Uplift and Erosion Histories of Continents From Inversion of Drainage Networks

The physiography of landscapes is a complex response to uplift generated by crustal and sub-crustal processes. Conversely, landscapes, when properly decoded, could provide information about histories of uplift and denudation rates. On most continents drainage networks set the pace of denudation. Since these networks are widespread, the notion of combining a quantitative understanding of drainage development with independent calibration is attractive. We build upon our recent work to show that it is possible to determine meaningful spatial and temporal patterns of uplift rates from linearised inversion of longitudinal river profiles. The uplift rate histories of Africa and Australia are estimated by inverting 964 river profiles, following careful calibration of a simplified version of the stream power erosional model (∂z/∂t=-KAmSn+Upartial z/partial t=-KA^mS^n+U, where n=1n=1). Misfit between calculated and theoretical profiles is small (Africa, χ2=2.4\chi^2=2.4; Australia, χ2=1.8\chi^2=1.8). Calculated patterns of uplift suggest that the topography of both continents grew during the last 65 million years. The calculated uplift histories are consistent with the age of emergent marine terraces, sedimentary flux information, the history of magmatism, rock cooling and denudation estimates in both continents. Using more general non-linear inverse methods we show that precipitation rate has to vary with a periodicity of 10 million years or more to significantly effect our results. Large changes in upstream drainage area (±50%pm50%) have a small effect on the timing or amplitude of calculated uplift. Residual misfit between families of observed and theoretical river profiles is smallest when n=1n=1. Drainage networks contain coherent signals that record the growth of topography on the continents.