3D modeling of crustal shortening influenced by along-strike lithological changes: Implications for continental collision in the Western and Central Alps

The European Alps show major along-strike variations in the partitioning of crustal shortening between the upper and the lower plates, either explained by lateral variation in temperature and rheology, or by along-strike changes in crustal-scale lithology. Here, we present the first 3D thermomechanical geodynamic model to test the potential impact of along-strike lithological (and associated rheological) changes and lateral temperature variations on crustal shortening during continental collision in the Western and Central Alps. Numerical modeling results suggest a minor impact of lateral thermal variations and lithological changes in the lower plate for the Alpine orogeny. In contrast, lateral lithological changes in the upper plate structure, defined by the presence of the buried Ivrea Body in the Western Alps, should play a major role in determining the present-day architecture of the Alpine belt. Our models suggest that the Ivrea Body acts as a strong, rigid buttress constraining crustal shortening to the lower plate, promoting the formation of the Jura fold-and-thrust belt, and supporting the higher surface elevation observed in the Western Alps. On the other hand, in the Central Alps where the Ivrea Body is absent, much broader distribution of crustal shortening results in lower surface elevation. Numerical modeling results also suggest that crustal shortening in the Central Alps is focused within the upper plate during the final stages of continental collision, favored by the indentation of thickened upper crust of the lower plate, and by detachment of the Adriatic upper crust from the underlying lithosphere.