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Quartz arenites characterize much of the early Paleozoic sedimentary history of the midcontinent region. Despite numerous studies, the century-long debate on how these arenites formed is still unresolved, primarily because of the compositional and textural purity of the deposits. In this study, we present an extensive data set of detrital zircon geochronology from the early Paleozoic supermature arenites of the midcontinent region, and we offer newconstraints about their origin. Our results coupled with compiled provenance information from older basins and orogens may indicate that the Cambrian and Ordovician arenites represent sediment reworking primarily of two different older basins. The Cambro-Ordovician sediment was transported to the midcontinent region by two early Paleozoic river systems that sourced from the paleo-east (Huron basin) and paleo-northeast (midcontinent rift region). [ABSTRACT FROM AUTHOR]

The Archean nucleus of Laurentia, the Superior province, formed between 2.7 and 2.6 Ga. There is little record of sediment deposition on the craton for 100 m.yr. until deposition of the Huronian clastic sedimentary rocks (4-12 km thick) began along the south-central margin of the Superior province between 2.5 and 2.2 Ga. Huronian detrital zircon ages ( zircon SHRIMP 207Pbx/206Pbx np266 ages from six samples) are dominantly 2.6-2.7 Ga, with a small population aged 3.0-3.5 Ga in the middle of the Huron section. The mainly younger, and western, Animikie basin (6-12 km thick; 2.21-0.8 Ga) contains a wide range of nearshore and deep-water clastic rocks, including banded iron formations and the 1.85 Ga Sudbury "impactite" deposits with overlying turbidites. Animikie detrital zircon ages (np724 laser ablation ICP-MS 207Pbx/206Pbx zircon ages from 10 samples) contain a complex spectrum, with ages ranging from 1.8 to 3.8 Ga: the basal Chocolay (Denham, East Branch Arkose) samples contain zircons ranging in age from 2.1 to 3.7 Ga, with a dominant population at ~2.6 Ga; the basal Animikie (Menominee) quartzites contain zircons with ages between 2.1 and 3.8 Ga, with peaks variably at 2.1, 2.3, 2.6, and 3.0 Ga; the upper Animikie (Baraga) turbidites contain zircons with ages between 1.8 and 3.6 Ga, with a dominant peak at 1.85 Ga. The Huron and Animikie basins were intensely deformed by Penokean orogenic (1.85 Ga) accretion from the south. Deposition into the Huron basin was from the north and west for 200 m.yr.; then the depocenter shifted to the west at ~2.2 Ga, with the Animikie basin receiving clastic debris from all directions, including from terranes (e.g., Marshfield and the Wisconsin Magmatic Terrane) approaching from the south. Combined Huron and Animikie detrital zircon results record a migrating eastto- west depocenter, perhaps in conjunction with the dynamics of the central Marathon large igneous province mantle plume and dike swarm (~2.07 Ga), over a period of 500 m.yr. [ABSTRACT FROM AUTHOR]