The Caucasian-Arabian Segment of the Alpine-Himalayan Collisional Belt: Geology, Volcanism and Neotectonics

Geoscience Frontiers xxx (2014) 1e11

HOSTED BY Contents lists available at ScienceDirect

China University of Geosciences (Beijing) Geoscience Frontiers

journal homepage: www.elsevier.com/locate/gsf

Review The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt: Geology, volcanism and neotectonics

E. Sharkov a, V. Lebedev a, A. Chugaev a, L. Zabarinskaya b, A. Rodnikov b, N. Sergeeva b, I. Safonova c,d,* a Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Staromonetny Line, 35, Moscow 119017, Russia b Geophysical Center of RAS, Molodezhnaya St. 3, Moscow 119296, Russia c Institute of Geology and Mineralogy SB RAS, Koptyuga Ave. 3, Novosibirsk 630090, Russia d Novosibirsk State University, Pirogova St. 2, Novosibirsk 630090, Russia article info abstract

Article history: The Caucasian-Arabian belt is part of the huge late Cenozoic Alpine-Himalayan orogenic belt formed by Received 26 January 2014 collision of continental plates. The belt consists of two domains: the Caucasian-Arabian Syntaxis (CAS) in Received in revised form the south and the EW-striking Greater Caucasus in the north. The CAS marks a zone of the indentation of 2 July 2014 the Arabian plate into the southern East European Craton. The Greater Caucasus Range is located in the Accepted 11 July 2014 south of the Eurasian plate; it was tectonically uplifted along the Main Caucasian Fault (MCF), which is, in Available online xxx turn, a part of a megafault extended over a great distance from the Kopetdag Mts. to the Tornquist- Teisseyre Trans-European Suture Zone. The Caucasus Mts. are bounded by the Black Sea from the west Keywords: East European Craton and by the Caspian Sea from the east. The SN-striking CAS is characterized by a large geophysical isostatic Calc-alkaline and shoshonite-latite anomaly suggesting presence of mantle plume head. A 500 km long belt of late Cenozoic volcanism in the volcanism CAS extends from the eastern Anatolia to the Lesser and Greater Caucasus ranges. This belt hosts two Mantle plume head different types of volcanic rocks: (1) plume-type intraplate basaltic plateaus and (2) suprasubduction- Basaltic plateaus type calc-alkaline and shoshonite-latite volcanic rocks. As the CAS lacks signatures of subduction Plume-crust interaction zones and is characterized by relatively shallow earthquakes (50e60 km), we suggest that the “supra- “ ﬂ ” Tectonic dif uence subduction-type” magmas were derived by interaction between mantle plume head and crustal material. Those hybrid melts were originated under conditions of collision-related deformation. During the late Cenozoic, the width of the CAS reduced to ca. 400 km due to tectonic “difﬂuence” of crustal material provided by the continuing Arabia-Eurasia collision. Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction typical collision-type orogenic belt, which formed during tens of millions of years after the closure of the Mesozoiceearly Cenozoic Structures of zones of continental collisions are very complex Tethys Ocean and is characterized by intensive processes of compared to those of island arcs and active continental convergent mountain building and rifting, which were accompanied by margins, however, many of them have not been sufﬁciently studied. extensive plateau-basaltic and andesite-latite magmatism (e.g., This remains valid for the world largest modern Alpine-Himalayan Grachev, 2000; Sharkov, 2011; Sharkov et al., 2012; Trifonov et al., continental collision-type convergent belt (AHB), which is 2012; Safonova and Maruyama, 2014 and references therein). The extended over a distance more than 16,000 km across Eurasia from Caucasian-Arabian segment of this belt is of special interest the western Mediterranean to the western Paciﬁc. The AHB is a because abundant recent geological, geochronological and petrologic data have allowed us to consider this region as a type area of still active tectonic and petrologic processes related to continental * Corresponding author. Institute of Geology and Mineralogy SB RAS, Koptyuga collision (Keskin, 2003; Sandvol et al., 2003; Saintot et al., 2006; Ave. 3, 630090 Novosibirsk, Russia. E-mail addresses: [email protected], [email protected] (I. Safonova). Kopp, 2007; Leonov, 2007; Eppelbaum and Khesin, 2012; Sharkov Peer-review under responsibility of China University of Geosciences (Beijing). et al., 2012; Lebedev et al., 2013). http://dx.doi.org/10.1016/j.gsf.2014.07.001 1674-9871/Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

The Caucasian-Arabian segment consists of two major domains: in a multi-author monograph of “European Lithosphere Dynamics” (1) a linear system of Greater Caucasus in the north, and (2) an (Gee and Stephenson, 2006 and references cited therein). Accord- active arc-like system of tectonic elements of the Minor Caucasus ing to geophysical data, the structure of the lithosphere of the and eastern Anatolia in the south, known as Caucasian-Arabian Alpine orogen is quite complex and variable beneath ridges and Syntaxis (CAS), which was formed by indentation of the Arabian basins (Hearn, 1999; Artemieva et al., 2006; Kissling et al., 2006). plate into the southern border of the Eurasian plate and is currently Artemiev (1971) was the ﬁrst to show two types of basins moving to the north (Fig. 1)(Burtman, 1989; Reilinger et al., 2006; (Fig. 3). Type 1 basins include the Tyrrhenian, Aegian, and Alboran Leonov, 2007 and references therein). Tectonic processes accom- seas and the Pannonian depression. They are back-arc basins panied by almost coeval manifestations of two types of magma- formed by the rollback of andesite-latite volcanic arcs (Rehault tism, i.e., basaltic and andesitic-latitic, occur over the entire length et al., 1987; Royden, 1989; Lonergan and White, 1997; Harangi of the CAS (Keskin, 2007; Koronovsky and Demina, 2007; Keskin et al., 2006 and references therein). These back-arc basins are et al., 2013). However, the origin of these magmatic units remains characterized by thinned crust, high heat ﬂow, and manifestations debatable (Lebedev et al., 2013; Neill et al., 2013 and references of basaltic volcanism suggesting either asthenospheric upwelling therein). This paper presents a synthesis of geological, petrologic and/or the presence of mantle plume heads. We argue for a plume- and geophysical data on the geodynamic history of the CAS, with a related model based on three main facts: (1) presence of positive focus to the geological structure of the region, mantle and crust isostatic anomalies; (2) plume-type character of magmatism; and dynamics and geodynamic settings of the different magmatic units. (3) geophysical data, which all are discussed below. However, the asthenospheric upwelling can be also linked to a mantle plume. 2. The Alpine-Caucasian orogen A special feature of the back-arc basins is presence of large positive isostatic anomalies underneath (Fig. 3). These anomalies The Alpine-Caucasian segment of the Trans-Eurasian Belt or the could result from regular “injections” of deep mantle material into Alpine Orogen, a key part of the Alpine-Himalayan collisional zone, plume heads, which led to increased loading onto the lithosphere formed during the late Cenozoic and is characterized by a very and disturbing the isostatic equilibrium. The largest positive complex geological structure. It consists of sea basins of the Med- isostatic anomalies occur beneath the Aegean Sea and the Pan- iterranean and the Pannonian depression separated by fold-thrust nonian back-arc basin (Fig. 3), which may be indicative of a rapid belts of the Alps, Carpathians, Apennines, and others, all hosting supply of mantle material. Several researchers (Reilinger and andesite-latite volcanic units (Fig. 2). The Alpine orogen has been McClusky, 2011; Faccenna et al., 2013) suggested that the Aegian studied by many research groups, whose results were summarized Sea was a back-arc basin of the modern Arabia-Anatolia-Aegian

