NOT FEELING THE BUZZ: TECTONICS-NOT CLIMATE-SETS MOUNTAIN HEIGHTS (Invited Presentation)

Rapid denudation of topography at and near the Equilibrium Line Altitude (ELA), where glacial erosion is thought to be most efficient is explored in the glacial buzzsaw hypothesis [1]. This hypothesis emerged as an important top-down mechanism controlling the Earth’s tectonic and climatic engine-fueled by correlations between mountain heights and ELAs and the hypothesis that global cooling during the Plio-Pleistocene elevated rates of erosion in mountain belts. Glaciated plateaus have also been argued to result from glacial buzzsaw smoothing of possibly once-rugged topography along passive margins. Here, we present a counter hypothesis from an analysis of compiled bottom-up tectonic rates and top-down erosion rates. We use tectonic convergence rates, topographic data, and erosion rate data from cordilleran-style, arc-continent convergent margins (Andes, Central America, Cascadia, British Columbia, Alaska) to propose an alternative primary control on mountain height. We observe a linear correlation between various metrics (erosion rates, elevation maxima and mean, orogen widths, crustal thickness) and plate convergence rates, including heavily glaciated mountain ranges (Alaska, Cascadia, and Patagonia). That mountain ranges in different climatic regimes fall within the same trend implies that sustained plate convergence velocity is the primary control of mountain range mass and height. Moreover, a closer look at the Andean mountain ranges, commonly depicted as a type-example of constructive and destructive glacial controls, reveals that the latitudinal variations of mountain heights closely mirror the maximum rotation velocities of the converging plates (i.e. Nazca and Antarctica) predicted by Euler pole rotation. We also use compiled erosion rates derived from cosmogenic nuclides from flat surfaces (including tors) around the world. We find that erosion rates in glaciated plateaus (>50°) along passive margins do not systematically vary with latitude, and have a range in glacial erosion rates that is not significantly different from non-glaciated flat regions with median erosion rates in summits over several degrees of latitude (glaciated or not) at or below 20 m/Ma.

[1] Brozović N. et al. 1997. Science (80) 276: 571–574. doi:10.1126/science.276.5312.571