The Slab Puzzle of the Alpine-Mediterranean Region : Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle
Mediterranean tectonics since the Lower Cretaceous has been characterized by a multiphase subduction and collision history with temporally and spatially variable, small ‐ scale plate con ﬁ gurations. A new shear wave velocity model of the Mediterranean upper mantle (MeRE2020), constrained by a very large set of over 200,000 broadband (8 – 350 s), interstation, Rayleigh wave, phase velocity curves, illuminates the complex structure and fragmentation of the subducting slabs. Phase velocity maps computed using these measurements were inverted for depth ‐ dependent, shear wave velocities using a stochastic particle ‐ swarm ‐ optimization (PSO) algorithm. The resulting three ‐ dimensional (3 ‐ D) model makes possible an inventory of slab segments across the Mediterranean. Fourteen slab segments of 200 – 800 km length along ‐ strike are identi ﬁ ed. We distinguish three categories of subducted slabs: attached slabs reaching down to the bottom of the model; shallow slabs of shorter length in downdip direction, terminating shallower than 300 km depth; and detached slab segments. The location of slab segments are consistent with and validated by the intermediate ‐ depth seismicity, where it is present. The new high ‐ resolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the Mediterranean realm.