THRUST DEVELOPMENT IN THE EASTERN JURA MOUNTAINS RELATED TO PREEXISTING EXTENSIONAL STRUCTURES

From tunnel and map data, three detailed balanced cross-sections of th e Mesozoic cover of the Jura fold and thrust belt in the Hauenstein ar ea (eastern Jura Mountains, Switzerland) were constructed. Viable mode ls of the kinematic evolution of the structures document different sta ges of thrust development. Most thrusts propagate first from the basal decollement in the Middle Triassic evaporites to the Opalinus shales. In some cases they continue for a short distance layer parallel and t hen break through to the surface. In other cases they get stuck in the Opalinus shales. With further shortening, either a delamination occur s, where the incompetent layers are wedged under the overlying compete nt limestones. The thrust breaks through the limb of the anticline at a higher level. Otherwise, the thrust steepens and breaks through the hinge of the fold. The resulting, kinematically viable sections confir m that the Miocene thrusts nucleate at inhomogeneities of the sub-deco llement relief. These are possibly related to the borders of an underl ying Palaeozoic trough system, reactivated as faulted flexures during the Eocene to Early Miocene.