Quaternary tectonic response to intensified glacial erosion in an orogenic wedge

Active orogens are thought to behave as internally deforming critical-taper wedges that are in rough long-term equilibrium with tectonic influx and erosional outflux. Spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation, topography and deformation of orogens, thereby affecting wedge taper. However, the impact of the most severe transition in Northern Hemisphere climate during the Cenozoic era—the onset of glaciation—has hitherto not been empirically documented. Here we analyse the spatial patterns of denudation and deformation, and their temporal variations, in the heavily glaciated St Elias orogen in southern Alaska. Low-temperature thermochronometry, thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global-scale intensification of glaciation in the middle Pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf. This led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment. We propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper. Our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics. Intense glaciation during the middle Pleistocene epoch led to focused denudation and mass redistribution within the St Elias orogen in southern Alaska, and resulted in structural reorganization of the orogen. The tectonic response of this orogen to climate change is consistent with predictions of numerical models.