SANDSTONE PETROGRAPHY AND DETRITAL ZIRCON GEOCHRONOLOGY OF NEOPROTEROZOIC- THROUGH PENNSYLVANIAN-AGE SANDSTONES FROM THE CENTRAL APPALACHIANS WITH IMPLICATIONS FOR MULTIPLE RECYCLING

The composition and age of provenance terranes during the late Neoproterozoic through Pennsylvanian evolution of the central Appalachians has been characterized by a combination of sandstone petrography and ICP-MS laser ablation dating of detrital zircons. Sandstones display stratigraphic variations in petrography that reflect changing provenances during this 300 million year time interval. In contrast, Grenville-age (950-1250 Ma) zircons dominate sandstones from all stratigraphic units. Neoproterozoic, rift-related sandstones are mostly feldspathic arenites and contain detrital zircons that are exclusively of Grenville age. Cambrian passive-margin sandstones are quartz arenites that contain, in addition to Grenville-age zircons, significant numbers of older Mesoproterozoic (1250-1800 Ma) zircons indicating derivation, in part, from older provenances to the west. Sandstones from the overlying foreland-basin clastic wedges typically are litharenites and sublitharenites. Those of Taconic age contain both sedimentary and metamorphic (polycrystalline quartz and chlorite schist) rock fragments whereas Acadian and Alleghenian sandstones are dominated by metamorphic rock fragments (schist, detrital mica and polycrystalline quartz). Detrital zircons are mainly of Grenville age but a few younger (Taconic) zircons are present in the clastic-wedge sandstones and, significantly, Pennsylvanian-age sandstones contain Paleoproterozoic and up to 10% Archean zircons of probable Penokean and Superior Province heritage, respectively. Sandstone petrography and detrital zircon geochronology indicate that Taconic-age sandstones and conglomerates represent recycled, older passive-margin sedimentary rocks that, most likely, were uplifted in an accretionary prism in front of the approaching Taconic magmatic arc, and that Acadian and Alleghenian sandstones were derived mostly from deeper levels of this fold-thrust complex. The absence of Carolina- and almost complete lack of Taconic-age zircons in the clastic-wedge sandstones is attributed to the presence of the accretionary prism as a tectonic highland between the magmatic arcs and the foreland basins.