Magmatically driven uplift in the central Cascades arc, USA, revealed by fluvial incision dynamics of Columbia River tributaries

Abstract:

The largest river on Earth to cross an active volcanic arc, the Columbia River has provided a near-sea-level base level relative to the uplifting Cascade Arc for at least the last 17 Myr. In this setting, uplift is driven by tectonics as well as magmatic addition by intrusive and extrusive materials. Are these uplift signals recorded in topography? Can tools of geomorphology be used to infer long-term variations in mantle-driven magma flux or changes in crustal magma transport processes? To address these questions, we focus on a sequence of hyaloclastites filling a Columbia paleo-channel, which record ~800 m of uplift at the arc axis beginning about 3.5 Ma. The deformation pattern is signaled by the widespread distribution of prominent knickpoints in 17 fluvial networks tributary to the Columbia, where uplift has caused accelerated erosion rates (>0.2 mm/yr) resulting in the removal of ~450 km^3 of bedrock.

We co-invert deformation and landscape disequilibrium signals using a flexural model for a thin elastic plate subject to varying basal pressure distributions from intruding magma. This forces a forward model for bedrock erosion in the tributary drainages. We use a Bayesian-Markov-Chain Monte-Carlo inversion framework to generate probability density functions for each model parameter in order to explore trade-offs in the 22-dimensional parameter space. By testing the magmatic uplift hypothesis in this way, we gain insight into the potential distribution of magma at depth, with temporal boundary conditions that inform rates of magma flux into the crust. Preliminary results suggest an effective elastic thickness of ~10 km and an inferred magma flux of at least 10 km^3/km/my, though tradeoffs between bedrock erodibility and uplift onset time in the fluvial model are evident in inverted posterior probability distribution functions. The magma flux estimate agrees with estimations of Quaternary extrusion rates (O’Hara et al., 2020, Geology), assuming an intrusive:extrusive ratio of ~5:1, while also falling within the range of flux estimates from heat flow modeling (Ingebritsen and Mariner, 2010, JVGR). Linking magmatic processes to evolving surface topography thus provides a new quantitative tool for studying volcanic processes at large scales.