Unraveling the crustal structure of hyper-extended rifted margins: the example of the Bernina domain in the Alpine Tethys (SE Switzerland)

A long-standing problem in Earth Sciences is to understand how continents break apart to form new oceanic basins. The discovery of exhumed continental mantle and hyper-extended crust devoid of significant normal faulting directly overlain by shallow marine sediments, as observed in many rifted margins, is proving fundamental in defining the controls and processes that thin the continental lithosphere. This leads to the questions of what structures/processes can explain major crustal thinning and when and where they were active? A more direct access to the sedimentary record of deep rifted margins and the underlying crust/mantle lithosphere is exposed in the Alps in Western Europe. Remnants of the ancient Alpine Tethys rifted margins are well exposed and the palaeo-geographic position of these units can be reconstructed satisfactorily. We initiated a research project in the Bernina domain in SE Switzerland, where remnants of the transition between the proximal and the distal/deep Adriatic margin, comparable with the necking zone in present-day magma-poor rifted margins are exposed.