Evidence for distributed active strike-slip faulting in ...

Tectonophysics 742–743 (2018) 15–33

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Evidence for distributed active strike-slip faulting in NW Iran: The Maragheh and Salmas fault zones

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Karim Taghipoura, , Mohammad Mahdi Khatiba, Mohmoudreza Heyhata, Esmaeil Shabanianb, Abdorreza Vaezihirc a

Department of Geology, University of Birjand, Birjand, Iran Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran c Department of Earth Sciences, University of Tabriz, Tabriz, Iran b

A R T I C LE I N FO

A B S T R A C T

Keywords: Iran Maragheh Salmas Lake Urmia Active transtension Distributed strike-slip faulting

The study area is located in the northwestern Iranian plateau and exhibits ongoing convergence between the Arabian and Eurasian plates not absorbed by the Zagros orogenic belt. In this paper, we provide our geological observations made along the Maragheh and Salmas strike-slip fault zones that affect the southern portion of northwest Iran to the south of the North Tabriz Fault. We use a combined methodology to characterize active faulting along these fault zones that included remote-sensing analysis of high-resolution satellite imagery and aerial photographs, digital elevation models (DEMs), tectonic geomorphology investigations and geological field surveys. Active transtension is a common feature along the Maragheh and Salmas faults, and our observations suggested that the onset of active transtension and related local extension along the faults in Pleistocene occurred no earlier than ~2 Ma. The Maragheh and Salmas fault zones contribute to the accommodation of dextral strike-slip faulting in the region between the Main Recent Fault to the south and the North Tabriz Fault to the north. The spatial pattern of strike-slip faulting over the northwest Iranian region (including the North Tabriz fault, the Ahar fault, Salmas and Maragheh fault zones) favors a distributed deformation model, which could help to advance our understanding of geodynamic processes and the level of seismic hazard in this part of the Iranian plateau.

1. Introduction The kinematics of deformation in the continental lithosphere has been a contentious topic over the last three decades (e.g., Molnar, 1988; England and Jackson, 1989; Gordon and Stein, 1992; Thatcher, 1995, 2003, and references therein). Two idealized end-member kinematic models have been proposed for the accommodation of ongoing deformation in continental domains. In the first model, actively deforming continents are composed of several microplates or small rigid blocks separated by narrow major fault zones cutting through the entire crust (e.g., Thatcher, 1995, 2003). In the second model, deformation is almost uniformly distributed over the continent and can be treated as a continuously deforming viscous medium (e.g., England and McKenzie, 1982; Vilotte et al., 1982). Recognition of the most reliable model for an area has significant implications for better understanding the rheology and seismotectonic characteristics of the deforming lithosphere (Thatcher, 2003). The Turkish – Iranian plateau, along with the surrounding deformation

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Corresponding author. E-mail address: [email protected] (K. Taghipour).

https://doi.org/10.1016/j.tecto.2018.05.022 Received 11 September 2017; Received in revised form 18 May 2018; Accepted 20 May 2018 Available online 22 May 2018 0040-1951/ © 2018 Published by Elsevier B.V.

belts, represents a complex assemblage of distinct continental regions that are characterized by different tectonic and lithospheric evolutionary histories (e.g., Dewey et al., 1986). The region of NW Iran, which is subdivided into the southern and northern sections by the North Tabriz Fault (Hessami et al., 2003; Karakhanian et al., 2004; Solaymani Azad, 2009; Solaymani Azad et al., 2015) (Fig. 1), is among the lesser studied regions of the Turkish – Iranian plateau. The northern part, often referred to as the Persian block, has been considered to be a nearly rigid continental block (e.g., Jackson, 1992; Cisternas and Philip, 1997) with minor internal deformation. Using seismologic and geologic data, however, Ghods et al. (2015) demonstrated that kinematic adjustment occurs via distributed deformation and structural deflections in the region north of the North Tabriz Fault. For the southern portion that includes the area of interest, there is no detailed study focusing on the kinematics of active deformation. This region is bounded to the south by the NW-striking Main Recent Fault (Braud and Ricou, 1971; Ricou et al., 1977; Tchalenko and Braud, 1974) (MRF; Fig. 1), which is an active dextral strike-slip fault system that developed between the Arabian plate and the Iranian micro-continent during the last 5 Ma (Tchalenko and Braud, 1974;

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Fig. 1. GTOPO30. Shaded relief image of NW Iran showing the main tectonic subdivisions and locations discussed in the text (modified from the structural map of National Geoscience Database of Iran, http://www.ngdir.ir). Fault traces (red lines) are after Bozkurt (2001), Koçyigit et al. (2001), Jackson et al. (2002), Hessami et al. (2003), Copley and Jackson (2006), Solaymani Azad et al. (2011) and Shabanian et al. (2012b). GPS velocity vectors (black vectors: SGPS sites, grey vectors: CGPS sites) are after Djamour et al. (2011) and blue vectors after Reilinger et al. (2006). Lower left inset shows the geodynamic setting of Arabia-Eurasia collision/ subduction framework. Black arrows and associated numbers (in mm/yr) represent the present-day Arabia-Eurasia plate velocities after Reilinger et al. (2006). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

geometry of fault systems that affect northwest Iran (e.g., Taghipour, 2004; Karakhanian et al., 2004; Solaymani Azad et al., 2015). In this paper, we provide insight into the detailed geometry and kinematics of the Maragheh and Salmas strike-slip fault zones, which affect the portion of NW Iran south of the North Tabriz Fault. We used a multidisciplinary approach based on remote-sensing analysis of very high-resolution satellite imagery and aerial photographs, DEMs, tectonic geomorphology investigations and geological field surveys to (1) characterize active faulting along the Maragheh and Salmas strike-slip fault zones and (2) describe the role of these faults in the accommodation of ongoing deformation due to the Arabia – Eurasia convergence.

