Orogen-wide erosional patterns in the Alps: Insights from unmixing modeling of modern-day and Miocene orogenic fluvial sediments

It is hypothesized that lithospheric reorganisation, including slab breakoff and tearing, leads to shifts in crustal buoyancy, which then influences rock uplift, erosion and weathering on the surface. This process can be ideally studied in compressional orogenic settings with complex fluvial drainage systems, such as the European Alps. Changes in uplift and erosion can be studied using sedimentary provenance techniques, such as major element geochemistry and petrographic point counting. First we use modern-day fluvial sands to understand how major element geochemistry and petrography reflect the modern erosional pattern of the Alps. In a second step, the signatures of modern river sands are compared to those of sandstones deposited in the Alpine foreland basin, which was a major sedimentary sink throughout the Oligocene and Miocene.

Here, we present two datasets consisting of major element geochemistry (ca. n=180) and petrography (ca. n=200) data of modern Alpine rivers. We use smaller rivers draining specific source rock types within the orogen to define geochemical and petrographic end-member lithological fingerprints. These fingerprints are subsequently used to deconvolve via unmixing modeling 9 larger fluvial drainage basins in the Alps: the Adige, Dora Baltea, Drau, Enns, Inn, Mur, Rhine, Rhone andSalzach rivers. We compare themodeled relative contributions of specific source rocks/areas with the modern-day erosion patterns in those drainage basins based on geological maps and published erosion rates. The comparison with detrital spectra in foreland basin deposits provides insights into the change of watershed locations and river networks from the Miocene to today.