Mississippian Paleogeography, Southwestern US

Mississippian Paleogeography, Southwestern US (340 Ma). The colliding Antler arc shoved strata deposited in deep water over the continental shelf to form the Antler orogeny. The weight of the thickened crust caused eastern Nevada and western Utah to subside and thick Upper Devonian and Lower Mississippian strata formed there. Farther east a broad carbonate shelf blanketed much of the Western Interior

View to west of above. The Antler arc has collided with the continental margin. However some parts of the arc possibly collided with the off shore continental blocks. Here subduction continued but the polarity of the subduction (direction of dip of subduction zone) reversed so that subduction now dipped eastward. One or more of these portions of the reversed Antler arc may have been the precursor of the McCloud arc, a Late Paleozoic tectonic element of western North America. Many of the interpretations of events off the western margin of North America continue to be strongly debated. As will be shown beginning with Permian paleogeography, some geologists interpret the McCloud arc to be exotic to North America

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