Perturbation of isotherms below topography: constraints from tunnel transects through the Alps

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... This study, in contrast, aims to directly measure the position of isotherms below topographic relief under a given framework of denudation rate, topographic wavelengths, relief amplitued, and geothermal gradient. Our study areas are three tunnel transects through the Central and Western Alps; the Gotthard, Lötschberg, and Mont Blanc tunnels. All three profiles are situated in rapidly exhuming areas with relief between 1500 and 2800 m and topographic wavelength of about 10 km, thus representing typical geomorphic features of active orogens. Samples from the tunnel profiles and their corresponding surface profile will be dated by zircon fission track, apatite fission track, and apatite (U-Th)/He analysis. Distributions of these ages will yield two-dimensional profiles showing the positions of isotherms below topography. The two-dimensional profiles may at least partly be correlated to three-dimensional images, show the sensitivity of the different thermochronologic dating techniques to the perturbation effect, and give a measure of the perturbation-induced overestimation of exhumation rates inherent to the different dating techniques. The results will be used to test existing models and to provide benchmarks for future model concepts.