Masters Theses

John H. Weitz

Date of Award

3-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

N. B. Woodward

Committee Members

Kula Misra, Don Byerly

Abstract

Mesoscopic fabric analysis in a portion of the Middle Ordovician Tellico-Sevier belt indicates that relative deformation intensity increases southeastward toward the overlying Great Smoky thrust. Bed-parallel shortening (early), mesoscopic folding, spaced cleavage and contraction faulting developed during a single, partially noncoaxial deformation during thrust sheet emplacement. Buckle folding and associated contraction faulting were the predominant means of lateral shortening. Irregular, modified concentric, precleavage folds developed above a major décollement dominantly by flexural slip, modified by strain at the hinges, flattening, and pressure solution cleavage. Cleavage often transects folds, in which case it is subvertical while the axial plane is inclined in the direction of transport on the associated dominant set of contraction faults. Cleavage transection angle ranges from 0 degrees (axial planar) to more than 45 degrees. Cleavage development was related to second order and small-scale contraction faulting, which occurred in late stages of folding. Mechanisms for producing folds transected by cleavage included: (a) overprinting of irregular folds by cleavage, (b) a fault-controlled local reorientation of strain axes prior to cleavage development, and (c) fault drag-induced rotation of a fold core prior to cleavage development.

The shortening axis varied from southeast dipping in the northwest (above a postulated ramp in the Saltville fault), through horizontal to northwest dipping in the central and southeastern portions of the shale belt. A minimum of 23 percent buckle shortening was calculated for the north western half of the Tellico-Sevier belt.

The Douglas décollement underlies the deformed Middle Ordovician shales and is exposed at the northwest boundary of the shale belt. It is localized at a zone of major ductility contrast at the contact between Blockhouse shale and under lying carbonates. Location of the fault coincides with a previously hypothesized décollement having 20 kilometers of slip. Aside from early bed-parallel shortening, most deformation within the shale belt occurred during emplacement of the Douglas décollement. A high angle fault, possible representing a splay from this décollement, causes repetition of the lower mudstones and siltstones at the surface. An unmapped low angle thrust may underlie a large, second order, nearly recumbent anticline.

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