Control of mechanical heterogeneities on nappe detachment, transport and stacking in the Helvetic Nappe System
Abstract
Nappe systems are typical of many orogenic belts. A well-known example is the Helvetic nappe system in
the Swiss Alps, which consist of sedimentary units that have been sheared and thrusted over the crystalline
basement of the European passive margin during the Alpine orogeny. These sedimentary units form, for
example, the parautochtonous Morcles nappe of the infrahelvetic complex, which is situated below the
Helvetic Wildhorn super-nappe.
Although nappes were recognized a century ago and have been studied since then, the mechanisms
responsible for nappe generation and nappe stacking are still debated. We present 2D high-resolution
thermo-mechanical numerical simulations of the shearing of basement-cover system with half-graben
representing the upper crust of the European passive margin. The scope of the numerical simulations is to
evaluate the impact of the (1) geometry of the basement-cover interface, (2) presence of mechanical layering
resembling the alternation of shale-rich and carbonate-rich sedimentary units. We are identifying the
controlling mechanisms of the formation of the basal detachment zone. The final aim of the simulations is to
reconstruct the overthrusting of the Helvetic nappes over the nappes of the Infra-Helvetic complex