Thermochronologic data collected along age-elevation profiles are
commonly interpreted as recording temporally variant but spatially
constant exhumation rates. However, thermochronologic age-elevation
relationships are known to be perturbed by topographic effects and
potential changes in relief, which are neglected in the inherently 1-D
interpretation commonly applied. Such data thus potentially record both
the denudation and relief history of the sampled region but extracting
this information is challenging. In a companion paper, we develop a
methodology for rigorously interpreting thermochronologic age-elevation
profiles in terms of exhumation rates and relief development through
time, and to independently quantify the resolution of these constraints.
Here we test this approach using a thermochronological dataset
consisting of apatite and zircon fission-track and (U-Th)/He data,
collected at La Meije Peak in the Pelvoux-Ecrins massif (French Western
Alps). Our data and models suggest a three-phase exhumation history in
the Pelvoux-Ecrins massif, including a pulse of rapid exhumation at
similar to 6-5.5 Ma, preceded and followed by more moderate rates of
denudation in the order of 0.3-0.4 km Myr(-1). This rapid exhumation
event appears to occur coevally in other external crystalline massifs in
the Alps but is not detected by qualitative inspection the age-elevation
relationships. Both our synthetic results and inversion of the La Meije
data strongly suggest that apatite fission-track age-elevation
relationships alone cannot resolve both denudation and relief histories
independently and that multiple thermochronometers are required.
Combining apatite fission-track and (U-Th)/He ages and, particularly,
including fission-track-length data greatly improves the resolution of
the inferred exhumation histories. Although denudation rates through
time and the timing rate changes are generally well resolved, our data
have insufficient resolution to satisfactorily constrain the relief
history. Synthetic results reported in the companion paper suggest that
the reason for this limitation is that relief increase through valley
carving has been insufficient with respect to the regional denudation
rates to be unambiguously extracted from the data. (C) 2010 Elsevier
B.V. All rights reserved.