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Abstract Late Mesoproterozoic to Neoproterozoic sedimentary sequences within the Lake Superior region preserve critical paleogeographic records of the position of Laurentia spanning from the end of Midcontinent Rift extension through to the end of the Grenvillian Orogeny. Temporally calibrated paleomagnetic poles from these sequences are essential for resolving Laurentia's plate motion during these tectonic events. The 5 km thick ca. 1,080 to 1,045 Ma fluviolacustrine Oronto Group was deposited during thermal subsidence following rifting prior to onset of Grenvillian contractional deformation in the region. Prior paleomagnetic work has focused on the basal Freda Formation (ca. 1,075 Ma) leaving a long temporal gap in poles from that time until the ca. 990 Ma pole of the unconformably overlying Jacobsville Formation. A new U‐Pb detrital zircon maximum depositional age for the upper Freda Formation of 1,051.6 1.1 Ma indicates that Oronto Group deposition was prolonged. We have developed new inclination‐shallowing corrected paleomagnetic data from the Freda Formation that can be temporally calibrated within this improved chronostratigraphic framework. A new pole from the ca. 1,045 Ma upper Freda Formation is similar in position to that from the ca. 1,075 Ma lower Freda Formation. These data indicate that Laurentia's rapid motion of 20 cm/year from ca. 1,110 to 1,080 Ma significantly slowed to 2 cm/year following onset of the continent‐continent collision of the Grenvillian orogeny. These dynamics are what is predicted if the rapid motion was associated with differential plate tectonic motion that closed an ocean basin leading up to collisional orogenesis and the associated assembly of Rodinia. 

Abstract 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 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. 

Abstract The magnetization of hematite‐bearing sedimentary rocks provides critical records of geomagnetic reversals and paleogeography. However, the timing of hematite remanent magnetization acquisition is typically difficult to constrain. While detrital hematite in sediment can lead to a primary depositional remanent magnetization, alteration of minerals through interaction with oxygen can lead to the postdepositional formation of hematite. In this study, we use exceptionally preserved fluvial sediments within the 1.1‐billion‐year‐old Freda Formation to gain insight into the timing of hematite remanence acquisition and its magnetic properties. This deposit contains siltstone intraclasts that were eroded from a coexisting lithofacies and redeposited within channel sandstone. Thermal demagnetization, petrography, and rock magnetic experiments on these clasts reveal two generations of hematite. One population of hematite demagnetized at the highest unblocking temperatures and records directions that rotated along with the clasts. This component is a primary detrital remanent magnetization. The other component is removed at lower unblocking temperatures and has a consistent direction throughout the intraclasts. This component is held by finer‐grained hematite that grew and acquired a chemical remanent magnetization following deposition resulting in a population that includes superparamagnetic nanoparticles in addition to remanence‐carrying grains. The data support the interpretation that magnetizations of hematite‐bearing sedimentary rocks held by >400‐nm grains that unblock close to the Néel temperature are more likely to record magnetization from the time of deposition. This primary magnetization can be successfully isolated from cooccurring authigenic hematite through high‐resolution thermal demagnetization.