3 times higher than those of the basic subduction model (Figure 5b). The upper plates strain rates in these models show a periodicity, which is due to the continued piling over the transition zone (Figure 3b). The same is valid for models of different gLM, with minor variations in the strain history. [12] In models where far‐field convergence constraints are included, margins largely rollback, stretching the upper plates (Figure 4c). Velocities and upper plates’ strain rates equilibrate in 15–20 m.y. after the constraints are applied, in hampered models, and in as long as 30 m.y., in the locked subduction (Figure 3), with strain rates up to 3000 times larger than the basic models’. In this configuration, large trench motions and strain rates are sustained until upper plates Figure 3. (a) Surface horizontal velocities of different yield, occurring at 50 and 30 m.y. following the constraints models with a thick upper plate. Vsub is for the velocity of application (Figures 3a and 3b), in hampered and locked subducting plate (thick lines), vup is the velocity of the upper subduction, respectively. At which point the retreating slab plate (thin lines) and (b) strain rates in the upper plate versus rearranges the mantle flow and extending laterally the con- time. Vertical thin line marks where the constraints are vecting cell (Figure 4c). applied to the basic setup (black line) and boundary condi- tions change. 5. Discussion at the transition zone at depth. Flow in the lower mantle is [13] Several published models have investigated the role of slightly perturbed (Figure 4a), while strain in the upper plate far‐field boundary conditions as well as three‐dimensional is negligible (Figures 3b and 5b, solid line). complexities to the single subducting plate [i.e., Stegman [11] In the models allowing for a deep penetration of et al., 2010, and reference therein]. However, we have the slab, a deeper convective cell in the mantle is induced shown here that the trench motions, and hence the tectonic (Figure 4b). The lower mantle penetration drives larger style of subduction, might be strongly controlled by the transient subducting plate velocities (Figures 3a and 5a), upper plate in the system. +20% to +70% for the values of lower mantle’s density [14] The long‐term stationary trench in the Hellenic sub- contrasts and viscosities used here. However, the upper duction zone can be reconciled with the thickening due to plate motions are negligible and strain rates are only 2– the Hellenic orogeny during the initial 100–40 Ma phase.

Figure 4. Second invariant of the strain rates and flow streamlines. (a) Free subduction (Basic) at the end of the simulation with a thick upper plate of 80 km. (b) Slab‐lower mantle Dr/r 30% at the end of the simulation. (c) Locked subduction after 500 km of trench rollback.

3

energy dissipation, Earth Planet. Sci. Lett., 262, 284 297, doi:10.1016/j. Mediterranean orogens, Am.J.Sci., 303, 353 409, doi:10.2475/ epsl.2007.07.039. ajs.303.5.353. Capitanio, F. A., C. Faccenna, and R. Funiciello (2009), Opening of Sirte Kincaid, C., and P. Olson (1987), An experimental study of subduction and Basin: Result of slab avalanche?, Earth Planet. Sci. Lett., 285, 210 216, slab migration, J. Geophys. Res., 92, 13,832 13,840. doi:10.1016/j.epsl.2009.06.019. Lister, G. S., G. Banga, and A. Feenstra (1984), Methamorphic core com- Capitanio, F. A., D. R. Stegman, L. Moresi, and W. Sharples (2010), Upper plexes of the Cordilleran type in the Cyclades, Aegean Sea, Greece, plate controls on deep subduction, trench migrations and deforma- Geology, 12,221 225, doi:10.1130/0091-7613(1984)12<221: tions at convergent margins, Tectonophysics, 483,8092, MCCOCT>2.0.CO;2. doi:10.1016/j.tecto.2009.08.020. Moresi, L., F. Dufour, and H. B. Mülhaus (2003), A lagrangian integration Christensen, U. R. (1995), Effects of phase transition on mantle convection, point finite element method for large deformation modeling of viscoelastic Annu. Rev. Earth Planet. Sci., 23,65 87, doi:10.1146/annurev. geomaterials, J. Comput. Phys., 184, 476 497, doi:10.1016/S0021-9991 ea.23.050195.000433. (02)00031-1. Faccenna, C., F. Funiciello, D. Giardini, and P. Lucente (2001), Episodic Piromallo, C., and A. Morelli (2003), P wave tomography of the mantle back arc extension during restricted mantle convection in the central under the Alpine Mediterranean area, J. Geophys. Res., 108(B2), Mediterranean, Earth Planet. Sci. Lett., 187,105 116, doi:10.1016/ 2065, doi:10.1029/2002JB001757. S0012-821X(01)00280-1. Schellart, W. P. (2004), Kinematics of subduction and subduction induced Faccenna, C., L. Jolivet, C. Piromallo, and A. Morelli (2003), Subduction flow in the upper mantle, J. Geophys. Res., 109, B07401, doi:10.1029/ and the depth of convection in the Mediterranean mantle, J. Geophys. 2004JB002970. Res., 108(B2), 2099, doi:10.1029/2001JB001690. Spakman, W., M. J. R. Wortel, and N. J. Vlaar (1988), The Hellenic sub- Funiciello, F., G. Morra, K. Regenauer Lieb, and D. Giardini (2003), duction zone: A tomographic image and its geodynamic implication, Dynamics of retreating slabs: 1. Insights from two dimensional numeri- Geophys. Res. Lett., 15,60 63, doi:10.1029/GL015i001p00060. cal experiments, J. Geophys. Res., 108(B4), 2206, doi:10.1029/ Stampfli, G. M., and G. D. Borel (2002), A plate tectonic model for the 2001JB000898. Paleozoic and Mesozoic constrained by dynamic plate boundaries and Goes, S., F. A. Capitanio, and G. Morra (2008), Evidence of lower mantle restored synthetic oceanic isochrons, Earth Planet. Sci. Lett., 196,17 slab penetration phases in plate motions, Nature, 451,981 984, 33, doi:10.1016/S0012-821X(01)00588-X. doi:10.1038/nature06691. Stegman, D. R., R. Farrington, F. A. Capitanio, and W. P. Schellart Jolivet, L. (2001), A comparison of geodetic and finite strain pattern in the (2010), A regime diagram for subduction styles from 3 D numerical Aegean, geodynamic implications, Earth Planet. Sci. Lett., 187,95 104, models of free subduction, Tectonophysics, 483,2945, doi:10.1016/ doi:10.1016/S0012-821X(01)00277-1. j.tecto.2009.08.041. Jolivet, L., and C. Faccenna (2000), Mediterranean extension and the Africa Eurasia collision, Tectonics, 19, 1095 1106, doi:10.1029/ F. A. Capitanio and S. Zlotnik, School of Geosciences, Monash 2000TC900018. University, Clayton, VIC 3800, Australia. Jolivet, L., C. Faccenna, B. Goffé, E. Burov, and P. Agard (2003), Subduc- C. Faccenna, Dipartimento di Scienze Geologiche, Universitá di Roma tion tectonics and exhumation of high pressure metamorphic rocks in the Tre, Rome I 00146, Italy.

5