Date of Award

8-2012

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Robert D. Hatcher, Jr.

Committee Members

Harry Y. McSween, Micah J. Jessup

Abstract

Detailed geologic mapping in the central Georgia Inner Piedmont has revealed a plutonic complex in the Cat Square terrane (CST) between the Brindle Creek and Towaliga faults ~80 km SE of Atlanta. The complex has an area ~235 km2 and is composed of two distinct mappable granitoids. The High Falls Granite (HFG) is a Siluro-Devonian (424-380 Ma) porphyritic granite with characteristic blocky microcline megacrysts. The Indian Springs Granite (ISG, 313-299 Ma) has an equigranular, fine- to medium-grained texture. Some foliation in the HFG is concordant with regional trends, but a relict magmatic or secondary tectonic foliation was also observed in many parts of the pluton.The location of two terrane boundaries was delineated during field mapping. The Brindle Creek fault and terrane boundary is a narrow (<30 >m) mylonite zone that accommodated oblique-dextral strike-slip displacement likely during the Neoacadian orogeny. The Towaliga fault zone and terrane boundary formed as a dextral strike-slip fault, producing a wide (up to 1 km) mylonite zone during the Alleghanian orogeny. The Walker Top Granite (WTG, 407-357 Ma) in the North Carolina CST is roughly the same age, and is mineralogically, texturally, and geochemically similar to the HFG. This suggests the HFG and WTG may be consanguineous. Crystallization ages of the Walker Top Granite have been used as a proxy for the closure of the Cat Square remnant ocean basin in the northern Inner Piedmont. Geochemical and geochronologic data suggest that the emplacement of the oldest portion of the HFG may not be coeval with the closing of the southern end of the Cat Square basin. Instead, the oldest portions of the HFG may have been generated above a subduction zone prior to the Acadian/Neoacadian collisional event, while the youngest portions of the HFG could have been generated by crustal anatexis when the Carolina superterrane was obducted onto the Laurentian + Taconian margin. If the entire HFG batholith was generated by anatexis, obduction of the Carolina superterrane must have occurred well before the 424 Ma crystallization age of the oldest sample of HFG, requiring revision of tectonic models for the southern Appalachians.

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Plate 1 Geologic Map

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