Abstract This one-day field trip highlights research into the late Cenozoic evolution of topography in the Appalachian Mountains through geomorphic observations in the Cullasaja River basin, located in Macon County, North Carolina. Herein we present observations, data, and modeling results that challenge the paradigm of the Appalachians as a dead and slowly decaying orogen. Previous studies on the Cenozoic evolution of topography in the Appalachians are reviewed, showing that the post-orogenic history of eastern North America is best described by spatial and temporal changes in topographic relief, erosion rate, and sediment flux. When these data sets are placed in the context of other geologic and geophysical studies, they indicate that the Appalachians are a dynamic mountain range. We review previous studies in the Cullasaja basin that document and characterize the magnitude of base-level fall, relief production, and ensuing landscape response to such changes. These studies show that topographic relief within the basin was relatively subdued in the Miocene and subsequently has been rejuvenated ~160%, transforming the landscape into the rugged mountains we recognize today. We highlight hillslope and fluvial geomorphic observations that show landscape disequilibrium associated with ongoing adjustment to ~500 m of late Cenozoic base-level fall. Potential mechanisms for topographic rejuvenation of the Appalachians, such as climate change and epeirogenic uplift, are discussed using available field observations.

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 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.