Masters Theses

Date of Award

5-2010

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Robert D. Hatcher, Jr.

Committee Members

Micah J. Jessup, Theodore C. Labotka

Abstract

The Inner Piedmont (IP) is the Neoacadian migmatitic orogenic core of the southern Appalachians, exhibiting the widest area of high-grade metamorphism; regional upper amphibolite facies with isolated pods of granulite grade metamorphism. Peak P-T conditions in central GA reached 4.0-7.6 kbars and 630-715 ̊ C. The Brindle Creek fault (BCf) separates high-grade metasedimentary rocks of the eastern Tugaloo terrane (Tt) and Cat Square terrane (CSt). The Tt consists of the Neoproterozoic to early Paleozoic(?) Tallulah Falls Formation, Chauga River Formation, and the Mid-Ordovician Poor Mountain Formation, intruded by Early to Middle Ordovician granitoids. The CSt consists of Siluro-Devonian metasedimentary rocks, such as sillimanite-schist, biotite gneiss, amphibolite, and minor calc-silicate, intruded by Acadian-Neoacadian plutons.

Original termination of the CSt was mapped by the USGS just south of Athens, GA, against the central Piedmont suture; however, new evidence from aeromagnetic anomalies and detailed geologic mapping revealed that the CSt and BCf extend into central GA. The BCf truncates a suite of curved magnetic anomalies on the aeromagnetic map. The curved anomalies that truncate against the linear feature may represent the Neoacadian deflection of the IP southwestward along the crustally weak Brevard fault zone. Another prominent lineament was identified southeast of the BCf; detailed geologic mapping revealed an additional thrust sheet in the CSt.

Mesozoic brittle reactivation of the late Paleozoic dextral Towaliga fault was also identified striking NE-SW through the field area. Multiple episodes of movement were observed in outcrop and at the micro-scale, defined by crosscutting fracture sets. Low temperature quartz mylonite (350-450 ̊ C) may signify continued shearing of the IP into the late Alleghanian orogeny.

A felsic plutonic suite extends the length of the field area, consisting of three distinct granitoids: (1) an older biotite-rich megacrystic granite with megacrysts of K-feldspar; (2) a weakly foliated medium to coarse grained inequigranular granodiorite; and (3) a younger non-foliated fine-grained granodiorite. Analysis revealed that granitoids from central GA are similar texturally and petrographically with granitoids from NC’s CSt. Further whole-rock geochemical analysis revealed that these rocks share similar REE, trace element, and tectonic discriminate patterns. The most important point garnered from the trace element and REE patterns in spider diagrams, such as similarities in peaks and troughs, is that they must share either a common parent, process, or contaminant.

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