The common-Pb isotope composition (²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb) of detrital K-feldspar was measured on the same clastic units from southeastern Laurentia that were previously characterized by detrital zircon and detrital monazite geochronology for provenance analysis. The purpose is to test a model that invokes late Paleozoic recycling of sediment initially sourced from erosion of exhuming Grenvillian basement in the Neoproterozoic. The approach takes advantage of the difference in Pb isotope compositions between Laurentian and Amazonian cratonic sources documented by previous workers. Neoproterozoic samples sourced from southern Amazonia and central Laurentian basement that serve as controls on methodology plot within Pb isotope space characteristic of their respective sources. K-feldspar in the Cryogenian Ocoee Supergroup in the southern Appalachian orogen falls within the field of Pb isotope compositions defined by south-central Appalachian basement (SCAB). The latter, in turn, exhibits Pb isotope compositions characteristic of Amazonia, because SCAB was transferred to Laurentia from Amazonia during Rodinian assembly. In contrast, K-feldspar in early Cambrian arenite falls within the Laurentian field, indicating a shift in the early Paleozoic to a sediment source from the Laurentian Craton. K-feldspar in Lower Pennsylvanian lithic arenites of the Central Appalachian Basin exhibit Pb isotope compositions that fall within the SCAB field but at higher Pb isotope ratios than in the inferred Ocoee sources. Incorporation of all provenance constraints requires an immediate source that is isotopically more radiogenic than the Ocoee but similar in all other petrologic and geochronologic characteristics, for example, other Cryogenian to Ediacaran units along strike in the Appalachian orogen. The results further demonstrate the importance of having multiple detrital mineral proxies for accurate provenance analysis rather than using detrital zircon geochronology alone.

Six Proterozoic, two Cambrian, and two Cretaceous paleosols in the Lake Superior region of midcontinental Laurentia were investigated in detail. All but the Cretaceous paleosols experienced potassium metasomatism, which resulted in the precipitation of muscovite in Proterozoic paleosols or illite and microcline in Cambrian paleosols. A comparison of the magnitude of potassium metasomatism among the paleosols is provided by depth-normalized mass flux (DNMF), where DNMF=1000×[(mass flux)/(depth of weathering)], which normalizes for different thicknesses of weathering profiles. Average DNMF values for the total addition of K₂O are 0.98 ± 0.19 mol cm⁻³ for the Proterozoic paleosols and 1.27 ± 0.06 mol cm⁻³ for the Cambrian paleosols. The ages of potassium metasomatism were determined by ⁴⁰Ar/³⁹Ar isotopic dating of metasomatic muscovite in the Proterozoic McGrath, Ville Marie, and Baraboo paleosols, which yielded ages of 1742 ± 3, 1589 ± 3, and 1467 ± 11 Ma, respectively, the former being coeval with the Yavapai orogeny and the latter with the Baraboo orogeny. Metasomatic microcline in the Cambrian Trempealeau paleosol yielded a plateau age of 488.0 ± 1.0 Ma, which corresponds to the age of the Cambrian-Ordovician boundary. SiO₂, CaO, and Na₂O were substantially removed from the paleosols by weathering, as was K₂O (before metasomatism). The average total amount of SiO₂, CaO, Na₂O, and K₂O removed was 17.6% ± 1.9% from six Proterozoic paleosols, 28.5% ± 4.2% from two Cambrian paleosols, 36.5% ± 8.6% from two Cretaceous paleosols, and 34.2% ± 2.7% from five modern soils. The greater magnitude of weathering in the Phanerozoic weathering profiles compared with the Proterozoic ones, despite lower levels of CO₂ in the Phanerozoic atmosphere, may reflect the emergence of land plants at ∼500 Ma and their profound effects on weathering.

