RESEARCH Lithospheric Structure and the Isostatic State of Eastern

Home , Anatolian Plate, Eastern Anatolia Region, Eurasian Plate

RESEARCH

Lithospheric structure and the isostatic state of Eastern Anatolia: Insight from gravity data modelling

Rezene Mahatsente*, Gökay Önal, and Ibrahim Çemen DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF ALABAMA, TUSCALOOSA, ALABAMA 35487, USA

ABSTRACT

Eastern Anatolia, Turkey, is a part of the Alpine-Himalayan collisional belt where continental crust is relatively thin for a collisional belt. The region contains part of the Zagros suture zone, which formed during collision of the Arabian and Anatolian plates in the Miocene. It is underlain by a low-velocity zone associated with asthenospheric flow in the uppermost mantle. We constructed gravity models of the crust and upper-mantle structures to assess the driving mechanism of asthenospheric flow and the isostatic state of Eastern Anatolia. Our density models are based on terrestrial and satellite-derived gravity data, and they are constrained by receiver function and seismic tomography. The gravity models show significant lithospheric thickness variations across the Anatolian and Arabian plates. The lithospheric mantle in Eastern Anatolia is thinner (~62–74 km) than the Arabian plate (~84–95 km), indicating that part of the Anatolian mantle lithosphere might have been removed by delamination. The lithospheric removal process might have occurred following the detachment of the Arabian slab in the Miocene. Widespread Holocene volcanism and high heat flow in Eastern Anatolia can be considered as evidence of lithospheric delamination and slab break-off. The upward asthenospheric flow and subsequent asthenospheric underplating beneath Eastern Anatolia might have been induced by both delamination and slab break-off. These two processes may account for the rapid uplift of the Anatolian Plateau. There is a residual topography of ~1.7 km that cannot be explained by crustal roots. Based on our gravity models, we suggest that part of the eastern Anatolian Plateau is dynamically supported by asthenospheric flow in the upper mantle.

LITHOSPHERE; v. 10; no. 2; p. 279–290; GSA Data Repository Item 2018111 | Published online 22 February 2018 https://doi.org/10.1130/L685.1

INTRODUCTION 2003). This is much less than the 100–125 km thickness of the cold and stable mantle lithosphere in the Arabian Shield and Iranian Plateau (e.g., The Eastern Anatolia region, Turkey, with an average elevation of 2 km Angus et al., 2006). Consequently, delamination and slab break-off models above sea level, is a classic example of a young continental collision zone have been proposed to explain the thin lithosphere (e.g., Al-Lazki et al., (Fig. 1). The geodynamic evolution of the region involved major ocean 2003; Gök et al., 2003; Keskin, 2003; Şengör et al., 2003; Faccenna et closures (e.g., Şengör and Yılmaz, 1981; Okay and Tüysüz, 1999; Okay al., 2006; Lei and Zhao, 2007; Göğüş and Pysklywec, 2008; Toksöz et al., et al., 2010) due to subduction of oceanic lithosphere and continental col- 2010; Biryol et al., 2011; Koulakov, 2011; Fichtner et al., 2013; Bartol and lision of the Arabian and Eurasian plates (e.g., Keskin, 2003; Faccenna et Govers, 2014). The rapid topographic uplift in Eastern Anatolia between al., 2006; Göğüş and Pysklywec, 2008; Koulakov, 2011). The complex the late Miocene and early Pliocene might be attributed to the dynamic combination of these processes resulted in the present-day crustal structure and isostatic effects of delamination, slab break-off, and a compressional of Eastern Anatolia and surrounding regions. These structures include the regime between the Arabian and Eurasian plates (Keskin, 2003; Şengör et Zagros fold-and-thrust belt, the north, northeastern, and east Anatolian fault al., 2003; Faccenna et al., 2006; Göğüş and Pysklywec, 2008). zones, the Anatolian Plateau, and east Anatolia volcanic centers (Fig. 1). The upper-mantle structure of Eastern Anatolia has been imaged in During the 1970s and 1980s, crustal thickening due to continental col- various body and surface wave tomography experiments (Al-Lazki et al., lision was proposed by several models to explain the geodynamic evolu- 2003; Gök et al., 2003; Lei and Zhao, 2007; Toksöz et al., 2010; Biryol et tion of the eastern Anatolian Plateau and high topography (e.g., Şengör al., 2011; Salaün et al., 2012; Koulakov, 2011; Fichtner et al., 2013; Delph and Kidd, 1979; Şengör and Yılmaz 1981; Dewey et al., 1986; McKenzie et al., 2015). The lithosphere in Eastern Anatolia is underlain by a low- and Bickle, 1988). To test the proposed geodynamic models, the Eastern velocity zone (Pn velocity = 7.6–7.9 km/s), and this has been interpreted Turkey Seismic Experiment Project was conducted in the 1990s (Sandvol as anomalously hot asthenosphere in the uppermost mantle (Toksöz et et al., 2003). The results of the project suggested that mantle lithosphere is al., 2010; Biryol et al., 2011; Salaün et al., 2012; Koulakov, 2011; Fich- either absent or extremely thin beneath the eastern Anatolian Plateau (Al- tner et al., 2013; Delph et al., 2015). The hot asthenospheric flow in the Lazki et al., 2003; Gök et al., 2003; Sandvol et al., 2003). The thickness upper mantle might have affected the crustal and lithospheric structure of the lithospheric mantle in the Eastern Anatolian region is ~60 km (e.g., in Eastern Anatolia (e.g., Keskin, 2003). The presence of low-velocity Pearce et al., 1990; Al-Lazki et al., 2003; Gök et al., 2003; Sandvol et al., structures within the lower crust might be attributed to the low-velocity zone in the uppermost mantle (e. g., Pamukçu and Akçığ, 2011; Warren *Corresponding author: [email protected] et al., 2013; Delph et al., 2015).

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

Figure 1. (A) Simplified tectonic map of Turkey and surrounding regions Ş( engör et al., 1985; Barka, 1992). (B) Regional map of eastern Turkey with topographic relief and Holocene volcanoes. The digital elevation model is from the Shuttle Radar Topography Mission (SRTM; Jarvis et al., 2008). The circles represent earthquakes (M ≥4.2) that occurred between 1985 and 2016. The earthquake data were obtained from Boğaziçi University Kandilli Observatory and Earthquake Research Institute (http://koeri.boun.edu.tr/sismo/2/earthquake-catalog/). The red dashed lines show the locations of the 2.5-dimensional (2.5-D) gravity models. Abbreviations: NAFZ—North Anatolian fault zone, EAFZ—East Anatolian fault zone, DSFZ—Dead Sea fault zone, NEAFZ—Northeast Anatolian fault zone.

280 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 Lithospheric structure and isostatic state of Eastern Anatolia | RESEARCH

