murphy area, however, the dominant and apparently earliest foliation is axial planar to a major structure which clearly folds isograds.

A stratigraphic model for upper Precambrian to lowest Cambrian sediments in the Blue Ridge suggests that the Chilhowee, Walden Creek, Snowbird, and Great Smoky groups are partly facies equivalent strata. This model is based on a lower Ordovician or younger age of the Murphy marble and the assumption that the floor of the basin descends monotonically southeastward. Strike of facies boundaries, in palinspastic restoration, is east-west, or as much as 30 degrees more easterly than the strike of faults of the COCORP thrust system. In its restored position, the sedimentary wedge can be tied to a wedge of autochthonous sediments beneath east-central Georgia, evident in an interpretation of COCORP seismic reflection data. There is rough correspondence between the tapered edge of the sediments and a prominent gravity gradient.

In thin-section, rocks of the Great Smoky Mountains and foothills, ranging from unmetamorphosed to the garnet zone of metamorphism, show less increase in grain size of layer silicates than expected. However, differences in character of both the main foliation in particular areas, and less obvious foliations, suggest increasing mobility of silica and other constituents and increasing dominance of lattice diffusion over grain-boundary diffusion in rocks deformed at higher temperatures

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