Composition, pressure, and temperature of the mantle source region of quaternary nepheline-basanitic lavas in Bitlis Massif, Eastern Anatolia, Turkey: A consequence of melts from Arabian lithospheric mantle

Lithos 328–329 (2019) 115–129

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Composition, pressure, and temperature of the mantle source region of quaternary nepheline-basanitic lavas in Bitlis Massif, Eastern Anatolia, Turkey: A consequence of melts from Arabian lithospheric mantle Yavuz Özdemir a,⁎, Çağrı Mercan a,b, Vural Oyan c, Ayşe Atakul Özdemir d a

Department of Geological Engineering, Van-Yuzuncu Yıl University, 65080 Van, Turkey Natural Buildings Stones Technology Program, Mardin Artuklu University, Mardin, Turkey c Department of Mining Engineering, Van-Yuzuncu Yıl University, 65080 Van, Turkey d Department of Geophysical Engineering, Van-Yuzuncu Yıl University, 65080 Van, Turkey b

a r t i c l e

i n f o

Article history: Received 12 November 2018 Accepted 16 January 2019 Available online 22 January 2019 Keywords: Eastern Anatolia Arabian Lithosphere Ne-basanite Mineral chemistry Petrology

a b s t r a c t The Quaternary (0.66–0.63 Ma) nepheline basanites (ne - basanite) are the firstly observed volcanic products of Arabia-Eurasia collision on Bitlis Pötürge Massif. They composed of clinopyroxene, olivine, Ti-magnetite, Cr spinel, and nepheline. The forsterite compositions of olivines range between 73 and 83%, calcic clinopyroxenes show modest variations in Wo48–57-En37–45-Fs5–7 and nephelines occur as minor minerals within the networks of other groundmass minerals. They are characterized by low SiO2 (40.16–41.96 wt%), high MgO contents (8.54–9.73 wt%) and similar Sr\\Nd isotopic compositions with Arabian Plate volcanics. Mineral and whole rock thermobarometry yield crystallization pressure and a temperature range between 8 and 20 kbar and 1301 °C – 1035 °C respectively. Lavas have high Mg-number (N0.58), high Cr and Ni contents and strong LREE enrichment but depletion in Rb, K, and Pb. Trace elements together with Sr isotopic compositions inferred negligible assimilation of the local upper crustal material. The calculated average pressure and temperature of mantle melting for ne-basanites is 2,85 kbar and 1353 °C respectively. FC3MS (wt% FeO/CaO-3*MgO/SiO2) parameter and melting models using REE data reveal Çatak basanites are products of amphibole and phlogopite bearing metasomatised lithospheric mantle in garnet stability field. They seem to originated from depths of ~ 85 km which corresponds to the base of the Arabian lithosphere in the region. © 2019 Elsevier B.V. All rights reserved.

1. Introduction Cenozoic Eastern Anatolian post-collisional volcanism was started in Middle Miocene as a result of the collision between the Anatolian and Arabian plates. The ongoing convergence has given rise to the uplift of the Eastern Anatolia (Şengör and Kidd, 1979) and widespread volcanism within the plateau (e.g. Oyan et al., 2017; Özdemir, 2016; Özdemir et al., 2006, 2011). Volcanism in the region characterized by mainly stratovolcanoes, basaltic lava plateaus and is mainly spread between Bitlis Suture Zone (BSZ) and Erzurum-Kars plateau (Fig. 1). Generally Miocene and Quaternary represented by stratovolcaoes and small volume basaltic lava flows, however Pliocene characterized by voluminous basaltic plateaus. Many studies have been proposed to explain the origin of the postcollisional volcanics in Eastern Anatolia, however melting region and time-space distribution of volcanics still remain as a matter of debate. Considering the petrological studies on the northern parts of the Bitlis ⁎ Corresponding author. E-mail address: [email protected] (Y. Özdemir).

https://doi.org/10.1016/j.lithos.2019.01.020 0024-4937/© 2019 Elsevier B.V. All rights reserved.