The presence of widespread Miocene to Pleistocene volcanism across gravity models, representative of the eastern, central, and western parts of the region and the existence of hot asthenospheric material in the upper Eastern Anatolia, and we discuss the dynamic implications of the models. mantle suggest that delamination and slab break-off might have occurred in the late Miocene (Al-Lazki et al., 2003; Gök et al., 2003; Keskin, 2003; GEOLOGIC OVERVIEW Şengör et al., 2003; Faccenna et al., 2006; Lei and Zhao, 2007; Göğüş and Pysklywec, 2008; Toksöz et al., 2010; Biryol et al., 2011; Koulakov, 2011; Although Eastern Anatolia has a long geological history since the Fichtner et al., 2013; Bartol and Govers, 2014). Distinguishing between fragmentation of Rodinia in the late Proterozoic, only the neotectonic the two processes is not easy, since both processes equally explain the evolution of the region will be discussed here. The reader is referred to genesis of widespread volcanism and the dynamic topography in the Şengör and Yılmaz (1981), Yılmaz (1993), Keskin (2007), and Şengör region. Although several studies have been carried out in Eastern Anatolia et al. (2008) for a comprehensive discussion of the geology of Eastern to understand the crust and upper-mantle structure, the driving mechanism Anatolia and surrounding regions. of asthenospheric flow in the uppermost mantle beneath Eastern Anatolia Neotectonic deformation in the eastern Anatolian Plateau was initiated and isostatic state are not well understood (Şengör et al., 2003; Keskin, during the Arabian-Eurasian collision in the early Miocene. The collision 2007; Pamukçu and Akçığ, 2011). formed the thrust faults of the Zagros fold-and-thrust belt and initiated In this paper, we assessed the lithospheric structure and isostatic state of contraction and shortening across Eastern Anatolia due to the northward Eastern Anatolia based on gravity data modeling. The main purpose of this motion of the Arabian plate (e.g., Şengör and Yılmaz, 1981; Perinçek and study was twofold: (1) to determine the detailed lithospheric structure of Çemen, 1990; Yılmaz, 1993; Faccenna et al., 2006). The collision and Eastern Anatolia down to a depth of 250 km, and (2) to interpret the grav- associated plate indentation increased the accumulation of stress across ity model to determine the driving mechanism of asthenospheric flow and Eastern Anatolia and led to the formation of the North and East Anatolian residual topography in the region. Our density model is based on gravity fault zones in the late Miocene (Şengör et al., 1985; Perinçek and Çemen, data from the European Improved Gravity Model of the Earth (EIGEN- 1990; Çemen et al., 1992; Yılmaz, 1993; Faccenna et al., 2006). Both the 6C4; Förste, et al., 2015). To reduce ambiguity inherent in potential field North and East Anatolian faults are responsible for the westward lateral interpretations, the gravity model was constrained using results from seis- motion of the Anatolian plate (Figs. 1 and 2). Contraction and strike- mic-reflection, seismic-refraction, and earthquake tomography studies in slip tectonics across the region are still active (e.g., Şengör et al., 2003; Eastern Anatolia. In this paper, we present four 2.5-dimensional (2.5-D) Yılmaz, 2017). However, few extensional basins, probably associated with

oE oE oE

oN Figure 2. Simplified geologic map of Eastern Anatolia, showing the main tectonic features and volcanic centers (after Keskin, 2007). Abbre- viations: EATF—East Anatolian transform fault, E-K-P—Erzurum- Kars Plateau, NATF—North Anato lian transform fault, NEAFZ— Northeast Anatolian fault zone.

oE oE oE

LITHOSPHERE | Volume 10 | Number 2 | www.gsapubs.org 281

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

the rapid uplift of the topography and subsequent gravitational forces, of the Anatolian plate between the North and East Anatolian fault zones, are controlled by normal faults (Göğüş and Pysklywec, 2008). After the and northeast motion of the Anatolian plate northeast of the Bitlis-Zagros rapid uplift of the region between the late Miocene and early Pliocene, the suture zone (Reilinger et al., 2006). Most of the shortening in the eastern eastern Anatolian Plateau experienced widespread Pliocene–Quaternary Anatolian Plateau is being accommodated by lateral motion of the Anato- volcanism (Fig. 2), represented by calc-alkaline to alkaline volcanic rock lian plate along the North and East Anatolian fault zones (Reilinger et al., sequences (Pearce et al., 1990; Keskin, 2003; Şengör et al., 2003). Geo- 2006, 2010). The southern part of the eastern Anatolian Plateau moves chemical studies indicate that the volcanic centers in the region consist faster than the northern part, and the rate of motion gradually decreases of enriched asthenospheric material (Keskin et al., 1998; Keskin, 2003). from south to north (Reilinger et al., 2006, 2010; Şengör et al., 2008; The eastern Anatolian Plateau consists of different tectonic units Yılmaz, 2017). accreted during the Late Cretaceous to Early Tertiary (Fig. 2). The East- ern Rhodope–Pontide metamorphic massif is located in the northern part DATA AND METHODS of Eastern Anatolia (Şengör and Yılmaz, 1981). The massif is overlain by a thick volcano-sedimentary rock sequence (Yılmaz, 1993). The Eastern Gravity Database Anatolian accretionary complex is located in the middle of Eastern Anato- lia and trends northwest-southeast. The complex consists of remnants of a The gravity data used for this study are based on the European Improved subduction-accretion complex, including a Late Cretaceous–age ophiolitic Gravity Model of the Earth (EIGEN-6C4; Förste et al., 2015). The EIGEN- mélange and Paleogene-age flysch sequences (e.g.,Ş engör and Yılmaz, 6C4 geopotential model is a spherical harmonic representation of the 1981). The flysch sequences in the north are older than the ones in the gravitational field of Earth up to degree and order of 2190 (spatial resolu- south, indicating that the area gradually became shallower from north to tion ~ 8 km). The model is constrained by terrestrial and satellite gravity south (e.g., Şengör and Yılmaz, 1981; Yılmaz, 1993). The Bitlis-Poturge data from the LAGEOS (Laser Geodynamics Satellites), GRACE (Gravity Massif is exposed in the southernmost portion of Eastern Anatolia (Fig. 2) Recovery and Climate Experiment), and GOCE (Gravity Field and Steady- and is composed of medium- and high-grade metamorphosed sediments State Ocean Circulation Explorer) satellite missions (Förste et al., 2015). and igneous rocks formed between Late Cretaceous and middle Eocene The spherical representation is based on the World Geodetic System 1984 time (Okay and Tüysüz, 1999; Yılmaz, 1993). The Miocene Bitlis-Zagros (WGS1984) reference system. suture zone marks the closure of the southern branch of the Neotethys The spatial resolution of the Earth Gravitational Models (e.g., Ocean (Fig. 2). Shallow-marine deposits and collision-related subaerial EGM2008, EIGEN-6C4) depends on the availability of high-quality volcanic units are Neogene to Quaternary in age, and the volcanic units land gravity data (Köther et al., 2012; Gutknecht et al., 2014; Godin and become younger from north to south/southeast (Keskin, 2003). Harris, 2014). We would like to emphasize that the land gravity data In Eastern Anatolia, global positioning system (GPS) measurements in the EIGEN-6C4 model are based on the Earth Gravitational Model (Fig. 3) clearly show north-south shortening, coherent westward escape (EGM2008; Pavlis et al., 2012), which includes all available land gravity

Figure 3. Digital elevation map of Eastern Anatolia and surroundings, showing global positioning oN system (GPS) velocities relative to the Eurasian plate. The elevation data are from the SRTM30 PLUS (http://topex.ucsd.edu/WWW _html/srtm30 _plus.html; Reilinger et al., 2010).

oN oE oE oE oE

282 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

data. Existing land gravity data in Eastern Anatolia are available at 2–5 km station intervals (Ates et al., 1999; Ekinci and Yiğitbaş, 2015). The land gravity data sets from Eastern Anatolia are provided to the National Geo- spatial-Intelligence Agency (NGA) by external organizations in Turkey without any restriction and are included in the EGM2008 (Data Reposi- tory Fig. DR11; Pavlis et al., 2012) and EIGEN-6C4 models (Förste et al., 2014). In some areas, the available land gravity data sets are included with restrictions (e.g., Himalaya). Their use is limited to a resolution corresponding to 15 arc-minute area-mean value (Fig. DR1 [see footnote 1]; Pavlis et al., 2012). To develop the 2.5-D gravity models of the deep crust and upper- mantle structure of Eastern Anatolia, we downloaded the free air anomaly of the region between 38°E and 37°N and 44°E and 41°N from the data portal of the International Centre for Global Earth Models (ICGEM: http:// icgem.gfz-potsdam.de/ICGEM/). Then, we computed the complete Bou- guer anomaly of the study area using Gravity Terrain Correction code Bouguer anomaly (mGal) (GTeC; Cella, 2015). The complete Bouguer anomaly (Fig. 4) is based on

