Large bodies of eclogite in the Eastern Blue Ridge Province of western North Carolina crop out immediately southeast of the Burnsville fault zone, an Acadian dextral strike-slip fault that separates Laurentian Mesoproterozoic basement and Neoproterozoic to early Paleozoic units (Western Blue Ridge) from an inferred accretionary wedge complex (Eastern Blue Ridge). The peak metamorphic assemblage in eclogite is omphacite (Jd 27–35 ) + garnet (Alm 48 Prp 30 Grs 22 ) + quartz + rutile ± zoisite ± zircon ± apatite ± sulfides ± Fe-Ti oxides; evidence of an amphibolite-facies overprint is regionally widespread but variably developed. Geochemical and isotopic characteristics of the eclogites and some surrounding amphibolites are consistent with their derivation from mid-ocean-ridge basalt protoliths. Zircon from the least-altered eclogite yielded a U-Pb, isotope dilution–thermal ionization mass spectrometry age of 459.0 +1.5/−0.6 Ma. Multimineral plus whole-rock Sm-Nd isotopic data indicate that Sm-Nd mineral systematics were disturbed, likely during amphibolite-facies metamorphism. Partly amphibolitized eclogite contains titanite with a U-Pb age of 394 ± 4 Ma; titanite from another sample shows disturbed U-Pb systematics with apparent ages between 448 Ma and 417 Ma. Both eclogite and partly amphibolitized eclogite contain rutile with a U-Pb age of ca. 334–340 Ma. These ages correspond broadly to the time of the Taconian, Acadian, and Alleghanian orogenesis, respectively, and match the timing of metamorphic events and pluton emplacement in the Eastern Blue Ridge Province. The Ordovician geodynamic setting in which the eclogite formed was possibly a complex plate arrangement of island arcs, accretionary complexes, rift basins, and rifted microcontinental blocks, perhaps similar to the Australia-Pacific plate boundary between New Zealand and Papua New Guinea. Taconian collisional orogenesis was either synchronous with or closely followed high-pressure metamorphism, and both Acadian and Alleghanian events completely to partially reset titanite and rutile chronometers.

To promote a wider use of S and Z buckle folds in field-based structural studies, we first formulate three conditions under which quasi-cylindrical segments of gentle to close S and Z folds indicate the sense of finite-shear components. Based on our results of shear-sense mapping, we then assess the validity of published geological hypotheses in well-exposed parts of the western Grenville Province and the Southern Appalachians. Near the Central metasedimentary belt boundary of southeastern Ontario, which is widely interpreted as a 1090–1050 Ma ductile thrust, most orogen-normal, southeasterly plunging, gentle to close folds in the main foliation prove to have S style. This attests to a regional component of orogen-parallel sinistral shear that probably postdates the ductile thrusting. In gneisses and schists of the northern Inner Piedmont, six deformation events (D 1 –D 6 ) are recognized by other workers. We focus attention mainly on early Alleghanian, orogen-parallel folds (F 3 ) and associated mineral-shape fabrics in the Salem-Sunset area, western Inner Piedmont of South Carolina. Here, the orientation and S and Z style of mesoscopic F 3 features attest to an orogen-normal component of distributed thrust shear, and thereby strengthen the case for northwest-directed displacements of ductile thrust sheets during early stages of the Alleghanian orogeny.

Abstract The E5 transect extends southeastward from the Cumberland Plateau across the Appalachian orogen, the Atlantic Coastal Plain, Continental Shelf and Slope, and the Blake Plateau Basin; it is a transect through the Precambrian-early Paleozoic and Mesozoic-Tertiary continental margins of North America. The transect consists primarily of a 100-km-wide geologic strip map, a cross section, and supporting geophysical data. The cross section is based on surface geology, surface and subsurface data from Coastal Plain and offshore drill holes, shipboard and aeromagnetic data, and gravity and seismic reflection data, including the ADCOH and COCORP southern Appalachians lines. Elements of the map and cross section include: (1) the Appalachian foreland fold-thrust belt and western Blue Ridge Late Proterozoic-Paleozoic continental margin; (2) the eastern Blue Ridge-Chauga belt-Inner Piedmont oceanic-continental fragment terrane; (3) the volcanicplutonic Carolina terrane containing the middle to late Paleozoic high-grade Kiokee belt; and (4) a major geophysical ly defined terrane beneath the Coastal Plain. Three Paleozoic sutures may be present along the section line: the Hayesville thrust, the Inner Piedmont-Carolina terrane boundary (Taconic or Acadian suture?), and an eastern boundary of the Carolina terrane (Alleghanian? suture) in the subsurface beneath the Coastal Plain. The modern continental margin consists of the terrestrial clastics-filled Triassic-Jurassic basins and offshore marine Jurassic- Cretaceous clastic-carbonate bank succession overlain by younger Cretaceous and Tertiary sediments. Above the Late Cretaceous onshore unconformity lie Cenozoic sediments that represent seaward prograding of the shelf-slope, truncated by Miocene to recent wave abrasion and currents.

Abstract DNAG Transect E-5. Part of GSA's DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.