ABSTRACT The eastern Great Smoky Mountains basement complex consists of the following components: (1) ca. 1350–1325 Ma orthogneiss and mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (similar to “pre-Grenville” basement components in the Adirondack, Green Mountain, Hudson Highland, and Shenandoah massifs); (2) ca. 1150 Ma augen orthogneisses and granitic orthogneisses correlating with the Shawinigan phase of Grenville magmatism; and (3) paragneisses (cover rocks) that have either pre- or syn-Grenville (i.e., Mesoproterozoic) versus post-Grenville (Neoproterozoic) depositional ages, and that experienced Taconian metamorphism and migmatization. Mesoproterozoic paragneisses contain major zircon age modes that require a component of Proterozoic crust in the source region. The Neoproterozoic paragneisses exhibit the archetypical “Grenville doublet” in detrital zircon age distributions that matches the age distribution of Ottawan and Shawinigan magmatic/metamorphic events in eastern Laurentia. Most zircon U-Pb age systematics exhibit variable lead loss interpreted to result from high-grade Taconian (ca. 450 Ma) regional metamorphism and migmatization. Neodymium mantle model ages (T DM ) for ortho- and paragneisses range from 1.8 to 1.6 Ga, indicating that all rocks were derived from recycling of Proterozoic crust (i.e., they are not juvenile), which is consistent with Proterozoic detrital zircon ages in pre- to syn-Grenville paragneisses. Lead isotope compositions confirm the presence of an exotic (Amazonian) crustal component in the source region for the protoliths of the pre-Grenville orthogneisses and xenoliths, and that this exotic component was incorporated to varying degrees in the evolution of the basement complex. The oldest age component may represent an Amazonian pre-Grenville analog to the ca. 1.35 Ga native Laurentian crust present in Adirondack and northern Appalachian basement massifs.

The southern Appalachian crystalline core is composed of lithotectonic assemblages that are largely sedimentary in origin. Sixteen paragneiss samples from the Blue Ridge and Inner Piedmont of North Carolina and Georgia, and one sample of Middle Ordovician rocks from the Sevier-Blountian clastic wedge in the Tennessee Valley and Ridge were sampled for sensitive high-resolution ion microprobe (SHRIMP) U-Pb detrital zircon geochronology, whole-rock geochemistry, and zircon trace-element analyses. Detrital zircon ages range from Archean (~2.7 Ga) to Middle Paleozoic (~430 Ma), with a notable abundance of Mesoproterozoic zircons (1.3–0.9 Ga). Many samples also contain moderate populations of slightly older Mesoproterozoic zircons (1.5–1.3 Ga). Minor populations of Paleoproterozoic (2.3–1.5 Ga) and Neoproterozoic (754–717 and 629–614 Ma) ages occur in several samples; however, Paleozoic detrital zircons (478–435 Ma) are restricted to samples from the Cat Square terrane. Depositional periods of the metasedimentary terranes are bracketed by detrital zircon, metamorphic, and magmatic ages, and include: (1) Mesoproterozoic, (2) Neoproterozoic to early Paleozoic, and (3) middle Paleozoic. A xenolith from the ~1.15 Ga Wiley Gneiss suggests a post–~1.2 Ga period of sedimentation prior to the ~1.15 Ga Grenvillian magmatic event. Detrital zircon populations of Neoproterozoic to Middle Ordovician suggest a mixed Laurentian provenance with Amazonian and peri-Gondwanan sources deposited in divergent and convergent plate settings. Blue Ridge and Inner Piedmont detrital zircon ages, whole-rock geochemistry, lithologic assemblages, and field relationships are compatible with deposition of immature clastic material in a rift and passive-margin setting from the Neoproterozoic to early Paleozoic. Occurrence of 1.3–0.9 Ga, 1.5–1.3 Ga, and 754–717 Ma detrital zircon ages indicate a dominantly Laurentian provenance for the Cartoogechaye, Cowrock, Dahlonega gold belt, Smith River allochthon, and Tugaloo terranes. Minor Paleoproterozoic populations in these terranes suggest input from distal terranes of the Laurentian midcontinent or the Amazonian craton. Transition to a convergent plate margin in the Middle Ordovician resulted in collision of central Blue Ridge and Tugaloo terranes and recycling of material from these terranes into the Mineral Bluff Formation and Sevier Shale. Ordovician and 629–614 Ma detrital zircons from the Cat Square terrane document the first occurrence of peri-Gondwanan material, which was deposited in a convergent setting between the Laurentian margin and the accreting Carolina superterrane during the Late Silurian to Devonian.

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.

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.

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.