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Abstract
The Midcontinent Rift system (ca. 1.1 Ga) is a 2000-km-long series of elongated volcanic and sedimentary troughs and associated intrusive centers exposed chiefly in the Lake Superior region of North America. The rift system represents a long history of intense magmatism and subsequent sedimentation that was arrested by far-field tectonic events before sea-floor spreading was established. The premature cessation preserved a record of processes related to the beginning of continental rifting.
The rift system under Lake Superior has been long studied using seismic-reflection data collected as part of the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE). We reexamine GLIMPCE Line C by developing a detailed velocity model for time to depth conversion constrained by other legacy data. We corroborate the model and develop a geologic interpretation using gravity and magnetic modeling and ties to geology mapped onshore.
We recognize superposed subsiding sedimentary and volcanic basins for the southern half of the Line C depth section. This interpretation differs from previous paradigms that show major crustal faults that bound half-grabens or full grabens. We conclude that high-velocity (6.9 km/s) intrusive zones rather than major crustal faults border the sides of the basins. We speculate that the volcanic basin represents the initiation of seaward dipping reflectors.
The syn-magmatic subsidence can be explained by dike injection and volcanic loading. Discrete lava basins throughout the region likely subsided at different times in a disorganized manner along the rift trend, raising questions about the long-term role of lithospheric thinning and melt generation.
Suggested Citation
Grauch, V.J., Woodruff, L.G., Heller, S.J., and Stewart, E.K., 2026, Syn-magmatic subsidence during the early stages of continental rifting in the Mesoproterozoic—A reanalysis of legacy data for the Midcontinent Rift, western Lake Superior: Geosphere, https://doi.org/10.1130/GES02899.1.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Syn-magmatic subsidence during the early stages of continental rifting in the Mesoproterozoic—A reanalysis of legacy data for the Midcontinent Rift, western Lake Superior |
| Series title | Geosphere |
| DOI | 10.1130/GES02899.1 |
| Edition | Online First |
| Publication Date | May 14, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | Geological Society of America |
| Contributing office(s) | Central Energy Resources Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Energy & Minerals Science Center |
| Country | Canada, United States |
| State | Michigan, Minnesota, Ontario, Wisconsin |
| Other Geospatial | Lake Superior |