Paper No. 166-15
Presentation Time: 5:15 PM-5:30 PM
METAMORPHIC AND STRUCTURAL EVOLUTION OF THE EASTERN BLUE RIDGE-WESTERN BLUE RIDGE BOUNDARY ("THE HAYESVILLE FAULT") ALONG THE BLUE RIDGE PARKWAY, WESTERN NC
MASSEY, Matthew A., Geological Sciences, Univ of Kentucky, Lexington, KY 40506-0059, mamass1@pop.uky.edu and MOECHER, David P., Univ Kentucky, 101 Slone Bldg, Lexington, KY 40506-0053

Classical interpretations concerning evolution of the Eastern Blue Ridge (EBR)-Western Blue Ridge (WBR) boundary, or Hayesville fault (HF), involve emplacement of the HF (Taconic suture) by thrusting of an oceanic fragment/accretionary wedge/island arc upon Laurentian basement and metasedimentary cover, followed by Taconian regional metamorphism with an Alleghanian greenschist overprint. Detailed structural and petrologic analysis of exposures along the Blue Ridge Parkway south of Maggie Valley, NC reveals the EBR-WBR boundary is a folded contact between WBR paragneisses and EBR orthogneisses. Two stages of early isoclinal folding (F1 and F2) are overprinted in both gneisses by F3 open to tight folds and crenulations; late F4 open folding is associated with brittle faulting. S2 transposes to an S3 axial planar position as a result of F3. S3 is characterized by crystallization and reorientation of micas, and deformation of quartz, as seen by lobate grain boundaries, undulose extinction, and subgrain development; this is the youngest penetrative feature in both WBR and EBR assemblages. Two ductile shear zones in the WBR, recognized by 10- and 3-m wide mylonite zones, show amphibolite facies recrystallization of feldspar porphyroclasts; rotation of local S2 trends, resorbed Grt within the matrix, and S3 deformation indicate post-kinematic activation relative to S2, and pre-kinematic to S3. Ky-St grade metamorphism in the WBR is pre- to syn-kinematic, as almost all are included within S2. Ky contains numerous inclusions of Qtz and Grt, however, Grt within S2 also includes Ky; late Sil (fine-grained acicular and/or fibrolite) nucleates on Grt, St, and Ky; coarse Mus overprints S2 porphyroblasts and Sil, but Mus is deformed by S3. Mafic EBR rocks attained amphibolite grade (Pl+Grt+Hbl+Bt+Ttn+Ep), consistent with peak WBR grade. Bt+Chl replacement of Grt, Chl replacement of Bt, and sericitization, locally static, of Fs, Mus, and Ky characterize a late greenschist event. We observe no structures at the contact indicative of premetamorphic faulting, and cannot discern any evidence, at this locality, that the contact is a fault. Any premetamorphic fabrics and mineralogy must have been obliterated by Taconian deformation and metamorphism.

2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 166
Structural Geology: Deformation, Intrusion, and Volcanism
Colorado Convention Center: C109
1:30 PM-5:30 PM, Tuesday, October 29, 2002
 

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