Sebastian Wolf

Why do back-arcs open and the Andes form?

The crustal structures of overriding plates in subduction settings around the world can vary between a wide range of deformation styles, ranging from extensional structures and back arc opening induced by slab roll back as in the Tonga or Hellenic subduction zone to large, plateau-like orogens such as the central Andes. Both end member types have been intensively studied over the last decades and a range of hypotheses has been proposed to explain their characteristics.
To investigate the behavior of overriding plates in subduction zones we use high resolution, upper mantle scale plane-strain thermo-mechanical models, which also account for phase changes of rocks that enter the eclogite stability field and the phase transition at the 660 km mantle discontinuity. We consider varying plate velocities and back-arc lithospheric strength as the main variables affecting the strain regime of the overriding plate in subduction zones and conducted a sensibility study with those parameters. Our results show that the back arc lithospheric strength plays a pivotal role in determining whether and when the overriding plate will deform, and the combination of subduction and overriding plate velocity determines the type of strain regime in the overriding plate. Additionally, the interface strength of the subduction zone has an important impact. To verify our results we will have a closer look at the central Andes.