TECTONIC DIFFUSION AND RATE OF GLOBAL EROSION

Understanding relations between global rates of tectonic uplift and continental denudation is an important challenge to a wide range of scientists interested in describing the evolution of the Earth’s surface environment and topography. Here, we describe a theoretical link between vertical (orogenic) tectonism and associated erosion, which is analogous to thermally-driven diffusion of isotopes and elements in minerals. Thermochronometric data and isotopic ages of now-exposed minerals and hydrothermal ore deposits show that bodies of rock (lithosomes) ‘diffuse’ tectonically relative to the Earth’s erosive surface, that rates of vertical diffusion increase with depth in the crust, and that those nearest the Earth’s surface are best described by mean vertical displacement of ~200 m per million years. This average amount of vertical displacement yields ~15 Gt/yr of sediment if distributed over an area ~22 x 10⁶ km². This corresponds to ~15% of the total modern continental surface area, which is approximately the area occupied by currently or recently active (eroding) orogens with mean local relief in excess of 500m³. The sediment flux predicted by our tectonic diffusion model is comparable to the erosional sediment flux delivered to the global oceans by rivers as well as rates of continental denudation estimated from sedimentary rock volumes. Thus, the erosional flux of sediment to the global ocean is the same as that estimated from data on ages and amounts of now-exposed crustal lithosomes, providing an empirical basis for modeling the long-term tectonic history of uplift and denudation.