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 southwestwarddirected 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 analy ses 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 longi tudinal 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 Cana dian 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). INTRODUCTION The late Paleozoic Appalachian orogen along eastern North America (Fig. 1) long has been recognized as the dominant source of clastic sediment spreading cratonward into orogenic foreland basins (e.g., King, 1959; Thomas, 1977) and beyond, into intracratonic basins and farther across the North American Midcontinent (e.g., Gehrels et al., 2011). The late Paleozoic orogen represents the final assembly of supercontinent Pangaea as a result of a succession of Ordo vician–Permian (Taconic, Acadian, and Alleghanian) accretionary processes along the Neoproterozoic–Cambrian Iapetan rifted margin of Laurentia and the Cambrian–Ordovician passive margin (e.g., Hatcher et al., 1989a; Williams, 1995). The orogen includes the Precambrian Grenville province of supercontinent Rodinia assembly, synrift and passive-margin rocks of the Laurentian margin, and Ordovician through Permian synorogenic rocks and accreted terranes of the Appalachian and Ouachita orogenic belts (Fig. 1). The objectives of this article are to characterize the detrital-zircon populations of the late Paleozoic synorogenic clastic wedges within the Appalachian foreland and to evaluate the contributions of the various components of the provenance within the Appalachian orogen. This characterization of Appalachian detrital-zircon populations provides a template to determine possible Appalachian contributions to more distal intracontinental dispersal systems. LATE PALEOZOIC SYNOROGENIC SEDIMENTARY DEPOSITS Mississippian–Permian Alleghanian synorogenic clastic deposits vary significantly along the orogen. Between the New York and Alabama promontories, two late Paleozoic classic synorogenic clastic wedges filled foreland basins centered on the Pennsylvania and Tennessee embayments (Fig. 2). From the New York promontory northward to Newfoundland, late Paleozoic clastic sedimentation along the Appalachian orogen filled fault-bounded pull-apart basins along a regional system of dextral strike-slip faults (Fig. 1) (e.g., Thomas and Schenk, 1988; van de Poll, 1995). From the Alabama promontory westward along the Ouachita and Marathon embayments, late Paleozoic synorogenic clastic wedges GEOSPHERE GEOSPHERE; v. 13, no. 6 doi:10.1130/GES01525.1 12 figures; 3 supplemental files CORRESPONDENCE: geowat@uky . edu CITATION: Thomas, W.A. , Gehrels, G.E. , Greb, S.F. , Nadon, G.C. , Satkoski, A.M., and Romero, M.C. , 2017, Detrital zircons and sediment dispersal in the Appala­ chian foreland: Geosphere, v. 13, no. 6, p. 2206–2230, doi:10.1130/GES01525.1. Received 6 March 2017 Revision received 10 July 2017 Accepted 27 September 2017 Published online 19 October 2017 For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. © 2017 Geological Society of America Downloaded from https://pubs.geoscienceworld. org/gsa/geosphere/article-pdf/13/6/2206/3990899/2206.pdf by guest on 22 December 2018