1-Introduction
The Eastern Anatolian region is part of the Alpine-Himalayan belt. It is usually referred to as an East Anatolian High Plateau because it is on average 2000 m in elevation. The region is a 200 km wide belt between the Pontide Mountains to the North and the Bitlis-Zagros suture mountains to the south (Fig 1).
The Pontides were formed during consecutive collisions between the Andean-type volcanic arcs and continental blocks of Gondwanan origin (Yılmaz et al., 1997) (see an accompanying paper on the Pontide in this volume). The Bitlis-Zagros suture mountains were formed as a result of the continent-continent collision (Yılmaz 2019 and the references therein) (see the accompanying paper on the Southeast Anatolian Orogenic Belt in this volume). The Eastern Anatolian orogen was formed during the later stages of development of the surrounding orogenic belts.
The most significant structural features of Eastern Anatolia are the North Anatolian Transform Fault (NATF) and the East Anatolian Transform Fault (EATF) (Figs 1 and 2). The two faults converge in the Karlıova junction (KJ in Fig 1) and define the Anatolian Plate. The transform faults are long recognized as the major manifestation of the escape tectonics and associated lateral extrusion of the Anatolian Plate (e.g., Şengör 1979; Şengör and Yilmaz, 1981; Çemen et al. 1993; Yılmaz 2017).
The eastern Anatolia is covered by a thick, interbedded Neogene volcanic and sedimentary rocks and contains many conical peaks and ENE and WNW trending hills (Figs 1 and 2). The individual peaks correspond to volcanic cones (Fig 1) (Yılmaz et al. 1987, 1998; Pearce et al. 1990; Yılmaz 2017). The volcanoes produced a wide range of edifices from plateau basalts to ignimbrite deposits (Yılmaz et al. 1998; Kaygusuz et al. 2018).
The Neogene sedimentary cover rocks of Eastern Anatolia extend mainly along with two separate stripes of depressions adjacent to the peripheral mountains (Figs 1 and 2) (Yılmaz 2017). Rates of uplift in the bordering mountains are greater (0.2- 0.3 mm/y; Keskin et al. 2011) than the plateau’s uplift (0.1-0.2 mm/y; Mc Nab et al. 2018). Therefore, headword erosion across the peripheral mountains cannot keep pace with the elevation increase in Eastern Anatolia. Consequently, major rivers in the plateau flow generally in east-west directions (Fig 1).
The thick Neogene cover sequence is commonly flat but is locally tightly folded and faulted. The morphological pattern of Eastern Turkey resembles a sheave of wheat tied at the center (the inset in Fig 1), reflecting strict structural control of the ongoing tectonics. The peripheral mountains on both sides curve around a central dome, which determines the regional structures and the present drainage network (Şaroğlu and Güner 1981; Maggie and Priestley 2005; Yılmaz 2017) (Figs 1 and 1 inset). The hills, depressions, and rivers fan out from the central high (Fig.1).
Outcrops of the basement rocks below the thick Neogene volcano-sedimentary layer are rare. As a result, contrasting views were proposed on the nature of the basement rocks, which made the orogenic evolution of the belt controversial. This paper aims to document new data leading to clarify the nature of basement rocks in Eastern Anatolia and discuss the orogenic development based on the new data.