Along-strike variations in thin-skinned thrusting style controlled by pre-existing basement structure in the easternmost Jura Mountains (Northern Switzerland)

Abstract

AbstractA detailed analysis of the Late Miocene Mandach Thrust, a key tectonic structure of the easternmost Jura Mountains (northern Alpine foreland), is presented providing insights into the modes of along-strike structural cover–basement interactions in a classical foreland setting. Our study builds on the construction, restoration and forward modelling of eight closely spaced cross-sections constrained by depth-migrated 2D seismics and geological maps. The results indicate predominantly thin-skinned thrust tectonics without significant inversion of underlying basement structures. However, inherited pre-thrusting normal faults exerted a strong control on the observed thrusting style, changing along-strike from a comparatively simple geometry to a complex, partly overthrust, partly reactivated normal fault. The observed variations relate to changes in the relief of the mechanical basement and the characteristics of pre-thrusting normal faults. The thrust's complexity is further increased by the local activation of secondary detachment horizons and possibly along-strike sedimentary facies changes within the thrust-faulted sedimentary sequence. The variations in thrusting style go along with subtle changes in shortening that may point towards as yet undetected transfer structures. As such, our structural analysis of the Mandach Thrust provides an improved understanding of the fault's kinematics and serves to highlight existing exploration uncertainties.