U-PB AND (U-TH)/HE ZIRCON DOUBLE DATING OF PALEOZOIC APPALACHIAN VALLEY AND RIDGE STRATA: SEDIMENT ROUTING AND OROGENIC UPLIFT

The Valley and Ridge province in the southern Appalachians is composed of sedimentary rocks that record the Cambrian through Pennsylvanian depositional history and Pennsylvanian and Permian Alleghanian deformation. Timing estimates for orogenic deformation of the fold and thrust belt are based on the ages of the youngest deformed strata (Pennsylvanian), while the sequence of thrust fault development is based on cross-cutting relationships. However, the field-based understanding of temporal development of deformation in the southern Appalachian Valley and Ridge fold and thrust belt, however, is difficult to correlate with magmatism, metamorphism, and deformation in the adjacent southern Appalachian Piedmont. The lack of correlation fails to provide precise timing and rates that may yield insight into along-strike variability within the 1,500 km Appalachian Valley and Ridge province.

To investigate the sediment sources for Appalachian sediment and estimate the timing of uplift, deformation, and inferred burial and exhumation, we present zircon LAICPMS U–Pb and (U-Th)/He data from Cambrian, Ordovician, Mississippian, and Pennsylvanian units. Lower Cambrian sandstones (Chilhowee Group) contain zircon from the mid-continental Granite–Rhyolite Province (1300-1500 Ma) and the Canadian Shield (>2500), sourced from the Laurentian continent during passive margin sedimentation. The Ordovician Colvin Mountain Sandstone is dominated by Grenville-age zircon (900-1200 Ma) and contains Paleozoic zircon with U–Pb ages as young as 416 Ma, which may represent a younger-than-previously realized age for the Colvin Mountain Sandstone or Pb-loss. This unit also yields a population of (U–Th)/He dates ~406 Ma The shift from cratonic-sourced sediment in the Cambrian to by the Ordovician-Silurian (?) represents uplift of crystalline Grenville rocks during the Taconic and/or Acadian orogenies. Mississippian and Pennsylvanian sandstones (Hartselle Sandstone, Pottsville Formation) are dominated by zircon sourced from the uplifting Alleghanian orogeny and record cooling below zircon (U-Th)/He closure between ca. 250 and 330 Ma.