Tectonic Evolution of the Aegean Domain, Eastern Mediterranean, since the Early Mesozoic Based on 3D Slab Mapping, Unfolding, and Characterization from Seismic Tomography

The geological evolution of the Balkan region is recorded by ophiolites and stacked nappes near Greece. Tomographic studies have identified slab anomalies beneath the Balkan region (i.e., the Aegean, Egypt, and Emporios slabs) and have linked these slabs to the tectonic evolution of the western Tethyan domain since the Mesozoic. However, controversies exist on the spatiotemporal reconstruction of various lost oceans and the possibility of subducted continental lithosphere. The focus of this study is to: (1) constrain the plate tectonic evolution of the Aegean domain since the Mesozoic from seismic tomography using 3D mapping, slab unfolding, and characterization of intra-slab seismic velocities from global tomographic models. Our results are compared against published tectonic reconstructions, geology, and geodynamic models to synthesize a tomography-led plate reconstruction of the region since ~240 Ma; (2) test whether presently subducting continental and oceanic lithospheric along the Western Hellenic Subduction Zone (WHSZ) can be differentiated from a local tomography (Halpaap et al., 2018).

Our Aegean slab mapping shows two trench-parallel discontinuities characterized by relatively slow P-wave velocities between 200-400 km and 650-800 km depths. We link the shallower Aegean slab discontinuity to a change in arc-volcanic geochemistry in northwest Greece; the deeper discontinuity corresponds to a regional 68-52 Ma magmatic gap. Volume unfolding of the Aegean slab produces a slab volume of 1.66x108 km3 that accounts for subduction initiation at ~130 Ma, which is older than recently proposed. Unfolding of the Egypt slab gives a slab length of ~630 km, which fits previous reconstructions of the West Vardar ocean. Unfolding of the Emporios slab gives a ~2300 km long slab, which fits Paleo-Tethyan subduction. At the WHSZ, we show that subducted oceanic lithosphere has a ~40% faster P-wave perturbation (dVp) than subducted continental lithosphere across the Kephalonia Transform fault, providing insight for future studies that image continental subduction. Our linking of mapped tomographic features to geology implies that slab detachments, tears, and subduction discontinuities are resolvable from global tomography and shows the utility of slab unfolding for reconstructions back to the Triassic.