Figure 1. Location of the Caucasian-Arabian Syntaxis (modiﬁed from Reilinger et al., 2006). Abbreviations: NAF e North-Anatolian Fault; EAF e East-Anatolian Fault; DSF eDear Sea Fault; MF e Mosha Fault; PSSF e Pembak-Sevan-Sunik Fault; Cor e Gulf of Corinth; Pe e Peloponnes; Aeg e Aegian Sea; LC e Lesser Caucasus; Cyr e Cypris trench; Sin e Sinai; Cas e Caspian Sea; EAR e East-African Rift; Lpr e Kopetdag; AR e Apsheron Peninsula; Al e Alborz (Elburs) Mountains. Red line: Kopetdag-Causasian-Trans-European megafault.

Figure 2. Distribution of late Cenozoic igneous rocks within the Alpine Belt. 1 e back-arc seas (A e Alboran, T e Tyrrhenian; Aeg e Aegian) and “downfall” seas (B e Black, C e Caspian); 2 e back-arc sedimentary basins (P e Pannonian, Po e Po valley); 3 e late Cenozoic andesite-latite volcanic arcs (in circles): 1 e Alboran, 2 e Cabil-Tell, 3 e Sardinian, 4 e South-Italian, 5 e Drava-Insubrian, 6 e Evganey, 7 e Carpatian, 8 e Balkanian, 9 e Aegian, 10e12 e Anatolian-Caucasian-Elburssian (10 e Anatolian-Caucasian, 11 e Transcaucasian belt, 12 e Caucasus-Elburssian); 4 e areas of ﬂood basaltic volcanism (in squares): 1 e South Spain and Portugal, 2 e Atlas, 3 e Eastern Spain, 4 e Central France massif, 5 e Rhine graben, 6 e Czech-Silesian, 7 e Pannonian, 8 e western Turkey, 10 e northern Arabia; 5 e suture zones of major thrust structures. convergent system, but of a special origin. We think that the Aegian (Zonenshain and Le Pichon, 1986). Those “asymmetric” mantle Sea is similar to others back-arc basins of the Alpine Belt in terms of plumes are different from “common” plumes, which have geophysical features and dynamic settings (Khain, 1984; Artemieva mushroom-shaped heads resided in relatively homogeneous et al., 2006; Sharkov and Svalova, 2011). The only distinctive feature within-plate environment. An “asymmetric” plume head may occur is the very young age of the Hellenic suprasubduction volcanic arc as a “tongue” extended towards the less viscous oceanic litho- and of the Carpatian Arc, which were initiated as late as 2 Ma sphere including relics of the Tethys. The roof of such a “tongue” (Harangi et al., 2006). Possibly, as the present-day geological pro- initially consisted of continental lithosphere material of the African cesses of these localities proceed at shallow levels, they have not plate, which formerly was exposed in the western Mediterranean had time enough to respond to the processes in the deep mantle. (Ricou et al., 1986). The transportation and accumulation of the Support for such a suggestion comes from the lower magnitudes of “cut-off” this material at the front of the “tongue” leads to the positive isostatic anomalies beneath the other back-arc seas thinning of back-arc basin crust by subcrustal erosion and emer- (Artemiev, 1971), which may indicate longer interactions of shallow gence of oceanic crust (Sharkov and Svalova, 2011). and deep mantle processes. The formation of a new subduction zone can be triggered by the Those “volcanic arc e back-arc basin” systems could result from cooling of the frontal part of the “tongue”, which density increases, a unidirectional displacement/propagation of mantle plumes heads and which acquires negative buoyancy and consequently descends caused by the heterogeneous structure of the lithosphere of the to initiate the beginning of subduction (Fig. 4). The crustal material, eastern Mediterranean due to the presence of Tethys relics which was consolidated and metamorphosed during the

Figure 3. Distribution of regional isostatic anomalies and areas of Cenozoic volcanism in the Alpine Belt (modiﬁed from Artemiev, 1971). Brown line: Kopetdag e Causasian e Trans- European megafault. EAF e East Anatolia Fault, KDF e Kopetdag Fault, MCF e Mina Caucasian Fault, NAF e North Anatolia Fault, TESZ e Trans-European suture zone.

