One Billion Years of Stability in the North American Midcontinent Following Two‐Stage Grenvillian Structural Inversion.

The North American craton interior preserves a >1 Ga history of near surface processes that inform ongoing debates regarding timing and drivers of continental‐scale deformation and erosion associated with far‐field orogenesis. We tested various models of structural inversion on a major segment of the Midcontinent Rift along the Douglas Fault (DF) in northern Wisconsin, which accommodated ≳10 km of total vertical displacement. U‐Pb detrital zircon and vein calcite Δ47/U‐Pb thermochronometry from the hanging wall constrain the majority of uplift (≳8.5 km) and deformation to 1052–1036 Ma during the Ottawan phase of the Grenvillian orogeny. Combined U‐Pb zircon dates, Δ47/U‐Pb calcite thermochronometry, and field data that document syn‐ to early post‐depositional deformation in the footwall constrain a second stage of uplift (1–1.5 km) ca. 995–980 Ma during the Rigolet phase of the Grenvillian orogeny. A minor phase of Appalachian far‐field orogenesis is associated with minimal thrust reactivation. Our combined analyses identified the 995–980 Ma Bayfield Group as a Grenvillian foreland basin with an original thickness 0.5–2 km greater than currently preserved. By quantifying flexural loading and other subsidence mechanisms along the Douglas Fault, we identify dynamic subsidence as a mechanism that could be consistent with the development of late‐Grenvillian transcontinental fluvial systems. Minimal post‐Grenvillian erosion (0.5–2 km) in this part of the craton interior has preserved the Bayfield Group and equivalent successions, limiting the magnitude of regional erosion that can be attributed to Neoproterozoic glaciation. Plain Language Summary: Around 1.1 billion years ago, volcanic rocks and sediments began accumulating in a large rift basin around the present‐day Lake Superior region of North America. Continent‐continent collision on the edge of North America caused rifting to cease and major uplift to occur on thrust faults in the rift. The timing of the tectonic shift and the amount of crustal uplift and the number of uplift episodes are all poorly constrained. Our new geochronology precisely identifies the age of two major uplift episodes, ∼1.05 and ∼0.98 billion years ago. Mineral veins that formed during uplift record the age and temperature of formation, which enables reconstruction of an uplift history. We conclude that the collisional event ∼1.05 billion years ago resulted in ≳8.5 km of uplift followed by 1.0–1.5 km of uplift ∼0.98 billion years ago. A sedimentary basin associated with collision ∼1.0 billion years ago may have been part of a vast transcontinental river system. The surface underlying the Great Unconformity, a surface representing missing time, regionally did not undergo much erosion following uplift, suggesting long‐term stability of the North American craton interior over the last ∼0.98 billion years. Key Points: U‐Pb zircon and calcite dates constrain two‐stage Grenvillian inversion of the Midcontinent Rift on the Douglas Fault (DF) in northern WisconsinΔ47/U‐Pb thermochronometry constrains vertical displacement of ≳8.5 and ∼1.5 km in the Ottawan and Rigolet Grenvillian phases, respectivelyBasin analysis and clay mineralogy constrain original thickness, subsidence drivers, and erosion of a ca. 1010–980 Ma Grenvillian foreland [ABSTRACT FROM AUTHOR]