Talebian and Jackson, 2002). Vernant et al. (2004) calculated a short-term (derived from the GPS velocity field) right-lateral slip rate of 3 ± 2 mm/yr along the Main Recent Fault in northern Zagros. The remaining right-lateral shear component of the Arabia – Eurasia convergence is suggested to be principally taken up by the North Tabriz Fault as the main active structure in the north of the MRF (Berberian and Arshadi, 1976; Hessami et al., 2003; Solaymani Azad, 2009; Djamour et al., 2011; Rizza et al., 2013; Solaymani Azad et al., 2015). Another unresolved issue in NW Iran is the active extension in the NE-SW direction, which contrasts the regional transpressional to compressional tectonic regime prominent in the Eurasia-Arabia collision zone (e.g., Vernant et al., 2004; Masson et al., 2006, 2007; Kheirkhah et al., 2009; Copley and Jackson, 2006; Allen et al., 2011; Djamour et al., 2011; Mohajjel and Taghipour, 2014; Solaymani Azad et al., 2015). There is no consensus of opinion on the scale and possible mechanisms producing this extension; however, this extension may be a result of present-day geodynamical processes in lithosphere or a representation of a series of local extensions in relation to overlapping

2. Tectonic and geological setting NW Iran is a part of the Turkish-Iranian plateau, which is located in the central part of the Arabia-Eurasia collision zone (e.g., Copley and Jackson, 2006). This region is bounded by the Caucasus Mountains to 16

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Fig. 2. General fault map of the Maragheh and Salmas fault zones comprising discrete segments. Capital letters represent fault segments (NMF: North Maragheh Fault, AF: Ahoq Fault, DF: Dashkassan fault, DA: Dashkassan Assemblage, ELF: Eastern Lake Fault, NLF: Northern Lake Fault, ESF: Eastern Salmas fault, WSF: Western Salmas Fault). Rose diagrams (grey) represent the predominant orientation of the fault zones deduced from the statistical analysis of individual fault segments discussed in text. Blue rose diagrams represent the predominant orientation of extensional fractures along the Maragheh and Salmas fault zones: (h) Normal faults along the NMF, (i) Fissure-ridges in DA, (j) The major axis of ellipse which is plotted around the Eslamy peninsula, (k) Syntaxial veins accompanied travertine deposits in the Eslamy peninsula, (l) Fissure-ridges in Derik. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

proposed an alternative model that emphasized partitioning of oblique convergence between dextral strike-slip faulting on NW-striking faults in the south (eastern Turkey) and shortening perpendicular to the Greater Caucasus thrust front in the north. The author considered partitioning as an explanation for the apparent eastward continuation of dextral faulting along the North Anatolian fault into NW Iran (Westaway, 1990, 1994). The rates of short-term deformation have recently been estimated through geodetic GPS measurements. Geodetic data show that the Arabia–Eurasia convergence is northward (~N05°W) at the longitude of Maragheh (46.40°E) with a rate of 18 ± 2 mm/yr (Vernant et al., 2004). This overall convergence is taken up as N-S shortening across the Zagros Mountains (~4 mm/yr) and the NW Iranian region (~14 mm/ yr). The NW Iranian region contains several seismically active faults where the WNW-ESE trending dextral North Tabriz Fault (NTF) is the most prominent (e.g., Solaymani Azad et al., 2015) (Fig. 1). Most studies in the region have focused on the NTF because of the importance of Tabriz city, which has a population of approximately 1.5 million, and its well-documented historical seismicity (e.g., Ambraseys and Melville, 1982; Berberian and Yeats, 1999). Both geological and GPS studies (e.g., Hessami et al., 2003; Djamour et al., 2011; Rizza et al., 2013; Solaymani Azad et al., 2015) suggested a coherent slip rate of ~7 ± 1 mm/yr for this fault. The NW-SE trending Salmas and Serow active faults both display dextral oblique-slip normal displacement (Copley and Jackson, 2006). The 1930 Salmas earthquake, that ruptured part of the Salmas fault, produced spectacular surface faulting with a NW-SE strike, and involved almost equal components of normal and right-lateral slips (Tchalenko and Berberian, 1974; Berberian and Tchalenko, 1976).

the north, Zagros Mountains in the south, Talesh (western Alborz) Mountains to the east and Eastern Anatolia to the west. The crustal structure and magmatic evolution of NW Iran have been controlled by Neotethyan subduction and the Zagros orogeny since Mesozoic (see Agard et al., 2011 and references therein). The region encompasses the northern part of the Sanandaj-Sirjan Zone (SSZ) as the Central Iranian active margin during the subduction of Neotethys beneath Eurasia (Stöcklin, 1968; Hassanzadeh and Wernicke, 2016; Aflaki et al., 2017), and the Urumieh-Dokhtar Magmatic Arc (UDMA),which is a Cenozoic magmatic strip (Alavi, 1994) parallel to the SSZ (Fig. 1). The Eocene and Oligocene rocks are related to arc magmatism (e.g., Agard et al., 2011 and references therein), while the late Miocene to Quaternary units with adakitic character are likely formed in a post-collisional setting resulting from slab break-off or mantle delamination (e.g., Kheirkhah et al., 2009; Chiu et al., 2013; Pirmohammadi Alishah and Jahangiri, 2013). Sahand and Sabalan volcanoes are part of the northern sector of UDMA and are the prominent Pliocene-Quaternary magmatic edifices in the landscape of NW Iran (Fig. 1). Current crustal deformation in NW Iran is caused by the N-S convergence between Arabia and Eurasia. This northward motion causes thickening and shortening in the Zagros fold and thrust belt, intense earthquake activity and high topography in eastern Turkey and the Caucasus Mountains. Indenter models of the Arabia-Eurasia collision indicate that this northward motion has led to westward extrusion of the Anatolian block (McKenzie, 1970; Westaway, 1994), eastward motion of the Iranian block, and the central region began to deform in a continuous way initiating the uplift of the Lesser and Great Caucasus (e.g., Zonenshain and Le Pichon, 1986; Philip et al., 1989; Rebai et al., 1993; Cisternas and Philip, 1997; Ghods et al., 2015). Jackson (1992) 17

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Fig. 3. (a) SPOT 5 image of the North Maragheh Fault (NMF). Yellow circle shows the location of photographs of normal faults. (b) Field photographs of NNWstriking normal faults within the Pliocene-Quaternary strata related to the NMF. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3. The Maragheh and Salmas fault zones The Maragheh and Salmas fault zones discontinuously affect the area between Maragheh city to the southeast and Salmas city to the northwest (Fig. 2) and represent several fault segments. Part of the general structure of the Maragheh fault zone has been mapped by Solaymani Azad (2009); however, current knowledge of the Salmas fault zone is more complete due to the study conducted after the 1930 Salmas earthquake (Tchalenko and Berberian, 1974; Berberian and Tchalenko, 1976). A more comprehensive and detailed study is being conducted along these fault zones (personal communication with Sh. Solaymani Azad). To characterize these fault zones, we subdivided them into seven segments with distinct geomorphic, structural and kinematic characteristics separated by persistent or end-point boundaries (i.e., Knuepfer, 1989). The Maragheh fault zone is constituted by the North Maragheh, Ahoq, Dashkassan and Eastern Lake faults.