Figure 4. A scheme showing the mechanism of formation of back-arc basins in the Alpine Belt by an asymmetric plume. deformation and accumulated at the front of the “tongue”,isan Mediterranean are indicative of derivation of their parental melts additional load contributing to the descending of the “tongue” and from a similar source, a Common Mantle Reservoir (Hofmann, initiation of subduction. Finally, the consolidated higher density 1997; Lustrino and Wilson, 2007). Such a reservoir could be crust together with surrounding fragments of oceanic lithosphere related to a modern mantle plume or even superplume, with the become parts of the subducting slab (Sharkov and Svalova, 2011). head located beneath the Alpine-Caucasian region from which The melting of the subducting slab of a “mixed” composition over a plumelets/branches spread out beneath the back-arc basins. Thus, newly formed subduction zone can produce calc-alkaline and the Alpine orogen having a complex structure of multiple ridges shoshonite-latite magmas and finally volcanic arcs. and basins is probably located over the central part of that plume or The formation of the back-arc basins resulted in rifting and its superplume. This does not contradicts the model of asthenospheric related basaltic volcanism to form volcanic fields and plateaus at upwelling though, which can be related to a mantle plume splitting the frontal edge of the mountain ranges of central and western into smaller plumelets/branches, which heads form positive Europe, in North Africa and North Arabia (Fig. 2). The late Cenozoic isostatic anomalies affecting the whole geodynamic pattern of the volcanic units are mostly Fe-Ti-rich alkaline basalts, which are region. This idea agrees well with the geophysical data (e.g., geochemically similar to typical intraplate (plume-related) magmas Smewing et al., 1991; Hearn, 1999) suggesting that several smaller erupted in oceanic (oceanic island basalts, OIB) and continental plumes could be merged to form a huge asthenospheric upwelling (flood basalts) environments (Hofmann, 1997; Grachev, 2003; area at depths of 200e250 km. Medvedev et al., 2003; Lustrino and Sharkov, 2006; Wilson and Type 2 basins include the eastern Mediterranean, the Black Sea Downes, 2006; Safonova and Santosh, 2014). The geochemical and the Caspian Sea (Fig. 5). Unlike the Type 1 back-arc seas of the and isotopic characteristics of magmatic rocks of the western Mediterranean, Type 2 seas are characterized by passive

Figure 5. Heat ﬂow distribution in the Caucasian region (modiﬁed from Pollack et al., 1993).

Please cite this article in press as: Sharkov, E., et al., The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt: Geology, volcanism and neotectonics, Geoscience Frontiers (2014), http://dx.doi.org/10.1016/j.gsf.2014.07.001 E. Sharkov et al. / Geoscience Frontiers xxx (2014) 1e11 5 margins, i.e., thick (16e20 km and more) sequences of Meso- up to the NeogeneeQuaternary Arabia-Eurasia collision-related eCenozoic sediments, by the absence of volcanism and by low heat orogeny, which formed the present-day structure of the Caucasus. flow (Fig. 5). They look like large “downfalls”, especially the Black The Greater Caucasus (GC) orogen is located in the northern CAS Sea and Caspian Sea, which cut the pre-Pliocene structures of the and aligned along the Main Caucasus Fault (MCF). The GC repre- Caucasus and the Kopetdag. According to geological data, the Black sents the southern end of the Eurasian plate (Leonov, 2007). The Sea and Caspian Sea represent small relics of the Tethys Ocean, MCF is a part of the megafault extending from the Kopetdag across which were relatively shallow during the Miocene, but started to the Caspian Sea to the Caucasus and Crimea (Sharkov et al., 2012). A subside in the Pliocene and continued to sink during the Holocene probable farther continuation of the MCF is the Trans-European (Zonenshain and Le Pichon, 1986). The subsidence was coeval with Suture Zone (Tornquist-Teisseyre Fault Zone), which separates the the growth of the Caucasian Mountain Range and with the rise of East European Craton from the European Variscides and Alpides the Crimea Peninsula, both topographically much less evident (Artemieva et al., 2006) and is evidenced by a chain of weak but still during the OligoceneeMiocene (Grachev, 2000). active seismicity. Thus, the Kopetdag-Caucasus-Trans-European Unlike the first type basins, the second type depressions are megafault separates the modern Alpine orogen and the stable characterized by large isostatic negative anomalies (Fig. 3). The Eurasian plate sensu stricto (Fig. 1). isostatic “minima” are indicative of a deficiency of rock masses The modern Alpine tectonic structure of the Caucasus was formed underneath, probably, due to downward flows of lithospheric ma- by the NS horizontal compression related to the collision of two terial in the mantle or “antiplumes”, which separate the upwelling plates: Arabian (as indenter) and East European (cratonic). The tec- plume heads (Maruyama et al., 2007). The propagating mantle tonic push from the Arabia indentation is transmitted along the Bitlis- plume head pushes the lithosphere and may displace old litho- Zagros belt to the Greater Caucasus to form the CAS. The rate of Arabia spheric material to make it descending down to the mantle, i.e. to indentation into the Eurasian plate is of several centimeters per year form downwelling mantle currents or “antiplumes”. Such down- (Saintot et al., 2006). According to paleomagnetic data, during the welling is responsible for the formation of depressions on the late-Alpian, the distance between Arabian and Eurasia shortened by surface, i.e. second type basins. The largest isostatic anomalies are ca. 400 km (Bazhenov and Burtman, 1990; Leonov, 2007), however, located in the Levantine basin of the eastern Mediterranean, with structural data, e.g., the strike and dimension of folds and tectonic rapid subsidence to depths below the sea level occurred approxi- nappes, indicate a much smaller shortening, hardly over 200 km mately at 3e3.5 Ma (Emels et al., 1995; Novikov et al., 2013). No (Kopp, 2007). The largest shortening was south of the MCF. The significant isostatic anomalies have been found close to the basin of reduction within the Greater Caucasus was significantly smaller, less the Black Sea, suggesting a relatively low rate of subsidence and not then several tens of kilometers (Leonov, 2007 and references herein). enough to disturb the isostatic equilibrium. Many scientists believe that the MCF is due to the overthrust or un- The geophysical data from the peripheral parts of those basins, derthrust of the Transcaucasian massif under the Greater Caucasus e.g., under the northern margins of the Black Sea and eastern (e.g., Khain, 1984; Saintot et al., 2006 and references therein). How- Mediterranean, indicate the presence of steeply-dipping seismi- ever, direct geological observations suggest the linear shape of the cally active zones. The seismic zones are associated with strong fault, as well as rather steeply dipping imbricate structures and/or local positive gravity anomalies formed by blocks of high-density reverse faults. In addition, geophysical data suggest a steep or vertical rocks, which are separated by nearly vertical faults extended to angle of the MCF up to depths of 70e80 km (Shempelev et al., 2005). mantle depths of 60e70 km (Shempelev et al., 2001; Zverev, 2002). Consequently, according to Leonov (2007) we accept that the MCF is a An exception is a large positive isostatic anomaly beneath the reverse fault with a large rate of vertical displacement and minimal Caucasian-Arabian Syntax (Fig. 3). The anomaly is located between horizontal displacement. the Black Sea and Caspian Sea and continues southward, to the If so, the shortening south of the GC could result from a lateral Lesser Caucasus and eastern Anatolia. We suggest that this anomaly “diffluence” or “spreading” of lithospheric material under the push is also related to an ascending mantle plume. Unlike the Mediter- of the Arabian indenter in two opposite directions away from the ranean and the Pannonian, there is no any depression there. GC in front of the rigid East European Craton (Fig. 6). More evidence for this comes from geological (Kopp, 2007) and GPS data from the 3. Structural features of the Caucasian-Arabian segment zone of the Africa-Arabia-Eurasia continental collision (Reilinger et al., 2006; Reilinger and McClusky, 2011)(Fig. 7). We suggest The northern termination of the Caucasian-Arabian Syntax that the convergence of Arabia and Eurasia resulted in lithosphere (CAS) is represented by the Caucasian Mountains with a pre-Alpine shortening and bi-lateral transportation of excessive lithosphere basement consisting of pre-Jurassic structures and rock complexes. material, i.e., its “diffluence” both to the south-west and south-east The structure and composition of the Caucasian basement is vari- of the collision zone, which formed the tectonic sheets of the able (Somin, 2007 and references cited herein): it consists of two eastern Asia Minor Peninsula and Zagros Mountains, respectively. major tectonic domains, North-Caucasian and South-Caucasian Obviously, the removal of a significant part of the basement in front (Svanetian), divided by the active Main Caucasian Fault (Fig. 2). of the MCF can be responsible for the difference between the The first Variscan domain is characterized by numerous occur- structures of the northern and southern Caucasian domains. rences of granitoids and regionally metamorphosed rocks. Those rock units are absent in the southern domain, where the pre- 4. Late Cenozoic volcanism in the CAS Jurassic sequences consist of marine Devonian to late Triassic sedimentary rocks. These two units are probably an eastern Another important feature of the CAS is a large, TransCaucasian, continuation of the Central European Variscides (Franke, 2006). NS-trending zone of late Cenozoic to modern volcanism, which The Cimmerian Orogeny (early and middle Jurassic) of the extends from eastern Anatolia to the Lesser and Greater Caucasus Caucasian region, according to Leonov (2007) included two geo- with the largest Caucasian volcanoes of Elbrus and Kazbek (Fig. 8). dynamic stages: (1) early JurassiceAalenian passive margin and (2) There are two types of geochemically and petrologically different Bajocian-Bathonian active margin. Their separating interval at the types of volcanic rocks: (1) “suprasubduction” type calc-alkaline end of the Aalenian e beginning of the Bajocian demarcates the and shoshonite-latite, and (2) volcanic rocks of basaltic intra- major Cimmerian and Alpine stages of the evolution of the Greater plate (plume-related) type. Type 1 “suprasubduction” volcanic Caucasus. The Aalenian-Bajocian tectonic zoning remained stable rocks are dominated by basaltic andesite, andesite, dacite and

