Abstract

In terms of plate tectonic theory, and by analogy with modern continental margins, the Appalachian orogen evolved through a sequence of interrelated sedimentation-deformation-metamorphism patterns within a tectonic belt situated along the eastern margin of the North American continent. As exemplified by the northern part of the orogen, Appalachian stratigraphic-tectonic zones and deformation sequences are related to Late Precambrian to Ordovician expansion, followed by Ordovician through Devonian contraction, of a Proto-Atlantic ocean. This oceanic opening and closing was achieved by initial extensional necking of a single North American/African continent and by lithosphere plate accretion, followed by contractional plate loss along a trench, or complex of trenches, marginal to the drifted North American continent. A lithosphere plate model for the evolution of the orogen incorporates spatial and chronologic relations within and between bulk stratigraphic units and tectonic events. Pre-orogenic Appalachian sedimentation patterns were essentially the same as those found along modern continental margins; that is, shelf/slope/rise/abyss. Appalachian tectonic patterns are also analogous with modern tectonic patterns of continental margins, island arcs, and trenches, and involved continent-ward driven thrust sheets and ancillary exogeosynclines.

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