Geochronological evidence for continuous exhumation through the ductile-brittle transition along a crustal-scale low-angle normal fault: Simplon Fault Zone, central Alps

摘要: [1] Major low-angle normal faults juxtapose different structural levels of the crust that record both brittle and ductile deformation. Field relationships alone cannot establish whether these responses to deformation represent (1) parts a single process exhumation along detachment or (2) two separate events, with later, more discrete exhuming fossil shear zone from depth. These general models are critically assessed for Simplon Fault Zone (SFZ) in central Alps. The SFZ shows spatial transition broad mylonitic identical kinematics. age ductile-brittle is controversial. We present detailed geochronological study based on fission track, 40Ar/39Ar, Rb/Sr microsampling dating, coupled structural, petrological, chemical analyses provides tight constraints timing. Discontinuous mineral cooling ages over range temperatures across fault argue activity between 20 3 Ma. On basis synkinematic white mica low-temperature zones necks foliation boudinage, brittle-ductile footwall could be dated at ∼14.5–10 Overall, data presented here consistent continuous shearing localized within same geological framework, period ∼15 therefore an example telescoped crustal section major fault, involving rather than two-stage structure.