Figure 6. Collision-related tectonic deformations associated with the Caucasian-Arabian Syntaxis (based on a simplified tectonic map of the eastern Mediterranean region; McClusky et al., 2000). The topography-based lines of major tectonic structures, e.g., strike-slip faults, large thrusts and folds, of the region illustrate the modern “diffluence” of crustal material in front of the rigid East-European Craton. The arrows show plate motions relative to Eurasia. rhyolite with subordinate low-Ti basalt and rhyolite (Lebedev et al., towards Mountain Elburs (Alborz) and the Zagros Mountains. 2006; Koronovsky and Demina, 2007; Keskin, 2007; Gurbanov However, the Caucasian-Arabian Syntaxis is characterized by et al., 2008; Keskin et al., 2013), as well as shoshonite, latite and shallow seismicity, with earthquake hypocenters mostly at depths potassic dacites and rhyolites (unpublished data). Structurally, of less 50e60 km. Deep-focus earthquakes (up to 120 km) are those volcanoes are characterized by numerous calderas and extremely rare and occur sporadically in the eastern part of the CAS, abundant felsic pyroclastic rocks, which are typical for volcanoes of at the boundary with the Caspian Sea (Figs. 9 and 10). Conse- island arcs and active continental margins. quently, we think that there is no evidence of active subduction Type 2 volcanic units form large lava plateaus of alkaline basalts beneath the Caucasus and eastern Anatolia (Sandvol et al., 2003). of within-plate (plume-related) type erupted as typical shield Those “supra-subduction type” volcanic rocks possess geochemical volcanoes, e.g., Javakheti, Geghama, Syunik, Kars, etc. Type 2 and isotope characteristics of both mantle plume-derived lavas and magmatism suggests the activity of a mantle plume head under the continental crust material, suggesting a complex mantle-crustal CAS. Thus, two different types of magmatism are manifested in the origin, e.g., of the NeogeneeQuaternary volcanic rocks of the Cau- CAS. Type 1 magmatism was possibly related to converging mar- casus (Lebedev et al., 2010). 87 86 gins settings, whereas Type 2 magmatism was initiated in an For example, the ratios of Sr/ Sr and εNd range, respectively, intraplate plume-related geodynamic setting, which was first from 0.7045 to 0.7058 and from þ0.1 to þ2.1 for the Quaternary recognized by Yarmolyuk et al. (2004). andesite-felsic volcanic rocks of the Keli Mountain, from 0.7054 to Geochemically, the lava flows of the Javakheti, Geghama, Central 0.7064 and from 2.3 to þ0.8 for the late-Quaternary dacites of the Georgia, and other plateaus are dominated by moderately alkaline Elbrus Volcano, and from 0.7075 to 0.7086 and from 2.2 to 4.3 basalts enriched in Zr, Sr and Ba (Lebedev et al., 2006). Their iso- for the late Miocene alkaline granites of the Caucasian Mineral 87 86 topic ratios of Sr/ Sr ¼ 0.7041e0.7043 and εNd ¼þ3.5 to þ4.5) Waters area. The contribution of upper crust material to the correspond to those of a “Common” lower-mantle source petrogenesis of parental melts produced the late Cenozoic magmas 87 86 ( Sr/ Sr ¼w 0.7035, εNd ¼w þ5; Hofmann, 1997), which is is from ca. 50e60% for the late Miocene granitoids to ca. 20% in considered as a possible source of plume-related basalts. moderate-alkaline plateu basalts. The Elbrus dacites and the The volcanic rocks of “suprasubduction” type are of special in- andesite-felsic volcanic rocks of other volcanoes are characterized terest. Unlike many paleo- and modern-island arcs and active by transitional proportions of mixed crustal and mantle-derived continental margins, the East-Anatolian-Caucasian volcanic belt is materials. Evidence for the presence of the mantle material also extended over the whole Caucasus, matching the strike of the comes from the Pb/Pb isotope ratios in dacites of the Elbrus Volcano TransCaucasian isostatic anomaly (Fig. 3). South of Lake Van this (206Pb/204Pb ranging from 18.621 to 18.670, 207Pb/204Pb from volcanic belt splits into two branches: one branch is trending to the 15.636 to 15.659 and 208Pb/204Pb from 38.762 to 38.845), suggest- west, to Central Anatolia, the second branch extending to the east, ing a mantle source close to that to the Afar triangle plume in East

