Linking the NE Anatolian and Lesser Caucasus ophiolites: evidence for large-scale obduction of oceanic crust and implications for the formation of the Lesser Caucasus-Pontides Arc

Abstract

In the Lesser Caucasus and NE Anatolia, three domains are distinguished from south to north: (1) Gondwanian-derived continental terranes represented by the South Armenian Block (SAB) and the Tauride–Anatolide Platform (TAP), (2) scattered outcrops of Mesozoic ophiolites, obducted during the Upper Cretaceous times, marking the northern Neotethys suture, and (3) the Eurasian plate, represented by the Eastern Pontides and the Somkheto-Karabagh Arc. At several locations along the northern Neotethyan suture, slivers of preserved unmetamorphozed relics of now-disappeared Northern Neotethys oceanic domain (ophiolite bodies) are obducted over the northern edge of the passive SAB and TAP margins to the south. There is evidence for thrusting of the suture zone ophiolites towards the north; however, we ascribe this to retro-thrusting and accretion onto the active Eurasian margin during the latter stages of obduction. Geodynamic reconstructions of the Lesser Caucasus feature two north dipping subduction zones: (1) one under the Eurasian margin and (2) farther south, an intra-oceanic subduction leading to ophiolite emplacement above the northern margin of SAB. We extend our model for the Lesser Caucasus to NE Anatolia by proposing that the ophiolites of these zones originate from the same oceanic domain, emplaced during a common obduction event. This would correspond to the obduction of non-metamorphic oceanic domain along a lateral distance of more than 500 km and overthrust up to 80 km of passive continental margin. We infer that the missing volcanic arc, formed above the intra-oceanic subduction, was dragged under the obducting ophiolite through scaling by faulting and tectonic erosion. In this scenario part of the blueschists of Stepanavan, the garnet amphibolites of Amasia and the metamorphic arc complex of Erzincan correspond to this missing volcanic arc. Distal outcrops of this exceptional object were preserved from latter collision, concentrated along the suture zones.

Keywords:

• Lesser Caucasus
• NE Anatolia
• Tethys
• ophiolite
• obduction

1. Introduction

During the Mesozoic, the southern margin of the Eurasian continent was involved in the closure of Palaeo-Tethys and the opening of Neotethys oceans. Later, from the Jurassic to the Eocene, subductions, obductions, micro-plate accretions and finally continent–continent collision occurred between Eurasia and Arabia, and resulted in the closure of Neotethys.

In order to better understand the different phases linked with the opening and closing of the Tethyan Ocean leading to the current structure of the Lesser Caucasus and the Eastern Pontides (Figure 1), it is important to identify the different units involved in the Tethyan suture s.l. and their corresponding geodynamic context including the lateral continuation of the structures. The evolution of northern Neotethys can be deduced from the structural, geochemical and geochronological studies of preserved oceanic crust domains obducted (ophiolites) in the Lesser Caucasus and in NE Anatolia and of the metamorphic rocks beneath these ophiolites. These studies yield key time and palaeogeographic data from the East Mediterranean area to the NW Himalayan belt (Barrier & Vrielynck, 2008; Dercourt et al., 1986; Galoyan, Rolland, Sosson, Corsini, & Melkonyan, 2009; Hafkenscheid, Wortel, & Spakman, 2006; Hässig et al., 2013; Okay & Tüysüz, 1999; Ricou, 1994; Ricou et al., 1985; Robertson, 2004; Rolland, Galoyan, Sosson, Melkonian, & Avagyan, 2010; Şengör & Yılmaz, 1981; Sosson et al., 2010; Stampfli, Borel, Cavazza, Mosar, & Ziegler, 2001). Supra-subduction zone (SSZ) ophiolites provide chronologic constraints related to oceanic crust formation by repetitive extension in a fore- and/or back-arc context, linked to the behavior of an intra-oceanic subduction, by the dating of related magmatic rocks. The study of these remarkable objects also contributes to understand oceanic closure, particularly ophiolite emplacement processes, by the dating of metamorphic rocks underlying the preserved (non-metamorphic) ophiolites and post-accretionary sedimentary series unconformably overlying the suture zone. Datings undertaken along the Ankara–Erzincan–Sevan-Akera suture zone suggest a similar Lower–Middle Jurassic age of the oceanic crust of c. 180–150 Ma (Çelik, Chiaradia, Marzoli, Billor, & Marschik, 2013; Çelik et al., 2011; Dilek & Thy, 2006; Galoyan, 2008; Galoyan et al., 2009; Hässig et al., 2013; Rolland, Galoyan, et al., 2009; Rolland et al., 2010; Topuz, Çelik, et al., 2013). A major difficulty in Mesozoic geodynamic reconstruction of the Lesser Caucasus–Eastern Pontides is the paucity of outcrops due to thick post-obduction (Eocene to Quaternary) deposit of sediments and volcanics that overly the ophiolitic nappe (Avagyan et al., 2010; Gürer & Aldanmaz, 2002; Sosson et al., 2010). Therefore, to link the NE Turkey and Armenia ophiolitic domains, three questions are posed in this study concerning the continuity of the main structural units: (1) are all the NE Turkey–Armenia ophiolites remnants of the same oceanic lithosphere, (2) are they partly obducted over a continuous continental ribbon (including the South Armenian and Tauride–Anatolide blocks to the south) and (3) does the oceanic domain subduct under a common margin?”

Figure 1. Structural sketch map of the Tauride–Anatolides, Caucasus and Iranian belts (modified after Avagyan et al., 2005). Location of Figure 2 is indicated.

In this paper, we present field geological, structural and whole-rock geochemical data on the crustal rocks of the NE Anatolian and Armenian ophiolites. These data in conjunction with those from the literature strongly suggest a common origin and Late Cretaceous emplacement onto the leading edge of the passive continental margin leading to the current positioning of NE Anatolian and Lesser Caucasus ophiolites.

2. Previous works across the NE Anatolia-Lesser Caucasus region

2.1. Lesser Caucasus

Previous geological, petrological and geochemical works on the Lesser Caucasus ophiolites were carried out mostly during the 1970s and 1980s (Adamia et al., 1981; Knipper, 1975; Knipper, Bragin, & Satian, 1997; Knipper & Khain, 1980; Knipper, Ricou, & Dercourt, 1986; Knipper & Sokolov, 1977; Satian, 2005; Sokolov, 1977; Zakariadze et al., 1983, 1990, 2005). These works mainly showed a Jurassic age for the ophiolite bodies, and variable geochemical affinities (ranging from tholeiitic to calc-alkaline and alkaline), which was interpreted as a complex oceanic context with variable magmatic sources, and closed mainly by subduction in the Late Cretaceous (e.g. Zakariadze et al., 1990). More recent works along the Neotethys domain evidence processes which include Neotethyan oceanic crust obduction and the collision–accretion of microplates to the Eurasian margin before the final Arabia–Asia collision or India–Asia collision (Agard, Searle, Alsop, & Dubacq, 2010; Avagyan et al., 2010; De Sigoyer, Guillot, & Dick, 2004; Ding, Kapp, & Wan, 2005; Galoyan et al., 2009; Hacker, 1991; Hacker, Mosenfelder, & Gnos, 1996; Harper, Grady, & Coulton, 1996; Okay, Tansel, & Tüysüz, 2001; Rice, Robertson, & Ustaömer, 2009; Rolland et al., 2012; Rolland, Billo, Corsini, Sosson, & Galoyan, 2009; Rolland, Galoyan, et al., 2009; Rolland, Sosson, Adamia, & Sadradze, 2011; Searle & Cox, 1999; Sosson et al., 2010; Stampfli et al., 2001; Yılmaz, Yiğitbaş, & Can Genç, 1993). In these works, the presence of several geochemical suites in a given suture zone is interpreted as the tectonic collage of petrological slivers originating from various oceanic environments: volcanic arc, oceanic islands and seamounts, oceanic crust from mid oceanic ridge or from back-arcs.

