THE PENNSYLVANIA SALIENT: AN EXAMPLE OF THE RAGGED IAPTEAN RIFTED MARGIN OF LAURENTIA

Integration of 11 types of data, including proprietary seismic data from the Appalachian Basin of NYS and northern PA, indicate that an arcuate (in map view) system of Iapetan opening/Rome Trough rift faults defined a ragged Iapetan margin of Laurentia now represented by the Alleghanian Pennsylvania Salient, and that this arcuate system dominated other Iapetan opening faults to the north that include northerly-striking reactivated Grenvillian faults and E-striking faults.

In the Appalachian Basin of NYS, shallow structural-level features were assumed to reflect Alleghanian salt-cored folds and associated thrusts related to the arcuate map pattern of the fold and thrust belt in Pennsylvania. However, seismic reflection data across arcuate satellite imagery lineaments in the Appalachian Basin of NYS and PA show that many of the arcuate lineaments are related to deep structures as well (many of which continue higher into the section). In western NYS several of the NE-trending lineaments mark fault systems that were initially Iapetan-opening growth faults. In northwestern PA, a dramatic hinge in Iapetan opening time lies below the Alleghanian Smethport-Sharon Anticline that is coincident with an arcuate aeromagnetic anomaly. In central NYS seismic integrated with aeromagnetics and fracture data demonstrate that Iapetan rift faults follow the arcuate lineament trend. These and 3-D seismic surveys in western and central NYS suggest that the Iapetan opening faults in this “corner” zone have an original arcuate map pattern. The arcuate faulting was interrupted by northerly-trending Iapetan-rift faults that are reactivated intra-Grenvillian suture faults. East-striking Iapetan faults are found primarily north of the arcuate system, and are judged to be relatively minor from seismic surveys. The intersecting pattern of northerly, easterly and arcuate fault trends have an analog in the present eastern North Atlantic corner zones west of the UK where northerly-trending micro-continents such as Porcupine and Rockall banks lie north (and east) of the present deep Atlantic that sweeps around the banks and their intervening deeps. The Iapetan arcuate faults (and intersecting faults) controlled (through weakened, fractured rock from fault reactivations) the locations of later Alleghanian faults (including ramps).