Suture Zone, proposed petrogenetic models on those volcanics divided into three major groups: first group assumed lithospheric origin (Kaygusuz et al., 2018; Pearce et al., 1990; Şen et al., 2004; Yılmaz et al., 1998); in the second group, an astenospheric source with or without subduction component is considered (Keskin 2007, 2003; Lebedev et al., 2016; Şengör et al., 2008, 2003); in the third group variable mixed melts from asthenosphere and lithosphere and increase in lithospheric contribution from Miocene to Quaternary are suggested (Oyan et al., 2016; Özdemir and Güleç, 2014) for the source of the eastern Anatolian volcanics. Additionally lower crustal-derived volcanics (e.g. Çoban et al., 2007; Karslı et al., 2008) and sub-slab derived volcanics after the onset of Northern Anatolian and Eastern Anatolian strike slip tectonics are also described in the region (Di Giuseppe et al., 2017). The triggering mechanisms for the onset of volcanism proposed as whole scale or small scale removal of lithospheric mantle, slab breakoff and mantle convection in the region. All these models have been proposed for the Cenozoic volcanism at the northern parts of the BPM. However, there is no data regarding the young Neogene volcanism within the BSZ. This is the first study on Quaternary post-collisional volcanic products in BSZ and also on the low silica highly alkaline rocks

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Fig. 1. A topographic relief map of the Eastern Turkey and distribution of the post-collisional volcanics (dark grey). Red circle is the location of the ne-basanitic flows.

ever seen in Eastern Anatolia. Our study focuses on a small scale ne-basanitic system; we present detailed results of geology, majortrace element, Sr\\Nd isotope and mineral chemistry of the ne-basanitic rocks from Çatak region together with new K\\Ar ages. The aim of this study is two-fold: first, to determine the conditions under which very small-volume mafic magma batches are generated and are modified during their journey to the Earth's surface, second, to discuss the place of these rocks within the overall evolution of the post-collisional volcanism in the region. 2. Background geology and age of volcanism Continental collision between Anatolian-Iranian and Arabian plates was initiated at the Early Miocene by consuming last oceanic lithosphere between Arabian and Eurasian plates (Okay et al., 2010). The ongoing convergence throughout the Bitlis Suture Zone has resulted to the uplift of the Eastern Anatolian Plateau (EAP) (Şengör and Kidd, 1979). Currently, the average elevation of the EAP is about 2 km and is made of accreted micro continents which are separated by ophiolite belts and accretionary complexes (Şengör, 1990). Oligocene to Miocene sedimentary deposits and Late Cenozoic post-collisional volcanics overlie those basement rocks in the region. Temporal-spatial distribution of volcanic rocks displays different phases of magma generation with distinct geochemical signatures from Arabian Foreland to Iran and Lesser

Caucasus. The post-collision related primitive rock compositions such as basanites and/or alkaline basaltic rocks without metasomatized compositions (asthenospheric/lithospheric mantle source without subduction component) are absent/ limited between Bitlis- Zagros Suture Zone and Lesser Caucauses. The basanitic rocks of our study are located within the Bitlis Massif, the metamorphic equivalents of Tauride Belt (Atakul-Özdemir, 2019; Yilmaz et al., 2010) at Çatak town situated 50 km to the south of Lake Van (Fig. 1). They crosscut the Upper unit of the Bitlis Massif which includes amphibolites, green schists, calc schists, gneisses and marbles of the Pre-Permian (Samanlı, Toyaç, Hulkan Formations), Permian (Körüklü Formation) carbonates (Fig. 2). Permian carbonates mainly composed of recrystallized neritic limestone and dolomites. Based on the foraminiferal assemblages recorded within these carbonates comprising Agathammina pusilla, Agathammina sp., Globivalvulina vonderschmitti, Globivalvulina ex. gr. cyprica, Hemigodius guvenci, Hemigodius ovata, Hemigodius zaninettiae, Nankinella sp., Pachyphloia ovata, Paradagmarita planispiralis, Paradagmarita monodi, Paraglobivalvulina sp., this formation has been assigned to the Permian. Pre-Permian formations are devoid of fossils, however, on the basis of their stratigraphic positions the age of these units has been assigned to Pre-Permian. Basanitic volcanism exposed along K-G striking tensional fissures (Fig. 2).Initial products of the volcanism are pyroclastic rocks which include scoria fall deposits with size 0.3–0.5 cm and overlain by 10–30 cm sized younger fall deposits and

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Fig. 2. Geological map of the basanites and surrounding area (Modified from Aktürk, 1985).

volcanic bombs (Fig. 3a and b). Pyroclastics are overlain by thick columnar basanitic lava flows. 40K/40Ar ages of two basanitic volcanic rocks are 0.66 and 0.63 Ma (Electronic Supplement).

