DEFINING THE HAYESVILLE FAULT AND TERRANE BOUNDARY BETWEEN THE WESTERN AND CENTRAL-EASTERN BLUE RIDGE, GEORGIA-NORTH CAROLINA

The Hayesville fault (HF) was defined originally based on contrasting lithologic assemblages, windows, and footwall map-unit truncations; although it is folded, outcrop geometry implies northwest-directed thrust kinematics. Rocks of the western Blue Ridge (WBR) in the type HF footwall include truncated units of rifted-margin Great Smoky Group (GSG) rocks. Basal rifted-margin rocks nonconformably overlie Grenville basement farther NE. Grenville and pre-Grenville (Mars Hill terrane) basement rocks are widespread in the WBR, but occur only in isolated bodies in the central-eastern Blue Ridge (CEBR). CEBR rocks (HF hanging wall) include probable distal Iapetan-margin, Laurentian-derived, Neoproterozoic to early Paleozoic(?) metasedimentary rocks containing abundant mafic and ultramafic (MUM) rocks. Brasstown Bald and Shooting Creek windows, both cored by GSG rocks and framed by MUM rocks (oceanic crust?) beneath metasedimentary sequences, constitute primary evidence of a fault boundary. Paleozoic granitoid plutons occur only east of the HF. Near Hayesville, fault movement preceded the metamorphic peak (Ordovician?), although some HF and correlative Allatoona, Holland Mtn, and Gossan Lead fault segments show post-metamorphic-peak reactivation. Annealed mylonite locally occupies some premetamorphic-peak contacts, but elsewhere no fault rocks are present. Some premetamorphic-peak segments are folded by tight, roughly synmetamorphic-peak F2 (and later) folds, at map and outcrop scales. Although the HF typically dips SE, tightly folded segments are locally overturned and dip NW. In one such segment, detailed work indicates no significant offset of metamorphic isograds by the HF, and graded beds in WBR footwall rocks (GSG) confirm the overturning. Significant reactivation appears restricted to SE-dipping segments, and segments less tightly folded. A boundary with similar characteristics is traceable in a similar location throughout the Appalachian orogen, and probably represents closing of a small ocean and obduction of oceanic crust and Ordovician arcs onto the Laurentian margin.