2-2-Structural Geology
Eastern Anatolia displays most of the geological features of a
collisional orogen, which is similar in many respects to the Tibetan
Plateau (Şengör and Kidd 1979; Şengör 1979; Şengör and Yılmaz 1981;
Dewey et al 1986; Şaroğlu and Yılmaz 1984; Barazangi 1989; Şengör and
Natalin 1996; Şengör et al 2003; 2008) (Fig 4A). The GPS measurements of
crustal displacements (Fig 4B) (Reilenger et al. 2006; Şengör et al.
2008), focal mechanism of the earthquakes, and the distribution of
active faults (Figs 1, 2, 4 A) (Şengör et al. 2003; Bozkurt 2001; Yılmaz
2017) confirm that the eastern Turkey experiences an ongoing
north-directed compressional stress (Fig 4 A) (Yılmaz 2017 and the
references therein).
The present-day morphology in eastern Anatolia was developed under a
significant structural control (Yılmaz 2017) (Figs 1 and 2). The major
morphotectonic features, northeast, and northwest-trending hills, and
depressions (Fig 1) correspond to anticlines and synclines, respectively
(Fig.1) (Yılmaz 2017). There is a centrally located structural dome,
which may be regarded as the center of virgation (Fig 1), the maximum
indentation location. The peripheral mountains on both sides make curves
around the virgation (inset in Fig 1). The strike-slip faults disperse
away from this high (Figs 1, 2). The arrangement and interactions of the
structures demonstrate that eastern Anatolia has undergone a complex
tectonic evolution (Şengör and Kidd 1979; Şengör and Yılmaz 1981;
Şaroğlu and Yılmaz 1986; Copley and Jackson 2006; Yılmaz 2017) from the
time of collision along with the southeastern Anatolian suture zone in
the Late Eocene. This event corresponds to a wholesale elevation
reflected in eastern Anatolian stratigraphy as a marked angular
unconformity (Fig 3) (Yılmaz 2019 ) ( see the accompanying paper in this
volume by Yılmaz et al.).
In the East Anatolian High Plateau, the following major groups of
structures are readily observed (Fig 4A);
1- NE and NW striking strike-slip faults (Figs.1and 4A) forming
conjugated pairs (Şengör and Kidd 1979; Şaroğlu and Yılmaz 1984; Bozkurt
2001; Seyitoğlu et al. 2017; Yılmaz et al. 2017). The NE Striking faults
are commonly longer and more prominent (Fig. 1) (Bozkurt 2001; Seyitoğlu
et al. 2017). Most of these faults are young and active that generate
frequent earthquakes (i.e., the Elazığ earthquake, on the 24 January
2020, Mw= 6.7, the Iran-Turkey border earthquake on the 23 February
2020, Mw=6.0, and the Malatya earthquake on the 24 January 2020 Mw=6,7).
2- Approximately E-W or ESE-WNW- striking reverse faults (Fig 4A),
3- E-W trending open and tight folds (Şaroğlu et al 1980; Şaroğlu and
Yılmaz 1984;1986;1987; Koçyiğit et al. 2001; Yılmaz 2017).
4- N-S trending extensional structures (Fig 4A) (Şengör and Kidd 1979;
Şaroğlu and Yılmaz 1984;1987; Yılmaz 2017).
The trends of all these structures are compatible with the N-S
compressional stress field (Fig. 4A) generated from the northward
advance of the Arabian Plate (Fig, 4B), which also caused the peripheral
mountains to thrust over the eastern Anatolian plateau (Fig 2; 5A and
5C). Along the thrust boundary, the basement metamorphic rocks are
exposed on the hanging walls (Figs 2 and 5C). As a result, the crust
along the overthrust zones is thicker than the average, reaching up to
50 km (48 km beneath the Bitlis‐Pötürge massifs in the south and 50 km
under the Pontide Range (Barazangi et al. 2006; Şengör et. 2003; 2008:
Tezel et al. 2013; Pamukçu et al. 2007; Medved et al. 2021).
Two narrow, fault-bounded chains of depressions were formed between the
central high and the peripheral mountains during Pleistocene (Figs 1, 2,
5 A and 5B). The boundary faults give the young basins their distinct
rhombohedral or parallelogram geometrical patterns (Fig. 5B). The
transpressional faults with the major strike-slip, coupled with reverse
slip components, strike parallel with, and determine the basins’ long
axes (Fig 5B). Due to the reverse slip displacements along the boundary
faults, the depressions may be viewed as ramp basins or intermontane
basins (Figs 5A and 5C) as exemplified from the Muş, Bingöl, Murat,
Elazığ, Malatya basins to the south (Figs 1 and 5B) and the
Tercan‐Aşkale, Pasinler, Kağızman basins to the north (Figs 1 and 5B).
The Eastern Anatolian High Plateau may also be regarded as a giant ramp
basin between the thrust elevated peripheral mountains (Fig 5A).
Within the rhombohedral depressions where normal faults define the
releasing bends, the local basins were alternatively described as
pull-apart basins (Keskin et al. 1998). Some volcanos were built above
the extensional openings (Fig 1) (Dewey et al., 1986; Pearce et al.,
1990; Keskin et al., 1998; Yılmaz 2017).
The two transform faults, the North Anatolian Transform Fault and the
East Anatolian Transform Fault define the Anatolian Plate (Figs 1 and
2), which protrudes away from the area of convergence in the Karlıova
Junction (KJ in Fig 1) (McKenzie 1972; Şengör et al. 1975; Şengör and
Yılmaz 1981; McKenzie and Yılmaz 1991; Şaroğlu and Yılmaz 1991; Çemen et
al., 1993; Aktuğ et al. 2012; Karaoğlu et al. 2017) (Figs 1, 2, and 5B).
The area where the transform faults intersect is a wedge shape
depression (Fig 5 B), which widens progressively as the Anatolian Plate
moves away from the point of convergence (Şaroğlu and Yılmaz 1991;
Karaoğlu et al. 2016) (Fig 5 B). The oldest lateral fan deposits sourced
from the basin boundary faults (Fig 5 B) is Upper Pliocene (?)-
Pleistocene in age (Şaroğlu and Yılmaz 1991), which sets a lower limit
to the time of the westerly escape of the Anatolian Plate. The escape
tectonics partitions the N-S compressional stress (Yılmaz 2017).
Associated with the development of the two transform faults and the
consequent escape tectonics of Anatolia, a new tectonic regime, the Neo
Tectonics, began and has drastically changed the morphotectonic
character of the Anatolia and surrounding regions (e.g., Şengör 1979;
Şengör and Yılmaz 1981; Çemen et al., 1993; Yılmaz 2017).
The GPS vectors in Fig 4B shows that the eastward motion of Eastern
Anatolia is slower than its westward movement. Field and earthquake data
indicate that the N-S compressional stress is accommodated in this
region along with several small-size strike-slip faults with
right-lateral displacements (Fig 2).