Donald M. Davidson, Jr., 1982. "2: Geological evidence relating to interpretation of the Lake Superior Basin structure", Geology and Tectonics of the Lake Superior Basin, Richard J. Wold, William J. Hinze
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The Lake Superior Basin and the Lake Superior syncline are differentiated as tectonic elements; the syncline is locally defined within and adjacent to the southwestern and southern portions of the basin.
Formation of the basin apparently commenced with the extrusion of lava in sub-basins. As a result of rifting, the lava ponded and created the Keweenawan lava plateau about 1100 m.y. ago. Coalescence of subsiding sub-basins created the overall structure during Keweenawan time (1225 ± 50 m.y.-1100 ± 10 m.y. ago). Uncertainty exists as to the time of rift initiation dependent upon tectonic interpretation of the Sibley Group (1339 ± 33 m.y. ago) with respect to the rifting in the Lake Superior region. Faulting along sub-basin margins probably controlled subsidence locally.
The development of the Lake Superior syncline was dependent upon subsidence of the Keweenaw Point-Isle Royale lava plateau, the youngest of such features in the Lake Superior area, together with folding of units at the eastern end of Lake Superior.
Folding and faulting, particularly the development of major longitudinal and transverse faults, generally postdate volcanism and plateau subsidence. The basin appears to have been well developed by the time of deposition of Proterozoic Oronto and Bayfield Group sediments, although isostatic adjustments, which probably continued into the Phanerozoic, may have further accentuated the basin structure.
The structural trends of Keweenawan units along the midcontinent gravity high are coincident with those in older Precambrian units in the Lake Superior area but cut the predominant east-west fabric found in older units at high angles in the Minnesota-Kansas and Michigan segments.