Two‐ and three‐dimensional thermal modeling of a low‐angle detachment: Exhumation history of the Simplon Fault Zone, central Alps

Abstract

[1] 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°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 (∼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 (∼0.7 mm yr −1 ) until 4 Ma. The subsequent increase (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.Citation: Campani, M., F. Herman, and N. Mancktelow (2010), Two-and three-dimensional thermal modeling of a low-angle detachment: Exhumation history of the Simplon Fault Zone, central Alps,

Thermochronology in Orogenic Systems

“…However, such interpretations require caution, because both theoretical and empirical studies indicate that they may underestimate the true age of fault initiation by up to several million years (House and Hodges, 1994;Ruppel and Hodges, 1994). Some of the most interesting studies of normal fault systems involve the development of large thermochronologic databases from well-exposed footwalls and the use of cooling age patterns to deduce fault kinematics and slip rates Brady, 2002;Brichau et al, 2006;Campani et al, 2010;Ehlers et al, 2001;Ehlers et al, 2003;Foster and John, 1999;Stockli et al, 2001).…”

On the nucleation of non-Andersonian faults along phyllosilicate-rich mylonite belts

“…This corresponds to the lowermost structural level in the Alps, and has been exhumed in the last stages of the continental collision between c. 26 and 3 Ma. The final phases of this exhumation in the western part of the window took place along the SFZ and consist of a differential uplift of c. 15 km (Grasemann & Mancktelow 1993;Campani et al 2010b).…”

Late Neogene exhumation and relief development of the Aar and Aiguilles Rouges massifs (Swiss Alps) from low‐temperature thermochronology modeling and 4He/3He thermochronometry

“…The Neogene tectonic evolution of the study area is related to the activity of the Rhône‐Simplon fault (Figure 1a), a southward‐dipping low‐angle detachment fault [e.g., Mancktelow , 1985, 1992; Seward and Mancktelow , 1994] accommodating tectonic denudation since the early Miocene until Pliocene to recent times [ Reinecker et al , 2008; Campani et al , 2010]. However, the late Neogene activity of this structure is controversial, with some studies arguing for a Pliocene acceleration of tectonic denudation [ Soom , 1990; Reinecker et al , 2008], while others suggest a decrease in Rhône‐Simplon fault activity during the late Neogene [e.g., Mancktelow , 1992; Campani et al , 2010]. The present‐day kinematics of the area reveals no active compression [ Calais et al , 2002; Nocquet and Calais , 2004] and orogen‐perpendicular extension [e.g., Champagnac et al , 2004; Sue et al , 2007].…”