spherical cap and terrain corrections up to a radius of 168 km. The cor- -27.3--55.0 75.3 -91.8-104.4-118.9-131.5-147.0-159.6 -174.1-219.6 rections are based on elevation data from the Shuttle Radar Topography Figure 4. Complete Bouguer anomaly map of Eastern Anatolia from the Mission (SRTM; Jarvis et al., 2008) and a standard reduction density of European Improved Gravity Model of the Earth (EIGEN-6C4; Förste et al., 2.670 g cm–3. 2014). Red triangles show Holocene volcanoes. The numbers in the map show the lithosphere-asthenosphere boundaries (stars) and Moho depths Initial Model and Data Constraints (crosses) in the region from receiver function and seismic tomography (Angus et al., 2006; Kind et al., 2015; Delph et al., 2015). Abbreviations: NAFZ—North Anatolian fault zone, EAFZ—East Anatolian fault zone, In this paper, we discuss four 2.5-D gravity models, representative of NEAFZ—Northeast Anatolian fault zone. the western, central, and eastern parts of the Eastern Anatolia region. The models depict the deep crust and upper-mantle structure of the Anatolian and Arabian plates at 38°E, 41°E, 42°E, and 44°E longitude and span Different lithospheric thickness values obtained from receiver func- from 37°N to 41°N (Fig. 1). tion analysis show that the Arabian lithosphere is thicker, ranging from To reduce the ambiguity inherent in potential field interpretations, the 75 to 160 km, than the Eastern Anatolian lithosphere, which ranges from densities and geometric structures of the sediments, crust, lithospheric 40 to 90 km (e.g., Angus et al., 2006; Özacar et al., 2008; Zor, 2008; mantle, and asthenosphere were constrained by velocity models from Pasyanos et al., 2014; Kind et al., 2015). Low Pn velocities (7.6–7.9 receiver function analysis and seismic tomography (e.g., Örgülü et al., km/s) dominate the uppermost mantle of Eastern Anatolia, and these 2003; Piromallo and Morelli, 2003; Zor et al., 2003; Reiter and Rodi, 2006; are interpreted as indicative of asthenospheric underplating beneath Lei and Zhao, 2007; Özacar et al., 2008; Gans et al., 2009; Toksöz et al., Eastern Anatolia (Al-Lazki et al., 2003; Gök et al., 2003; Lei and Zhao, 2010; Biryol et al., 2011; Koulakov, 2011; Salah et al., 2011; Fichtner et 2007; Toksöz et al., 2010; Biryol et al., 2011; Koulakov, 2011; Fichtner al., 2013; Pasyanos et al., 2014; Delph et al., 2015). et al., 2013). The crustal thickness in Eastern Anatolia, as determined from receiver Table 1 shows the velocities of sediments, crust, lithospheric mantle, function and seismic tomography, ranges from 30 to 55 km (e.g., Zor et and asthenosphere in Eastern Anatolia, along with the corresponding al., 2003; Angus et al., 2006; Özacar et al., 2008; Gök et al., 2011; Gökalp, densities. The density values of major tectonic units were derived from 2012; Tezel et al., 2013; Vanacore et al., 2013; Pasyanos et al., 2014; empirical relationships between P-wave velocities and densities of rocks Schildgen et al., 2014; Delph et al., 2015), and the sediment thickness at relevant pressure and temperature conditions (Sobolev and Babeyko, ranges from 0 to 5 km, based on the global sediment map determined by 1994; Nafe and Drake, 1957). The velocity and geometric structures were seismic data (Laske and Masters, 1997). used to constrain the 2.5-D gravity models of Eastern Anatolia.

TABLE 1. P-WAVE VELOCITIES AND DENSITIES OF MAJOR TECTONIC UNITS IN EASTERN ANATOLIA Tectonic structureP-wave velocity Density References (km s–1 ) (g cm–3) Sediment 4.55–4.98 1.70–2.90 Maden et al. (2009); Yılmaz et al. (2010); Salah et al. (2011); Tezel et al. (2013); Warren et al. (2013) Upper crust 4.68–6.3 2.50–2.90 Reiter and Rodi (2006); Özacar et al. (2008); Maden et al. (2009); Yılmaz et al. (2010); Gök et al. (2011); Salah et al. (2011); Tezel et al. (2013); Warren et al. (2013); Delph et al. (2015) Lower crust 5.32–7.23 2.50–3.18Reiter and Rodi (2006); Özacar et al. (2008); Maden et al. (2009); Yılmaz et al. (2010); Gök et al. (2011); Salah et al. (2011); Tezel et al. (2013); Warren et al. (2013); Delph et al. (2015) Mantle lithosphere7.8–8.28 3.22–3.30 Al-Lazki et al. (2003); Piromallo and Morelli (2003); Reiter and Rodi (2006); Lei and Zhao (2007); Özacar et al. (2008); Maden et al. (2009); Yılmaz et al. (2010); Simmons et al. (2011); Tezel et al. (2013); Koulakov (2011) Asthenosphere7.6–8.3 3.15–3.35 Piromallo and Morelli (2003); Reiter and Rodi (2006); Lei and Zhao (2007); Pasyanos and Nyblade (2007); Maden et al. (2009); Simmons et al. (2011); Biryol et al. (2011); Koulakov (2011); Pasyanos et al. (2014) Note: The densities were derived from P-wave velocities using empirical relations (Sobolev and Babeyko, 1994; Nafe and Drake, 1957).

1 GSA Data Repository Item 2018111, Figure DR1: Land and ocean gravity anomaly data used to develop the EGM2008 model: (a) data availability, and (b) data source identification (Pavlis et al., 2012), is available at http://www.geosociety.org/datarepository/2018, or on request from [email protected].

LITHOSPHERE | Volume 10 | Number 2 | www.gsapubs.org 283

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

TABLE 2. DENSITY VALUES USED IN THE FINAL GRAVITY MODEL Tectonic units Density Density Density Density Average tolerable (g cm–3 ) (g cm–3 ) (g cm–3 ) (g cm–3 ) variations Profile @ 38°E Profile @ 41°E Profile @ 42°E Profile @ 44°E (± g cm–3 ) Sediment 2.55 2.55 2.55 2.55 0.108 Upper crust 2.71–2.78 2.69–2.73 2.67–2.732.68–2.720.021 Lower crust 2.8–2.83 2.72–2.88 2.71–2.852.75–2.820.031 Mantle lithosphere 3.27 3.27 3.27 3.27 0.017 Asthenosphere 3.24–3.32 3.23–3.32 3.23–3.323.23–3.320.023