North of the obduction zone, in the Eurasian part of the Lesser Caucasus the subduction of the Tethys is evidenced by a thick and mainly calc-alkaline volcanogenic and volcanoclastic series of Bajocian to Santonian age (e.g. Adamia et al., 1981 for a review). At this period of time, the northern Lesser Caucasus was characterized by an island arc domain called the Somkheto–Karabakh Island Arc (Adamia, Belov, Kekelia, & Shavishvili, 1987; Adamia, Lordkipanidze, & Zakariadze, 1977; Knipper, 1975; Ricou et al., 1986; Sosson et al., 2010). During Early Cretaceous, a part of the plutonic unit of this arc was unroofed due to tectonic erosion which was the result of significant uplift and denudation along the subduction zone (Rolland et al., 2011). Such a change in the Eurasian active margin strain field could be, and subsequent development of this unconformity is, ascribed to the subduction of more buoyant crustal domain such as the spreading ridge of the back-arc basin (Rolland et al., 2011). The basement formations are quite similar to those known all along the Eurasian margin (Sosson et al., 2010 for a review).

South of the obduction zone, the South Armenian Block (SAB) (Knipper, 1975; Knipper & Khain, 1980) is a microplate which also corresponds to the Turkish and Iranian platforms (Şengör & Yılmaz, 1981; Figure 1). In Armenia, the SAB is represented by a Proterozoic metamorphic basement, well-exposed north of Yerevan. An incomplete Paleozoic sedimentary succession (mainly represented by Upper Devonian to Upper Permian carbonates and shales) in the SW (north of the Araks Valley), widespread Triassic limestones and sandstones, and some Jurassic sedimentary and volcanogenic formations unconformably covered by Cenomanian to Turonian limestone and flysch (Nalivkin, 1976; Sosson et al., 2010; Figure 2).

Figure 2. Structural map of the Lesser Caucasus–Eastern Pontides–Northeast Anatolides regions. Turkish zone modified from the 1:1 250, 000 geological map of Turkey (MTA 2011); the Georgian–Armenian zone of the Caucasus after Sosson et al. (2010); the Iranian zone from Mederer (2013).

Upper Cretaceous obduction on the SAB is deduced from Upper Coniacian to Santonian flysch (reworking the ophiolites), which conformably covers Cenomanian–Turonian reef limestones and flysch of the SAB (Sokolov, 1977; Sosson et al., 2010). This obduction took place while a magmatic arc occurred along the southern edge of Eurasia (Somkheto–Karabakh island arc, Lesser Caucasus, Figure 2), which implies that at least two subduction zones were active at the same time (Rolland et al., 2011). The onset of collision or the continental subduction of the SAB below the Eurasian margin is dated as Late Cretaceous–Paleocene. This process occurred around 20 Ma later than the obduction (Late Coniacian–Santonian, 88–83 Ma) of the marginal basin over the SAB (Sosson et al., 2010). Oceanic closure is indicated by the Late–Middle Eocene unconformity on the SAB, the suture zone and the Eurasia margin. Ending of subduction and subsequent accretion of the SAB to the Eurasian margin resulted in the subduction jump to the south of the SAB (Rolland et al., 2012). Evidence for this southward jump in subduction can be found between the Bitlis–Pütürge massifs and SAB. There, HP metamorphic evolution due to continental subduction is bracketed between 74 and 71 Ma (Göncüoğlu & Turhan, 1984; Hempton, 1985; Oberhänsli et al., 2010). This metamorphic age is thus in agreement with a continental subduction event that occurred before the final closure of the southern Neotethys and Arabian–Eurasian collision. ⁴⁰Ar/³⁹Ar dates agree for initial subduction of the Eastern Bitlis Massif at 74 Ma followed by underthrusting of the Pütürge Massif under blueschists conditions at 71 Ma (Rolland et al., 2012).

For a compilation of works about the ophiolites of the Lesser Caucasus, the reader is referred to Galoyan et al. (2007, 2009), Rolland, Galoyan, et al. (2009, 2010), Sosson et al. (2010), and Hässig et al. (2013). These authors have shown the following geochemical affinities in the ophiolite-related nappes: (1) the basalts and gabbros mainly bear an enriched tholeiitic composition, contaminated by subduction components, (2) above these series, a layer of alkaline basalt lava flows with large pillows is supposed to represent Ocean Island Basalts (OIB) erupted in seamounts or oceanic plateau(s), and (3) locally some arc-related basalts have been described. In Armenia, the oceanic gabbros of the tholeiitic series were dated to 170–150 Ma similar to radiolarian ages (Danelian et al., 2010), while the alkaline series were dated at c. 117 Ma (Rolland, Galoyan, et al., 2009).

2.2. Northeast Anatolia

The East Anatolian Platform (EAP) represents a continental platform between the northern and southern branches of Neotethys (Bozkurt & Mittwede, 2001). As for the SAB, the EAP represents a sliver of continental crust having drifted-off northern Gondwana, which drifted to the north, which resulted into collision with Eurasia (Adamia et al., 1977; Biju-Duval, Dercourt, & Le Pichon, 1977; Dercourt et al., 1986; Şengün, 2006; Stocklin, 1974; Stöcklin & Bhattarai, 1977).

The Eastern Pontides are interpreted as a part of the Sakarya Zone (Okay & Şahintürk, 1997). It represents an active continental margin of Eurasia, which was formed as a result of northward subduction of Neotethys during Late Cretaceous (Akıncı, 1984; Okay & Şahintürk, 1997; Şengör & Yılmaz, 1981). There is no consensus concerning onset age of subduction, since Jurassic (Adamia et al., 1981; Hess, Aretz, Gurbanov, Emmermann, & Lippolt, 1995; Nikishin, Korotaev, Ershov, & Brunet, 2003; Topuz, Göçmengil, et al., 2013), Cenomanian–Turonian (Okay & Şahintürk, 1997; Yılmaz, Tüysüz, Yiğitbaş, Genç, & Şengör, 1997) or Albian (Okay et al., 2006) ages have been proposed. The lack of consensus equally stands when considering the end of subduction and the onset of continental collision as proposed range stretches out from the end of Eocene (Peccerillo & Taylor, 1976; Robinson, Spadini, Cloetingh, & Rudat, 1995; Şengör & Yılmaz, 1981) to the Middle Eocene (Yılmaz et al., 1997) and even the Paleocene (Okay & Şahintürk, 1997).