10 nA, and a 5 μm beam diameter. Calibration was performed on a diversity synthetic and natural minerals and glasses. 4. Results

3. Analytical methods 4.1. Petrography and mineral chemistry Whole rock major element compositions of 22 samples (Electronic Supplement) were measured by inductively coupled plasma emission spectrometry (ICP-ES) at ACME laboratories following lithium metaborate/tetraborate fusion and dilute nitric acid digestion. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the trace element contents in the same laboratory following the lithium tetraborate/metaborate fusion and nitric acid digestion. Isotopic compositions of seven selected samples (Electronic Supplement) from Çatak ne-basanites were carried out at the laboratories of the Middle East Technical University, Turkey. Sr and Nd isotope compositions were measured by thermal ionization mass spectrometry (TIMS) on a Thermo Fisher Triton system. Isotopic compositions were corrected for mass fractionation using 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, respectively. During the period of analysis international Sr standard, NIST SRM 987 was measured as an average of 0.710270 ± 10 (n = 3) and international Nd standard La Jolla gave an average 0.511846 ± 5 (n = 3). Detailed information about the analytical procedure can be obtained from Köksal and Göncüoǧlu (2008). The K\\Ar ages of 2 samples (Electronic Supplement) have been performed at the Isotope laboratory of IGEM-RAS, Moscow. The analysis of radiogenic 40Ar content in the basanites was done by the isotope dilution method with mono-isotope 38Ar as a spike on the mass spectrometer MI-1201 IG (SELMI). International standards MMhb-1 (amphibole), P-207-Bern-4 (muscovites) were used for spike calibration. Results were controlled by systematic determination of radiogenic 40Ar content in and intra-laboratory standards, and also by measurements of isotope composition of atmospheric argon. The spectrometer FPA-01 (ELAM-Center, Russia) was used to determine potassium content in the samples. Minerals were analyzed by electron microprobe (EPMA) at Middle East Technical University using Jeol JXA-8230 three-spectrometer (WDS) instrument using 15 kV accelerating voltage, beam current of

Ne-basanites are fresh and display porphyritic, seriate and poikilitic textures with variable sized phenocrysts of olivine, clinopyroxene and Ti-magnetite (Fig. 3c and d). Ne-basanites contain up to 40% volume of phenocrysts. The olivine phenocrysts are more abundant than the clinopyroxenes and their volume fraction reaches 20–30%. They have a size of up to 0.5 mm and display euhedral to subhedral shapes. Their rims are commonly replaced by reddish brown iddingsite (Fig. 3d). Clinopyroxenes are the second widespread phenocryst phase of basanitic rocks (~10–15 modal %), and are euhedral-subhedral phenocrysts with green to brown colors (Fig. 3d). Amount of Ti-magnetite phenocryts reaches up to 5%. The groundmass of the samples is composed of very fine grained anhedral olivine, clinopyroxene,Ti magnetite, Cr spinel, interstitial nepheline and glass. Forsterite contents of olivine phenocrysts-microphenocrysts are ranging from Fo73-Fo83 and exhibit normal zoning with a b 5% decrease in forsterite content from core to rim (Fig. 4a). CaO and MnO contents of olivine are increased with respect to Fo content decrease (Electronic Supplement). The phenocryst compositions are given in Fig. 4b on a diagram of bulk-rock mgnumber vs forsterite content. It seems that majority of the olivine cores are in equilibrium with their whole-rock compositions, using a Kd ol/liq = Fe-Mg between 0·27 and 0·33 (Roeder and Emslie, 1970). Clinopyroxenes are highly calcic and show modest variations in Wo48–57-En37–45-Fs5–7. They are weakly zoned with mg# 90–87 at cores to 86–87 to rims (mg# = Mg/Mg + Fe+2,Fig.4c). Compared to large phenocrysts, most of the micro crystals (except cmb8–16, cmb8– 18; Electronic Supplement) within ground mass have similar compositions and are diopside based on the classification of Morimoto et al. (1988). They all plot in CaMg-Fe pyroxene (Quad area) space in the Q-J diagram (not shown). The Fe\\Mg exchange partition coefficient between clinopyroxene and basaltic melts are between 0.27 ± 0.05–

