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Vermont Geological Survey
USGIN ISO 19139
Are the Ordovician Northern Appalachians and the Mesozoic Cordilleran System Homologous?
Cady, Wallace M
Recent syntheses presume that the Ordovician northwestern Appalachians and the Mesozoic Cordilleran system are genetically similar, as is indicated by subduction zones interpreted in the northern Appalachians. Actualistic models for the proposed relationships have commendably been suggested, and a predictive model that outlines a transition from present Atlantic-type to present Pacific-type margins has been presented. The syntheses complicate the model, however, by using in turn the lower Paleozoic Appalachians and Caledonides as a model for a possible present-to-future Atlantic margin. This assumes that the Appalachian-Caledonian belt is ensimatic and contains subduction zones, two quite essential features of cordilleran-type orogenic belts. Faunal paleogeographic, stratigraphic, petrologic, and structural evidence in the northern Appalachians nevertheless indicates a probable sialic basement overlain by lower and middle Paleozoic rocks that are stratigraphically and structurally continuous across the proposed subduction zones, and in which extension as opposed to compression predominates. These considerations indicate that a simatic basement is conjectural in the Appalachians and that subduction zones are very doubtful. Consequently the lower Paleozoic northern Appalachians and the Mesozoic Cordilleran system do not seem homologous.
Dec 30, 1972
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Cady, Wallace M
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Vermont Agency of Natural Resources
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