The NE Anatolian ophiolites have been studied to characterize their geodynamic environments (Eyüboğlu, Bektas, & Pul, 2007; Parlak et al., 2013; Rice et al., 2006; Sarıfakıoğlu, Özen, & Winchester, 2009; Topuz, Göçmengil, et al., 2013; Yılmaz, Yılmaz, Kaya, & Boztuğ, 2010). Geochemical analyses of these ophiolites show similar rock types as in Armenia as well as most of the ophiolites worldwide, that is to say Mid Ocean Ridge Basalt (MORB) to volcanic arc rocks and within-plate basalts. Lateral continuity between NE Anaolia and Armenia through the comparison of lithostratigraphic colons illustrates similar successions and relations as those well identified in the Lesser Caucasus, especially the timing of the emplacement of tectonic thrusts and related sedimentary deposits. Our field investigations to the north of the Erzincan Basin has also shed light on an outcrop of low-grade metamorphic rocks of volcanic origin overthrusted by the ophiolites towards the south on the northern side of the Erzincan basin, along the North Anatolian Fault and Northeast Anatolian Fault (Figure 3).

Figure 3. Geological map and cross-sections of the Refahiye ophiolite in the vicinity of Erzincan. (A) Geological map featuring the position of the cross-sections (modified after Aktimur et al., 1995; Özen et al., 2006; Sarıfakıoğlu et al., 2009). (B) Geological cross-section illustrating the positioning and structural relationships between the main units based on field observations.

3. Structural continuity

In order to highlight the main structural, geochemical and temporal evidences toward structural continuity between the Lesser Caucasus and NE Anatolia, we present new data pertaining to the ophiolites and potential sole lithologies of these bodies, as well as published data used to complete our data-set.

3.1. Lithostratigraphic sections

In this paper, we overview the lithostratigraphic sections compiled from Bergougnan (1987), Bozkurt and Mittwede (2001), Bozkuş (1998), Gedik (2008), Moix et al. (2008), Okay and Tüysüz (1999), Özgül and Turşucu (1984), and Sokolov (1977) for the Turkish and Armenian domains and their implications for the geological evolution of that region. These data are completed by investigations carried out during a field campaign in 2011 (Figure 4). This input from pervious works offers a series of well-constrained data on the ophiolites, with precise and modern dating of the magmatic and metamorphic events. Structural/paleogeographic units are linked to one another in order to precise their lateral continuation. Integrated in a larger tectonic framework, we use these lithostratigraphic sections to constrain the origin of the NE Anatolian ophiolite nappe as a portion of a greater nappe, including the Lesser Caucasus ophiolites.

Figure 4. Synthetic lithostratigraphic sections throughout the study area. (1), (3) and (4) modified after Gedik (2008); (2) modified after Moix et al. (2008); (5) modified after Bozkuş (1998); (6) and (7) modified after Sokolov (1977).

In the Lesser Caucasus, all ophiolite outcrops feature three main superposed lithotectonic units (Galoyan, 2008; Hässig et al., 2013; Rolland, Billo, et al., 2009; Rolland, Galoyan, et al., 2009; Rolland et al., 2010; Sosson et al., 2010). An upper unit with serpentinite, gabbro, pillow lava and volcanic rocks with interlayered reefal limestone is ascribed to the ophiolite. A Coniacian–Santonian detrital deposit, reworking elements from the entire ophiolitic unit is also included in this unit. Below the ophiolite unit is a tectonic mélange including rock types ranging from low-grade (greenschist facies) meta-basalts, meta-cherts, metamorphosed serpentinites, lenses of ophiolites, garnet-bearing amphibolites and/or alkali basalts. The lower unit comprises basalts, overlain by Lower Cretaceous (Valanginian–Barremian) limestones, which are in turn unconformably covered by Late Palaeocene flysch to Lower Eocene limestone as well as Middle–Upper Eocene volcanogenic deposits.

In NE Anatolia, the Tauride–Anatolide Platform (TAP) is made up of a succession of thrust sheets (Okay, 2008). The topmost thrust sheet is made up of ophiolite and/or ophiolitic mélange forming large isolated bodies (e.g. Gutnic et al., 1979; Özgül, 1984; Özgül & Turşucu, 1984). The thrusting occurred in the Late Cretaceous, in the Eocene and in the Early Miocene. The obduction of preserved ophiolite was associated with subduction and high-pressure metamorphism of the northern margin of the TAP. The more distal portions of the obducted ophiolite were emplaced over the Cretaceous sedimentary rocks.

The continental collision during the late Palaeocene–Early Eocene between the TAP and the Eastern Pontides led to a second phase of convergence by folding and thrusting.

3.2. Geochemical analyses

Samples from the Lesser Caucasus and NE Anatolian ophiolites and related metamorphics were analyzed for major elements, trace and rare earth elements (REE; Table 1). Samples were analyzed at the C.R.P.G. (Nancy, France). ICP-MS analytical procedures and analyses of standards for can be found on the following website (http://www.crpg.cnrs-nancy.fr/SARM).

Table 1. Representative whole-rock analyses of samples from ophiolitic complexes of NE Anatolia and Lesser Caucasus. “<LD”: under detection level.