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Fig. 3. (a) 0.3–0.5 cm scoria fall deposits (bottom), 10–30 cm scoria fall - bombs (middle) and ne-basanitic lavas (top), (b) columnar ne-basanitic lava flows, (c) olivine and clinopyroxene phenocrtsts in ne-basanites, (d) iddingsitized olivines along their rims. ol; olivine, cpx;clinopyroxene, Ti-mag; Ti-magnetite.

0.23 ± 0.05 (Putirka, 1999; Toplis and Carroll, 1995; Wang et al., 2012). Fig. 4d displays the relations between whole rock mg# and Cpx mg# with a Fe\\Mg KD of 0.23,0.25, and 0.27. Samples contain equilibrium clinopyroxene compositions are core compositions. Sample CMB-8 has contain some Mg-rich phenocrysts which are display disequilibrium compositions. Clinopyroxenes with high Mg-content would be products of less differentiated magmas with high Al/Ti and Na/Ti ratios at high pressure (e.g. Damasceno et al., 2002). The mg# values of clinopyroxenes have positive correlation with Al2O3/TiO2 and Na2O/TiO2,supporting the the high mg# pheocrysts are resulted from high-pressure crystallization (Damasceno et al., 2002). Nephelines occur as minor minerals within the networks of other groundmass minerals. Ti-rich magnetites occur as inclusions in olivine and clinopyroxenes as well as within the groundmass. Most analyzed grains have the composition of ulvospinel with a range of TiO2 14–18%, total Fe 70–74%. Only a single Fe\\Cr spinel found in olivine with a Cr# value (=Cr/(Cr + Al)) of the 0.29. 4.2. Crystallization pressure and temperature The Fe\\Mg silicates were used to estimate intensive parameters (P,T) of the ne-basanites. 4.2.1. Clinopyroxene geothermobarometry Pressure and temperature calculations were performed on clinopyroxene phenocrysts using the model of Putirka et al. (2003) and Putirka (2008). For the calculations we only used the clinopyroxene

compositions which are fell into the Fe\\Mg equilibrium field in Fig. 4d. The whole-rock contents are used to represent the liquid compositions. The results show a crystallization temperature range of 1035– 1258 °C and have the main population of 1200–1250 °C (Fig. 5a). Clinopyroxene - liquid thermometers of Putirka et al. (2003) and Putirka (2008, equation 33) give a little bit higher temperature than the Cpx-only equation (Putirka, 2008, eq. 32d) (Fig. 5a). The calculated pressures range from 8 to 21 kbar and have two main populations of 11–17 kbar (Fig. 5c). 4.2.2. Olivine thermometry For calculating the olivine equilibrium temperatures, equations of Beattie (1993) and Putirka (2008) were used. The results of those three calculations are plotted in Fig. (Fig. 5b). The crystallization temperature range is between 1260 and 1301 °C and has the main population of 1250–1300 °C. All the different model calculations provide similar crystallization temperatures for T-P ranges of clinopyroxene and T ranges of olivines. The magma first crystallized at high pressures (~20 kbar) and high temperature (1301 °C) and then mostly fractionated at 11–17 kbars at 1200–1250 °C. It seems that the parental magma of Çatak basanites cooled from at least 1301 °C to 1035 °C. 4.3. Major and trace element compositions The Çatak volcanics display a narrow major element ranges (Electronic Supplement). The LOI values are generally low and are b2 wt%

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Fig. 4. Frequency distribution diagram of olivine (a) and clinopyroxene (c) comparison of olivine (b, Fo content) and clinopyroxene (d, Mg#) compositions with the Mg# of whole rock, where mg-number = Mg2+/(Mg2+ + Fe2+) calculated assuming Fe2+/Fetotal = 0.9. Fe/Mg exchange partition coefficients (KD) between olivine and basaltic liquid vary from 0.3 (Roder & Emslie, 1970) to 0.31–0.34 (Ulmer, 1989). The Fe\ \Mg KD for clinopyroxene falls between 0.27 ± 0.05 (Putirka, 1999) and 0.23 ± 0.05 (Toplis and Carroll, 1995).