In order to determine the deep crust and upper-mantle density structure (<200 km) were attenuated at a height of 50 km above the surface. The of Eastern Anatolia, we applied two modeling approaches: First, 2.5-D gravity anomalies at heights >50 km are regional in nature. In the second forward modeling of the Bouguer anomaly was performed using GM-SYS step, the Bouguer gravity anomalies were filtered using a low-pass filter Gravity and Magnetic Modeling Software (Geosoft Oasis Montaj, 2017), for various cutoff values. The cutoff wavelength (300 km) was selected which makes use of the method of Talwani et al. (1959) and Talwani and based on similarity of amplitudes of gravity anomalies obtained using Heirtzler (1964) to calculate gravity anomalies. We would like to empha- the upward continuation and wavelength filtering methods. size here that the strike lengths of the geological units in the study area The regional gravity anomaly map of Eastern Anatolia (Fig. 5) does are not long enough to assume 2-D modeling. The strike length of a linear not suggest direct spatial correlation between the locations of volcanic structure should be at least 4–5 times the width of the geologic features for centers and the broad long-wavelength regional gravity anomaly, although 2-D modeling. The 2-D and 2.5-D gravity modeling techniques are gener- the centers are associated with rapid asthenospheric upwelling beneath ally applicable to profiles nearly perpendicular to linear structures. The Eastern Anatolia. This implies that the regional gravity anomalies of East- main difference between 2-D and 2.5-D modeling is that a 2-D model has ern Anatolia are mainly due to density variations in the deep crust and an infinite strike length, whereas a 2.5-D model has a finite strike length. upper-mantle structures. In the second step, to improve the fit of the calculated gravity to the Three distinct positive and negative anomalies can be identified on the observed data, the density values of all tectonic units along each of the regional gravity map (Fig. 5): The negative anomaly in the northeastern cross sections were inverted using a ridge-regression algorithm, taking all part of the map area (north of the Bitlis-Zagros suture zone) correlates available geological information into consideration. The errors in the mis- with the eastern Anatolian Plateau, and the two positive anomalies in fits were minimized in a least-square sense. The density values of the final the north and southwestern sections of the map coincide with Black Sea gravity models and their average tolerable variations are given in Table 2. and Arabian plates, respectively. The transition from high- to low-grav- The 2.5-D gravity models were set perpendicular to geologic strike, ity anomalies (gravity gradients) in Eastern Anatolia is marked by four and the strike length was constrained by the physical limits of geologic major tectonic structures (Figs. 4 and 5). This indicates that the deforma- units. The modeling space, and hence the mass therein, is a small fraction tion associated with major tectonic structures in Eastern Anatolia most of the entire Earth. This has an effect on the forward gravity modeling, probably affects the deepest part of the lower crust. The residual gravity because the levels of the observed and modeled gravity values are not iden- anomalies of Eastern Anatolia, as obtained from high-pass filtering, are tical and can result in offsets between the measured and modeled gravity shown in Figure 6. The residual gravity anomalies range from 93 mGal to values. To account for the effect of the surrounding mass on the forward –64 mGal (Fig. 6) and appear to correlate inversely with the topography, gravity modeling, the dimension of the modeling space was extended to 10,000 km beyond the dimension of the 2.5-D gravity models.

RESULTS AND DISCUSSION

Gravity Anomalies and Analysis

The Bouguer gravity map of Eastern Anatolia contains long- and short- wavelength gravity anomalies (Fig. 4). The gravity map reveals broad regional negative and positive Bouguer anomalies over the Anatolian and Arabian plates, respectively. A negative Bouguer anomaly as low as −219 mGal coincides with the highest elevation in Eastern Anatolia, and the anomaly increases with decreasing elevation to the NW and SW of the eastern Anatolian Plateau. To better understand the gravity anomalies of Eastern Anatolia, we applied upward continuation and wavelength filtering. The upward continuation process enhances long-wavelength anomalies and attenuates short wavelengths. The low-pass or long-wavelength filter suppresses Regional gravity anomaly (mGal) short-wavelength anomalies and enhances regional long-wavelength grav-

ity anomalies. Practically, both low-pass filtering and upward continuation -23.1 -56.5 -75.9 -90.5 -106.2 -121.4 -133.6 -145.1 -157.8 -168.2 -177.9 accentuate long-wavelength anomalies of deep origin. In the first step, the Figure 5. Regional gravity anomaly map of Eastern Anatolia. Four major Bouguer gravity anomalies were continued upward to various heights. tectonic features of the region are Bitlis-Zagros suture zone, East Anato- The purpose of this process is to help us select the cutoff wavelength lian fault zone (EAFZ), North Anatolian fault zone (NAFZ), and Northeast for the low-pass filtering. We found that most of the short wavelengths Anatolian fault zone (NEAFZ). Red triangles show Holocene volcanoes.

284 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

Residual gravity anomaly (mGal) Residual topography (meter) 92.5 29.9 19.5 10.9 4.8 -1.4-6.3 -11.2 -17.3 -25.9 -64.0 -3,166 -1,004 -526 -258 -4886 296 449 602 870 1,712 Figure 6. Residual gravity anomaly map of Eastern Anatolia. Red triangles and dashed black line show Holocene volcanoes and the location of Figure 7. Residual topography of Eastern Anatolia based on Airy isos- Lake Van, respectively. Abbreviations: NAFZ—North Anatolian fault zone, tasy model. Red triangles show Holocene volcanoes. Abbreviations: EAFZ—East Anatolian fault zone, NEAFZ—Northeast Anatolian fault zone. NAFZ—North Anatolian fault zone, EAFZ—East Anatolian fault zone, NEAFZ—Northeast Anatolian fault zone.

indicating a crustal root beneath the eastern Anatolian Plateau that causes a low in the gravity anomaly. residual values (~1.7 km), indicating that the eastern Anatolian Plateau may be undercompensated. This further implies that the crustal thickness Isostatic State of Eastern Anatolia beneath the eastern Anatolian Plateau may not be sufficient to isostatically support the observed topography. This is in agreement with some of the The region beneath Eastern Anatolia may not have a sufficient crustal recent studies in Eastern Anatolia (e.g., Faccenna et al., 2014; Komut, root to explain the observed topography (cf. e.g., Zor et al., 2003; Vana- 2015). Thus, the Anatolian plateau may be partly compensated by another core et al., 2013). Thus, part of the eastern Anatolian Plateau may not be mechanism, most probably by asthenospheric flow in the uppermost man- isostatically compensated. To assess the isostatic state and compensation tle. Other possible compensation mechanisms include density heterogene- mechanism of Eastern Anatolia, we determined residual topography of the ity in the crust and upper mantle, as well as thickness of the lithosphere. region (Fig. 7) from differences between observed and calculated isostatic topography based on the Airy isostasy model. The observed topographic Lithospheric Structure and Driving Mechanism of data were obtained from the SRTM (Jarvis et al., 2008). The isostatic topog- Asthenospheric Flow in Eastern Anatolia raphy was determined based on crustal thickness derived from receiver function analysis (Tezel et al., 2013) and the Crust1.0 model (Laske et al., Our gravity models (Fig. 8) along longitude 38°E, 41°E, 42°E, and 44°E 2013). We assumed a global mean crustal thickness of 31.2 km for the are representative of the western, central, and eastern sectors of Eastern Airy isostatic model (Watt, 2015). The assumed crustal and mantle densi- Anatolia and show the crust and upper-mantle structure of the Arabian ties for the Airy model were 2.750 g cm–3 and 3.250 g cm–3, respectively. and Anatolian plates. As shown in Figure 8, the long-wavelength gravity The reliability of the calculated residual topography depends on the anomaly of Eastern Anatolia is well explained in terms of a thin lithosphere accuracy of crustal thickness and density data. To quantify the effects of and anomalous asthenosphere in the uppermost mantle. There are signifi- density variation in the calculated residual topography and determine the cant variations in the lithospheric structure of Eastern Anatolia. The litho- corresponding uncertainty, we used a range of density values for the crust spheric mantle beneath Eastern Anatolia is thinner (~62–74 km) than the (2.7–2.8 g cm–3) and upper mantle (3.2–3.35 g cm–3). The effect of density Arabian plate (~84–95 km), indicating that the mantle lithosphere beneath variation of the residual topography is in the order of 50 m. We did not Eastern Anatolia may have been delaminated. This is in agreement with include the contribution of mantle lithosphere to isostatic compensation, results of S-wave receiver function studies in Eastern Anatolia (Fig. 9; cf. because the available information on the depth of the lithosphere-asthe- e.g., Angus et al., 2006; Kind et al., 2015). The lithospheric instability and nosphere boundary beneath Eastern Anatolia is limited (cf. e.g., Angus the subsequent delamination of the Anatolian mantle might have occurred et al., 2006; Kind et al., 2015). However, this limitation did not affect the following slab break-off in the region. Several receiver function studies results of our analysis, because the contribution of the continental crust have determined the presence of the detached Arabian slab at the base of to isostatic compensation is more than the lithospheric mantle (Faccenna the transition zone (Lei and Zhao, 2007; Özacar et al., 2008; Zor, 2008; et al., 2014). This should be due to the contrasting composition between Biryol et al., 2011). Thus, the upward asthenospheric flow and subsequent continental crust and lithospheric mantle. asthenospheric underplating in the uppermost mantle beneath Eastern The residual topography map (Fig. 7) shows negative and positive Anatolia might be attributed to both detachment of the Arabian slab in the topographic anomalies (residuals) over Eastern Anatolia where negative Miocene and delamination of the Anatolian mantle in the late Miocene. and positive residuals indicate over- and undercompensation conditions. The lithospheric delamination of the Anatolian continental mantle and The high topography in Eastern Anatolia is characterized by positive slab break-off might have induced asthenospheric flow beneath Eastern