Lab no.		700a	701a	713c	729b	730	733	737	743b
Locality		Kemah	Kemah	Kemah	Kemah	Kemah	Kemah	Erzincan	Erzincan
Latitude		39.61185°N	39.60997°N	39.54635°N	39.54635°N	39.54635°N	39.69487°N	39.60615°N	39.83641°N
Longitude		39.22681°E	39.22995°E	38.96879°E	38.96879°E	38.96879°E	39.05207°E	39.19323°E	39.33277°E
Formation		Gabbro	Gabbro	Gabbro	Gabbro	Gabbro	Gabbro	Gabbro	Gabbro
SiO2	%	46.96	46.52	47.09	49.40	48.58	53.87	48.87	48.49
TiO2	%	.13	.09	2.65	.69	.95	.85	.25	1.85
Al2O3	%	18.05	19.13	15.29	15.61	18.72	17.61	18.65	14.43
Fe2O3	%	3.96	3.39	9.70	9.49	9.53	8.38	4.69	13.74
MnO	%	.07	.06	.12	.16	.17	.15	.09	.21
MgO	%	10.97	9.95	5.21	7.01	4.71	4.49	7.83	5.69
CaO	%	16.49	17.53	11.58	10.68	8.62	7.10	17.06	7.38
Na2O	%	.88	.71	3.89	3.76	4.03	4.97	1.59	4.70
K2O	%	.02	.01	1.08	.12	1.55	.95	.05	.20
P2O5	%	<LD	<LD	1.28	.06	.22	.19	<LD	.16
LOI	%	1.82	1.42	1.15	3.01	3.26	2.45	1.41	2.28
Total	%	99.34	98.81	99.04	99.97	100.35	101.00	100.49	99.11
Ba	ppm	1.54	<LD	184.20	202.40	876.50	381.00	23.33	91.43
Rb	ppm	.38	.30	18.53	2.88	28.08	20.12	.80	1.74
Sr	ppm	63.35	85.09	873.00	119.30	659.70	555.00	132.90	151.10
Ta	ppm	<LD	<LD	2.29	.06	.75	.63	<LD	.15
Th	ppm	<LD	<LD	3.10	.15	2.88	4.96	<LD	.17
Zr	ppm	1.68	<LD	190.70	29.65	91.22	105.10	2.73	94.67
Nb	ppm	<LD	<LD	33.13	.69	9.19	7.57	<LD	1.81
Y	ppm	3.32	2.18	28.38	17.16	19.99	20.31	6.46	37.68
Hf	ppm	.08	.04	4.44	.98	2.33	2.76	.15	2.70
V	ppm	102.60	92.43	162.80	264.30	310.80	259.00	176.60	414.90
Cr	ppm	1493.00	957.40	169.70	97.08	34.21	24.24	398.60	27.32
Ni	ppm	162.10	173.50	114.10	50.63	34.94	24.89	96.62	14.91
Co	ppm	30.56	28.07	38.49	34.92	32.25	24.88	25.43	33.76
U	ppm	<LD	<LD	1.71	.06	1.36	1.42	<LD	.09
Sc	ppm	38.28	38.37	24.61	39.47	21.59	24.14	53.99	36.67
Cu	ppm	25.29	109.80	33.00	75.20	148.60	82.69	<LD	47.16
Zn	ppm	20.71	14.12	124.70	65.76	85.75	67.60	14.78	112.30
Pb	ppm	<LD	<LD	3.27	<LD	8.65	15.50	<LD	<LD
Cs	ppm	<LD	<LD	.08	7.48	.21	.15	.10	.14
La	ppm	<LD	<LD	32.60	1.22	13.62	16.47	.14	3.85
Ce	ppm	.32	.15	61.02	3.31	26.62	32.07	.48	11.44
Pr	ppm	.06	.03	7.01	.53	3.14	3.63	.10	1.85
Nd	ppm	.44	.26	32.19	3.36	14.36	16.03	.80	10.49
Sm	ppm	.22	.14	6.76	1.41	3.54	3.62	.49	3.72
Eu	ppm	.17	.11	2.32	.58	1.16	1.05	.33	1.39
Gd	ppm	.37	.26	6.28	1.98	3.40	3.52	.83	5.01
Tb	ppm	.07	.05	.87	.39	.56	.57	.16	.90
Dy	ppm	.54	.38	4.83	2.67	3.42	3.41	1.11	6.08
Ho	ppm	.12	.08	.88	.60	.69	.70	.24	1.32
Er	ppm	.34	.23	2.21	1.76	1.97	1.95	.65	3.78
Tm	ppm	.05	.04	.30	.28	.30	.30	.10	.59
Yb	ppm	.33	.21	1.83	1.87	2.04	2.04	.61	3.88
Lu	ppm	.05	.03	.27	.29	.31	.31	.09	.61
745b	746c	746d	751	755a	774	776	777	780	788
Erzincan	Erzincan	Erzincan	Erzincan	Erzincan	Erzincan	Erzincan	Erzincan	Erzincan	Erzincan
39.88024°N	39.79576°N	39.79576°N	39.64722°N	39.58129°N	39.79455°N	39.78600°N	39.78463°N	39.80939°N	39.76208°N
39.16705°E	39.48271°E	39.48271°E	39.51133°E	39.62554°E	39.59068°E	39.51395°E	39.51402°E	39.54614°E	39.73071°E
Gabbro	Gabbro	Gabbro	Gabbro	Gabbro	Peridotite	Gabbro	Gabbro	Gabbro	Gabbro
46.40	76.50	47.90	50.93	47.96	42.68	39.14	50.00	47.54	44.11
2.52	.14	.15	.97	.25	.02	1.90	1.74	.67	1.22
14.39	13.09	21.08	15.62	16.39	1.23	15.29	14.72	14.94	14.17
16.94	.24	6.76	9.95	7.27	8.68	13.21	12.57	10.19	11.47
.26	.00	.13	.16	.12	.13	.23	.21	.16	.19
5.66	.18	8.77	5.79	10.24	38.99	8.15	4.71	9.54	7.36
9.67	4.66	14.53	6.96	14.65	1.66	15.05	10.21	11.81	14.09
3.09	2.83	.78	5.28	1.62	.03	.46	4.39	2.49	2.37
.10	.15	.07	.38	.02	.02	.04	.27	.04	.06
.25	<LD	<LD	.09	<LD	<LD	.16	.20	<LD	.11
.60	.71	.80	3.34	.86	6.08	6.27	1.46	2.79	3.41
99.87	98.51	100.97	99.47	99.38	99.51	99.91	100.47	100.17	98.55
50.72	37.34	8.24	42.56	<LD	<LD	10.25	110.60	5.90	83.32
.79	2.03	1.23	7.09	.50	.65	.48	3.28	<LD	1.04
132.30	206.20	147.80	139.80	96.47	<LD	38.11	185.60	103.00	121.10
.25	.14	<LD	.06	<LD	<LD	.18	.23	<LD	.09
.04	3.27	<LD	.20	<LD	<LD	.21	.51	<LD	<LD
133.00	67.76	1.12	52.96	3.09	<LD	96.90	122.70	7.09	46.48
3.18	1.00	<LD	.67	<LD	<LD	2.24	2.79	<LD	1.18
50.67	49.31	2.42	21.46	6.41	<LD	34.99	41.47	10.24	27.23
3.27	2.76	.06	1.61	.16	<LD	2.67	3.32	.30	1.40
530.30	5.87	153.40	280.50	153.70	59.15	437.50	301.10	354.20	333.30
32.15	7.14	69.50	34.81	551.10	3030.00	71.83	57.83	447.10	148.90
29.65	<LD	43.42	26.79	145.30	1793.00	39.16	35.16	113.80	52.51
46.33	1.05	36.50	31.73	46.26	107.70	39.74	35.27	58.23	39.90
<LD	.50	<LD	.09	<LD	<LD	.10	.16	<LD	<LD
45.64	2.20	38.03	35.43	46.63	13.44	43.55	35.57	52.54	45.65
64.40	<LD	27.12	63.52	118.90	19.39	34.00	60.48	187.70	94.54
131.60	<LD	29.01	81.02	38.28	49.10	91.43	98.15	47.07	89.08
<LD	<LD	<LD	<LD	<LD	<LD	1.11	<LD	<LD	<LD
.11	.15	<LD	.53	.24	.76	.19	11.06	<LD	.31
5.04	11.57	.19	2.25	.14	<LD	4.23	5.81	.31	2.23
15.59	26.05	.44	6.71	.55	<LD	11.91	15.73	1.14	7.15
2.57	3.30	.07	1.09	.12	<LD	1.88	2.37	.23	1.22
15.17	16.11	.45	6.25	.91	<LD	10.77	13.53	1.65	7.26
5.36	4.27	.20	2.18	.50	<LD	3.65	4.40	.81	2.67
1.86	.23	.17	.97	.34	<LD	1.26	1.58	.43	1.03
6.87	5.42	.30	2.97	.83	<LD	4.88	5.59	1.23	3.70
1.25	.97	.06	.52	.16	<LD	.86	1.02	.24	.66
8.22	6.82	.41	3.48	1.08	.04	5.74	6.69	1.71	4.40
1.79	1.54	.09	.76	.24	.01	1.24	1.46	.38	.96
5.05	4.69	.26	2.17	.65	.04	3.55	4.17	1.04	2.71
.79	.75	.04	.34	.09	.01	.54	.64	.16	.42
5.23	5.04	.27	2.24	.62	.06	3.64	4.33	1.03	2.77
.79	.82	.04	.36	.09	.01	.57	.68	.16	.43
796a	797a	T-11-01	T-11-02	T-11-04	T-11-08	T-11-22	T-11-27	T-11-34	T-11-36
Aşkale	Aşkale	Refahiye	Refahiye	Erzincan	Erzincan	Erzincan	Hınıs	Aşkale	Aşkale