investigations. Despite all these human-made changes, the main fault trace is geomorphically expressed as clear SW-facing fault scarps that form a nearly linear fault scarp-line with the higher NW block. Incision depth of transversal streams is systematically increased uphills from the fault trace. Geomorphic analysis of DEMs (SRTM and DEMs were created from 1:25000 digital topographic maps), satellite images and aerial photos (1956 & 1967) allowed the observation of several geomorphic features that were characteristics of active strike-slip faults and included linear valleys, deflected and offset streams and ridges. Our estimates of the right-lateral (330 ± 70 m) and reverse (~54 m) cumulative offsets implied that an oblique-slip displacement existed in the middle part of the NMF (Fig. 5). A maximum cumulative horizontal offset of 420 ± 80 m was reconstructed along the northwestern part of the NMF (Fig. 6). The distribution of faulting along sub-parallel fault strands of the NMF implied that the total offset was more than what was directly measured along a single fault.

3.1. The North Maragheh fault

3.2. The Ahoq fault

The North Maragheh Fault (NMF) is approximately 30 km long (Fig. 3) and extends southeast from the vicinity of the Alavian dam (NW Maragheh city) to Moghanjiq village (~N 37° 20′; E 46° 25′). The fault cuts through poorly cemented conglomerate and very loose pyroclastic strata of Pliocene-Quaternary age and originated from the Sahand volcanic complex in the northeast. The NMF comprises several ~N120°E-striking fault strands. In the mid-length of the fault, the ~N155°E-striking normal faults splay from the main fault creating clear horst and graben morphology to the south (Figs. 3 and 4). The NMF is covered by the rapidly developing town of Maragheh with a population of ~200,000 and by recent agricultural activities, precluding direct access to the fault scarp-line and related outcrops (Fig. 4). Very low strength of materials and effect of erosion besides debris, landslides and colluviums also restricted direct fault kinematic

From the vicinity of Alavian dam to the west, the fault system strikes WNW with an arcuate geometry (Fig. 7). The Ahoq fault (AF) is 20 km in length and ~4 km in width and comprises fault strands oriented from N080°E to N115°E. Successive NNE-dipping faults along the AF thrust Mesozoic rocks over Pliocene-Quaternary deposits with minor strikeslip components and form topographic steps approximately 500 m higher than the southern plain. Farther north, thrust faulting exposed Paleozoic rocks (e.g., Lalun, Zagun and Mila Cambrian formations). Measurements of different generations of fault-slip data on individual fault planes revealed signatures of at least two distinct tectonic stages. An older normal faulting kinematics was systematically overprinted by a younger reverse movement on the inspected fault planes. Stratified Pliocene-Quaternary deposits cut by normal faults were affected by reverse faulting, which consequently thrusted Pliocene-Quaternary 18

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oblique reverse kinematics of the DF and was consistent with mesoscale structural relationships observed in the area. The kinematic measurements were done in Cretaceous rocks, while the presence of active travertine–made provinces along and at the termination of the fault zone exemplified Quaternary activity of the DF. The NW termination of the DF splayed into a series of distributed sub-parallel NW-SE fault branches, which cut lower Cretaceous limestone to Quaternary travertine deposits (Figs. 10 and 11). Geomorphic features such as systematically deflected streams imply dextral component of faulting. A right-lateral cumulative offset of 250 ± 5 m was measured through the restoration of streams offset (Fig. 10). Farther west, these fault branches splay and connect to the accumulation of travertine fissure-ridges, which we named them as the Dashkassan assemblage. 3.4. Dashkassan assemblage It has been known that most of travertine fissure-ridges occur along active normal faults or releasing step-over zones of strike-slip faults causing over-pressured hydrothermal fluids to rise upward in these zones (e.g., Hancock et al., 1999; Atabey, 2002; Altunel, 2005). In the study area, the best correlation between travertine ridges and adjacent faults can be seen in the Dashkassan assemblage, which consists of several travertine fissure-ridges (Fig. 11). Travertine fissure-ridges usually comprise vertical fissures occupied by banded travertine (central fissure or vein) and inclined bedded (stratified) travertine flanking the fissures (e.g., Bargar, 1978; Chafetz and Folk, 1984). In the Dashkassan assemblage, ridges are mainly straight. Unique and high-altitude leads to the ridges were easily detected in aerial photographs and satellite images as linear topographic features arranged at different angles to each other. The length of individual ridges extended beyond 2 km in some cases. For comparison, the heights of the world's best-known travertine ridges, such as Bridgeport in California, Pamukkale and Balkayasi in West Turkey (Hancock et al., 1999) and Serre di Rapolan in Italy (Ford and Pedley, 1996; Brogi and Capezzuolli, 2009), do not exceed 15 m. Cumulative heights of some ridges in the Dashkassan assemblage extend 150 m with respect to the surrounding plain (Fig. 11). Most of the ridges have a NNW orientation and are generally obliquely oriented to the DF and the eastern lake fault (ELF). In comparison to the same types of ridges in other countries, travertine ridges in the Dashkassan assemblage have a unique reach and height, indicating a long, continuous process of extension and deposition of travertine. The arrangements of these travertine ridges and their spatial relationships to the related fault zone suggest that these ridges were formed in the releasing relay zones of the faults. Accordingly, long-lasting continuous activity of these ridges implies stable activity of related strike-slip faults. Banded travertines which seal the central fissures are mainly syntaxial veins that have been made by the crack-seal mechanism which proposed by Ramsay (1980). In active and fresh ridges (see Fig. A in the supplementary material), the width of veins is too small (a few millimeters). However, thicker veins in lower levels of travertine ridges were exposed thanks to deep exploitation trenches in travertine quarries as well as relatively deep erosion of some ridges. The width of banded travertines increases downward. In some cases, the width of veins reaches to 50 m (Taghipour and Mohajjel, 2013) indicating a stable continuous local extension in the area. The fibrous crystals in syntaxial veins grow in the direction of differential displacement. In the study area, fibrous minerals in the central veins (fissures) often grow perpendicular to the walls during all growth increments; therefore, the direction of opening has steadily been perpendicular to the strike of veins. The central fissures of the ridge are considered mode I opening fractures. The stable and continuous activity of the veins helps determine the orientation of local extension since the onset of travertine activity (deposition). Even though the lower-most portions of the ridges in the Dashkassan assemblage are not exposed, a rough estimate of ~250 m seemed to be reasonable for cumulative

