4D reconstruction of the Doldenhorn nappe-basement system in the Aar massif: Insights into late-stage continent-continent collision in the Swiss Alps

Abstract

The inversion of passive margins and their transportation into fold-and-thrust belts is a critical stage of mountain-building processes. In this study, we selected the Doldenhorn Nappe and Aar/Gastern Massifs (Central Swiss Alps) system as an ideal laboratory to document the impact of inherited structures, their along-strike variations, and basement tectonics on the evolution of a fold-and-thrust belt. Three-dimensional geological modelling and cross-section restoration allowed us to reconstruct the 4D evolution of the investigated area during the late-stage Alpine orogeny (30 to 0 Ma). Our results demonstrate that: (i) the Doldenhorn Nappe is the product of the inversion of an asymmetric half-graben basin; (ii) variations in incipient basin sediment thicknesses correlate directly with the along-strike variation of the deformation of the Doldenhorn Nappe; and (iii) the multiphase thick-skinned deformation that overprinted the Doldenhorn Nappe from 22 Ma until today changed the shape of the Doldenhorn Nappe and Aar/Gastern Massifs. This reconstruction shows how thin-skinned nappe formation mechanisms and the nappe geometries are controlled by the initial basement geometry and by the rheological strength contrasts between basement and cover sediments. Basement-involved uplift and shortening controls then the late-stage collisional 3D overprint and mechanics of the fold-and-thrust belts.