COMPLEX DEFORMATIONAL HISTORY OF PARTS OF THE NORTH CAROLINA EASTERN BLUE RIDGE, SOUTHERN APPALACHIANS: NEW EVIDENCE OF WIDESPREAD ALLEGHANIAN DEFORMATION

The Tugaloo terrane (Tt) in the eastern Blue Ridge (EBR) is in the high-grade southern Appalachian crystalline core and consists of small internal basement massifs, the Neoproterozoic Tallulah Falls Formation (tff), and several low-K, peraluminous plutons that intruded during the Taconic (e. g., Whiteside, ~466 Ma, Ow), Neoacadian (e. g., Pink Beds, ~371 Ma), and Alleghanian (e. g., Looking Glass, ~333 Ma) orogenies. Detailed geologic mapping in the Tt of SW NC has raised questions about EBR tectonic history.

The Tt contains at least six deformations. Inclusion trails in garnets, foliations preserved in amphibolite boudins, and intrafolial folds in the ~1.15 Ga Toxaway Gneiss (Yt) preserve D₁. Although the Yt-tff contact has been called a fault, no direct observations in the study area or further south support that conclusion: it probably is a nonconformity. D₂ includes the regionally dominant S₂ foliation and F₂ inclined to recumbent isoclinal folds. Crosscutting relationships and map patterns show that D₂ was coeval with Ow intrusion. D₃ structures crosscut D₂ throughout the Tt. Major D₄ structures here include NE- and SE-plunging crenulations, at least four Alleghanian plutons, and the steep NW-dipping Cradle-of-Forestry-in-America (dextral), Dill Falls (thrust), and Pisgah Ridge (thrust) faults. D₃, D₄, and D₅ are also observed in the Brevard fault zone (BFZ), the E boundary of the EBR. Later open to gentle, NE and NW-trending folds are also present in the EBR. All deformations have been recognized in Toxaway dome, but the map structure is an F₃ fold.

Although D₂ is thought to be the principal deformational event in the EBR, tectonic foliations in Mississippian plutons parallel the regional foliations in the Tt, suggesting that the Mississippian Alleghanian orogeny coaxially overprinted and possibly reactivated older planar fabrics. Regional foliations near the BFZ are folded about a NE-plunging axis, while to the west in the Tt foliations in Mississippian plutons are folded about a gently SW-plunging axis. These variations indicate the possibility of larger map-scale gently NE-SW plunging folds produced by Alleghanian deformation.