Figure 7. GPS velocities and directions of plate movements with respect to Arabia (spatially decimated for clarity) in and adjacent to the Arabian plate with 95% conﬁdence ellipses (modiﬁed from Reilinger and McClusky, 2011).

Africa (Chugaev et al., 2013 and references therein). In general, the spreading or “diffluence” of crustal material apart from the Arabian isotope systematics of the late Cenozoic volcanic rocks of the CAS indenter, i.e. in two directions. Those arcs possibly trace a kind of suggests that their source was contaminated by upper crust ma- “suture” zones, along which the crustal material tectonically terial from the Paleozoic basement granite-metamorphic com- migrated during the collision of the continents. The “suture” zones plexes (Lebedev et al., 2010). could be defined by the shape of the plume head stretching to the As the strike of the 500 km long East-Anatolian-Caucasian vol- north and overflowing from both sides by the oncoming strongly canic belt coincides with that of the syntaxis, i.e. with the zone of deformed material of shallow lithosphere. maximal stress, we suggest that those magmas could be derived by The late Cenozoic volcanic rocks of the Alpine-Mediterranean interaction between mantle plume head and crustal material. Such belt, which was formed by the Africa-Eurasia continental collision, an interaction could be accompanied by the melting of lithospheric possess isotopic and geochemical characteristics similar to those of material triggered by high pressure deformation. the Caucasian-Arabian Syntaxis. For example, the Cenozoic calc- It is common knowledge that crystal lattices of minerals become alkaline volcanic rocks and plume-related basaltic magmatic units less stable under deformation and/or stress and consequently the co-exist in the Carpatian-Pannonian region, where no modern melting requires much less heat (Sharkov, 2004 and references subduction has been found (Seghedi and Downes, 2011 and refer- herein). Possible sources of heat can be deformation-related fric- ences therein). These authors note that there is no much difference tion (Frischbutter and Hanisch, 1991; Molnar and England, 1995), between calc-alkaline magmas derived from subcontinental litho- conductive heating above plume head, and decompression-related spheric sources and those derived from subduction-related mantle degassing/fluid release of hot mantle plume material. wedge sources. We think that calc-alkaline and shoshonite-latite The geological, geochemical, isotopic and geophysical data from magmas can form in both suprasubduction and intracontinental the CAS suggest a collision-related rather than suprasubduction settings, however, necessarily under conditions of continuing plate origin of the calc-alkaline and shoshonite-latite magmas. Conse- convergence. Those associated with the melting of crustal material quently, the formation of the Anatolian-Caucasian and Caucasian- may result from interaction of continental crust material and mantle Elbrusian volcanic arcs may be linked with the deep tectonic plume head under strong collision induced deformations.

Figure 8. Distribution of late Cenozoic volcanism in the Caucasian-Arabian Syntaxis. Yellow: volcanic rocks of calc-alkaline and shoshonite-latite series, pink: plume-related basaltic plateaus, brown-alkaline rocks.

5. Deep structure and surface geology continuing subsidence of the sea basin, which affects the surface geological structures (Figs. 2 and 3). In addition, geological data The Kopetdag-Caucasian-Trans-european megafault can be traced (Kopp, 2007; Lebedev et al., 2011, 2013) indicate that since the late beneath the Caspian Sea as evidenced by earthquakes foci. The sharp Miocene the head of the mantle plume has been migrating to the bend of this megafault north of the Black Sea may be indicative of the north. The plume intersected the Main Caucasian Fault at depth and

Figure 9. Distribution of earthquakes showing that the region is dominated by shallow focuses (from the NEIC PDE catalog; data selection: Historical and Preliminary Data, 1973e 2010).

Figure 10. Distribution of earthquake focuses beneath the Eastern Turkey e Caucasus volcanic area.