40.01914°N	40.01914°N	39.81766°N	39.81766°N	39.64293°N	39.64722°N	39.72808°N	39.45520°N	40.01676°N	40.02484°N
40.53653°E	40.53653°E	38.85969°E	38.85969°E	39.51794°E	39.51133°E	39.71039°E	42.09869°E	43.53854°E	40.53245°E
Gabbro	Gabbro	Plagiogranite	Gabbro	Basalt	Gabbro	Meta-Basalt	Amphibolite	Gabbro	Plagiogranite
46.14	50.69	51.58	47.10	46.86	50.84	54.27	43.70	47.28	75.81
1.95	.05	.59	1.62	1.14	.91	.97	3.26	1.95	.15
14.42	.69	22.72	13.86	15.36	15.59	15.05	12.56	14.14	12.99
14.07	3.70	4.32	13.59	6.54	9.69	12.26	13.69	13.74	2.36
.21	.08	.07	.22	.10	.15	.14	.18	.21	.05
5.26	23.75	2.26	6.74	6.52	6.39	5.41	9.94	4.45	.34
7.59	17.76	9.98	9.81	14.49	8.30	5.22	11.70	8.72	.57
4.46	.12	5.79	3.17	2.80	3.59	2.72	3.15	4.54	6.41
1.14	<LD	.06	.18	1.29	1.08	.01	.20	2.22	.23
.17	<LD	.09	.15	.34	.09	.08	.39	.18	.04
3.52	2.28	3.00	3.49	4.96	3.26	3.51	1.15	2.56	1.34
98.94	99.13	100.46	99.94	100.39	99.89	99.64	99.89	99.98	100.29
69.63	<LD	27.94	54.49	490.20	42.92	9.84	46.31	83.25	30.42
19.27	<LD	1.43	2.34	38.73	14.24	<LD	1.30	17.75	4.48
131.80	8.80	340.10	1298.00	1014.00	267.40	195.70	542.40	118.10	134.10
.19	<LD	.05	.15	1.00	.06	.02	3.37	.20	.19
.48	<LD	.05	.11	5.57	.20	.05	3.90	.47	19.06
107.60	<LD	74.15	86.26	129.30	59.28	14.90	226.20	113.80	135.10
2.29	<LD	.73	1.95	14.34	.71	.21	44.75	2.38	1.83
39.27	.69	9.52	33.97	16.19	22.56	18.55	26.52	39.88	22.15
2.96	<LD	1.70	2.34	2.88	1.73	.60	5.39	3.09	3.84
440.20	52.42	113.50	412.00	147.50	268.30	391.00	299.00	451.10	4.09
38.65	3877.00	18.61	94.26	182.60	58.06	7.19	407.50	19.82	8.09
13.56	379.10	17.18	38.38	65.21	36.94	11.00	192.60	15.06	<LD
37.40	45.46	12.73	40.89	26.35	35.29	29.27	56.68	36.88	1.32
.16	<LD	.04	.04	1.51	.09	<LD	1.10	.16	.82
38.91	26.55	8.94	45.20	22.80	36.72	47.84	31.62	38.00	2.67
188.00	39.26	11.49	55.11	39.30	56.93	64.79	113.20	55.48	40.32
98.96	<LD	28.03	100.40	50.93	71.25	103.60	118.80	96.65	172.80
<LD	<LD	<LD	<LD	4.66	.79	1.78	4.55	<LD	7.87
9.56	<LD	.27	.24	.96	.12	.14	<LD	3.24	.56
5.39	<LD	1.92	4.45	26.41	2.39	.78	35.62	5.20	80.14
14.33	<LD	4.31	11.99	46.38	6.87	2.25	70.88	14.04	173.30
2.23	<LD	.60	1.83	4.87	1.08	.41	8.29	2.12	19.76
11.98	.09	3.25	10.36	20.00	6.40	2.95	36.55	11.92	73.90
4.02	.05	.92	3.53	3.92	2.27	1.42	7.59	4.08	12.41
1.69	.02	.97	1.26	1.25	.89	.66	2.45	1.45	.85
5.29	.08	1.17	4.53	3.46	2.97	2.10	6.96	5.31	8.13
.93	.01	.21	.82	.52	.55	.41	.99	.95	1.03
6.28	.11	1.45	5.60	2.96	3.64	2.93	5.44	6.36	4.92
1.36	.03	.32	1.19	.56	.78	.64	.95	1.39	.82
3.91	.07	.96	3.42	1.51	2.25	1.95	2.42	4.02	2.27
.60	.01	.16	.53	.22	.35	.31	.32	.61	.34
4.01	.07	1.13	3.50	1.43	2.37	2.10	1.97	4.27	2.47
.63	.01	.18	.54	.22	.37	.33	.29	.65	.39
T-11-39	ARM-11-01	ARM-11-02	ARM-11-06	ARM-11-08	ARM-11-09	ARM-11-10	ARM-11-13	ARM-11-26	ARM-11-27
Aşkale	Stepanavan	Stepanavan	Stepanavan	Stepanavan	Stepanavan	Stepanavan	Stepanavan	Vedi	Vedi
39.95417°N	40.95105°N	40.95061°N	40.95727°N	40.95444°N	40.95465°N	40.96111°N	40.97181°N	39.98949°N	39.9861°N
40.23643°E	44.33044°E	44.33114°E	44.34209°E	44.30867°E	44.30893°E	44.36245°E	44.34361°E	44.97837°E	44.97505°E
Gabbro	Basalt	Basalt	Meta-Basalt	Gabbro	Plagiogranite	Blueschist	Amphibolite	Gabbro	Gabbro
47.86	63.10	51.32	64.50	43.73	77.22	43.74	55.08	45.56	46.38
.17	.71	.95	.71	.07	.16	2.29	1.31	2.30	.15
23.84	10.95	16.45	15.04	20.55	11.27	16.22	14.66	16.90	18.89
.99	5.05	10.62	5.34	8.10	2.32	8.68	12.68	13.33	4.19
.02	.10	.17	.08	.12	.03	.11	.23	.21	.08
.91	2.41	3.69	3.22	9.19	.81	4.53	3.32	5.67	9.11
2.12	5.90	4.59	.79	9.50	2.06	10.05	3.34	10.45	16.42
15.41	1.89	5.27	6.31	1.50	4.85	3.83	6.86	2.90	1.27
.13	1.70	.92	.39	1.32	.02	1.98	.15	.13	.48
<LD	.14	.17	.13	<LD	<LD	.67	.11	.05	<LD
9.19	7.69	5.09	2.83	5.14	1.20	6.68	1.27	2.69	3.78
100.65	99.64	99.23	99.35	99.21	99.93	98.78	99.02	100.20	100.74
153.00	194.90	217.60	59.84	170.70	9.05	442.10	23.21	27.28	79.39
.61	58.43	16.52	13.79	27.25	<LD	46.43	.59	.92	5.42
125.60	110.70	327.30	55.01	449.00	73.08	445.20	56.81	234.20	199.50
.26	1.05	.26	.96	<LD	<LD	4.71	.11	.06	<LD
1.46	8.10	1.64	10.02	.04	<LD	7.58	.38	.11	<LD
122.00	175.40	89.06	174.30	<LD	1.42	238.40	65.41	34.08	1.98
2.38	12.58	3.19	11.15	<LD	<LD	66.57	1.31	.68	<LD
4.76	20.02	23.02	22.18	.93	1.70	25.32	25.93	14.16	3.29
3.35	4.50	2.50	4.48	.05	.04	5.10	1.93	1.00	.09
9.82	81.88	261.40	95.65	141.90	25.03	177.60	358.40	379.20	123.50
5.52	92.19	14.11	114.40	17.38	11.97	122.40	19.39	9.09	1113.00
<LD	41.04	18.53	60.48	31.01	<LD	127.00	14.30	13.53	136.00
1.06	9.33	24.56	16.86	47.56	4.80	37.25	30.97	38.97	30.03
1.61	1.93	.36	2.32	<LD	<LD	2.21	.13	<LD	<LD
1.96	11.43	29.14	13.08	50.13	6.47	20.96	35.89	46.08	46.72
<LD	18.94	65.07	47.35	69.90	23.38	49.75	31.80	13.97	124.00
17.60	71.52	117.90	76.51	45.07	11.09	87.01	110.80	71.42	12.31
36.75	5.80	5.94	3.25	<LD	<LD	3.42	2.44	<LD	1.02
.90	1.77	.27	.60	.90	<LD	1.06	<LD	<LD	.27
1.79	25.86	7.85	37.52	.13	2.06	51.32	3.34	1.26	.09
5.67	54.11	17.19	70.97	.30	3.10	95.26	8.67	3.34	.31
.95	5.69	2.35	7.13	.04	.32	9.52	1.38	.53	.06
5.11	23.74	11.36	28.78	.23	1.34	38.75	8.05	3.09	.49
1.52	4.65	3.14	5.36	.11	.24	7.07	2.76	1.22	.27
.53	.89	.96	1.27	.06	.52	2.25	.98	.71	.19
1.29	3.92	3.55	4.57	.17	.25	6.17	3.72	1.80	.43
.18	.61	.59	.69	.03	.03	.88	.65	.33	.08
.90	3.58	3.79	4.07	.24	.20	4.89	4.27	2.33	.57
.15	.70	.81	.79	.06	.05	.90	.92	.51	.12
.37	2.00	2.34	2.20	.17	.15	2.43	2.66	1.48	.34
.05	.31	.36	.33	.03	.03	.33	.41	.22	.05
.33	2.09	2.39	2.24	.19	.20	2.24	2.74	1.50	.32
.05	.32	.38	.35	.03	.04	.34	.43	.24	.05