for lavas and b 2.2 wt% for the pyroclastic members. Low LOI values and the petrography confirm that the samples selected for the geochemical analysis are weakly altered or unaltered. SiO 2 contents are ranging between 40.16 and 41.96 wt%, MgO contents are between 8.54 and 9.73 wt%. The total alkali contents (Na2O + K2O) of the lavas are higher than 5.95 wt% and the Na2O/K2O ratios are higher than 2.77 wt% indicating their high alkali and sodium nature (Fig. 6a). All Çatak volcanics are plotted within the basanite field (Fig. 6b). Normative nepheline and olivine contents are range between 8 and 22 wt% and 9–13 wt% respectively. Because of their nepheline rich nature we use the term nephelinebasanites (ne-basanites) for these rocks. Bivariate plots of selected major and trace elements are used to examine the evolutionary trends of Çatak lavas. Al 2O3, TiO2, K 2O, FeO T, slightly decreases, however, Cr, Ni, Sc and CaO/Al2O3 (not shown) contents increase with increasing MgO wt% content of the basanites (Fig. 7). The negative correlation of Cr, Ni, Sc and CaO/Al2O3 indicate fractionation of one or more ferromagnesian phases. The primitive mantle normalized trace element patterns (Fig. 8a) of the Çatak nebasanites are identical to typical OIB and show significant enrichment of LIL elements. The most striking feature is negative Rb, K, and Pb troughs with a positive spike of Nb. Chondrite normalize REE patterns (Fig. 8b) have significant enrichment of LEE over HREE with a ratio of (La/Yb)N and (La/Lu)N ratios ranging between 37 and 49 and 39–52 respectively. None of the basanites display negative Eu anomaly and have small positive Sr anomalies. Çatak lavas have comparable trace elements contents with within plate basalts such as OIB (Fig. 8a).

4.4. Sr\\Nd Isotope systematics Sr\\Nd isotopic compositions are provided together with other post-collisional volcanics of Eastern Turkey, Kula and Arabian plate in Fig. (Fig. 9). Çatak basanites have a narrow 87/86 Sr and 143/144Nd compositions ranging between 0.703908 and 0.70415 and 0.512772–0.512795 respectively. The all Çatak basanites plot depleted quadrant of the diagram (Fig. isotope) and have unradiogenic Sr-and Nd isotopes. They all have similar Sr\\Nd isotopic systematics similar to Arabian plate. However, they have more radiogenic Sr isotopes relative to the Kula and Karacadağ, less radiogenic than post-collisional volcanics at the northern parts of the Bitlis Suture Zone (such as, Kars-Ararat MuşNemrut, Süphan Tendürek). 5. Discussion 5.1. Role of crustal contamination The limited SiO2 and MgO contents and fine-grained nature of the Çatak ne-basanites reflect rapid rise towards the surface within the lithosphere. La/Nb N 1.5, La/Ta N 22 and K/P N 7 ratios can be used to decide whether or not the mafic magmas affected by the crustal lithologies (e.g.Ali et al., 2013; Hart et al., 1989). The low amounts of those elemental ratios (La/Nb = 0,94;La/Ta = 23,6;K/P = 1,59) and their Sr\\Nd isotopic composition suggest Çatak lavas affected negligible crustal contamination. Additionally, Çatak basanites have high Ce/Pb, Nb/U and low Th/Nb ratios which are in the range of average ocean island and mid-ocean ridge basalts (Hofmann et al.,

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Fig. 6. (a) K2O vs. Na2O plot of the Çatak ne-basanites. Division lines are from (Middlemost, 1975). (b) Total alkalis versus silica (TAS recalculated volatile-free) of same rocks.

5.2. Mantle thermal state and melting conditions

Fig. 5. Crystallisaition temperature estimates for basanites using clinopyroxene (a) and olivine (b) compositions. (c), Crystallization pressure estimates for same rocks using clinopyroxene compositions.