initiated the modern volcanism, e.g., the late Quaternary volcanoes, 3. The Alpine structure of the Caucasus formed by NS horizontal especially Elbrus, which are characterized by shallow magmatic compression generated by interaction of two plates: the chambers (Gurbanov et al., 2008; Sobisevich et al., 2012). Such a Arabian indenter and the East European Craton. In the late “diving” of the plume head under the edge of the Eurasian plate, Cenozoic, that plate interaction resulted in the transverse which started in the Miocene and is continuing now, could have re- shortening of the CAS to 400 km, mainly at the expense of the generated/reactivated an older suture zone and led to the growth of territory south of the Main Caucasian Fault. As the available the Greater Caucasus. Thus, the geological situation of the region is seismic data do not reveal any subduction zone beneath the still developing under the effect of deep large-scale tectonic pro- Caucasus, that shortening was due to the tectonic “difﬂuence” cesses and mantle plumes, which go ahead of the tectonic processes of crustal material apart from the Arabian indenter, in front of at shallower (crustal) levels and on the surface. the East European Craton. It is of interest to note that the orientation of the Anatolian- 4. The CAS includes a NeogeneeQuaternary volcanic belt, which Caucasian volcanic arc does not coincide with the strike of the is extended from eastern Anatolia and to the Lesser Caucasus North-Anatolian and East-Anatolian fractures zones, which are the and farther to the Greater Caucasus. The belt is dominated by largest neotectonic structures (Fig. 3). Moreover, there is no clear two types of volcanic rocks: (1) extensive plateau basalts pos- correlation between volcanism and the present-day surface dis- sessing geochemical characteristics of intra-plate (plume- placements of the crust, which are recognized within the zone of the related) rocks, and (2) calc-alkaline and shoshonite-latite vol- Africa-Arabia-Eurasia continental collision by GPS (Reilinger et al., canic rocks, which are petrologically and geochemically similar 2006). Consequently, the deep processes in the mantle may not be to those formed in a suprasubduction setting. manifested at shallower crustal levels or on the surface, e.g., in form 5. Geophysical data support a suggesting a mantle plume head of extensional faulting or rifting, but that could be expected for future. beneath the CAS. The origin of Type 2 volcanic rocks is unclear because no subduction zone has been identiﬁed in the region. 6. Conclusions We think that the calc-alkaline and shoshonite-latite magmas were derived by interaction of the mantle plume head with the 1. The Caucasian-Arabian segment of the huge Cenozoic Alpine- crustal material at relatively shallow depths under strong high- Himalayan collisional belt consists of two domains: the EW- pressure deformations. Such a deformation-related interaction striking Greater Caucasus to the north and the Caucasian- could have led to the melting of both mantle and crustal ma- Arabian Syntaxis (CAS) to the south. The CAS includes arc-like terials and formation of “mixed mantle-crust” magmas within tectonic domains of the Lesser Caucasus and eastern Anatolia the zone of collision. and is characterized by a large NS-trending positive isostatic 6. At present, the processes of deep mantle dynamics are anomaly, which suggests presence of mantle plume head continuing to destroy the pre-Pliocene structure of the collision underneath. zone. However, the response of “shallow” tectonics to the deep 2. The Greater Caucasus constitutes the southern margin of the mantle processes is delayed. Consequently, the mantle plumes Eurasian plate; it is uplifted over the Main Caucasian Fault, which are not manifested on the surface, e.g., in form of extensional is part of the Kopetdag-Caucasian-Trans-European megafault. faulting or rifting, but that could be expected in future.

