EXPLORING CONTROLS ON POST-OROGENIC TOPOGRAPHIC STASIS OF THE PYRENEES MOUNTAINS WITH INVERSE LANDSCAPE EVOLUTION MODELING AND LOW-TEMPERATURE THERMOCHRONOLOGY (Invited Presentation)

The sustainability of high topography over long timescales in post-orogenic mountain belts is a longstanding puzzle in tectonic geomorphology and geodynamics. Here we utilize the well-documented orogenic paleo-topography and spatial-temporal exhumation patterns of the Pyrenees Mountains in a numerical modeling study investigating controls on post-orogenic topographic stasis. Orogenic activity in the Pyrenees Mountains ceased ca. 25 Ma, but topographic decay has only been on the scale of hundreds of meters since that time. We use the landscape-evolution model FastScape coupled with the neighborhood-algorithm inversion method to explore how various parameters influence the post-orogenic topographic stability. The inversions are constrained using topography (elevation, slope) and a low-temperature thermochronology dataset including AHe, AFT, ZHe, and ZFT cooling ages. We find that incorporation of an erodibility threshold is required for moderating post-orogenic topographic decay. Without incorporation of this parameter, which is a proxy for critical shear stress, post-orogenic topography declines rapidly on Myr timescales. Thermochronologic constraints are crucial to this conclusion by quantifying the syn- and post-orogenic exhumation. In the absence of thermochronologic constraints in the model, the LEM predicts excessive post-orogenic topographic reduction and associated rock exhumation. While other evaluated parameters like lithology and precipitation also contribute to topographic stability, they are secondary to the erodibility threshold in maintaining long-term post-orogenic topography. Our results provide valuable insights into the mechanisms governing post-orogenic landscape evolution and emphasize the importance of thresholds in landscape evolution modeling of mountain belts.