Fig. 4. (a) Georeferenced aerial photo of the SE part of the NMF taken in 1956 on the scale of ~ 1:50,000. (b) A morphotectonic interpretation of the aerial photo showing systematic right-lateral offsets/deflections recorded by streams; piercing points are intersections of reference lines with the fault trace. See Fig. 3 for the location. (c) Rosediagram of normal faults associated with the NMF and resulted extension and compression directions.

deposits in hanging wall over the southern Quaternary plain (Figs. 7 and 8). These observations provided evidence for at least two tectonic stages during which an older extensional regime was superimposed by the younger compressional regime. 3.3. The Dashkassan fault zone The Dashkassan fault (DF) with a length of 28 km and strike of ~N145°E is at the western continuation of the AF. The DF has a defined boundary between Early Cretaceous limestone in the east and Late Cretaceous Flysch-type rocks in the west; the latter are partially covered by Neogene pyroclastic rocks (Fig. 7). Fault kinematic measurements along the DF were represented by steep fault planes with low pitch angles ranging from 5 to 10° indicating the pure strike-slip character of the DF (Fig. 9). Several fault planes contained older striations indicating 19

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Fig. 5. (a) SRTM (1 Arc second resolution) of the middle part of NMF. (b) A morphotectonic interpretation based on SRTM and DEM data. Piercing points are intersections of reference lines with the fault trace. The grey dashed line shows the location of topographic profile (A-A`). See Fig. 3 for the location. (c) The topographic profile is drawn based on RTK surveying along corresponding geomorphic features and used for estimation of maximum cumulative vertical offset.

ellipses were oriented ~N168°E and ~N078°E, respectively. At the northeastern end of the ELF, the occurrence of tensile fracturing, travertine deposition and N130°E to N185°E striking syntaxial veins (see Fig. B in the supplementary material) indicated local transtensional activity of the fault in Quaternary. Volcanoes and related structural features have commonly been used as paleostress indicators (e.g., Feraud and Campredon, 1983; Bosworth and Strecker, 1997; Shabanian et al., 2012b). The aligned and elongated volcanoes, in particular, were widely used as stress indicators (e.g., Fiske and Jackson, 1972; Nakamura, 1977; Jackson et al., 1975; Feraud et al., 1980; Bosworth et al., 2003; Shabanian et al., 2012b). For the Eslamy peninsula and other extensional features, the main structural trend indicated a general NNW orientation for the maximum horizontal compression during Quaternary. This direction of Quaternary compression was consistent with dextral faulting along the ELF and active extension across the Dashkassan assemblage (Fig. 2).

extension accommodated by the assemblage. This estimate was based on the number of ridges and comparison of their aspect ratio with other well-exposed ridges in the area, such as mount Qezeldagh (Taghipour and Mohajjel, 2013) located north of the Dashkassan assemblage. 3.5. The eastern lake fault In the NW of the Dashkassan assemblage, another fault appears in a right-step array with respect to the DF and cuts into recent alluviums and travertine deposits. The ELF, ~35 km in length and ~6 km in width, comprises several NW-striking faults located between the Dashkassan assemblage and Lake Urmia. The ELF passed through the northeastern lowlands (floodplain) of Lake Urmia, where surficial processes of erosion and incision were greatly changing on the surface due to fluctuations in the lake's water level. For this reason, the geomorphic expression of the fault was very delicate and evidence of faulting was rather subtle. Despite this difficulty, the geomorphic analysis of ASTER and SPOT 5 satellite images led to the detection of several NW-trending lineaments in the eastern floodplain of Lake Urmia. These lineaments represented geomorphic characteristics of active faults and subtle geomorphic evidence of right-lateral faulting was also observed. To the west, the fault zone was intersected by a ~N120°E-trending fault, which cut deltaic branches of the Aji-chay River. Tentative reconstruction of geomorphic features indicated the right-lateral characteristic of the fault had a probable cumulative offset of 360 ± 50 m (Fig. 12). Farther west, the ELF turned to ~N140°E and was distributed into several small segments, one of which affected the Eslamy peninsula complex to the east of Lake Urmia (Fig. 2). The Eslamy peninsula is a Pliocene-Quaternary complex stratovolcano (e.g., Moine-Vaziri, 1985; Hajalilou et al., 2009; Chiu et al., 2013) with a collapsed central caldera, which later was elevated due to intrusions of sub-volcanic masses. This stratovolcano showed a preferred elongation in map view. The major and minor axes of best-fit

3.6. The Salmas fault zone The 60-km-long SFZ is nearly parallel to the Maragheh fault zone and cuts through the western terrains of Lake Urmia (Fig. 13a). The Salmas fault produced the destructive 1930 earthquake with Mb = 7.3 (Tchalenko and Berberian, 1974; Berberian and Tchalenko, 1976); however, minimal information was known about structural characteristics and the geodynamic role of this fault. The SFZ comprises several strands, forming a fault zone of several hundred meters to approximately 4 km in width. This study subdivided the SFZ into two subsegments in consideration of the changes in strike of the fault strands. 3.6.1. The Eastern Salmas Fault (ESF) The eastern part of the SFZ, 23 km in length and striking at ~N110°E, cut mainly through metamorphic rocks of unknown age and made spectacular deep linear valleys (see Fig. C in the supplementary 20