1986; Weaver, 1991) reflecting mantle composition rather than the crust. To better constrain the effect of assimilation from crustal lithologies EC-AFC model of Bohrson and Spera (2001) to the model variation of 87Sr/86Sr vs. Sr (Fig. 10). The EC-AFC model assumes heating and partially melting of the wall rocks during the crystallization of magma. The compositional and thermal parameters of the model calculation for the Çatak suites are given in Table 1. We used a local crustal composition as an assimilant during the calculations. Sample CMB-8 was taken as the starting magma based on its low 87 Sr/ 86 Sr and high 43 Nd/144 Nd, MgO contents. It is obvious from the model using upper crustal thermal and local crustal compositional parameters crustal contamination ranges from 0 to 2% reflects little or negligible crustal assimilation during their en route to the surface.

5.2.1. Major element constraints We have applied the geothermobarometric calculations of Lee et al. (2009) to make assumptions to the melting conditions of the Çatak nebasanites. This thermobarometer has been calibrated for olivine and orthopyroxene bearing primary mantle-derived magmas with SiO2 content of N40 wt%. Using primary magma composition obtained from reverse olivine fractionation as input in Lee (2009) lead extremely high temperatures and pressures. Most of the basanitic rocks of Çatak have nearly similar MgO (MgO N 9 wt%) and Ni contents (Ni N 100 ppm, e.g. Witte et al., 2017) nearly similar primary magmas. Because of their primitive nature, we used the original rock compositions for calculating the melting pressure and temperature without olivine adding. Calculated mantle potential temperatures are range between 1331 and 1369 °C with an average of 1353 °C and pressures between 2.64 and 3.04 GPa with an average of 2.85 Gpa. 5.2.2. Constraint from REE composition Mckenzie and O'nions (1991) have developed an inversion program (INVMEL) by using the REE patterns of the basaltic rocks in order to

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Fig. 7. Variation diagrams of selected trace elements vs MgO for Çatak ne-basanites. The line in the MgO vs CaO diagram represents the MgO/CaO (CaO = 13.81–0.274MgO) division between peridotite and pyroxenite from Herzberg and Asimow (2008).

model melt distribution through depth. INVMEL calculate the best fit of observed REE concentrations using the amount of melting and related depth at which it takes place. The melting amount is critical as it controls the mineralogy of the residue and the source. In our modeling we have used a garnet peridotite source with clinopyroxene, orthopyroxene,

olivine, apatite and phlogopite. The observed REE concentrations of Çatak basanites by INVMEL required three steps of melting; (i) The depletion of the peridotite source by extracting 23% of melt in garnet spinel transition zone (The depletion occurred in garnet spinel transition zone with assumed depth of 80–100 km), (ii) 1.8% metasomatic enrichment

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Fig. 8. Primitive mantle normalized multi-element and Chondrite normalize REE patterns of Çatak ne-basanites. Normalisation values are from (Sun and McDonough, 1989).

of this already depleted source by a MORB type melt, (iii) small fraction melting in garnet stability field. The best fit REE patterns are displayed in Fig. 11 along with some other trace element concentrations. The patterns in Fig. 11 are from melting of 4% peridotitic source in the garnet stability field assuming garnet spinel transition zone between 60 and 80 km. The best-fit model is very good for REE and good for the most of other trace element considered, except for K, Pb, Zr, Ti, and Na. This may be related to the lack of some partition coefficient data or may be the source associated. The results of the REE inversion method demonstrate that the melts generated for the Çatak basanites are derived from depths that correspond to a garnet-spinel transition in garnet stability field at the base of the lithospheric mantle. 5.3. Nature of the mantle source Çatak ne-basanites display distinct geochemical features such as low silica content, enrichment of both large ion lithophile elements and high

field strength elements and negative anomalies of K, Rb, in spiderdiagrams. The inferred origin for the Çatak ne-basanite like silica-undersaturated rocks as follows: (1) silica-poor eclogite and garnet pyroxenite (Hirschmann et al., 2003; Kogiso et al., 2003; Kogiso and Hirschmann, 2006), (2) matasomatised hornblendite (Mckenzie and O'nions, 1995; Niu and O'Hara, 2003; Pilet et al. 2008;2005;2004), (3) metasomatised peridotite (Dasgupta et al., 2007; Hirose, 1997; Sisson et al., 2009), and (4) mixed sources (Chen et al., 2009; Dasgupta et al., 2010; Liu et al., 2008; Prytulak and Elliott, 2007; Zeng et al., 2010). Recently new studies have been put forward to differentiate the source type (peridotite type pyroxenite/eclogite) of the intraplate low silica alkaline basaltic rocks using the chemistry of olivine minerals and also the major element compositions of the volcanics (e.g. Herzberg et al., 2007; Herzberg and Asimow, 2008). Such as olivines from an pyroxenite source which is result of reaction between high silica melts from an eclogite and surrounding peridotite have low CaO and

