Abstract
AbstractMediterranean tectonics since the Lower Cretaceous has been characterized by a multiphase subduction and collision history with temporally and spatially variable, small‐scale plate configurations. 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 identified. 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.
Highlights
After opening of the east‐west trending Tethys Ocean, Gondwana, and Eurasia separated from the Triassic onward (e.g., Dewey et al, 1989; Gaina et al, 2013; Maffione & van Hinsbergen, 2018; Schmid et al, 2008; Stampfli, 1991; van Hinsbergen et al, 2019), with the total plate separation probably ranging between 1,000 km in the western and approximately 2,000 km in the eastern Mediterranean (e.g., Stampfli & Borel, 2002)
A slab segment is defined if the corresponding high‐velocity anomaly meets the following conditions: (i) its velocity is 2% greater than the depth‐dependent average velocity model (Figure 8); (ii) it is strongly dipping; (iii) it is located beneath or near a subduction zone, (iv) it is elongated laterally following, at least partly, the strike of a subduction zone; (v) it has a width between about 80–250 km, (vi) if the lateral resolution indicated by the checkerboard tests (Figures S4, S5, and S6) is better than 150 km in the region of the anomaly; and (vii) if present, intermediate‐depth seismicity at the location of the high‐velocity anomaly is used to identify the top of the slab segment
Our results show that the dip of the slab in the central Alps can be imaged by surface wave tomography, the detailed shape of the south dipping anomaly remains to be resolved
Summary
After opening of the east‐west trending Tethys Ocean, Gondwana, and Eurasia separated from the Triassic onward (e.g., Dewey et al, 1989; Gaina et al, 2013; Maffione & van Hinsbergen, 2018; Schmid et al, 2008; Stampfli, 1991; van Hinsbergen et al, 2019), with the total plate separation probably ranging between 1,000 km in the western and approximately 2,000 km in the eastern Mediterranean (e.g., Stampfli & Borel, 2002). Surface waves are well suited to study the three‐dimensional shear wave velocity structure in the shallower upper mantle down to about 300 km depth (Biryol et al, 2011; Boschi et al, 2004; Chang et al, 2010; Legendre et al, 2012; Levshin et al, 1989; Marone et al, 2004; Montagner & Tanimoto, 1990; Schivardi & Morelli, 2011; Shapiro & Ritzwoller, 2002; Salaün et al, 2012; Schaeffer & Lebedev, 2013; van der Lee & Nolet, 1997) It remains, a challenge to resolve the small slab segments in the Mediterranean. We focus on the identification of slab segments in the Mediterranean upper mantle and distinguish attached slab segments reaching down to the bottom of the model from slab segments that terminate at shallower depth and slab segments that are detached from the lithosphere above
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