The sampling was undertaken during a field campaign in 2011. Additional data pertaining to the other Armenian ophiolites along with the Turkish ophiolites are published in Galoyan (2008), Hässig et al. (2013), Parlak et al. (2013), Rolland, Billo, et al. (2009), Rolland, Galoyan, et al. (2009), Rolland, et al. (2010). In order to designate submarine alteration has been tectonic environments (Floyd & Winchester, 1975, 1978; Pearce, 1982, 1983, 1996; Pearce & Cann, 1973; Pearce & Norry, 1979), relatively immobile elements, such as Ti, Zr, Y, Nb, Ta, Th, V and REEs, were chosen since the immobility of these elements during low-grade submarine alteration has been constrained in a number of studies (e.g. Hart, Erlank, & Kable, 1974; Humphris, Morrison, & Thompson, 1978). We analyzed three types of rocks: (1) gabbro (Figure 5(A1)–(A3) and (2) basalt (Figure 5(B1)–(B3) from the ophiolite unit, as well as (3) metamorphic rocks (mainly amphibolites but also greenschist) (Figure 5(C1)–(C3) from the metamorphic rocks.

Figure 5. Diagrams for crustal rocks of the ophiolites. Data concerning Erzincan–Erzurum region (Refahiye, Şahvelet and Karadağ) are from Parlak et al. (2013) and this study. Data concerning Amasia, Stepanavan, Sevan and Vedi are from Hässig et al. (2013), Galoyan et al. (2007, 2009), Rolland, Billo, et al. (2009), and Rolland et al. 2010). (A1), (B1), and (C1) Ti/Y vs. Nb/Y discrimination diagram (after Pearce, 1982). (A2), (B2), and (C2) Zr/Ti vs. Nb/Y classification diagram (after Pearce, 1996). (A3), (B3), and (C3) Ta/Yb vs. Th/Yb tectonic emplacement diagram (after Pearce, 1982).

A tholeiitic (MORB-type) affiliation is found in samples, some with variable enrichment in large ion lithophile elements (LILE). In Ti/Y vs. Nb/Y and Zr/Ti vs. Nb/Y diagrams, these samples plot as basaltic tholeiites. The trace element patterns show generally marked negative anomalies in Ta–Nb and enrichment in LILE (Figure 6). The gabbros have rather flat spectra. This variable enrichment is interpreted as a contamination of a depleted mantle source by a subduction component. The association of serpentinites, gabbros, plagiogranites and basalts is typical of ophiolite assemblages, suggestive of an oceanic crust. Therefore, ophiolite rocks, as ophiolite mélange rocks, probably represent supra-subduction back- or fore-arc basins. The second tendency observed is formed by rocks with an alkaline basalt composition.

Figure 6. Chondrite normalized REE spider diagrams and N-MORB normalized multi-element spider diagrams. Data concerning Erzincan–Erzurum region (Refahiye, Şahvelet and Karadağ) from Parlak et al. (2013) and concerning Stepanavan, Sevan and Vedi from Galoyan et al. (2007, 2009) and Rolland, Galoyan, et al. (2009) and Rolland et al. (2010). Normalizing values are from Sun and McDonough (1989).

The metamorphic rocks have a very similar composition to that of alkaline basalts either plotting in Ti/Y vs. Nb/Y and Zr/Ti vs. Nb/Y diagrams as alkaline or transitional rocks. Spidergrams show neat enrichments in LILE, LREE, Ti and Pb for these samples, with no Nb–Ta negative anomalies in respect to LREE enrichment (Figure 6). The sub-ophiolitic metamorphic rocks also display similar patterns as alkaline basalts in spider diagrams. The basalt MORB-normalized spider diagrams are consistent with an OIB signature, characterized by lack of Nb and Ta negative anomalies and general enrichment in incompatible elements. As quoted by Galoyan (2008) and Galoyan et al. (2009), we interpret these features as representing an OIB signature.

Similar trends have been described by Eyüboğlu et al. (2007), Sarıfakıoğlu, Özen, Çolakoğlu, and Sayak (2008, 2010), and Sarıfakıoğlu et al. (2009). The likeness of these data-sets strongly enforces the parallel between NE Anatolia and the Lesser Caucasus and argues that the ophiolites originate from a common supra-subduction oceanic domain.