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Salmas earthquake and ruptured through a left-stepping array. The main rupture was associated with two NW-trending oblique-slip faults with a maximum right-lateral displacement of 4 m and a normal (vertical) component of 5 m (Tchalenko and Berberian, 1974). Toward the northwest, the SFZ splayed into NW-trending faults, which cut Quaternary basaltic lava flows, volcanic domes (Kheirkhah et al., 2009) and Quaternary travertine deposits. These faults were intersected by the NE-trending Derik earthquake fault (see Fig. D in the supplementary data) that ruptured in the 1930 earthquake with ~1 m of normal and an unknown amount of left-lateral displacement (Berberian and Tchalenko, 1976). The Derik fault is juxtaposed to a set of active travertine fissure-ridges and thermal springs that were reactivated during the 1930 earthquake. Yigit Daghi is a Quaternary basaltic volcano (Kheirkhah et al., 2009) located in the transtensional termination of the SFZ (Fig. 13). A 40 Ar/39Ar dating provides an age of 1.8 Ma for the Yigit Daghi basalts (Allen et al., 2011). To the west of the Yigit Daghi volcano, the SFZ is suggested to merge with the eastern Turkey NW-trending right-lateral faults, such as the Hasantimur Lake fault, Saray fault zone and the Erciş fault (e.g., Koçyigit et al., 2001). In the south of Yigit Daghi, the SFZ intersects the NE- trending left-lateral Başkale fault (Emre et al., 2012). This fault pattern forms a fault network that likely accommodates active deformation of the East Anatolia–NW Iran transition with crosscutting dextral and sinistral faults. 3.7. Possible structural connection of the Salmas and Maragheh fault zones The ELF aligns with the ESF on both sides of Lake Urmia. These two faults are prominently dextral strike-slip and likely contribute to the ongoing dextral shear between the Zagros suture and the North Tabriz fault. This suggests that there was a possible structural linkage between the two aligned ELF and ESF faults. Recent fluctuations in lake water levels were ascertained by satellite images and revealed very subtle geomorphic signatures of a lineament across the lake bed. The analysis of ASTER, SPOT and QuickBird (Google Earth) satellite images led us to detect several lineaments in the lake's floor (Fig. 14a) corroborated by bathymetric data. The overall WNW-ESE trend of this ~25 km-long lineament aligns with the NW continuation of the ELF in right-step array across the lake floor and separates the northern and southern parts of the lake with different depths (Fig. 14b). Considering the structural importance of this lineament, we preferred to highlight the importance, albeit very speculative, as an inferred fault defined as the North Lake Urmia fault. However, further detailed geological and geophysical data, such as precise bathymetry, seismic reflection profiles, and lake-floor sediment cores, are needed to support our suggestion. Fig. 6. (a) SPOT-5 image centered of the northwestern part of NMF superposed over SRTM (1 Arc-second resolution) image. Corresponding stream counterparts are shown with the same colour (See Fig. 3 for the location.) (b) SRTM image of the same area after reconstruction of 420 ± 80 m dextral offset. (c) Panoramic view of a linear valley along the North Maragheh fault. Black dashed line marks the trace of the fault. The number inside white circle refers to stream 5 in Fig. 6a and b. The location and look direction are marked in Fig. 6a.

4. Discussion 4.1. Variations in the geomorphology and kinematics of the Maragheh and Salmas fault zones Based on our geological and geomorphic observations (Section 3), the overall kinematics of the Salmas and Maragheh fault zones was dextral strike-slip with normal or reverse components of faulting according to the orientation of the fault relative to the regional stresses (N10 W oriented σ1 – Figs. 2, 4 and 9). The arrangement and orientation of their fault portions vary along strike (Fig. 2) and imply important changes in both kinematics and geomorphology signatures of the faults due to local tectonic uplift or subsidence along the faults. Drastic changes were, however, observed at the fault relay/overlap zones and fault bends and were considered as common features for strike-slip faults (e.g., Sylvester, 1988). A typical uplifting topography is found along the AF segment. Because of its different orientation with respect to the southern and northern fault segments, the AF acts as a large restraining bend along

material). To the west, the ESF linked to the western Salmas fault. The restoration of geomorphic offsets recorded by two large streams along this part of the SFZ suggested a cumulative right-lateral offset of 630 ± 50 m (Fig. 13b). 3.6.2. The Western Salmas Fault (WSF) Near Shorgöl village (~N 38°, 05′, E 44°, 51′), strike of the fault turned to ~N150°E and formed a 4-km-long releasing bend (Fig. 13). Widespread travertine deposition and hot springs occurred due to extension in this releasing bend. The bend was connected to the 1930 21

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Fig. 7. (a) Geological map of the AFZ and adjacent segments superposed on the shaded relief image of SRTM (see Fig. 2 for the location). Yellow circles show the sites in which kinematics data were measured. Squares 1 to 3 represent the location of stereoplots in Fig. 9. The black lines delineate fault segment boundaries. (b) A 3d cross-section with simplified geological and structural interpretation. See Fig. 7a for the location. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

(Fig. 2). At its northwest termination, the Salmas fault zone splays into several NW-trending faults with arcuate geometry forming an extensional horsetail splay (Fig. 13). This provided a suitable location for the extrusion of basaltic lavas and the formation of travertine fissure-ridges (Fig. 13). As for the Salmas fault zone, kinematic and geomorphic variations were limited to the range of strike-slip to extensional faulting. The WNW-striking dextral strike-slip fault segments were connected through NW- to NNW-striking steps along areas where transtensional to extensional faulting was dominant. The significant dextral normal faulting and associated geomorphic features of the 1930 Salmas earthquake were produced along these fault-linking segments (Fig. 13) (Tchalenko and Berberian, 1974; Berberian and Tchalenko, 1976). In summary, the overall kinematics of the Salmas and Maragheh fault zones coincided with the orientation of principal stresses, with an average direction of N10 W for σ1 (Figs. 2, 4 and 9), while significant

the Maragheh fault zone. Field investigations and kinematic measurements revealed that the AF and DF had been subjected to different tectonic stages. The inversion of normal faults in Pliocene-Quaternary deposits along the AF implied a drastic change in the state of stress during the Pleistocene. Normal faulting had possibly occurred when the fault bend (the AF) was subjected to local extension due to an earlier left-lateral kinematics of the entire fault system. The modern reverse kinematics was established when the overall kinematics of the fault zone had changed into the present-day dextral kinematics, due to the last change in the stress state. The Dashkassan assemblage is another local positive topographic feature formed between the ~N145°E striking DF and the ~N120°E striking ELF. Contrary to the AF, the positive topographic feature of the Dashkassan assemblage was formed in a releasing relay zone affirmed by the activity of travertine fissureridges. Active deposition of travertine, especially travertine fissureridges, was observed all along the Maragheh and Salmas fault zones 22

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Fig. 8. Thrust faulting within Pliocene-Quaternary strata in the AF segment overprints older normal faulting. See Fig. 7 for the location.