Acknowledgments Kopp, M.L., 2007. Late Alpine collisional structure of Caucasus region. In: Leonov, Y.G. (Ed.), Alpine History of the Great Caucasus. GEOS, Moscow, pp. 285e316 (in Russian). We are thankful to Prof. M. Keskin (Istanbul University, Turkey) Koronovsky, N.V., Demina, L.I., 2007. Late Cenozoic magmatism of Greater Caucasus. and his colleagues for joint field trips and discussions, to Profs. I.M. In: Leonov, Y.G. (Ed.), Alpine History of the Great Caucasus. GEOS, Moscow, e Artemieva (University of Copenhagen, Denmark), S. Maruyama pp. 251 284 (in Russian). Lebedev, V.A., Bubnov, S.N., Chernyshev, I.V., Gol’tsman, Yu.V., 2006. Basic mag- (Titech, Tokyo), A.L. Sobisevich (IFZ RAS, Moscow), and V.V. Yar- matism in the geological history of the Elbrus Neovolcanic area, Greater Cau- molyuk (IGEM RAS, Moscow) for their insightful comments. The casus: evidence from K-Ar and Sr-Nd isotope data. Doklady Earth Sciences 406 study was partly supported by a RFBR-TUBITAK grant (Project No. (1), 37e40. ’ ST a fi Lebedev, V.A., Chernyshev, I.V., Chugaev, A.V., Gol tsman, Yu.V., Bairova, E.D., 2010. 09-05-91220- - ; co-leaders E. Sharkov and M. Keskin), Scienti c Geochronology of eruptions and parental magma sources of Elbrus volcano, the Project of IGM SB RAS, Ministry of Education and Science (Russia) Greater Caucasus: K-Ar and Sr-Nd-Pb isotope data. Geochemistry International Project No 14.B25.31.0032 and JSPS Grant-in-Aid No. 14526 (I. 48, 41e67. Lebedev, V.A., Chernyshev, I.V., Sharkov, E.V., 2011. Geochronological scale and Safonova). The comments from two reviewers and Handling Editor evolution of late Cenozoic magmatism within the Caucasian segment of the Prof. Franco Pirajno, which were very helpful for improving the alpine belt. Doklady Earth Sciences 441, 1656e1660. manuscript, are greatly appreciated. Contribution to IGCP#592. Lebedev, V.A., Volkov, V.N., Sagatelyan, A.K., Chernyshev, I.V., 2013. Spatial migra- tion of magmatic activity within the Caucasian segment of the alpine belt in the early Neogene under the conditions of geotectonic change: isotope- geochronological data. Doklady Earth Sciences 448 (2), 225e231. References Leonov, Yu.G., 2007. Cimmerian and late alpine tectonics of the Greater Caucasus. In: Leonov, Y.G. (Ed.), Alpine History of the Great Caucasus. GEOS, Moscow, Artemiev, M.E., 1971. Some peculiarities of deep-seated structure of depressions of pp. 317e340 (in Russian). Mediterranean type: evidence from data on isostatic gravity anomalies. Bulletin Lonergan, L., White, N., 1997. Origin of the Betic-Rif mountains belt. Tectonics 16, of the Moscow Society of Nature Investigators, Geology Series 4, 5e10 (in 504e522. Russian with English abstract). Lustrino, M., Sharkov, E., 2006. Neogene volcanic activity of western Syria and its Artemieva, I.M., Thybo, H., Kaban, M.K., 2006. Deep Europe today: geophysical relationship with Arabian plate kinematics. Journal of Geodynamics 42, synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga. 115e139. In: Gee, D.G., Stephenson, R.A. (Eds.), European Lithosphere Dynamics. Lustrino, M., Wilson, M., 2007. The circum-Mediterranean anorogenic Cenozoic Geological Society of London Memoir, 32, pp. 11e42. igneous province. Earth Science Reviews 81, 1e65. Bazhenov, M.L., Burtman, V.S., 1990. Structural Arcs of Alpine Belt (Carpatian, Maruyama, S., Santosh, M., Zhao, D., 2007. Superplume, supercontinent and post- Caucasus, Pamir). Nauka Publ., Moscow, 167 p. (in Russian). perovskite: mantle dynamics and anti-plate tectonics on the core-mantle Burtman, V.S., 1989. Kinematics of Arabian syntaxis. Geotectonics 2, 67e75. boundary. Gondwana Research 11, 7e37. Chugaev, F.V., Chernyshev, I.V., Lebedev, V.A., Eremina, A.V., 2013. Lead isotope McClusky, S., Balassanian, S., Barka, A., Demir, C., Ergintav, S., Georgiev, I., Gurkan, O., composition and origin of the quaternary lavas of Elbrus volcano, the Greater Hamburger, M., Hurst, K., Kahle, H., Kastens, K., Kekelidze, G., King, R., Kotzev, V., Caucasus: high-precision MC-ICP-MS data. Petrology 21, 16e27. Lenk, O., Mahmoud, S., Mishin, A., Nadariya, M., Ouzounis, A., Paradissis, D., Emels, K.-Ch., Robertson, A., Richer, C., 1995. Mediterranean Sea.1. Science Operator Peter, Y., Prilepin, M., Reilinger, R., Sanli, I., Seeger, H., Tealeb, A., Toksöz, M.N., Report DSDP Leg.160, pp. 11e20. Veiss, G., 2000. Global Positioning System constraints on plate kinematics and Eppelbaum, L., Khesin, B., 2012. Geophysical Studies in the Caucasus. Springer, 401 dynamics in the eastern Mediterranean and Caucasus. J. Geophys. Res. 105 (B3), p. 5695e5719. Faccenna, C., Becker, T.W., Jolivet, L., Keskin, M., 2013. Mantle convection in the Medvedev, A.Y., Al’mukhamedov, A.I., Reichow, M.K., Saunders, A.D., White, R.V., Middle East: reconciling Afar upwelling, Arabiain dentation and Aegean trench Kirda, N.P., 2003. The absolute age of basalts from the pre-Jurassic basement of rollback. Earth and Planetary Science Letters 375, 254e269. the West Siberian plate (from Ar-40/Ar-39 data). Russian Geology and Franke, W., 2006. The Variscan orogen in central Europe: construction and collapse. Geophysics 44 (6), 588e592. In: Gee, D.G., Stephenson, R.A. (Eds.), European Lithosphere Dynamics, Molnar, P., England, P., 1995. Temperatures in zones of steady-state under- Geological Society of London Memoir, 32, pp. 333e344. thrusting of young oceanic lithosphere. Earth and Planetary Science Letters Frischbutter, A., Hanisch, M., 1991. A model of granitic melt formation by frictional 131, 57e70. heating on shear planes. Tectonophysics 194, 1e11. Neill, I., Meliksetian, Kh., Allen, M.B., Navarsardian, G., Karapetyan, S., 2013. Plio- Gee, D.G., Stephenson, R.A. (Eds.), 2006. European Lithosphere Dynamics. Geolog- cene-Quaternary volcanic rocks of NW Armenia: magmatism and lithospheric ical Society of London Memoir, 32. dynamics within an active orogenic plateau. Lithos 180e181, 200e215. Grachev, A.F. (Ed.), 2000. Neotectonics, Geodynamics and Seismicity of the North- Novikov, I., Vapnik, Y., Safonova, I., 2013. Mud volcano origin of the Mottled zone, ern Eurasian. PROBEL, Moscow, 487 p. (in Russian with English abstracts). South Levant. Geoscience Frontiers 4, 597e619. Grachev, A.F., 2003. Final volcanism of Europe and its geodynamic nature. Physics of Pollack, H.N., Hurter, S.J., Johnson, J.R., 1993. Heat flow from the earth’s interior: the Earth 5, 11e46. analysis of the global data set. Reviews of Geophysics 31, 267e280. Gurbanov, A.G., Bogatikov, O.A., Sharkov, E.V., Gazeev, V.M., Lexin, A.B., 2008. Recent Rehault, T.G., Moussat, E., Fabri, A., 1987. Structural evolution of Tyrrhenian back-arc magmatism of northern part of transcontinental East-African-Transcaucasian basin. Marine Geology 74, 123e150. riftogenic belt. In: Kovalenko, V.I., Yarmoluyk, V.V., Bogatikov, O.A. (Eds.), Reilinger, R., McClusky, S., 2011. Nubia-Arabia-Eurasia plate motions and the dy- Changes of Natural Environment and Climate: natural and Possibly Consequent namics of Mediterranean and Middle East tectonics. Geophysical Journal In- Human-induced Catastrophes. V. II. Recent Volcanism of Northern Eurasia: ternational 186, 971e979. evolution, Volcanic Hazard, and Connection with Deep Processes and Envi- Reilinger, R., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Cakmak, R., ronmental and Climate Changes. IGEM RAS, Moscow, pp. 188e205 (in Russian). Ozener, H., Kadirov, F., Guliev, I., Stepanyan, R., Nadariya, M., Hahubia, G., Harangi, S., Downes, H., Seghedi, I., 2006. Tertiary-Quaternary subduction processes Mahmoud, S., Sakr, K., ArRajehi, A., Paradissis, D., Al-Aydrus, A., Prilepin, M., and related magmatism. In: Gee, D.G., Stephenson, R.A. (Eds.), European Lith- Guseva, T., Evren, E., Dmitrotsa, A., Filikov, V., Gomez, F., Al-Ghazzi, R., Karam, G., osphere Dynamics. Geological Society of London Memoir, 32, pp. 167e190. 2006. GPS constraints on continental deformation in the Africa-Arabia-Eurasia Hearn, T.M., 1999. Uppermost mantle velocities and anisotropy beneath Europe. continental collision zone and implications for the dynamics of plate in- Journal of Geophysical Research 104 (B7), 15123e15139. teractions. Journal of Geophysical Research 111, B05411. Hofmann, A.W., 1997. Mantle geochemistry: the message from oceanic volcanism. Ricou, L.E., Dercourt, J., Geyssant, J., Grandjacquet, C., Lepvrier, C., Biju-Duval, B., Nature 385, 219e229. 1986. Geological constrain on the alpine evolution of the Mediterranean Tethys. Keskin, M., 2003. Magma generation by slab steepening and breakoff beneath Tectonophysics 123, 83e122. subduction-accretion complex: an alternative model for collision-related vol- Royden, L.H., 1989. Late Cenozoic tectonics of the Pannonian basin system. Tectonics canics in Eastern Anatolia, Turkey. Geophysical Research Letters 30, 8046. 8, 51e61. Keskin, M., 2007. Eastern Anatolia: a hotspot in a collision zone without a mantle Safonova, I.Y., Santosh, M., 2014. Accretionary complexes in the Asia-Pacific region: plume. In: Foulger, G.R., Jurdy, D.M. (Eds.), Plates, Plumes, and Planetary Pro- tracing archives of ocean plate stratigraphy and tracking mantle plumes. cesses. Geological Society of America Special Paper, 430, pp. 693e722. Gondwana Research 25, 126e158. Keskin, M., Oyan, V., Sharkov, E., Chugaev, A., Can Genk, S., Aysal, N., Duru, O., Safonova, I., Maruyama, S., 2014. Asia: a frontier for a future supercontinent Amasia. Kavak, O., 2013. Magmatism and geodynamics of Eastern Turkey. Geophysical International Geology Review. http://dx.doi.org/10.1080/00206814.2014. Research Abstracts 15, 12874. 915586. Khain, V.E., 1984. Regional Geotectonics. Alpian-Mediterranean Belt. Nedra, Mos- Saintot, A., Brunet, M.-F., Yakovlev, F., Sebrier, M., Stephenson, R., Ershov, A., Chalot- cow, 344 p. (in Russian with English abstract). Prat, F., McCann, T., 2006. The Mesozoic-Cenozoic tectonic evolution of the Kissling, E., Schmid, S.M., Lippitsch, R., Ansorge, J., Fugenschuh, B., 2006. Litho- Great Caucasus. In: Gee, D.G., Stephenson, R.A. (Eds.), European Lithosphere sphere structure and tectonic evolution of the Alpine arc: new evidence from Dynamics. Geological Society of London Memoir, 32, pp. 129e145. high resolution teleseismic tomography. In: Gee, D.G., Stephenson, R.A. (Eds.), Sandvol, E., Turkelli, N., Barazangi, M., 2003. The Eastern Turkey Seismic Experi- European Lithosphere Dynamics, European Lithosphere Dynamics. Geological ment: the study of a young continent-continent collision. Geophysical Research Society of London Memoir, 32, pp. 129e145. Letters 30, 8038.

