The geological processes leading to the formation of mountain chains include processes going on at depths of up to 30 km beneath the Earth's surface and process shaping the surface of the mountain chain. In this project we study these processes studying the rocks within the Alpine chain and comparing the evolving model to sandbox experiments we performed in the laboratory and numerical modeling.
Mountain building processes at depth involve the deformation of rock units in the contact zone of the collision of two continents. In this process packages of rocks , 1 - 5 km thick and 10 - 50 km long, are placed on top of each other. These packages, called nappes, are intensively deformed during the stacking. This stacking results in a direct uplift of the rocks above and thus the land surface. But thickening the crust of the mountain chain also leads to buoyant rise of the entire chain because of the low density of the crust in comparison to the denser mantle beneath. In the Alps the nappe stacks that formed at depth are now directly observable at the surface because many kilometers of rock layers were removed by erosion. This allows us to study the deformations going on during nappe stacking. Structural analysis will allow to unravel the sequence of deformation events. At critical places we wish to date the deformation features by dating minerals that formed during the event. Previous work on these nappe stacks did not separate between structures due to folding from those caused by faulting. Our analysis includes both and involves a quantitative assessment of the strains accumulated.
By studying the Suretta nappe (Graubünden) and the Bernhard nappe complex (Valais) we compare two units that had much in common regarding their geological history and are key units in regard to deep crustal nappe stacking. Our early results suggest that the geometry of the nappes is strongly controlled by pre-existing heterogeneities (Permo-Carboniferous graben fills). Their lateral discontinuity explains differences in cross-sectional geometry that hitherto had been overlooked because of simple projections along strike of the Alpine chain.