LITHOSPHERE | Volume 10 | Number 2 | www.gsapubs.org 285

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

38oN 39oN 40oN vity anomaly (mGal) a Gr

+41 +41

*67

Figure 8. 2.5-dimensional (2.5-D) gravity models of Eastern Ana- tolia (EA). (A) Profile along 38°E. (B) Profile along 41°E. (C) Profile along 42°E. (D) Profile along 44°E. The locations of the profiles are shown in Figure 1. The white circles are earthquake hypocenters. The numbers in the models show the lithosphere-asthenosphere boundaries (stars) and Moho depths (crosses) in the region from receiver function and seismic tomography (Angus et al., 2006; Kind et al., 2015; Delph et al., 2015). The white dashed lines show the inferred locations of the Bitlis-Zagros suture, East Anatolian fault zone, North 38oN 39oN 40oN Anatolian fault zone, and Northeast Anatolian fault zone. Abbreviations: AP—Anatolian plate, EA—East- ern Anatolia, BZS—Bitlis-Zagros suture, EAFZ—East Anatolian fault zone, NAFZ—North Anatolian fault zone; NEAFZ—Northeast Anatolian fault zone. (Continued on following page). vity anomaly (mGal) a Gr

o o o 37 N 38 N 39oN 40oN 41 N

+40 +45

*70 *75 *93

286 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

38oN 39oN 40oN vity anomaly (mGal) a Gr

+40 +40

*68 *65

*94

Figure 8 (continued).

38oN 39oN 40oN vity anomaly (mGal) a Gr

+46 +44

*68 *73

LITHOSPHERE | Volume 10 | Number 2 | www.gsapubs.org 287

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

oE oE oE oE oE oE oE oE oE oE

Figure 9. S-wave receiver function of Eastern Anatolia showing common conversion point (CCP) stacking image at 40°N (Angus et al., 2006). Abbre- viations: UCD—upper-crust discontinuity; LAB—lithosphere-asthenosphere boundary; IB—Iranian block; NAF—North Anatolian fault; EAAC—East Anatolian accretionary complex. The letters U and D highlight regions of thin and thick lithosphere, respectively. Figure 10. Shear wave velocity model of Eastern Anatolia at 40°E (Delph et al., 2015). Abbreviations: BZS—Bitlis-Zagros suture; EAFZ— Anatolia. The NE-SW–oriented fast polarization direction of the upper-man- East Anatolian fault zone; IAESZ—Izmir-Ankara-Erzincan suture zone; tle seismic anisotropy in Eastern Anatolia may be considered as evidence NAF—North Anatolian fault; NEAFZ—Northeast Anatolian fault zone; of the direction of recent asthenospheric flow (Sandvol et al., 2003; Biryol Elv—elevation; L. crust—lower crust. et al., 2010; Yolsal-Çevikbilen, 2014; Vinnik et al., 2016). The polarization direction is nearly parallel to plate motion and may have provided driving topographic uplift and widespread Holocene volcanism in the region. The forces in a NE-SW direction (e.g., Vinnik et al., 2016). Thus, the astheno- models, based on EIGEN-6C4 data, show that the lithospheric mantle in East- spheric flow and subduction in the Caucasus region may have driven northern Anatolia is thinner (~62–74 km) than the Arabian plate (84–95 km) north eastward plate motion. The asthenospheric flow beneath Eastern Anatolia of the Bitlis-Zagros suture zone. These data support the hypothesis that the accounts for rapid topographic uplift in the late Miocene and early Pliocene, Anatolian lithosphere is delaminated and might have induced asthenospheric high heat flow, and widespread Holocene volcanism. The highest heat-flow flow beneath Eastern Anatolia. The lithospheric instability and the subsequent value (105 mW m–2) was observed in the Eastern Pontides orogenic belt, delamination probably occurred following slab break-off in the region in the associated with Neogene and Quaternary volcanism (Maden and Öztürk, late Miocene. The asthenosphere probably ascended to the base of the thin 2015). The exact contributions of delamination and slab break-off to the lithosphere following the slab break-off and delamination. The ascension overall upward asthenospheric flow, and hence to the dynamic topogra- of asthenosphere accounts for the rapid topographic uplift and extensive phy and volcanism in eastern Anatolia, is not easily determined, because melting that resulted in widespread Holocene volcanism across the region. the composition of magma derived from asthenospheric flow induced by The densities of the lower crust (2.71–2.88 g cm–3) beneath the central delamination and slab break-off may be the same. Moreover, delamination and eastern parts of Eastern Anatolia are less than the average density of and slab break-off could occur during and after subduction. the crust in the region (2.80–2.95 g cm–3). This indicates that the crustal The crustal structure of Eastern Anatolia is segmented, much like the rocks are probably thermally affected by asthenospheric underplating. underlying lithospheric mantle. The crustal thickness in Eastern Anatolia Based on our gravity models, we suggest that the hot asthenospheric increases with increasing elevation and ranges from 33 km in the west to material in the uppermost mantle might have induced thermal weaken- 46 km in the east (Fig. 8), similar to previous crustal thickness estimates ing in the overlying crust. for the eastern Anatolian Plateau (Fig. 9 [Angus et al., 2006; Motavalli- Our residual topographic model shows that part of the eastern Anato- Anbaran et al., 2016] and Fig. 10 [cf. e.g., Delph et al., 2015]). The crust lian Plateau is not isostatically supported. There is residual topography becomes thicker north of the Bitlis-Zagros suture zone. This might be up to ~1.7 km that cannot be explained by a crustal root. The residual attributed to the ongoing collision between the Arabian and Eurasian topography in Eastern Anatolia is probably supported by rising hot asthe- plates. The crust might have been affected by the hot asthenospheric nosphere in the uppermost mantle. However, this interpretation does not material in the uppermost mantle. The densities of the upper and lower exclude the possibility that the Anatolian Plateau may partly be compen- crust in the central and eastern sectors of Eastern Anatolia are less than sated by density heterogeneity in the crust and upper mantle, as well as the average density of the crust in the region, indicating that the crust thickness of the lithosphere. may be thermally weakened (Fig. 8). The receiver function analysis by Delph et al. (2015) also suggested that the shear wave velocity of the ACKNOWLEDGMENTS crust beneath the Anatolian plate is slower than the global average crustal This work was supported by a College Academy of Research, Scholarship, and Creative Activity (CARSCA, a unit of the College of Arts and Sciences, University of Alabama) grant to –1 shear wave velocity of 3.4 km s . We interpret the low densities in the Mahatsente. We thank the Turkish Petroleum Corporation (TPAO) for supporting Gökay Önal upper and lower crust beneath the central and eastern sectors of Eastern during his M.S. studies at the Department of Geological Sciences, University of Alabama. We Anatolia to indicate a thermally altered crust. also thank the two anonymous reviewers for thoughtful and constructive comments, which were of great help in the preparation of the final version of this paper. The data used in this study are available via file transfer protocol (FTP) by contacting the authors. CONCLUSIONS REFERENCES CITED Our 2.5-D gravity models (Fig. 8) in the Eastern Anatolian region pro- Al-Lazki, A., Seber, D., Sandvol, E., Türkelli, N., Mohamad, R., and Barazangi, M., 2003, To- mographic Pn velocity and anisotropy structure beneath the Anatolian Plateau (eastern vide a possible explanation of the density and geometric structures and Turkey) and the surrounding regions: Geophysical Research Letters, v. 30, no. 24, p. 8043, the driving mechanism of asthenospheric flow that resulted in the rapid https://doi.org/10.1029/2003GL017391.

