Structure and tectonic evolution of the Anatolian plateau in eastern Turkey

Abstract

The Cenozoic geology and the present lithospheric and upper-mantle structure of the Anatolian plateau in eastern Turkey and nearby regions are the result of the final collision and suturing of the continental Arabia plate to the Turkish terranes (i.e., microcontinents). This process of collision and suturing was strongly influenced by three active structures in the region: the Caucasus mountains, the Aegean subduction zone, and the Dead Sea fault system. Understanding these three major tectonic elements is important for the development of a robust model for the formation of the Anatolian plateau. We show that the Anatolian plateau lithosphere in eastern Turkey has no lithospheric mantle, i.e., the crust floats on a partially molten asthenosphere. The average thickness of the crust in the region is ∼45 km. The uppermost mantle beneath this crustal block strongly attenuates Sn waves and has one of the lowest Pn velocities on earth (∼7.6 km/s). The Anatolian plateau, with an average of 2-km elevation, is dissected by numerous active seismogenic faults (mostly strike-slip and some thrust-type). Neogene and Quaternary volcanism with varying composition is widespread and covers more than half of the region. We argue that the northward subduction of the northern and the southern branches of the Neo-Tethyan oceanic lithosphere since the Mesozoic has resulted in the development of arc and back-arc volcanism (i.e., the Pontide and Bitlis systems) and the development of the eastern Anatolian accretionary complex, which covers a large area of eastern Turkey. The northward subduction of the southern Neo-Tethys considerably thinned and weakened the overriding Eurasia plate above the descending oceanic lithosphere of the Arabia plate. The final suturing of the continental Arabia plate with the Turkish terranes in the Miocene and the continued convergence of Arabia relative to Eurasia has resulted in the shortening of the accretionary complex in both the forearc and the back-arc regions and the development of a broad zone with numerous strike-slip faults. The mobilization of the Caucasus is also partially a consequence of this convergence. The documented major episode of widespread volcanism at ca. 11 Ma is probably related to the break-off of the shallowly descending oceanic segment of the Arabian lithosphere beneath eastern Turkey. The continued convergence of Arabia relative to Eurasia resulted in the development of the North Anatolian fault and subsequently the East Anatolian fault in the Pliocene. At about this time, the northern segment of the Dead Sea fault also developed in Lebanon and northwest Syria and joined the East Anatolian fault to form the Anatolian-Arabian-African triple junction in the Maras region of southern Turkey. The development of these fault systems (i.e., North Anatolian fault, East Anatolian fault, and Dead Sea fault) provided the mechanism for the tectonic escape of the Anatolian crustal block toward the Aegean arc system.