Kinematics, U-Pb geochronology, and 40Ar/39Ar thermochronology of the Gold Hill shear zone, North Carolina: The Cherokee orogeny in Carolinia, Southern Appalachians

摘要

The Gold Hill shear zone is the most prominent pre-Carboniferous structure in the Southern Appalachian peri-Gondwanan tract of Carolinia. Common perception, based on indirect evidence, holds that it is an Acadian, dextral strike-slip shear zone. However, our recent structural and geochronologic studies directed at the shear zone indicate that it is a complex structure in both time and space. Structural studies in central North Carolina kinematically link deformation in the shear zone to regional shortening structures in both the hanging wall and footwall and indicate that there was a sinistral component to the deformation. Collectively, these structures constitute a regional sinistral transpressional system. We obtained nine new U-Pb zircon ages (Ediacaran–Devonian) and 12 new 40Ar/39Ar muscovite ages (Late Ordovician–Middle Mississippian); these data, in conjunction with the regional geology indicate that the shear zone has ∼12 km of stratigraphic throw and that the main motion on the zone was Late Ordovician. Collectively, geologic relations, structures, and the distribution of 40Ar/39Ar ages indicate that the shear zone was reactivated in the Late Devonian and the Middle Mississippian. The regional Late Ordovician–Silurian sinistral transpressive system, of which the Gold Hill shear zone is part, represents the most widespread tectonism documented in Carolinia; it overlaps in time with the Ordovician–Silurian Cherokee unconformity in Laurentian strata and Late Ordovician–Silurian suprasubduction-zone magmatism and metamorphism in peri-Laurentian rocks and consequently is considered a manifestation of the Southern Appalachian Cherokee orogeny, marking the accretion of Carolinia to Laurentia.