288 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

Angus, D.A., Wilson, D.C., Sandvol, E., and Ni, J.F., 2006, Lithospheric structure of the Arabian of Volcanology and Geothermal Research, v. 85, p. 355–404, https://doi.org/10.1016 /S0377 and Eurasian collision zone in eastern Turkey from S-wave receiver functions: Geophysical -0273(98)00063-8. Journal International, v. 166, p. 1335–1346, https://doi .org /10 .1111 /j .1365 -246X .2006 .03070 .x. Kind, R., Eken, T., Tilmann, F., Sodoudi, F., Taymaz, T., Bulut, F., Yuan, X., Can, B., and Schneider, Ates, A., Kearey, P., and Tufan, S., 1999, New gravity and magnetic anomaly maps of Turkey: F., 2015, Thickness of the lithosphere beneath Turkey and surroundings from S-receiver Geophysical Journal International, v. 136, p. 499–502. functions: Solid Earth, v. 6, p. 971–984, https://doi.org/10.5194/se-6-971-2015. Barka, A.A., 1992, The North Anatolian fault zone: Annals of Tectonics, v. 6, p. 164–195. Komut, T., 2015, High surface topography related to upper mantle flow beneath Eastern Bartol, J., and Govers, R., 2014, A single cause for uplift of the central and eastern Anatolian Anatolia: Geophysical Journal International, v. 203, p. 1263–1273, https://doi .org/10.1093 Plateau?: Tectonophysics, v. 637, p. 116–136, https://doi.org/10.1016/j.tecto.2014.10.002. /gji/ggv374. Biryol, C.B., Zandt, G., Beck, S.B., Ozacar, A.A., Adiyaman, H.E., and Gans, C.R., 2010, Shear Köther, N., Götze, H.-J., Gutknecht, B.D., Jahr, T., Jentzsch, G., Lücke, O.H., Mahatsente, R., wave splitting along a nascent plate boundary: The North Anatolian fault zone: Geophysi- Sharma, R., and Zeumann, S., 2012, The seismically active Andean and Central Ameri- cal Journal International, v. 181, p. 1201–1213. can margins: Can satellite gravity map lithospheric structures?: Journal of Geodynamics, Biryol, C.B., Beck, S.L., Zandt, G., and Özacar, A.A., 2011, Segmented African lithosphere be- v. 59, p. 207–218, https://doi.org/10.1016/j.jog.2011.11.004. neath the Anatolian region inferred from teleseismic P-wave tomography: Geophysical Koulakov, I., 2011, High-frequency P and S velocity anomalies in the upper mantle beneath Journal International, v. 184, p. 1037–1057, https://doi .org /10 .1111 /j .1365 -246X .2010 .04910 .x. Asia from inversion of worldwide travel time data: Journal of Geophysical Research, Boğaziçi University Kandilli Observatory and Earthquake Research Institute Regional Earth- v. 116, B04301, https://doi.org/10.1029/2010JB007938. quake-Tsunami Monitoring Center, 2015, Boğaziçi University Kandilli Observatory and Laske, G., and Masters, G., 1997, A global digital map of sediment thickness: Eos (Washing- Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center: http:// ton, D.C.), v. 78, p. F483. www.koeri.boun.edu.tr/sismo/2/ earthquake-catalog (accessed January 2016). Laske, G., Masters, G., Ma, Z., and Pasyanos, M., 2013, Update on CRUST1.0: A 1-degree Global Cella, F., 2015, GTeC—A versatile MATLAB tool for a detailed computation of the terrain cor- model of Earth’s crust: Geophysical Research Abstracts, v. 15, abstract EGU2013–2658. rection and Bouguer gravity anomalies: Computers & Geosciences, v. 84, p. 72–85, https:// Lei, J., and Zhao, D., 2007, Teleseismic evidence for a break-off subducting slab under east- doi.org/10.1016/j.cageo.2015.07.015. ern Turkey: Earth and Planetary Science Letters, v. 257, p. 14–28, https://doi.org/10.1016 Çemen, I., Goncuoglu, M.C., Kozlu, H., Perincek, D., and Dirik, K., 1992, Indentation in south- /j.epsl.2007.02.011. eastern Anatolia and its effect in central Anatolia, in Proceedings of the First International Maden, N., and Öztürk, S., 2015, Seismic b-values, bouguer gravity and heat flow data beneath Symposium of Eastern Mediterranean Geology: Adana, Turkey, Geosound, p. 324–325. Eastern Anatolia, Turkey: Tectonic implications: Surveys in Geophysics, v. 36, p. 549–570, Delph, J.R., Biryol, C.B., Beck, S.L., Zandt, G., and Ward, K.M., 2015, Shear wave velocity struc- https://doi.org/10.1007/s10712-015-9327-1. ture of the Anatolian plate: Anomalously slow crust in southwestern Turkey: Geophysical Maden, N., Gelişli, K., Eyüboğlu, Y., and Bektaş, O., 2009, Determination of tectonic and Journal International, v. 202, p. 261–276, https://doi.org/10.1093/gji/ggv141. crustal structure of the Eastern Pontide orogenic belt (NE Turkey) using gravity and Dewey, J.F., Hempton, M.R., Kidd, W.S.F., Saroglu, F., and Şengör, A.M.C., 1986, Shortening magnetic data: Pure and Applied Geophysics, v. 166, p. 1987–2006, https://doi.org/10 of continental lithosphere: The neotectonics of Eastern Anatolia, a young collision zone, .1007/s00024-009-0529-7. in Coward, M.P., and Ries, A.C., eds., Collision Tectonics: Geological Society, London, McKenzie, D.P., and Bickle, M.J., 1988, The volume and composition of melt generated by ex- Special Publication 19, p. 1–36, https://doi.org/10.1144/GSL.SP.1986.019.01.01. tension of the lithosphere: Journal of Petrology v. 29, p. 625–679, https://doi .org/10.1093 Faccenna, C., Bellier, O., Martinod, J., Piromallo, C., and Regard, V., 2006, Slab detachment /petrology/29.3.625. beneath Eastern Anatolia: A possible cause for the formation of the North Anatolian fault: Motavalli-Anbaran, S.-H., Zeyen, H., and Jamasb, A., 2016, 3D crustal and lithospheric model Earth and Planetary Science Letters, v. 242, p. 85–97, https://doi .org /10 .1016 /j .epsl .2005 .11 .046. of the Arabia-Eurasia collision zone: Journal of Asian Earth Sciences, v. 122, p. 158–167, Faccenna, C., Becker, T.W., Auer, L., Billi, A., Boschi, L., Brun, J.P., Capitanio, F.A., Funiciello, https://doi.org/10.1016/j.jseaes.2016.03.012. F., Horvath, F., Jolivet, L., Piromallo, C., Royden, L., Rossetti, F., and Serpellino, E., 2014, Nafe, J.E., and Drake, C.L., 1957, Variation with depth in shallow and deep water marine sedi- Mantle dynamics in the Mediterranean: Reviews of Geophysics, v. 52, p. 283–332, https:// ments of porosity density and the velocities of compressional and shear waves: Geophys- doi.org/10.1002/2013RG000444. ics, v. 22, p. 523–552, https://doi.org/10.1190/1.1438386. Fichtner, A., Saygın, E., Taymaz, T., Cupillard, P., Capdeville, Y., and Trampert, J., 2013, The Okay, A.I., and Tüysüz, O., 1999, Tethyan sutures of northern Turkey, in Durand, B., Jolivet, L., deep structure of the North Anatolian fault zone: Earth and Planetary Science Letters, Horváth, F., and Séranne, M., eds., The Mediterranean Basins: Tertiary Extension within v. 373, p. 109–117, https://doi.org/10.1016/j.epsl.2013.04.027. the