Landscapes buried beneath large-volume ignimbrites reveal preeruptive uplift rates.

Abstract

Pyroclastic density currents from large explosive eruptions can generate expansive ignimbrite deposits with planar, low-angle surfaces. We demonstrate the utility of these surfaces for constraining preeruptive rock uplift rates from the relief of buried paleolandscapes. Using a landscape evolution model driven by river erosion, we explore the range of permissible landscape geometries beneath an ignimbrite of a given surface slope. Our results demonstrate a clear correlation between river channel steepness and topographic slope as a function of rock uplift rate. We show that lower rock uplift rates are required to generate gentle landscapes buried by ignimbrite deposits and that ignimbrite burial therefore preferentially records landscapes formed during tectonomagmatic states of an orogen, potentially linking long-term landscape evolution with the conditions under which large explosive volcanic systems develop. Model application to the Early Miocene Cardones ignimbrite on the western flank of the Central Andes yields preeruptive rock uplift rates of <0.26 kilometers per million years, comparable with independent thermochronometric and geothermobarometric constraints.