Masters Theses

Date of Award

5-2013

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Micah J. Jessup

Committee Members

Robert D. Hatcher, Jr., Theodore C. Labotka

Abstract

Field mapping, microstructural analysis, and electron microprobe analysis were performed on rocks from the Bryson City and Ela domes, North Carolina, to help constrain the tectonic history of the region. The domes are en echelon northeast-trending antiformal structures formed by two perpendicular sets of folds. They are bounded by the Greenbrier fault, which forms a ductile shear zone that juxtaposes the Great Smoky Group in the hanging wall with Grenville basement in the footwall. Isoclinal folds (F2) and axial planar foliation (S2) characterize the regional deformation (D2). Inter- to syn-kinematic porphyroblasts (relative to D2) of kyanite, staurolite, and garnet grew during Taconic Barrovian metamorphism (M2). Compositional maps of garnet yield Ca and Mn zoning patterns that are consistent with multiple stages of garnet growth. Pressure-temperature estimates, calculated using THERMOCALC v3.33, indicate that the Great Smoky Group reached conditions of 667 degrees Celsius and 9.2 kbar. A high-strain mylonite zone (S2b) near the contact between the Great Smoky Group and the Greenville basement is parallel to the regional foliation (S2). Mineral stretching lineations trend northeast-southwest around the margins of both domes. Rotated porphyroblasts indicate that shear zone formation (S2b) post-dated Barrovian metamorphism. Quartz deformation mechanisms record shearing (D2) of the Greenbrier fault at 500-600 degrees Celsius. Shear sense indicators record top-to-the-northeast displacement that predates doming, consistent with orogen-parallel transport during this stage of deformation. A subsequent deformation event (D3) created open to tight isoclinal folds (F3) and a pervasive axial planar cleavage development (S3) that overprints earlier fabric. Brittle faults record the final stage of deformation (D4). Kyanite alteration to sericite or white mica and chlorite replacement of biotite and garnet is attributed to a post-kinematic, retrograde metamorphic event (M4). These data demonstrate that the ductile portion of the Greenbrier fault around the Ela and Bryson City domes accommodated orogen-parallel transport during the late Taconic orogeny.

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