Alpine Orogen: Geological Society, London, Special Publication 156, p. 475–515, Förste, C., Bruinsma, S.L., Abrikosov, O., Lemoine, J.M., Marty, J.C., Flechtner, F., Balmino, https://doi.org/10.1144/GSL.SP.1999.156.01.22. G., Barthelmes, F., and Biancale, R., 2014, EIGEN-6C4: The latest combined global grav- Okay, A.I., Zattin, M., and Cavazza, W., 2010, Apatite fission-track data for the Miocene Arabia- ity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and Eurasia collision: Geology, v. 38, p. 35–38, https://doi.org/10.1130/G30234.1. GRGS Toulouse: GFZ Data Service, https://doi.org/10.5880/icgem.2015.1. Örgülü, G., Aktar, M., Türkelli, N., Sandvol, E., and Barazangi, B., 2003, Contribution to the Gans, C.R., Beck, S.L., Zandt, G., Biryol, C.B., and Özacar, A.A., 2009, Detecting the limit of seismotectonics of the eastern Anatolian Plateau from moderate and small size events: slab break-off in central Turkey: New high-resolution Pn tomography results: Geophysical Geophysical Research Letters, v. 30, no. 24, p. 8040, https://doi.org /10 .1029 /2003GL018258. Journal International, v. 179, p. 1566–1572, https://doi .org /10 .1111 /j .1365 -246X .2009 .04389 .x. Özacar, A.A., Gilbert, H., and Zandt, G., 2008, Upper mantle discontinuity structure beneath Geosoft Oasis Montaj, 2017, GM-SYS Gravity and Magnetic Modelling Software, User’s Guide east Anatolian Plateau (Turkey) from receiver functions: Earth and Planetary Science Let- Version 9: Ontario, Canada, Geosoft, 8 p. ters, v. 269, p. 427–435, https://doi.org/10.1016/j.epsl.2008.02.036. Godin, L., and Harris, L.B., 2014, Tracking basement cross-strike discontinuities in the In- Pamukçu, O.A., and Akçığ, Z., 2011, Isostasy of Eastern Anatolia (Turkey) and discontinui- dian crust beneath the Himalayan orogeny using gravity data—Relationship to upper ties of its crust: Pure and Applied Geophysics, v. 168, p. 901–917, https://doi .org/10.1007 crustal faults: Geophysical Journal International, v. 198, p. 198–215, https://doi .org/10 /s00024-010-0145-6. .1093/gji/ggu131. Pasyanos, M.E., and Nyblade, A.A., 2007, A top to bottom lithospheric study of Africa and Göğüş, O.H., and Pysklywec, R.N., 2008, Mantle lithosphere delamination driving plateau up- Arabia: Tectonophysics, v. 444, p. 27–44, https://doi.org/10.1016/j.tecto.2007.07.008. lift and synconvergent extension in Eastern Anatolia: Geology, v. 36, p. 723–726, https:// Pasyanos, M.E., Masters, T.G., Laske, G., and Ma, Z., 2014, LITHO1.0: An updated crust and doi.org/10.1130/G24982A.1. lithospheric model of the Earth: Journal of Geophysical Research–Solid Earth, v. 119, Gök, R., Sandvol, E., Türkelli, N., Seber, D., and Barazangi, M., 2003, Sn attenuation in the p. 2153–2173, https://doi.org/10.1002/2013JB010626. Anatolian and Iranian Plateau and surrounding regions: Geophysical Research Letters, Pavlis, N.K., Holmes, S.A., Kenyon, S.C., and Factor, J.K., 2012, The development and evalua- v. 30, no. 24, p. 8042, https://doi.org/10.1029/2003GL018020. tion of the Earth Gravitational Model (EGM2008): Journal of Geophysical Research, v. 117, Gök, R., Mellors, R.J., Sandvol, E., Pasyanos, M., Hauk, T., Takedatsu, R., Yetirmishli, G., Teoman, B04406, https://doi.org/10.1029/2011JB008916. U., Türkelli, N., Godoladze, T., and Javakishvirli, Z., 2011, Lithospheric velocity structure Pearce, J.A., Bender, J.F., De Long, S.E., Kidd, W.S.F., Low, P.J., Güner, Y., Saroğlu, F., Yılmaz, of the Anatolian Plateau–Caucasus–Caspian region: Journal of Geophysical Research, Y., Moorbath, S., and Mitchell, J.G., 1990, Genesis of collision volcanism in Eastern Ana- v. 116, B05303, https://doi.org/10.1029/2009JB000837. tolia, Turkey: Journal of Volcanology and Geothermal Research, v. 44, p. 189–229, https:// Gökalp, H., 2012, Tomographic imaging of the seismic structure beneath the east Anatolian doi.org/10.1016/0377-0273(90)90018-B. Plateau, eastern Turkey: Pure and Applied Geophysics, v. 169, p. 1749–1776, https://doi Perinçek, D., and Çemen, I., 1990, The structural relationship between the East Anatolian and .org/10.1007/s00024-011-0432-x. Dead Sea fault zones in southeastern Turkey: Tectonophysics, v. 172, p. 331–340, https:// Gutknecht, B.D., Götze, H.-J., Jentzsch, G., Jahr, T., Mahatsente, R., and Zeumann, S., 2014, doi.org/10.1016/0040-1951(90)90039-B. Structure and state of stress of the Chilean subduction zone from terrestrial and satellite- Piromallo, C., and Morelli, A., 2003, P wave tomography of the mantle under the Alpine derived gravity and gravity gradient data: Surveys in Geophysics, v. 35, no. 6, p. 1417–1440, Mediterranean area: Journal of Geophysical Research, v. 108, p. 2065, https://doi.org https://doi.org/10.1007/s10712-014-9296-9. /10.1029/2002JB001757. Jarvis, A., Reuter, H.I., Nelson, A., and Guevara, E., 2008, Hole-filled SRTM for Globe Version Reilinger, R., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Çakmak, R., Özener, H., 4: The CGIAR-CSI SRTM 90m Database: http://srtm.csi.cgiar.org (accessed March 2016). Kadirov, F., Guliev, I., Stepanyan, R., Nadariya, M., Hahubia, G., Mamoud, S., Sakr, K., Keskin, M., 2003, Magma generation by slab steepening and break-off beneath a subduc- Arrajehi, A., Paradissis, D., Al-Aydrus, A., Prilepin, M., Guseva, T., Evren, E., Dmitrotsa, A., tion accretion complex: An alternative model for collision-related volcanism in Eastern Filikov, S.V., Gomez, F., Al-Ghazzi, R., and Karam, G., 2006, GPS constraints on continen- Anatolia, Turkey: Geophysical Research Letters, v. 30, no. 24, p. 8046, https://doi.org tal deformation in the Africa-Arabia-Eurasia continental collision zone and implications /10.1029/2003GL018019. for the dynamics of plate interactions: Journal of Geophysical Research, v. 111, B05411, Keskin, M., 2007, Eastern Anatolia: A hotspot in a collision zone without a mantle plume, in https://doi.org/10.1029/2005JB004051. Foulger, G.R., and Jurdy, D.M., eds., Plates, Plumes, and Planetary Processes: Geological Reilinger, R., McClusky, S., Paradissis, D., Ergintav, S., and Vernant, P., 2010, Geodetic con- Society of America Special Paper 430, p. 693–722, https://doi.org/10.1130/2007.2430(32). straints on the tectonic evolution of the Aegean region and strain accumulation along Keskin, M., Pearce, J.A., and Mitchell, J.G., 1998, Volcano-stratigraphy and geochemistry of the Hellenic subduction zone: Tectonophysics, v. 488, p. 22–30, https://doi .org/10.1016 collision-related volcanism on the Erzurum-Kars plateau, northeastern Turkey: Journal /j.tecto.2009.05.027.

