Geology of part of the eastern Blue Ridge, northeast Georgia and the adjacent Carolinas

Author

Janet L. Hopson

Date of Award

5-1994

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geology

Major Professor

Robert D. Hatcher Jr

Committee Members

Harry Y. McSween, Richard T. Williams, Matthew Mauldon

Abstract

Detailed geologic mapping in the Lake Burton and Hightower Bald quadrangles of northeastern Georgia reveals the eastern Blue Ridge may be subdivided into four major fault-bounded tectonic units, each characterized by distinct differences in stratigraphy. Mafic rocks of the Lake Burton complex and associated metasedimentary rocks of the Otto Formation are exposed in a complex window bounded by the Chattahoochee fault to the southeast and the Soque River fault to the northwest. The Chattahoochee thrust sheet is composed of Late Proterozoic basement overlain by metasedimentary sequences of the Tallulah Falls Formation. The Soque River thrust sheet consists of metaigneous and metasedimentary rocks of the Coweeta Group, which are preserved in a macroscopic synform. This synform is truncated to the north by the Shope Fork fault. Rocks exposed north of the Shope Fork fault are predominantly metasedi-mentary sequences and associated mafic rocks of uncertain stratigraphic affinity; they have been tentatively correlated with portions of the Tallulah Falls Formation and Coweeta Group, but may also contain basement units. The crystalline rocks of the eastern Blue Ridge reflect a complex deformational history involving multiple episodes of folding accompanied by moderate- to high-grade metamorphism. All of the tectonic units experienced similar deformational histories and contain up to six genera-tions of folds. Early folding was coeval with upper amphibolite facies metamorphism, whereas subsequent folds and faults developed as temperatures and pressures diminished, and successive generations of folds formed by distinctly different mechanisms. Early folds are typically isoclinal passive- to flexural-flow folds, whereas later folds are broad open flexural-slip folds. The charac-ter of associated foliations also changes with time; early foliations include penetrative gneissic banding and schistosity, whereas later fabrics are typically spaced crenulation cleavages. Detailed geologic mapping and structural analysis indicate that faulting in the crystalline rocks of the eastern Blue Ridge did not develop in a simple forward (northwest)-propagating manner. Structural and metamorphic constraints on the timing of faulting suggest that "out-o-fsequence" faults are common, i.e., younger faults developed in the hanging walls of older faults or older faults are truncated in the footwalls of younger faults. Macroscopic map patterns indicate the following relationships:

1. The Chunky Gal Mountain fault is crosscut by the pre- to synmetamorphic Hayesville fault.

2. The Soque River fault is truncated by the Shope Fork fault.

3. The Chattahoochee fault overlaps the Soque River fault. Structural and stratigraphic criteria indicate the core fault framing the Tallulah Falls dome developed as a minor fault entirely within the hanging wall of the Chattahoochee fault. The development of the core fault, recumbent fold nappes of the Tallulah Falls dome, shear zone 1 (located along the southeastern flank of the Tallulah Falls dome), the Chattahoochee fault, and possibly the Soque River fault can be viewed as a progressive post-metamorphic peak event leading to the development of a variety of northwest-vergent structures. Dextral strike-slip fabrics of the Dahlonega gold belt postdate formation of these structures. The relationship of these fabrics to similar features to the southeast is uncertain, but they may reflect the early stages of dextral shearing observed in the western Piedmont (Brevard fault zone) and eastern Blue Ridge (shear zone II (located along the southern flank of the Tallulah Falls dome)). The Alleghanian Rosman thrust fault, which bounds the eastern Blue Ridge to the southeast, post dates dextral shearing and is the youngest major fault observed in this region. The Warwoman and Lake Rabun lineaments are filled with siliceous cataclasite, but exhibit only minor displace-ment. These lineaments are thought to be roughly coeval with Mesozoic diabase dikes. Rocks of the Lake Burton mafic-ultramafic complex are preserved in a synform cored by amphibolite and associated metasedimentary rocks. The synform is incompletely framed by metagabbro and coarse-grained amphibolite to the north and southeast. All of the mafic rocks are interpreted to have igneous protoliths based on field relations, textural criteria, and geochemistry. Metagabbro of the northern plutonic sequence is interpreted to have formed from the same parent magma as amphibolite of the central layered sequence. Metagabbro of the southern plutonic sequence is geochemically different from the rest of the Lake Burton complex, suggest-ing it may have experienced a different petrogenetic history. Tectonic discrimination diagrams suggest the metavolcanic rocks of the central layered sequence may have originated in an island arc.

Recommended Citation

Hopson, Janet L., "Geology of part of the eastern Blue Ridge, northeast Georgia and the adjacent Carolinas. " PhD diss., University of Tennessee, 1994.
https://trace.tennessee.edu/utk_graddiss/10370