Seghedi, I., Downes, H., 2011. Geochemistry and tectonic development of Cenozoic waters). In: Tectonics of the Earth’s Crust and Mantle. Proceedings of XXXVIII magmatism in the Carpathian-Pannonian region. Gondwana Research 20, Tectonic Meeting. GEOS, Moscow, pp. 361e365 (in Russian). 655e672. Smewing, J.D., Abbots, I.L., Dunne, L.A., Rex, D.C., 1991. Formation and emplacement Sharkov, E., 2011. Does the Tethys begin to open again? Late Cenozoic tectono- ages of the Masirah ophiolite, Sultanate Oman. Geology 19, 453e456. magmatic activization of the Eurasia from petrological and geomechanical Sobisevich, A.L., Masurenkov, Yu.A., Pouzish, I.N., Laverova, I.N., 2012. Fluid- points of view. In: Sharkov, E.V. (Ed.), New Frontiers in Tectonic Research - magmatic systems and volcanic centers in Northern Caucasus. Geophysical General Problems, Sedimentary Basins and Island Arcs. InTech, Rijeka, Research Abstracts 14, 2500. pp. 4e18. Somin, M.L., 2007. Main features of structure of the pre-alpine basement of Great Sharkov, E.V., 2004. Role of the energy of interface formation in the melting and Caucasus. In: Leonov, Y.G. (Ed.), Alpine History of the Great Caucasus. GEOS, retrograde boiling. Geochemistry International 42, 950e961. Moscow, pp. 15e38 (in Russian). Sharkov, E., Svalova, V., 2011. Geological-geomechanical simulation of the late Trifonov, V.G., Bachmanov, D.M., Ivanova, T.P., 2012. Evolution of the central Alpine- Cenozoic geodynamics in the alpine-Mediterranean mobile belt. In: Himalayan belt in the late Cenozoic. Russian Geology and Geophysics 53, Sharkov, E.V. (Ed.), New Frontiers in Tectonic Research - General Problems, 221e233. Sedimentary Basins and Island Arcs. InTech, Rijeka, pp. 19e38. Wilson, M., Downes, H., 2006. Tertiary-Quaternary intra-plate magmatism in Sharkov, E.V., Lebedev, V.A., Rodnikov, A.G., Chugaev, A.V., Sergeeva, N.A., Europe and its relationship to mantle dynamics. In: Gee, D.G., Stephenson, R.A. Zabarinskaya, L.P., 2012. Features of Caucasian segment of the Alpine- (Eds.), European Lithosphere Dynamics. Geological Society of London Memoir, Himalayan convergence zone: geological, volcanological, neotectonical, and 32, pp. 147e166. geophysical data. In: Sharkov, E.V. (Ed.), Tectonics, Recent Advances. InTech, Yarmolyuk, V.V., Bogatikov, O.A., Kovalenko, V.I., 2004. Late Cenozoic trans- Rijeka, pp. 37e52. continental structures and magmatism of the Earth’s Euro-African segment and Shempelev, A.G., Prutsky, N.I., Feldman, I.S., Kukhmazov, S.U., 2001. Geologo- geodynamics of its formation. Doklady Earth Sciences 395, 183e186. geophysical model along proﬁle Tuapse-Armavir. In: Tectonics of the Neogea: Zonenshain, L.P., Le Pichon, X., 1986. Deep basins of the Black Sea and Caspian Sea as general and Regional Aspects. Proceedings of XXXIV Tectonic Meeting. GEOS, remnants of Mesozoic back-arc basins. Tectonophysics 123, 181e212. Moscow, pp. 316e320 (in Russian). Zverev, S.M., 2002. Features of structure of sedimentary sequence and basement in Shempelev, A.G., Prutsky, N.I., Kukhmazov, S.U., 2005. Materials of geophysical frontal zone of the Cyprian arc (Eastern Mediterranean). Oceanology 42, investigation along near-Elbrus proﬁle (volcano Elbrus-Caucasian mineral 416e428.