SUBDUCTION DRIVES ARABIA/AFRICA PLATE CONVERGENCE WITH EURASIA AND PROVIDES A UNIFYING, DYNAMIC MECHANISM FOR MEDITERRANEAN/MIDDLE EAST TECTONICS

To constrain plate driving forces and the dynamics of inter-plate deformation, we use geodetic and plate tectonic observations to determine the tectonic evolution of the Africa (AF)-Arabia (AR)-Eurasia (EU) plate system. In the Late Oligocene/Early Miocene (~25 Ma), the initiation of continental rifting, and the separation of AF from AR along the Red Sea and Gulf of Aden caused an ~50% slowing of AF-EU convergence, presumably due to a reduction in the slab-pull force transferred from the Bitlis-Zagros-Makran subduction system to the AF Plate (McQuarrie et al., 2003). The rate of AR - EU convergence remained constant as determined from plate tectonic reconstructions, and is indistinguishable from the present-day rate determined from GPS observations. A second major change occurred in the configuration and rate of motion across the AF-AR plate boundary at 11 ± 2 Ma, including an additional ~50% increase in the rate of AF-AR motion, and a corresponding decrease in the rate of AF-EU convergence (ArRajehi et al., 2010; McClusky et al., 2010). We relate these changes in plate rates and the configuration of the Red Sea (AF-AR plate boundary) at 11 ± 2 Ma to the initiation of ocean spreading in the Gulf of Aden that completely severed the continental lithosphere at this time, causing a further reduction in the N-S component of the slab-pull force transferred to the AF Plate. The timing of the initial slowing of AF-EU convergence (~25 Ma; Late Oligocene/Early Miocene) corresponds to the initiation of extensional tectonics in the Mediterranean Basin (Alboran, Central Mediterranean [Tyrrenian, Balearic], and Aegean basins), and the second phase of slowing to changes in the character of Mediterranean extension reported at ~ 11 Ma (Tortonian). Based on theoretical considerations indicating that, all else being equal, buoyancy forces on the subducted lithosphere are proportional to the rate of subduction (Turcotte and Shubert, 2002; pg. 242-244), we hypothesize that the slowing of AF-EU convergence caused an imbalance in the dynamic equilibrium of the subducting Neotethys oceanic lithosphere beneath the Mediterranean segment of the plate boundary, resulting in foundering of the subducted plate, and associated southward migration of the trench system. Southward trench migration resulted in contemporaneous ~N-S extension within the Mediterranean Basin. The detailed configuration of these extensional basins likely reflects the segmentation and geometry of the subducted lithosphere (Wortel and Spakman, 2000; Grovers and Wortel, 2005; Dilek et al., 2009). Furthermore, all plates converging with EU along its > 15,000 km long southern margin (AF, AR, India, Australia) rotate counterclockwise in a roughly coherent manner with rates increasing from west to east, corresponding to an increase in the width of the subducted Neotethys lithosphere since 150 Ma. We conclude that pulling by the subducted ocean lithosphere is the dominant force driving plate convergence with EU, and provides a unifying, and conceptually simple, dynamic mechanism for post-Late Oligocene (~30 Ma) tectonic deformation in the Mediterranean/Middle East zone of plate interaction.

References

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