(SKOH), D (MIAN), and E (MNDB), the slip rate estimates should have been considered an upper bound for the Maragheh fault zone. Our geological observations along with GPS-derived slip rate estimates suggest that the Maragheh and Salmas fault zones are actively contributing to the accommodation of right-lateral strike-slip faulting in the central part of the Turkish-Iranian plateau. Before this study, the NTF was in charge of the entire dextral shear component of the ArabiaEurasia collision beyond the Main Recent Fault (the northern Zagros suture) (e.g., Hessami et al., 2003; Vernant et al., 2004; Djamour et al., 2011; Rizza et al., 2013).

changes were observed at the fault relay/overlap zones and fault bends. This explains the important along-strike variations in both kinematics and geomorphic expression of the Salmas and Maragheh fault zones. 4.2. Possible present-day slip rate estimates In a lack of age constraints on geomorphic features offset along the Maragheh and Salmas fault zones, we used appropriate GPS stations (Global Positioning System geodetic measurements by Djamour et al., 2011) in the area to make a short-term estimate of the fault slip rate (Table 1). These GPS vectors subtraction is rough because (1) these corresponded to low strain vectors with large uncertainties and (2) the elastic strain loading in the upper crust and that part of the strain corresponding to possible block rotations were not taken into account. However, GPS vectors were used for a preliminary slip rate estimate. GPS stations A and B were located on both sides of the SFZ. Considering an average strike of N110°E for the SFZ, a possible slip rate of 2.9 ± 1.1 mm/yr was estimated for a right-lateral strike-slip component, and a − 4.6 ± 1.7 mm/yr extensional rate was derived for the fault perpendicular component. These estimates implied a prominent normal component of motion for the Salmas fault zone. Similarly, using stations C and D, a right-lateral slip rate of 2.2 ± 1.0 mm/yr and a fault perpendicular component of −0.4 ± 0.2 (normal) were calculated along the NMF (Fig. 15). These values greatly changed into a rightlateral slip rate of 4.8 ± 0.8 mm/yr and fault perpendicular of −0.7 ± 0.1 when using stations C and E. Considering the presence of other active structures such as the SMF in Fig. 15 between stations C

4.3. Onset of local extension in NW Iran The age relationships of several extension related features such as travertine deposition centers, Quaternary volcanoes, volcanic domes and extensional basins led us to investigate the initiation of local extension in NW Iran. Travertine layers and fissure-ridges along the Maragheh and Salmas fault zones cover the Pliocene-Quaternary conglomerate. There is no accurate age for these deposits, but the onset of extension post-dates the Pliocene–Quaternary deposits. Other indirect lines of evidence also suggest that active dextral strike-slip faulting and associated local extension along the Maragheh and Salmas fault zones should be established somewhere in Pleistocene and probably no earlier than ~2 Ma. Along its western termination, for instance, the Salmas fault zone cut through the Yigit Daghi volcano. 40Ar/39Ar dating on Quaternary volcanoes and lava flows indicated an age of 1.8 Ma for the Yigit Daghi basalts (Allen et al., 2011). Assuming a straightforward 23

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Fig. 9. Results of the analysis of fault kinematics data measured along the AF and DF. (a) A fault plane in the DF contains two striations. The older (yellow arrow) is the oblique left-lateral overprinted by a younger pure right-lateral (white arrow). Arrows indicate sense of movement of missing block. (b) A fault plane in the DF which contains pure right-lateral striations. The white arrow indicates sense of movement of missing block. (c) to (f) show results of the inversion analysis (Delvaux and Sperner, 2003) performed using data from sites 1(c and d), 2(e) and 3(f). The younger generation of slip in site 1 is shown in (d). See Fig. 7a for the location of sites 1–3. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

2004; Karakhanian et al., 2004; Rizza et al., 2013; Solaymani Azad et al., 2015) has long been suggested to be the only seismogenic and active fault system representing the greatest part of dextral shear in the region northeast of the MRF in NW Iran (e.g., Vernant et al., 2004; Reilinger et al., 2006; Djamour et al., 2011; Rizza et al., 2013). Deformation in the northern part of the NTF was distributed on WNW-ESE and N-S striking faults (Fig. 15) and was supported by both seismologically and geologically derived kinematics (e.g., Ghods et al., 2015). These crosswise to conjugate WNW-ESE and N-S striking faults accommodated active deformation by dextral and sinistral faulting, respectively. Western continuation of these faults connects to active strike-slip fault systems of the Lesser Caucasus (e.g., Pambak-SevanSunik fault and Nakhichevan fault; Fig. 15) or in eastern Turkey (e.g., GSKF) (e.g., Karakhanian et al., 2004). To the east, strikes of these faults turn to northeast against the rigid South Caspian Basin (see Ghods et al., 2015 and references therein). The lines of evidence presented in this study emphasized the role of NW-SE active strike-slip faults (Fig. 15) in the accommodation of rightlateral shear of the Arabia-Eurasia convergence in NW Iran. The Maragheh and Salmas fault zones belong to a regional fault network

relationship between this volcanism and local extension at the fault termination, the initiation of extension related to right-lateral faulting was estimated to be 1.8 Ma. Such drastic changes in fault kinematics during Quaternary were reported from other regions in the Arabia-Eurasia collision zone. Shabanian et al. (2010 and 2012a) documented a drastic change in the Quaternary state of stress (postdating volcanic domes intruded at ~2.3 Ma), which postdates the main tectonic reorganization of the Kopeh Dagh at ~3.5 Ma. Similar kinematic changes were also reported in the Alborz Mountains (Ritz et al., 2006; Abbassi and Farbod, 2009; Salmanlu, 2014), and NW Iran (Aflaki et al., 2018); the cause of these changes remain unclear. 4.4. Geodynamic implications 4.4.1. Deformation style During the last three decades, the region of NW Iran was considered to be a rigid block in both geodynamic and geodetic models (e.g., Jackson and McKenzie, 1984; Vernant et al., 2004; Djamour et al., 2011). The North Tabriz Fault (e.g., Hessami et al., 2003; Taghipour, 24

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Fig. 10. (a) Satellite image (Google earth) and the morphotectonic map of the northwestern part of DF showing systematic right-lateral offsets/deflections recorded by streams; piercing points are the intersection between the overall trend of steams and the fault trace. Corresponding stream counterparts are shown with the same colour. (b) Field photograph of the NW termination of the DF and its simplified sketch represents the location of fault traces. Travertine deposits highlighted by yellow colour. See Fig. 10a for the location. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

crustal and uppermost mantle physical properties of the Turkish – Iranian plateau using variations in velocities of Pn, Sn, and Lg. They found that Sn was strongly attenuated in the northernmost portion of the plateau, south of the Black and Caspian seas and in regions characterized by active volcanism, faulting, and folding. Using surface wave tomography, Maggi and Priestley (2005) reported slow upper mantle shear wave velocity beneath much of the Turkish-Iranian plateau and related it to a thin lithosphere and a hot upper mantle. Priestley et al.

