Thermochronological evidence for a late Pliocene climate-induced erosion rate increase in the Alps

(U-Th)/He and fission-track analyses of apatite along deep-seated tunnels crossing high-relief mountain ranges offer the opportunity to investigate climate-tectonic forcing on topographic evolution. In this study, the thermochronologic analysis along the Simplon tunnel (western-central Alps; Italy and Switzerland) constrains in detail the mechanisms controlling the topographic evolution of the Simplon Massif. Cooling rates vary from about 10A degrees C/Ma at about 10 Ma to about 35A degrees C/Ma in the last 3 Ma. Such increase in cooling rates corresponds to the inception of glacial cycles in the northern hemisphere. Age patterns show correlation with faults distribution until 2 Ma, suggesting that tectonics-controlled rocks exhumed up to that age. After 2 Ma thermo-chronometric data show that the Simplon area has experienced primarily erosional exhumation. All age patterns provided are not affected by topographic effects, thus indicating that present-day topography has been carved in the last 2 Ma, most likely controlled by glacial erosion.