Late Quaternary–Recent intraplate topographic uplift of the St. Francois Mountains (Ozark Plateau), Missouri (USA), driven by differential density and erosion

Abstract

The origin of relatively high topography in intraplate settings is elusive. The St. Francois Mountains, a tectonically inactive region with high relief, a Mesoproterozoic granite and rhyolite core, and Paleozoic sedimentary flanks, provide insights into the evolution of intraplate landscapes. We determined 14 in situ 10Be exposure ages, 23 10Be catchment-wide denudation rates (CWDRs), and geomorphic indices using a geographic information system, and we modeled surface uplift using an isostatic-flexure model. CWDRs varied from ∼5 to 10 ± 1.7 mm/k.y. and averaged 1.5 times greater in streams draining granite and rhyolite than in those draining flanking sedimentary rocks. In situ results from bedrock strath terraces gave Quaternary incision ages and incision rates that were tenfold higher than CWDRs. Major knickpoints (locally called shut-ins), all at 200 ± 70 m elevation, are located at contacts between the igneous and sedimentary rocks. Our exposure and denudation results inform isostatic-flexural modeling, which together support the conclusion that late Quaternary– Recent surface uplift driven by differential density and erosion focused in the igneous core is creating significant topography and relief in this intraplate setting.