including the NTF and other parallel faults (e.g., Karakhanian et al., 2004; Solaymani Azad et al., 2015; Ghods et al., 2015), which accommodate dextral shear to the north of the Main Recent Fault. The distribution of strike-slip faulting over the northwest Iranian region most likely favored a distributed deformation model where several semiparallel faults, such as the Ahar fault, NTF and Salmas and Maragheh fault zones, were active. This kind of deformation requires a thin and anomalously hot lithosphere. Kadinsky-Cade et al. (1981) investigated 25

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Fig. 11. (a) Geological map of the western termination of DF showing the Dashkassan assemblage in the fault relay zone; the background topography is based on SRTM digital elevation data. (b) Simplified structural map of the same area. Black arrows represent the attitude of active extension in the area deduced from the opening direction of fissure-ridges. (c) Rose-diagram shows the strike of fissure-ridges in the Dashkassan assemblage. Black open arrows represent the direction of active extension in the area. (d) A WSW-oriented topographic cross section across the Dashkassan assemblage represents an elevation difference of ~150 m across the ridges with respect to the adjacent plain. See Fig. 11a for the location. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

volcanism. These low-velocity features correlated with a long-wavelength free-air gravity anomaly (e.g., Dehghani and Makris, 1984; Hatam Chavari, 2010) and with Quaternary volcanism (e.g., Keskin, 2003; Chiu et al., 2013; Pirmohammadi Alishah and Jahangiri, 2013). The geodynamic characteristics of the area are analogous with observations made in eastern Turkey (e.g., Reilinger et al., 1997; Gök et al., 2007; McClusky et al., 2000; Al-Lazki et al., 2003; Keskin, 2003), where strike-slip faulting suggested to be distributed in a thin and hot lithosphere. In summary, seismology, gravity, volcanism and structural

(2012) carried out a more comprehensive surface wave tomography in the Middle East and showed that eastern Turkey and NW Iran had very low shear wave velocities down to a depth of 125 km, whereas the Zagros Mountains and the South Caspian Basin showed high shear velocities. More recently, P-wave tomograms calculated by Bavali et al. (2016) indicated a low-velocity region beneath NW Iran. The tomograms revealed two low-velocity zones located beneath the Sahand and Sabalan volcanic regions. These velocity anomalies are most likely thermal in origin and might point to the source region of Late Neogene

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Fig. 12. (a) ASTER satellite image (6–3-1) of the ELF (see Fig. 2 for the location). (b) Filtered band 7 image (low pass plus Sobel) of ASTER satellite. (c) Simplified morphotectonic interpretation of the Fig. 12a and b. Axial trace of fan shows right-laterally offset along the ELF. Piercing points are intersections of fan axial trace with the fault trace. (d) Field photograph of a deflected stream along the ELF. The location and look direction are marked in Fig. 12c.

to Copley and Jackson (2006), most of the strike-slip motion was accommodated in a band up to 80 km in wide north of Lake Van, with a shearing rate of 8 ± 2 mm/yr across the area (i.e. the Van shear zone). In contrast, right-lateral strike-slip deformation was localized on major faults such as the North Anatolian and Main Recent faults to the west and southeast of this area, respectively. A major part of NW Iran, especially areas around the study site, have been regarded as “relatively undeforming” areas. Copley and Jackson (2006) suggested that the North Anatolian and Main Recent faults represented long-living weak zones in the crust and served to localize deformation. The reintegration of our observations and existing models (Copley and Jackson, 2006; Ghods et al., 2015; Faridi et al., 2017) helped develop a distributed strike-slip faulting concept for the whole region to the north of the Arabian plate, which includes NW Iran, eastern Turkey and the Lesser Caucasus. We suggest that the presence of an anomalous hot lithosphere in the region caused this kind of distributed strike-slip faulting. The distribution of large-scale faults every 100 km or so (from MRF to Salmas - Maragheh fault zones to NTF and beyond) also supports the existence of a thin lithosphere. Although secondary faults are systematically located on the edges of the large active volcanic systems (e.g., Sabalan and Sahand), their mutual relationships are not straightforward. Whether these large volcanoes might have controlled the location of the secondary faults would need to be assessed by further detailed studies of fault kinematics. Conversely, previous studies have shown that strike-slip faults play a key role in creating zones of localized

characteristics all emphasize the presence of a thin lithosphere and warm upper mantle beneath the middle part of the Turkish-Iranian plateau (Kadinsky-Cade et al., 1981; Keskin, 2003; Maggi and Priestley, 2005; Priestley et al., 2012; Chiu et al., 2013; Pirmohammadi Alishah and Jahangiri, 2013; Bavali et al., 2016). Accordingly, we suggest that distributed deformation and strike-slip faulting is extended in NW Iran, eastern Turkey and the Lesser Caucasus (Fig. 16) due to partial delamination of lithospheric mantle resulting from earlier lithospheric thickening during the continental collision (Pearce et al., 1990; Keskin et al., 1998; Maggi and Priestley, 2005), or break-off of a subducting slab (Keskin, 2003, 2007; Şengör et al., 2003; Kheirkhah et al., 2009). At a larger scale, in the Alpine–Himalayan belts, distributed strikeslip faulting was documented in central Tibet (Armijo et al., 1989; Taylor et al., 2003; Taylor and Peltzer, 2006). The central Tibetan crust is spreading eastward via distributed extrusion of small wedge-shaped blocks along a series of conjugate fault systems in the interior of Tibet (Taylor et al., 2003). The mechanism of faulting and crustal structure of Tibet is not analogous with NW Iran. The characteristics of the NW Iranian regions contrasted with the observations made in other tectonic domains of the Arabia-Eurasia collision, such as Central Iran, Lut block and Kopeh Dagh; where crustal strike-slip faulting was localized along few distinct boundary fault systems (e.g., Le Dortz et al., 2009; Shabanian et al., 2009a, 2009b, 2012a; Farbod et al., 2016). The distributed character of strike-slip faulting in the TurkishIranian plateau was proposed by Copley and Jackson (2006). According

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Fig. 13. (a) Shaded relief map (SRTM data) of the Salmas fault zone. The black dashed line delineates the boundary between two sub-segments. (b) Shaded topographic image and the morphotectonic map of the ESF and eastern part of the WSF showing linear streams/valleys and systematic right-lateral offsets/deflections recorded by streams; piercing points are the intersection between the overall trend of steams and the fault trace. Corresponding stream counterparts are shown with the same number. See Fig. 13a for the location.

