All mixed up: Pb isotopic constraints on the transit of sands through the Mississippi-Missouri River drainage basin, North America

Abstract

Abstract Pb isotope data from over 2400 detrital K-feldspars in >50 modern sands sampled across the Mississippi-Missouri River drainage basin of North America have been collected in order to construct the first basin-wide provenance model using geochemical signals in a framework, rather than an accessory, mineral. This study represents a critical initial step in understanding the long-term routing of framework sand grains through the Mississippi-Missouri River drainage basin. Four unique Pb isotopic groups, otherwise petrographically and geochemically indistinguishable, are identifiable. Source comparisons reveal two groups corresponding to the Archean Superior and Wyoming terranes to the north of the catchment. The remaining two Pb groups represent a mixture of Appalachian, Grenville and older Granite-Rhyolite, and Yavapai-Mazatzal sourced-grains in the east of the catchment, with noteworthy input from Cenozoic volcanic rocks along the western fringe of the catchment to tributaries west of the Mississippi River, confirming prior assertions of zircon recycling in the lower drainage basin. Tracing suites of Pb isotopic groups provide a detailed map of previously undocumented tributary mixing and reveals the importance of long-lived, naturally formed impoundments in the Upper Mississippi River, which locally sequester and release sand. Tentative proportioning of sediment contributions to the terminus of the Mississippi River from individual tributaries produces similar results to recent U-Pb zircon models, boding well for the use of framework grain based modeling of sediment fluxes. The study is the largest application of Pb-in-K-feldspar fingerprinting to date and advocates its potential as a new and necessary tool for constraining relative source contributions to sinks—which will have wide applicability—especially if combined with provenance information from detrital grains of varying resilience, within large drainage systems.