AlpArray is changing notions of lithospheric subduction along the Alps and its effects on orogeninc lithosphere. Teleseismic Vp tomography reveals a slab of European lithosphere that is largely detached at and below 150 km in the Western Alps. Only in part of the Central Alps is the slab still attached, possibly reaching down to the mantle transition zone, where it appears connected to subducted remains of Alpine Tethys. SKS directions beneath the Alps suggest that asthenosphere not only flowed passively around the sinking slab, but may have induced the anomalous northward dip of the detached slab segment beneath the Eastern Alps.
The structure of the orogenic lithosphere differs profoundly along strike of the Alps, as revealed by local earthquake tomography, ambient-noise studies, as well as S-to-P receiver-functions and gravity studies: In the Central Alps where the slab is still attached, the exhumed retro-wedge of the orogen overrides a wedge of Adriatic lower crust. In the Eastern Alps where the slab has detached, exhumation is focused in the orogenic core (Tauern Window) north of and above bulged lower crust of presumed Adriatic origin. This indicates decoupling at the base of qtz-rich, presumably hydrous intermediate crust to accommodate coeval Miocene N-S shortening, orogen-parallel thinning and eastward extrusion of orogenic lithosphere.
We propose a new model for Alpine orogenesis that invokes changing wedge stability and migrating subduction singularities above the delaminating and detaching Alpine slab in the east to explain east-west differences in Oligo-Miocene structure, magmatism, erosion and sedimentation in peripheral Alpine basins.