Tectonic Escape Mechanism in the Crustal Evolution of Eastern Anatolian Region (Turkey)

Abstract

The Neotectonic evolution of Turkey has been dominated by the collision of the African and Arabian plates with the Eurasian plate along Hellenic arc to the west and the Bitlis-Zagros suture zone to the east. The Eastern Anatolian Contractional Province (EACP) including the Eastern Anatolian High Plateau (EAHP) and the Bitlis-Pötürge Thrust Zone (BPTZ) consists of an amalgamation of fragments of oceanic and continental crusts that squezzed and shortened between the Arabian and Eurasian plates. This collisional and contractional zone is being accompanied by the tectonic escape of most of the Anatolian plate to the west by major strike-slip faulting on the right-lateral North Anatolian Transform Fault Zone (NATFZ) and left-lateral East Anatolian Transform Fault Zone (EATFZ) which meet at Karlıova forming an east-pointing cusp (Figure 1). The present-day crust in the area between the easternmost part of the Anatolian plate and the Arabian Foreland gets thinner from north (ca 44 km) to south (ca 36 km) relative to its eastern (EAHP) and western sides (central Anatolian region). The contraction and thickening of the crust to ca 50-52 km (Dewey et al., 1986; Pearce et al., 1990) in the collisional zone has been accompanied by the tectonic escape of most of the Anatolian crustal block (Anatolian wedge in Dewey et al., 1986; Anatolian platelet in Koçyiğit et al., 2001; Anatolian plate in Yılmaz et al., 1998; Anatolian block in Lyberis et al., 1992) to the west-southwest towards the Aegean-Cyprean arc system by major strike-slip faulting on the right-lateral North Anatolian Transform Fault Zone (NATFZ) and left-lateral East Anatolian Transform Fault Zone (EATFZ) (Dewey et al., 1986; Şengör, 1979; Şengör and Yılmaz, 1981 and references therein; Şengör et al., 1985; Dilek and Moores, 1990; Tatar et al., 1996; Hubert-Ferrari et al., 2003; Allen et al., 2004; Barazangi et al., 2006) at a slip rate of 24±1 and 9±1 mm/yr, respectively (McClusky et al., 2000). Major tectonic structures such as the Aegean-Cyprean arc system, NATFZ, EATFZ, and Dead Sea Fault Zone (DSFZ) have been played a key role on the neotectonic evolution of the eastern Mediterranean region especially in Late Cenozoic. The westward escape of the Anatolian plate has been accompanied by counterclockwise rotation as well as lateral translation deduced from GPS and paleomagnetic data (Tatar et al., 1996; Reilinger et al., 1997; Platzman et al., 1998; Gürer and Gürer, 1999; McClusky et al., 2000; Özçep and Orbay, 2000; Bozkurt, 2001; Büyüksaraç, 2007). Therefore, the timing of collision-induced westward extrusion of the Anatolian plate has been widely accepted as the commencement of the Neotectonic history of Turkey (Şengör and Yılmaz, 1981; Koçyiğit et al., 2001). Koçyiğit et al. (2001) investigated the eastern Anatolian compressional tectonic regime in two main stages: the compressional-contractional and compressional-extensional tectonic regimes corresponding to the pre-tectonic escape period and the syn-tectonic escape period, respectively. However, the driving force causing the westward escape of the Anatolian plate is still under debate, e.g. orogenic collapse or gravity spreading following orogenic crustal shortening and thickening within the Anatolian plate (Seyitoğlu and Scott, 1996; Gautier et al., 1999; Dhont et al., 2006), mantle flow driven lithospheric extrusion (Faccenna et al., 2006; Çoban, 2007). Eastern Anatolia is dissected into three main lithospheric portions (the Eastern Anatolian High Plateau-EAHP, the Anatolian block, and the Arabian Foreland) by the major tectonic structures (Bitlis-Pötürge Suture Zone, NATFZ and EATFZ). The crust in the easternmost part of the Anatolian plate bounded by the NATFZ and the EATFZ, which corresponds to inner east Anatolia in Büyüksaraç (2007), mainly gets thinner from north (ca 43-44 km) to south (ca 36-37 km) relative to its eastern (EAHP) and western sides (central Anatolian region) (Figure 2), as proposed by Gök et al. (2007) for the east-southeast Anatolia. On the other hand, this thinner crustal terrain is characterized by very low Pn velocities (< 7.8 km/s) and high Sn attenuation which indicate existence of partially molten to eroded mantle lid or occurrence of asthenospheric mantle beneath the crust (Al-Lazki et al., 2003; Gök et al., 2003). This chapter is based on mainly the study of Elitok and Dolmaz (2008) who investigated the geodynamic evolution of crustal thinning in the area between the easternmost part of the Anatolian plate and the Arabian Foreland using the geological and geophysical data. They outlined Curie Point Depth (CPD) map of an area including the eastern Anatolia and the Arabian Foreland, and redrawn the crustal thickness map of the same area on the basis of the estimations of Gök et al. (2007) which are based on receiver functions from recordings of 29 broadband seismological stations.