Persistent long-term (c.24 Ma) exhumation in the Eastern Alaska Range constrained by stacked thermochronology

Abstract

AbstractTo address Miocene–present episodic v. persistent exhumation, we utilize a simple graphical procedure that vertically stacks spatially diverse K-feldspar 40Ar/39Ar multi-domain diffusion (MDD) models from the length of the approximately 100 km-long high-peak region of the Eastern Alaska Range. We supply additional constraints with 40Ar/39Ar mica dating because the higher closure-temperature-window places limits on the initiation of rapid Eastern Alaska Range exhumation. We also provide a broad 40Ar/39Ar K-feldspar minimum closure age data set to add more detail on spatial patterns in the regional exhumation history for the Eastern Alaska Range. We find that rapid and persistent exhumation has occurred in the Eastern Alaska Range since about 24 Ma at a long-term rate of approximately 0.9 km/Ma, but that this rapid exhumation is spatially variable through time. Onset of rapid Eastern Alaska Range exhumation is coincident with the initiation of rapid exhumation in SW Alaska, the Western Alaska Range and the Chugach–Saint Elias Range at around 25 Ma, implying a region-wide deformational response to a change in tectonic forcing. The initiation of highly coupled flat-slab subduction of the Yakutat microplate is probably responsible for this prolonged period of rapid exhumation in southern Alaska.Supplementary material:Sample locations from the Eastern Alaska Range, and 40Ar/39Ar data tables and age spectrum figures are available at www.geolsoc.org.uk/SUP18603.