Two alternative models have been proposed to explain footwall exhumation
along major low-angle detachments: (1) crustal-scale exhumation along a
detachment fault that maintained a low dip angle or (2) exhumation along
a high-angle fault passively rotated by isostatic rebound (''rolling
hinge model''). These proposed models were tested against a
well-documented example of a low-angle detachment fault in the European
central Alps, the Simplon Fault Zone (SFZ). An extensive
thermochronological data set provides the basis for 2- and 3-D
thermokinematic models (Pecube), coupled with a stochastic inversion
algorithm (the Neighbourhood Algorithm). Model results establish that
the thermochronological pattern is better reproduced by a low-angle
detachment that maintained a 30 degrees dip, rather than by a rolling
hinge model. Although a range of histories involving either steady state
or variable exhumation rates is possible, the preferred model of highest
probability is for a variable rate, with the fault zone initiated at
18.5 +/- 2.5 Ma and active until the present day. Footwall exhumation
was relatively fast until 14.5 +/- 1.5 Ma (similar to 1.4 mm yr(-1)).
This enhanced SFZ footwall exhumation is similar in timing and
kinematics to orogen-parallel extension reported throughout the Alpine
orogen. After 14.5 Ma, SFZ footwall exhumation continued at a reduced
rate (similar to 0.7 mm yr(-1)) until 4 Ma. The subsequent increase (to
similar to 1 mm yr(-1)) reflects enhanced regional erosion rates across
both footwall and hanging wall after circa 4 Ma (from 0.35 +/- 0.15 mm
yr(-1) to 0.70 +/- 0.15 mm yr(-1)), probably in response to climate
changes during the Pliocene.