Exhumation and relief development in the Pelvoux and Dora-Maira massifs (western Alps) assessed by spectral analysis and inversion of thermochronological age transects
We have used dedicated sampling and analysis of apatite fission track (AFT) and apatite (U-Th)/He (AHe) thermochronological data sets in an attempt to quantify relief evolution and exhumation rates in the Pelvoux and Dora-Maira massifs (western European Alps). A dual approach comparing spectral analysis and thermal-kinematic model inversion was applied. We sampled age-elevation relationships at a range of topographic wavelengths along two north-south transects crossing these massifs. For the 40-km-long Pelvoux transect we report 35 new AFT ages that range between 3.0 ± 0.4 Ma and 12.6 ± 1.0 Ma, and 8 new AHe ages between 3.5 ± 1.5 and 4.7 ± 0.7 Ma. The Dora-Maira transect spans a distance of 60 km and includes 28 (23 new and 5 previously published) significantly older AFT ages, which vary between 13.1 ± 0.2 and 27.3 ± 0.3 Ma. Inferred exhumation rates of 0.7 km m.y.−1 since ∼8 Ma in the Pelvoux and only 0.1 km m.y.−1 since ∼20 Ma in Dora-Maira are consistent between methods as well as with previous estimates, although they are associated with large uncertainties due to imperfect sampling and analytical errors. Neither massif displays clear evidence for relief change during the intervals constrained by the data. Data from the Dora-Maria massif suggest moderate recent relief increase, whereas the results from the Pelvoux are inconclusive but could imply relief decrease. Our study highlights the difficulties of applying thermochronology techniques to constrain relief changes. We show that an unreasonable number of samples is needed to perform reliable spectral analysis of age-elevation transects and discuss the overall limitations of both techniques to address relief evolution. We suggest that a more efficient approach would be to apply thermal-kinematic model inversion to relatively small study areas using spatially distributed sampling and multiple thermochronometer analyses per sample.