3.3. Datings

Ophiolite gabbro containing amphiboles, hydrated during hydrothermal circulation throughout rifting commonly occurs in ophiolite mélange units and massif gabbro outcrops of both NE Anatolia and Lesser Caucasus, and are of particular interest because they may provide constraints on the timing of oceanic accretion and/or of further ophiolite obduction. Similarly, palaeontological dating of the sedimentary cover of ophiolites (i.e. radiolarites) provide minimum age constraint on the timing of ocean opening (Bill, O’Dogherty, Guex, Baumgartner, & Masson, 2001; Chiari, Cortese, Marcucci, & Nozzoli, 1997; Chiari, Marcucci, & Principi, 2000; Danelian, Lekkas, & Alexopoulos, 2000; De Wever, Danelian, Durand-Delga, Cordey, & Kito, 1987; Göncüoğlu, Yalınız, & Tekin, 2006). Published geochronological data from ophiolite rocks of the İzmir–Ankara–Erzincan and Sevan-Akera suggest Middle–Upper Jurassic ages. Cretaceous ages are generally obtained from the metamorphic sole rocks (e.g. Harris, Kelley, & Okay, 1994; Önen, 2003) suggesting emplacement throughout these times.

These data (Figure 7) are suggestive of the formation of a continuous oceanic domain between the TAP and SAB to the south and the Pontides and Somkheto-Karabagh arc to the north. These ages also indicate emplacement due to a common obduction event.

Figure 7. Tectonic map of Mesozoic Ophiolites and ophiolitic mélanges from the Tethyan realm in Turkey and adjacent areas (modified after Stampfli, 2000) and representative geochronological data from rocks of the ophiolitic mélanges as well as from metamorphic soles (modified after Çelik et al., 2011). All data are from ⁴⁰Ar/³⁹Ar analyzes except where stated otherwise: (1) Dilek, Thy, Hacker, and Grundvig (1999); (2) Parlak and Delaloye (1999); (3) Çelik, Delaloye, and Feraud (2006); (4) Chan, Malpas, Xenophontos, and Lo (2007); (5) Galoyan et al. (2009); (6) Önen (2003); (7) Harris, Kelley, and Okay (1994); (8) Dimo-Lahitte, Monié, and Vergély (2001); (9) Spray, Bébien, Rex, and Roddick (1984); (10) Roddick, Cameron, and Smith (1979); (11) Koepke, Seidel, and Kreuzer (2002), K–Ar age data; (12) Hatzipanagiotou and Pe-Piper (1995), K–Ar age data; (13) Lanphere, Coleman, Karamata, and Pamić (1975), K–Ar age data; (14) Rolland et al. (2010); (15) Çelik et al. (2011); (16) Hässig et al. (2013). Abbreviations, AO, Antalya Ophiolite; BHO, Beyşehir-Hoyran Ophiolite; EO, Eldivan ophiolite; KO, Kınık Ophiolite; LO, Lesvos Ophiolite; MO, Mersin Ophiolite; ORO, Orhaneli Ophiolite; PKO, Pozantı-Karsantı Ophiolite; SO, Sevan Ophiolite; mu, muscovite; hb: hornblende. ^*Age data from gabbro.

4. Discussion and geodynamic implications

The emplacement of NE Anatolia and Lesser Caucasus ophiolites, now linked together, over the passive continental margin to the south requires at least 60 km tectonic transport from the northern Neotethyan suture to their emplacement in their current position, 60 km from Sevan–Akera suture to Vedi for the Lesser Caucasus and at least 80 km from Ankara-Erzurum suture to Hınıs for NE Anatolia. In all these areas, the obducted ophiolite sequences display supra-subduction affinities. The geochemical composition of the amphibolites in the metamorphic units beneath the Stepanavan, Amasia and Hınıs ophiolites shows a distinct alkaline affinity similar to the alkaline oceanic island basalts (OIB) suite ascribed to magmatic processes prior to obduction and so part of the ophiolites in Armenia (Vedi, Stepanavan and Amasia) (Galoyan, 2008; Galoyan et al., 2007, 2009; Rolland et al., 2010; Rolland, Galoyan, et al., 2009; Sosson et al., 2010).

The alkaline rocks in both regions (NE Anatolia and Lesser Caucasus) are not related to the generation of the SSZ-type oceanic crust. We consider these alkaline rocks, found directly on the ophiolite body in Armenia, outcropping as preserved metric pillow lavas as markers of an ocean environment at the time of alkaline volcanism dated c. 117 Ma (mid-Early Cretaceous) by Rolland, Galoyan, et al. (2009). Consequently, the alkaline lithologies are regarded as formations emplaced on the oceanic crust prior to the obduction event, thus, typical of the ophiolite series of this area.

When considering an intra-oceanic subduction model for the origin of slow-spreading ophiolites, observations lead to conclude that the volcanic arc is missing. The only evidence of any remains of such a volcanic arc structure can be found in the ophiolitic sole lithologies evidenced by geochemical tendencies. Determining whether ophiolites are of fore- or back-arc origin is not simple because of intricate obduction initiation as well as syn- and post-obduction processes. Both scenarios, fore- or back-arc origin, suggest the existence of an intra-oceanic arc. The structural and geochemical processes leading to their formation are almost identical, except for less important subduction contamination for back-arc tholeiites.

It has been suggested that the Karadağ ophiolites are representative of a fore-arc environment due to boninitic chemical signatures (Crawford, 1989; Falloon & Crawford, 1991), typical of SSZ magmatism (Parlak et al., 2013). In this scenario, the arc would then be either accreted to the Pontides margin (to the north) or subducted under it. There is no evidence of this arc to the north of the ophiolites, except for U–Pb ages which ascribe to a continuous activity along the southern margin of Eurasia (Rolland et al., 2011; Ustaömer, Ustaömer, & Robertson, 2012). The only arc is the Pontides and Somkheto–Karabakh, which are limited to the south by the north-dipping subduction of ophiolites evidenced by eclogite facies metamorphism (Topuz, Göçmengil, et al., 2013) in the Refahiye area.

However, more recent investigations have shown that boninites are not solely found in fore-arc but also in back-arc environments (Deschamps & Lallemand, 2003; Falloon, Malahoff, Zonenshaina, & Bogdanova, 1992; Teklay, 2006). In addition, Deschamps and Lallemand (2003) tends to ascribe boninites more to a back-arc environment. Furthermore, observations made by Rice, Robertson, Ustaömer, İnan, and Taslı (2009) state that the Karadağ ophiolites show proof of the presence of an intra-oceanic arc. The ages found for this formation are late Cretaceous but the authors also remarked by Rice et al. (2009) that “As no plutonic bodies were observed, it is inferred that only the upper part of the arc is preserved, possibly because the lower part of the arc was detached and subducted.” It is then arguable that the older part of the arc, older than Upper Cretaceous, has disappeared through a continent-arc accretion/subduction process as described in Boutelier, Chemenda, and Burg (2003), Shemenda (1994), and Ellis, Beaumont, and Pfiffner (1999).