LITHOSPHERE | Volume 10 | Number 2 | www.gsapubs.org 289

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021 MAHATSENTE ET AL.

Reiter, D., and Rodi, W., 2006, Crustal and upper mantle P and S velocity structure in cen- Talwani, M., Worzel, J.L., and Landisman, M., 1959, Rapid gravity computations for two di- tral and southern Asia from joint body and surface wave inversion, in Proceedings mensional bodies with application to the Mendocino submarine fracture zone: Journal of of the 28th Seismic Research Review, Ground Based Nuclear Explosion Monitoring Geophysical Research, v. 64, p. 49–59, https://doi.org/10.1029/JZ064i001p00049. Technologies, LA-UR-06–5471: Lost Alamos, New Mexico, Air Force Research Lab, Tezel, T., Shibutani, T., and Kaypak, B., 2013, Crustal thickness of Turkey determined by re- v. 1, p. 209–218. ceiver function: Journal of Asian Earth Sciences, v. 75, p. 36–45, https://doi.org/10.1016 Salah, M.K., Şahin, Ş., and Aydın, U., 2011, Seismic velocity and Poisson’s ratio tomography /j.jseaes.2013.06.016. of the crust beneath east Anatolia: Journal of Asian Earth Sciences, v. 40, p. 746–761, Toksöz, M.N., Van der Hilst, R.D., Sun, Y., and Zhang, H., 2010, Seismic tomography of the https://doi.org/10.1016/j.jseaes.2010.10.021. Arabian-Eurasian collision zone and surrounding areas, in Proceedings of the 28th Seis- Salaün, G., Pedersen, H.A., Paul, A., Farra, V., Karabulut, H., Hatzfeld, D., Papazachos, C., mic Research Review, Ground Based Nuclear Explosion Monitoring Technologies: Cam- Childs, D.M., and Pequegnat, C., 2012, High-resolution surface wave tomography be- bridge, Massachusetts, Air Force Research Laboratory, p. 292–301. neath the Aegean-Anatolia region: Constraints on upper-mantle structure: Geophysical Vanacore, E.A., Taymaz, T., and Saygın, E., 2013, Moho structure of the Anatolian plate from Journal International, v. 190, p. 406–420, https://doi.org/10.1111/j.1365-246X.2012.05483.x. receiver function analysis: Geophysical Journal International, v. 193, p. 329–337, https:// Sandvol, E., Türkelli, N., Zor, E., Gök, R., Bekler, T., Gürbüz, C., Seber, D., and Barazangi, M., doi.org/10.1093/gji/ggs107. 2003, Shear wave splitting in a young continent-continent collision: An example from Vinnik, L., Oreshin, S., and Erduran, M., 2016, Melt in the mantle and seismic azimuthal an- eastern Turkey: Geophysical Research Letters, v. 30, no. 24, p. 8041. isotropy: Evidence from Anatolia: Geophysical Journal International, v. 205, p. 523–530, Schildgen, T.F., Yıldırım, C., Cosentino, D., and Strecker, M.R., 2014, Linking slab break-off, Hel- https://doi.org/10.1093/gji/ggw021. lenic trench retreat, and uplift of the central and eastern Anatolian Plateaus: Earth-Science Warren, L.M., Beck, S.L., Biryol, C.B., Zandt, G., Özacar, A.A., and Yang, Y., 2013, Crustal veloc- Reviews, v. 128, p. 147–168, https://doi.org/10.1016/j.earscirev.2013.11.006. ity structure of central and eastern Turkey from ambient noise tomography: Geophysical Şengör, A.M.C., and Kidd, W.S.F., 1979, Post-collisional tectonics of the Turkish-Iranian Pla- Journal International, v. 194, p. 1941–1954, https://doi.org/10.1093/gji/ggt210. teau and a comparison with Tibet: Tectonophysics, v. 55, p. 361–376, https://doi.org/10 Watt, A.B., 2015, Crustal and lithosphere dynamics: An introduction and overview, in Schubert, .1016/0040-1951(79)90184-7. G., ed., Treatise on Geophysics (2nd ed.): Oxford, UK, University of Oxford, p. 1–44. Şengör, A.M.C., and Yılmaz, Y., 1981, Tethyan evolution of Turkey, a plate tectonic approach: Yılmaz, A., Yılmaz, H., Kaya, C., and Boztuğ, D., 2010, The nature of the crustal structure of Tectonophysics, v. 75, p. 181–241, https://doi.org/10.1016/0040-1951(81)90275-4. the eastern Anatolian Plateau, Turkey: Geodinamica Acta, v. 23, p. 167–183, https://doi Şengör, A.M.C., Görür, N., and Saroğlu, F., 1985, Strike-slip faulting and related basin forma- .org/10.3166/ga.23.167-183. tion in zones of tectonic escape: Turkey as a case study, in Biddle, K.T., and Christie-Blick, Yılmaz, Y., 1993, New evidence and model on the evolution of the southeast Anatolian orog- N., eds., Strike-Slip Faulting and Basin Formation: Society of Economic Paleontologists eny: Geological Society of America Bulletin, v. 105, p. 251–271, https://doi .org/10.1130 and Mineralogists Special Publication 37, p. 227–264. /0016-7606(1993)105<0251:NEAMOT>2.3.CO;2. Şengör, A.M.C., Özeren, S., Genç, T., and Zor, E., 2003, East Anatolian high plateau as a mantle- Yılmaz, Y., 2017, Morphotectonic development of Anatolia and the surrounding regions, in supported, north-south shortened domal structure: Geophysical Research Letters, v. 30, Çemen, I., and Yılmaz, Y., eds., Active Global Seismology: Neotectonics and Earthquake no. 24, p. 8045, https://doi.org/10.1029/2003GL017858. Potential of the Eastern Mediterranean Region: American Geophysical Union Geophysi- Şengör, A.M.C., Özeren, S., Keskin, M., Sakınç, M., Özbakır, A.D., and Kayan, I., 2008, East- cal Monograph 225, p. 11–91, https://doi.org/10.1002/9781118944998.ch2. ern Turkish high plateau as a small Turkic-type orogeny: Implications for post-collisional Yolsal-Çevikbilen, S., 2014, Seismic anisotropy along the Cyprean arc and northeast Mediter- crust-forming processes in Turkic-type orogens: Earth-Science Reviews, v. 90, p. 1–48, ranean Sea inferred from shear wave splitting analysis: Physics of the Earth and Planetary https://doi.org/10.1016/j.earscirev.2008.05.002. Interiors, v. 233, p. 112–134, https://doi.org/10.1016/j.pepi.2014.05.010. Simmons, N.A., Myers, S.C., and Johannesson, G., 2011, Global-scale P wave tomography Zor, E., 2008, Tomographic evidence of slab detachment beneath eastern Turkey and the optimized for prediction of teleseismic and regional travel times for Middle East events: Caucasus [Naf.]: Geophysical Journal International, v. 175, p. 1273–1282, https://doi .org 2. Tomographic inversion: Journal of Geophysical Research, v. 116, B04305, https://doi /10.1111/j.1365-246X.2008.03946.x. .org/10.1029/2010JB007969. Zor, E., Sandvol, E., Gürbüz, C., Türkelli, N., Seber, D., and Barazangi, M., 2003, The crustal Sobolev, S.V., and Babeyko, A.Yu., 1994, Modeling of mineralogical composition, density, structure of the east Anatolian Plateau (Turkey) from receiver functions: Geophysical and elastic wave velocities in anhydrous magmatic rocks: Surveys in Geophysics, v. 15, Research Letters, v. 30, no. 24, p. 8044, https://doi.org/10.1029/2003GL018192. p. 515–544, https://doi.org/10.1007/BF00690173. Talwani, M., and Heirtzler, J.R., 1964, Computation of magnetic anomalies caused by two MANUSCRIPT RECEIVED 26 JUNE 2017 dimensional bodies of arbitrary shape, in Parks, G.A., ed., Computers in the Mineral REVISED MANUSCRIPT RECEIVED 21 DECEMBER 2017 Industries, Part 1: Stanford University Geological Sciences Publication 9, p. 464–480. MANUSCRIPT ACCEPTED 30 JANUARY 2018

290 www.gsapubs.org | Volume 10 | Number 2 | LITHOSPHERE

Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/10/2/279/4102788/279.pdf by guest on 28 September 2021