This study presents the restored Pliocene topography along northerly trending profiles in Manitoba, northwestern Ontario, eastern North Dakota, Minnesota, and western Wisconsin. A top-of-bedrock slope profile of the Red River/Lake Winnipeg/Nelson River and 19 south-trending landscape topographic and top-of-bedrock slope profiles of the region were made from published elevation data. These profiles reveal a clear change in slope and slope direction (flexure) in the top-of-bedrock elevation. The flexure axis trends southeasterly across Manitoba into northwestern Ontario. The profiles were then tilted southerly by lifting the profiles along the southern margin of Hudson Bay to restore remaining glacial isostatic rebound. When imposing a minimum 80 m of isostatic rebound to the Nelson River/Lake Winnipeg/Red River profile, the northern portion of the profile slopes north but the southern portion of the profile slopes south at 0.01%. When imposing a minimum 60 m of isostatic rebound to all 19 top-of-bedrock profiles, the bedrock slopes north to Hudson Bay northeast of the flexure; however, southwest of the flexure, the southern portions of the 19 top-of-bedrock profiles slope south. We interpret the flexure axis to have been the northern divide of the Pliocene Mississippi River basin in Manitoba and northwestern Ontario and the divide that will lie between the north-flowing Nelson River and south-flowing Red River with future glacial isostatic adjustment.

The Ediacaran (607–593 Ma) Ferani volcanic rocks are exposed in South Sinai, at the extreme northern tip of the Arabian-Nubian Shield (ANS). The studied volcanics constitute a cogenetic continuous intermediate (andesite to dacite) to acid (rhyodacite to rhyolite) lava sequence with a high-K calc-alkaline metaluminous to slightly peraluminous nature. They contain a high concentration of large-ion lithophile elements (i.e., Ba, Rb, Pb, and Th), but lower contents of Nb, P, Ti, and Sr. They also have a general enrichment in light rare earth elements ((La/Sm)N=2.66–4.92), compared to heavy rare earth elements ((Gd/Yb)N=1.10–2.29), with a slightly negative Eu anomaly (Eu/Eu*=0.35–0.94). The cooling of the Ferani magma began at ∼1000°–1100°C and went to ∼700°C at low pressure (<5.1 kbar) and shallow crustal levels (<17 km), according to thermobarometric modeling. The low degree of partial melting of the mafic lower-crustal rocks could have produced the andesitic-dacitic magmas that ascended through the crust and fractionated, leading to the production of the early intermediate Ferani lavas. Progressive fractional crystallization of the intermediate melts could consequently have formed the rhyodacite and rhyolite melts, which were later erupted to form the upper acidic Ferani volcanic sequence. Petrological and geochemical features support a postcollisional setting of the Ferani volcanics. Lithospheric delamination is the main geodynamic process responsible for the formation of the Ferani volcanics during the postcollisional extensional stage in the northern ANS crust.

The Jianshan banded iron formation (BIF) is embedded in Paleoproterozoic strata. The Jianshan BIF can be divided into oxide and silicate facies. The former consists mainly of quartz and magnetite, and the latter contains hornblende and actinolite. Geochemical analyses of the Jianshan BIF show that Al₂O₃ and TiO₂ are quite scarce with no significant correlation, and the contents of incompatible elements and transition metal elements are low, indicating negligible involvement of terrigenous clastics during the deposition. The rare earth element (REE) curves reveal depletions in light REE, enrichments in heavy REE, and positive La, Y, and Eu anomalies, suggesting that the material source was a mixture of submarine hydrothermal fluid and seawater. Although the Ce anomalies are unobvious, the decoupling of Th and U and below-crustal Th/U ratios resulting from the oxidation of U⁴⁺, as well as the enrichment of heavy Fe isotopes, imply a rapid rise of oxygen content shortly after the Great Oxidation Event. The Jianshan BIF might deposit in a redox-stratified ocean. It might be an important possibility for the Jianshan BIF that Si deposition is likely attributed to oversaturation caused by a temperature drop of Si-rich hydrothermal fluids and that Fe deposition is probably due to rapid oxidization in the upper oxygenated layer of the redox-stratified ocean.