The mélanges found under the ophiolitic units represent, in part, dismembered pieces of the thrusted ophiolites which fell in front of the obduction front throughout obduction (Festa, Pini, Dilek, & Codegone, 2010; Vannucchi, Remitti, & Bettelli, 2008; von Huene, Ranero, & Vannucchi, 2004), as well as scraped off features of the underthrusted unit (Cloos & Shreve, 1988; Dilek & Whitney, 1997; Elitok & Drüppel, 2008). This lithologic blend was then overthrusted by the ophiolitic body during emplacement and incorporated and metamorphosed throughout thrusting with other metamorphics beneath the ophiolites (Engi, Berger, & Roselle, 2001).

In the Erzincan area, bibliographic sources as well as field observations evidence the presence of a dismembered thrust sheet of meta-carbonate rock containing Permian foraminifers (Özgül, 1981) topping highly schistosed metamorphosed magmatic rocks, directly under the obduction contact. These marbles could represent mega-lenses emplaced through tectonic transport due to differential movements between overthrusted upper ophiolite unit and underthrusted Tauride Anatolide Platform unit (TAP) or mega-olistolites. This interpretation only leads us to say that the foraminifers evidence that an oceanic domain existed during the Permian between the northern passive margin of the TAP and the area where the future ophiolite will be generated or formed, thus the existence of Neotethys during the Permian.

As for the metamorphic rocks, they may have originally been emplaced anywhere between the passive continental margin (to the south) and the future-obducted ophiolite (to the north). We ascribe their schistosity to the intense shearing endured by these rocks throughout ophiolite emplacement. The basal contact of this unit being shielded by Cenozoic deposits of the Erzincan Basin renders it difficult to affirm that these rocks were originally located on the passive (continental or oceanic) margin. This includes a fore- or back-arc environment which is now only testified by sub-ophiolitic metamorphics caught between the underthrusted continent and overthrusted ophiolites. Analyses of these Erzincan metamorphic rocks, phyllite with calc-alkaline affinities, are documented by Gücer, Aslan, and Bektas (2007). Their geochemistry testifies of meta-basalts with tholeiitic as well as calc-alkaline tendencies. Even if there is no geochronologic data to bracket the original emplacement of these rock types before obduction, the presence of these rocks argues the occurrence of a volcanic arc between the passive continental margin to the south and the future ophiolites to the north, prior to obduction. This further argues an intra-oceanic subduction which accounts for the creation of oceanic crust in a supra-subduction setting.

The geochemical affinities and corresponding protoliths determined for all of these metamorphic rocks are compatible with a volcanic arc environment (Gücer & Aslan, 2009). Also recent ⁴⁰Ar/³⁹Ar ages have been calculated by Aslan, Gücer, and Arslan (2011) for plagioclase populations which yield ages of 94.1 ± 3.3 and 60.7 ± 4.9 Ma for the metamorphism of this unit. Let us point out that these ages are similar to those of Stepanavan metamorphic unit (95–91 and 71 Ma; Rolland, Billo, et al. (2009)).

The field relations are thus compatible with a model of obduction of a back-arc domain with oceanic crust slicing after OIB emplacement, which explains why we find alkaline rocks both underneath and on top of the ophiolite. The alkaline outcrops would have been underthrusted as the ophiolite underwent an intra-oceanic scaling process. Two hypotheses can account for the absence of the expected intra-oceanic island arc: (1) the progressive slicing and alteration by tectonic erosion of the volcanic arc during the obduction or (2) a subduction “jump” behind the fore-arc block, dragging the volcanic arc with it as proposed by Shemenda (1994). This latter model is suggested by some volcanic blocks in the Stepanavan blueschists and by the palaeo-arc complex overprinted by low-grade metamorphism found under the obducted ophiolite sequence to the north of the Erzincan Basin. In central and eastern Turkey, remnants for such intra-oceanic subduction have also been documented between 169.91+/−.8 and 177.08+/−.96 Ma (Çelik et al., 2011).

From all the available geological data, we propose the following model for the evolution of the NE Anatolian and Lesser Caucasus regions (Figure 8):

1. The magmatic and metamorphic rocks of all the ophiolites have similar geochemical compositions. The ophiolitic rocks are all of similar age (between 150 and 170 Ma; Çelik et al., 2011; 2013; Galoyan et al., 2009; Rolland, Billo, et al., 2009; Rolland, Galoyan, et al., 2009; Sosson et al., 2010; Topuz, Çelik, et al., 2013; Topuz, Göçmengil, et al., 2013).

2. The two magmatic suites were emplaced one on top of the other: a gabbroic basement of supposedly back-arc oceanic crust topped by thick basaltic flows with an alkaline tendency. This confirms the hypothesis of a single ophiolitic nappe (Galoyan, 2008) over the SAB topped by a volcanic series of hot-spot type, dated c. 117 Ma in Rolland, Galoyan, et al. (2009).

3. The ages of the syn-tectonic sedimentary deposits limit the beginning of obduction of this oceanic domain to Coniacian–Santonian times. Datings on the flysch at Sevan and Vedi indicate similar dates as well as those found in the literature for the NE Anatolian domain (Dilek & Thy, 2006; Okay, 2008). This is compatible with the context of the closure of Neotethys.

4. This new contribution in the comprehension of the geodynamic evolution of NE Anatolia and the Lesser Caucasus supports the presence of two north dipping subduction zones: (1) a subduction under the Eurasian margin and (2) farther south, an intra-oceanic subduction allowing the continental domain to subduct under the oceanic lithosphere, thus leading to ophiolite emplacement. This extends recent geodynamic models for the Lesser Caucasus (Hässig et al., 2013; Rolland et al., 2010; Sosson et al., 2010) eastwards to include NE Anatolia.

5. The missing of the volcanic arc formed above the intra-plate subduction may be explained by its dragging under the obducting ophiolite with scaling by faulting and tectonic erosion. It is hypothesized that the part of the blueschists of Stepanavan corresponds to this missing volcanic arc (Galoyan et al., 2007; Rolland, Billo, et al., 2009). In the Erzincan region, geochemical traces (Parlak et al., 2013) and field observations lead to the confirmation of this hypothesis because of the presence of low-grade metamorphic rocks of volcanic origin that are found under the ophiolitic rocks obducted from north to south along the northern edge of the Erzincan basin.

Figure 8. Middle Toarcian (c. 180 Ma) to present day palaeotectonic evolution of the NE Anatolian–Lesser Caucasus region. Maps modified from Middle East Basins Evolution Programme palaeotctonic maps of the Middle East (Barrier & Vrielynck, 2008) illustrating our new interpretation.

When considering the discontinuous occurrences of metamorphic rocks with calc-alkaline tendencies along the northern Neotethyan suture, we do not see the problem with punctual occurrences of arc volcanism due to the intra-oceanic subduction, as opposed to a continuous uninterrupted volcanic arc.

Acknowledgements

This work was supported by the MEBE (Middle East Basin Evolution) and the DARIUS programs jointly supported by a consortium including oil companies, the University Pierre and Marie Curie and the INSU/CNRS. Fieldwork was partly facilitated by the support of the Armenian Academy of Science (Institute of Geological Sciences). We gratefully acknowledge help of M. Manetti and S. Gallet in Nice during sample preparation and data acquisition, respectively. Osman Parlak and anonymous reviewer are thanked for their valuable comments and suggestions that improved the manuscript. This publication is a contribution of “GEOAZUR”, University of Nice–Sophia Antipolis, and CNRS, France.