COCORP deep seismic reflection surveys in New England, Georgia, and Arkansas confirm that crustal scale overthrusting is an important aspect of Appalachian-Ouachita orogenic evolution. The southeastern Appalachian traverse, by tracing early Paleozoic shelf sedimentary rocks (or their metamorphic equivalents) eastward beneath the Blue Ridge and Piedmont, defined a master decollement above which crystalline rocks were transported 124 mi (200 km) or more. The Arkansas traverse likewise suggests that the southern part of the Ouachitas are allochthonous, with the deep water facies of the Benton uplift thrust over relicts of an early Paleozoic shelf. The southern Appalachian and Ouachita results are consistent with the tectonic burial of continental margins beneath crystalline hrust sheets during collisional orogeny. The New England surveys also testify to the importance of "basement" -involved thrusting, with indications that the the Green Mountain Precambrian massif is an allochthonous sliver and the crust beneath New Hampshire a complex of imbricate thrust slices of metasedimentary and igneous material.

While debate continues regarding interpretational details, these results provide clear support for the hypothesis that "thin-skinned" style overthrusting on a crustal scale is an important, if not the important, mode of continental accretion. It has been speculated that sediments and water emplaced in the lower crust by such megathrusts may explain certain types of magmas, high conductivity layers, and low velocity zones in the crust. A layered complex discovered in the lower crust beneath the eastern Adirondacks by COCORP profiling may represent just such a relict of underthrust sedimentary material, perhaps buried during the Grenville orogeny and thus representing the predecessor to Appalachian accretion.

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