D. K. Larue, 1983. "Early Proterozoic tectonics of the Lake Superior region: Tectonostratigraphic terranes near the purported collision zone", Early Proterozoic Geology of the Great Lakes Region, L. G. Medaris, Jr.
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Two assemblages of early Proterozoic rocks are present in the Lake Superior region: a northern miogeoclinal assemblage of stratified rocks overlying Archean basement; and a southern magmatic arc terrane composed of granitoid and volcanic rocks. The structural contact between the miogeoclinal assemblage and the magmatic terrane in northeastern Wisconsin and upper Michigan is the Florence-Niagara fault. Miogeoclinal assemblage rocks directly north of the Florence-Niagara fault in the study area are subdivided into two fault-bound, tectonostratigraphic terranes: the Crystal Falls terrane (or terrane 1); and the Florence-Niagara terrane (or terrane 3). These structural blocks are segregated from the miogeocline proper (terrane 2) to the north because of differences in sedimentary facies, and/or structure. I interpret the Penokean Orogeny (1.8-1.9 b.y.) as a product of the collision between the magmatic terrane and the miogeocline: terranes 1 and 3 probably were emplaced during or after this collision but may have been discrete from the miogeocline prior to collision. It is probable that the early Proterozoic evolution of the Lake Superior region is much like that of Phanerozoic orogens, but gross similarities are obfuscated by the presence of, and the deformation associated with emplacement of, tectonostratigraphic terranes, which occur both in the Phanerozoic and the Precambrian.