Masters Theses

Date of Award

12-2006

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Robert D. Hatcher, Jr.

Committee Members

Harry Y. McSween, Theodore C. Labotka

Abstract

Detailed geologic mapping of the Gilreath 7.5-minute quadrangle recognizes the northernmost continuation of the Brindle Creek fault, a terrane boundary that separates Neoproterozic-Ordovician metasedimentary and metavolcanic rocks of the western Tugaloo terrane (western Inner Piedmont) from Silurian-Devonian metasedimentary rocks and Devonian-Mississippian anatectic granitoids of the Cat Square terrane (eastern Inner Piedmont). The Brindle Creek fault is folded in the study area and exposes the Ordovician Brooks Crossroads Granite in a reentrant. Low high-field strength element concentrations and a flatter rare earth element patterns typical of western Inner Piedmont granitoids, support a footwall setting for the Brooks Crossroads Granite.

New geochemical analyses of Inner Piedmont amphibolites reveal a mixed volcanic arc and E-type MORB signature for eastern Inner Piedmont amphibolite. These preliminary data suggests the Cat Square terrane may have originated in a back-arc basin influenced by E-type MORB volcanism during the waning stages of Middle Ordovician-late Silurian volcanic arc magmatism in the western Inner Piedmont.

Subduction of the Inner Piedmont beneath a W- to NW-advancing Carolina superterrane resulted in possible early kyanite-grade metamorphism (7.0 to 8.7 kbars and 630 to 695°C), followed by sillimanite I and II grade metamorphism. High-temperature, upper amphibolite facies metamorphic conditions, in conjunction with pervasive migmatization, the presence of meso- and map-scale sheath folds, ubiquitous top-to-the SW shear-sense indicators, and protomylonitic to ultramylonitic deformation fabrics, suggests Inner Piedmont thrust sheets deformed as a viscous mass during SW-directed flow in a sub-simple shear to extreme simple shear stress regime. These data support models that reconcile the SW-directed arcuate trend of Inner Piedmont stretching directions, with a tectonically forced flow path resulting from oblique subduction of Inner Piedmont thrust sheets beneath the W- to NW-advancing Carolina superterrane. Flow was deflected to the southwest as Inner Piedmont thrust sheets buttressed against a primordial Brevard fault zone. Truncation of the Popular Springs and Big Warrior sheath folds against the Brindle Creek fault indicates SW-directed displacement of ductile, Inner Piedmont crystalline thrust sheets was prior to final emplacement of Cat Square terrane rocks.

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