Covariation of cross-divide differences in denudation rate and χ: Implications for drainage basin reorganization in the Qilian Shan, northeast Tibet

Drainage divide migration is of wide interest because it drives changes in topography, aquatic species habitat, and fluxes of water and nutrients across Earth's surface. To date, divide migration rates have been measured in relatively few places, partly because of the rarity of denudation rate measurements on opposing sides of drainage divides. Here we report 54 basin-averaged denudation rates across the Qilian Shan, China, inferred from Be-10 concentrations in stream-borne quartz. We combine these with 18 previously published basin-averaged denudation rates and new measurements of the topographic metric chi in the river networks. These data reveal divide migration rates of similar to 3-1385 mm kyr(-1) and area loss in the headwater reach of the Hei River basin. Cross-divide differences in denudation rate (Delta E) and channel-head chi values (Delta chi) follow an exponential relationship Delta E = Delta E(0)e(-b Delta chi), providing empirical support for the hypothesis that Delta chi values can reflect Delta E. Here, b has the same value within uncertainty as in Delta E-Delta chi data in the southern Appalachians and the Ozark Dome in previous studies, consistent with a common set of processes controlling divide migration in all three regions. The value of Delta E-0 is 1-2 orders of magnitude higher at Qilian Shan than at the two other sites, implying higher values of Delta E at a given Delta chi. Our numerical simulations show that near-exponential Delta E-Delta chi relationships can arise as topographic divides approach equilibrium under spatially uniform uplift rate, consistent with divide migration toward steady state in each of these regions. Further, they show that the magnitude of Delta E at a given Delta chi increases linearly with rock uplift rate. Together, these results suggest that ln(Delta E) exhibits the same sensitivity to Delta chi across mountain ranges, and that the magnitude of Delta E may be strongly sensitive to rock uplift rate. (C) 2021 Elsevier B.V. All rights reserved.