A DETRITAL-ZIRCON PERSPECTIVE ON SOUTHERN APPALACHIAN TERRANE COMPOSITIONS AND BOUNDARIES

The precise compositions, boundaries and relationships between various purported suspect and exotic terranes of the crystalline core of the greater southern Appalachian mountain belt have been a key focus of Appalachian research over the past four decades. Despite these efforts and clear progress forward, significant uncertainties remain. As a result, models for southern Appalachian terrane accretion and translation are numerous, varied and contentious. Whereas the detrital geochronology of metasedimentary units in the southern Appalachian crystalline core has contributed demonstrably to improved definition of the margins, origins and kinematic histories of these terranes, new results from the Carolinas presented herein, in a companion presentation (Love et al. in Session T.20: Undergraduate Research), and elsewhere suggest that the boundaries of these bodies and their relationships to one another remain unclear. In particular, several units contain detrital zircons not previously recognized within the terranes to which they are ascribed: (1) Some metasedimentary units of both Carolinia and the Piedmont Zone contain abundant Paleozoic detrital zircons, including a dominant Siluro-Devonian population in the Dreher Shoals terrane and the Eastern Tugaloo terrane, a dominant Carboniferous population in the Western Tugaloo terrane, and lesser late Carboniferous and late Devonian populations in the Eastern Tugaloo terrane. (2) Metasedimentary rocks interpreted as part of the Cat Square terrane that separates Carolinia and the Piedmont Zone contain a wide late Neoproterozoic age distribution that overlaps with previously identified populations in Carolinia, but were heretofore unknown in the Cat Square terrane itself. In this presentation I compile existing and new detrital-zircon age spectra according to existing terrane models, and compare the relative merits and uncertainties of those models through the lens of detrital-zircon geochronology.