Slab segmentation and late Cenozoic disruption of the Hellenic arc

Abstract

[1] The Hellenic subduction zone displays well-defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy, subduction rate, and tectonic deformation. In space, the active Hellenic subduction front is dextrally offset by 100-120 km across the Kephalonia Transform Zone, coinciding with the junction of a slowly subducting Adriatic continental lithosphere in the north (5-10 mm/yr) and a rapidly subducting Ionian oceanic lithosphere in the south (∼35 mm/yr). Subduction rates can be shown to have decreased from late Eocene time onward, reaching 5-12 mm/yr by late Miocene time, before increasing again along the southern portion of the subduction system. Geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic (Pindos) lithosphere until late Eocene time, followed by subduction of a broad tract of continental or transitional lithosphere (Hellenic external carbonate platform) and then by Miocene entry of high-density oceanic (Ionian) lithosphere into the southern Hellenic trench. Model results yield an initiation age for the Kephalonia Transform of 6-8 Ma, in good agreement with observations. Consistency between geodynamic model results and geologic observations suggest that the middle Miocene and younger deformation of the Hellenic upper plate, including formation of the Central Hellenic Shear Zone, can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab. Using this assumption, we make late Eocene, middle Miocene, and Pliocene reconstructions of the Hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation.

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

“…Further west, the Paxos carbonate platform continues to accrete to the Hellenides. At the junction between the slowly subducting Paxos continental platform and the fast retreating Mesogean oceanic lithosphere, the dextral strike-slip Kephalonia fault has developed since ~5 Ma, inducing a segmentation of the main thrust front (figures 8w-y) [Finetti, 1982;Royden and Papanikolaou, 2011]. Behind this subduction front, a medium-K calc-alkaline volcanic arc has been active in the south Aegean domain (figures 8x-y) [Pe-Piper and Piper, 2005].…”

“…Finally, additional extensional basins opened in the Peloponnese and along the eastern coast of the Hellenides, within the so-called Central Hellenides Shear Zone [Papanikolaou and Royden, 2007;Royden and Papanikolaou, 2011]. These basins include the Gulf of Corinth, which has accommodated ~15 km of N-S extension since the Pliocene (figure 3) [Armijo et al, 1996;Rohais et al, 2007;Jolivet et al, 2010b].…”

“…Similarly, the differential Pliocene-Quaternary large-scale counterclockwise rotations in the Hellenides and the Peloponnese (figure 3) and the second acceleration of trench retreat since ~5 Ma (figure 12b) could have been a consequence of a younger slab tear below the Corinth rift, decoupling the surface kinematics and crustal deformation between the Hellenides and the Peloponnese [Royden and Papanikolaou, 2011;Jolivet et al, 2013].…”

“…At the same time, extension ceased in the Cyclades and has localized at the edges of the Aegean domain, where highangle normal faulting has formed several grabens and half-grabens (figures 8w-y), such as in the Evvia island and the Corinth region (forming the Central Hellenic Shear Zone [Papanikolaou and Royden, 2007]), the Peloponnese, the Cretan Sea and the Menderes massif [Armijo et al, 1996;Royden and Papanikolaou, 2011;Pérouse et al, 2012]. This extensional tectonic regime has been accompanied in the Hellenides by a clockwise rotation of ~10° and ~23° north and south of the Central Hellenic Shear Zone [van Hinsbergen et al, 2005a;Bradley et al, 2013], increasing the curvature of the trench.…”

“…Along this oceanic subduction zone, a sedimentary wedge called the Mediterranean ridge developed since ~15 Ma against the Hellenic thrust belt (figures 1 and 4) Chaumillon et al, 1996;Kopf et al, 2003;Yem et al, 2011]. At the junction between the Paxos platform and the Mesogean oceanic basin, the Kephalonia strike-slip fault has accommodated 100-120 km of dextral offset since ~5 Ma, (figure 3) [Finetti, 1982;Royden and Papanikolaou, 2011].…”