the aforementioned faults and indicate local extension along strike-slip faults of the region with an important role in Quaternary volcanism. Examples of this volcanism are the Eslamy peninsula, basaltic lava flows in Salmas and Yigit Daghi, and several other quaternary volcanic edifices in Eastern Anatolia (Karakhanian et al., 2002; Kheirkhah et al., 2009; Shabanian et al., 2012b). The distributed pattern of strike-slip faulting over northwestern Iran and eastern Anatolia accompanied by features of local extension in the fault bends or relay zones caused a regionally distributed pattern of local extension could be confused with regional scale extension (e.g., such as produced by the Aegean subduction roll-back; Taymaz et al., 2007; Jolivet et al., 2013 and references therein). Yet local extensions can be produced along strike-slip faults in their structural complexities or at the back of reverse faults,

extension and may be the most effective means, within collisional settings, to provoke the rise and extrusion of magma from volcanoes (e.g., Acocella and Funiciello, 2010; Shabanian et al., 2012b). 4.4.2. Mechanism of extension in NW Iran Active transtension is a common kinematics characteristic along the Maragheh and Salmas fault zones. The related extensional features were created by either releasing relay fault zones or bends and were generally accompanied by active travertine deposition. Geomorphic features of active transtension were also documented along the NTF (Qurigöl pull-apart basin) and the Gailatu–Siah Cheshmeh–Khoy fault systems (Taghipour, 2004; Karakhanian et al., 2004; Solaymani Azad et al., 2015). All these features were found in structural complexities of

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Fig. 14. (a) Satellite (Google earth) image of the northern part of Lake Urmia after receding of the lake. Yellow arrows show the location of the inferred fault. (b) Bathymetric levels of Lake Urmia superposed on the satellite image (data after Water Research Institute of Iran, 2013). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

and regional-scale tensional regime would have to be recognized in both geology and seismotectonics of the region. The NW Iranian region is prominently affected by active strike-slip tectonic region and especially transpressional stress regime (e.g., Ghods et al., 2015 for both geological and seismological data; Solaymani Azad et al., 2015 for transpressional kinematics of the NTF). Almost all extensional features of the region are related to the overlapping zones of these strike-slip faults (e.g., Karakhanian et al., 2004; Taghipour and Mohajjel, 2013) and should not be confused with signatures of regional extension. The abundance of these extensional features throughout the region is

Table 1 East and North GPS velocity components (E Vel., N Vel.) and 1-sigma uncertainties (σE, σN) in a Eurasia-fixed reference frame are given in mm/yr (after Djamour et al., 2011). Station

Long (°E)

Lat (°N)

E vel.

N vel.

σE

σN

A (GGSH) B (MMKN) C (SKOH) D (MIAN) E (MNDB)

44.954 44.771 46.123 46.162 46.009

38.207 37.985 37.933 36.908 36.93

2.8 −1.52 −0.07 −2.16 −4.58

13.15 9.88 12.85 13.54 14.59

0.69 2.43 0.28 0.41 1.29

0.7 0.97 0.56 0.39 0.26

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Fig. 15. Shaded relief image of NW Iran with trace of the Maragheh and Salmas fault zones (mainly red lines) and other faults (AF: Akhourian Fault; AHF: Ahar Fault; ARF: Arasbaran Fault; BAF: Başkale Fault; CF: Chalderan Fault; GF: Garni Fault; GSKF: Gailatu–Siah Cheshmeh–Khoy Fault; KF: Khajeh Fault; MF: Maku Fault; NF: Nakhichevan Fault; NTF: North Tabriz Fault; PSSF: Pambak-Sevan-Sunik Fault; SFS: Serow Fault System; SMF: South Maragheh Fault; TF: Tasuj Fault; TAF: Talesh Fault; YFZ. Yüksekova fault zone). Black arrows are GPS velocity vectors after Djamour et al. (2011) and blue arrows after Reilinger et al. (2006). Green capital letters represent the stations used for slip rate estimation. Focal mechanisms for earthquakes are from Harvard catalog, 1976 to December 2016. The red and blue focal mechanisms are related to the mainshocks and aftershocks of the 2012 Varzeghan-Ahar earthquake, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

aligns with the Salmas fault zone on either side of the lake. Variations in the strike of these fault zones have caused local kinematic changes and resulted in different uplifting or subsiding areas along the fault system. The dextral shear component of the Arabia – Eurasia oblique convergence, north of the Main Recent Fault, is taken up by several subparallel strike-slip faults, such as the NTF, Maragheh and Salmas fault zones (investigated in this study), as well as other similar faults to the north of the NTF, such as the Ahar-Varzeghan fault network. This tectonic configuration supports a model of distributed deformation in northwest Iran, eastern Turkey and the Lesser Caucasus rather than rigid block faulting. This pattern of deformation is consistent with a thin lithosphere and warm upper mantle beneath the middle part of the Turkish-Iranian plateau, as documented by different geological and geophysical studies. The presence of releasing step-overs accompanied by deposition of travertine fissure-ridges along the Maragheh and Salmas fault zones, including other similar strike-slip faults in northwest Iran and eastern Anatolia, indicates active local extension along a complex fault

because strike-slip faulting is distributed over the region and naturally, the associated extensional features were also distributed; a fact that implied a thin and anomalously hot lithosphere for the region. Regarding this clear and sharp difference in the structural pattern and kinematics of the region with regions affected by tensional tectonic regimes, our suggestion for local extension due to distributed strike-slip faulting against distributed extension (e.g., Masson et al., 2006; Djamour et al., 2011) due to a regional tensional tectonic regime seems convincing. 5. Conclusion The Maragheh and Salmas fault zones are the most prominent dextral strike-slip faults affecting the northwestern part of the Iranian plateau between the North Tabriz Fault and the Main Recent Fault. The Maragheh fault zone is composed of four dextral NW-striking faults extending from the Eslami peninsula to the southeast of Maragheh town. The Salmas fault zone affects western terrains of Lake Urmia and

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Fig. 16. Simplified map shows the proposed area for zone of distributed strike-slip faulting in NW Iran, eastern Turkey and the Lesser Caucasus, based on results of this study and previous works (e.g., McClusky et al., 2000; Vernant et al., 2004). Red triangles show the location of Quaternary volcanic centers. Arrows and corresponding numbers show GPS-derived plate velocities relative to Eurasia, after Reilinger et al. (2006). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

network. This network is distributed over the region and could be confused with a tensional tectonic regime prevailing at the regional scale.

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