Detrital zircons and sediment dispersal in the Appalachian foreland

Seven new detrital-zircon U-Pb age analyses along with a compilation of previously published data from Mississippian-Permian sandstones in the Appalachian foreland (total n = 3564) define the provenance of Alleghanian synorogenic clastic wedges, as well as characterize the detritus available to any more extensive intracontinental dispersal systems. The samples are from the cratonward-prograding Mauch Chunk-Pottsville clastic wedge centered on the Pennsylvania salient, the cratonward-prograding Pennington-Lee clastic wedge centered on the Tennessee salient, and a southwestward-directed longitudinal fluvial system along the distal part of the foreland. Grenville-age detrital zircons generally are abundant in all samples; however, ages of the Taconic and Acadian orogenies are dominant in some samples but are minor to lacking in others. Taconic-Acadian ages are dominant in the Mauch Chunk-Pottsville clastic wedge, in parts of the longitudinal system, and in the upper part (above Middle Pennsylvanian) of the Pennington-Lee clastic wedge; but they are minor to lacking in the lower part (Upper Mississippian- Lower Pennsylvanian) of the Pennington-Lee clastic wedge. New Hf isotopic analyses show a similar distinction between the two clastic wedges, supporting an interpretation of differences in provenance contributions during the early stages of basin filling. U-Pb ages and Hf isotopic ratios also indicate that the Mauch Chunk-Pottsville transverse dispersal fed the northern part of the longitudinal system. A few samples in the distal southwestern part of the Mauch Chunk-Pottsville clastic wedge and adjacent parts of the longitudinal system have unusually large populations of grains with Superior and Central Plains ages. The relative distance and isolation of these samples from the Canadian Shield, which is the primary source of Superior and Central Plains zircons, indicates likely recycling from synrift sediment, passive-margin strata, or Taconic-Acadian clastic wedges. Among the lesser components are a few grains with ages that correspond to Iapetan synrift igneous rocks and also to Pan-African-Brasiliano components of Gondwanan accreted terranes. Synorogenic zircons of the Alleghanian orogeny are very rare (seven grains in the total of 3564).