Eastern U.S. crustal structure

Abstract

The Fifth Friends of Aeromagnetic Mapping (FOAM) Workshop was convened April 28–29, 1987, at the U.S. Geological Survey (USGS) National Center (Reston, Va.) by Isidore Zietz (George Mason University, Fairfax, Va.), Jeff Phillips (USGS, Reston, Va.), and Bob Hatcher (University of Tennessee, Knoxville/Oak Ridge National Laboratory, Oak Ridge, Tenn.). The purpose of this workshop was to discuss the crustal structure of the Appalachian region, including elements onshore covered by Coastal Plain sediments, as well as the continental shelf, slope, and rise offshore. The meeting was structured to maximize discussion. As in earlier FOAM workshops, the emphasis was upon thorough integration of potential field data, with seismic reflection, surface geology, and other data sets.The opening lecture by Hatcher outlined a block structure for the U.S. and Maritime Appalachians based primarily upon potential field data. Possible origins of the Appalachian gravity gradient, as a suture or post‐Paleozoic extensional feature, were mentioned, and it was noted that the Ouachitas have a similar gravity gradient. Hatcher also discussed the Late Paleozoic collisional tectonics of the Appalachians, which produce the huge Blue Ridge‐Piedmont thrust sheet, with 200‐500 km of displacement. The idea that the bend in the central Appalachians resulted from the collision of a promontory of Africa prior to the main collision during the late Paleozoic Alleghanian event was shown to be supported by evidence for large‐scale dextral motion along faults in the Southern Appalachians. Questions remain on the timing of motions and the continuity of deformation.