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Table 1 Compositional and thermal parameters used for EC-AFC modeling presented in Fig. 10. Sr and Nd isotopic values for the crust 1 and crust 2 are from local metamorphic sample.

Fig. 9. 143Nd/144Nd vs 87Sr/86Sr diagram for Çatak ne-basanites. Data Source for KarsArarat: Keskin et al. (1998) and Pearce et al. (1990), for Kula: Alıcı et al. (2002), for Muş-Nemrut-Tendürek-Bingöl: Oyan et al. (2017, 2016); Özdemir et al. (2006); Özdemir and Güleç (2014); Pearce et al. (1990), for Karacadağ: Keskin et al. (2012), for Arabian Plate: Krienitz et al., (2006); Lustrino and Wilson (2007), for Gloss Plank and Langmuir (1998).

MnO but high Ni contents (Sobolev et al. 2007;2005). Herzberg and Asimow (2008) proposed that basic rocks that have only contain olivine phenocrysts could be used to specify pyroxenite or peridotite sources using a MgO vs CaO plot. In Fig. 7 most of the Çatak basanites plot below the division line of Herzberg and Asimow (2008). This would be due to the clinopyroxene fractionation which lowers the CaO content of melts and also high Na2O + K2O content (Yang et al., 2016) Peridotite /pyroxenite index = CaO+(0,274MgO)-13.81 (Herzberg and Asimow, 2008) ranging between −1.27 to 1.06 which reflects the transition between peridotite and pyroxenite fields or mixing of peridotitic and pyroxenitic sources. Recently, Yang et al. (2016) suggested some alternatives for differentiating the peridotite-pyroxenite sources using the major element contents of the primitive basaltic rocks. Equation of Ol(%) = 144.27ln((Fe + Mg + Ca + 2Na)/Si)) could be used to differentiate peridotitic and pyroxenitic sources for a given bulk composition (Yang et al., 2016). Çatak basanites have olivine modal abundances (Ol, wt%) 40–52 wt% suggesting peridotitic source. However, high olivine modal abundances would also derived from minor amount carbonate bearing hornblendite sources (e.g. Pilet et al., 2008). Yang et al. (2016) proposed that the FC3MS parameter of Yang and Zhou (2013) (wt% FeO/CaO-3*MgO/SiO2) that is mainly controlled by the source bulk composition and melting degree is an alternative way for differentiating the peridotite versus pyroxenite melts. To make assumptions on the source regions of the Çatak basanites, we correlate them with experimentally derived phlogopite peridotite melts (Condamine et al., 2016; Condamine and Médard, 2014), carbonated peridotite melts (Dasgupta

Fig. 10. 87Sr/86Sr vs Sr (ppm) with EC-AFC curves calculated using the model of Bohrson and Spera (2001). Less radiogenic and most primitive member of the Çatak ne basanite (CAB-6) is used for the starting composition. A local metamorphic rock from Bitlis Massif with 87Sr/86Sr ratio of 0. 707,355 and Sr of 506 (ppm) is used for the modeling. Crust 1 represents the EC-AFC curve of local contaminant with upper crustal thermal and compositional parameters (Table 1). Crust 2 represents the EC-AFC curve of same contaminant with lower crustal parameters.

Thermal parameters

Crust 1

Crust 2

Magma liquidus temperature Tl, m Magma initial temperature Tmo Assimilant liquidus temperature Tl, a Assimilant initial temperature Toa Solidus temperature Ts Equilibration temperature Teq Crystallization enthalpy, Δhcry (J/Kg) Isobaric specific heat of magma Cp, m (J/Kg per K) Fusion enthalpy Δhfus (J/Kg) Isobaric specific heat of assimilant Cp, a (J/Kg per K)

1400 °C 1400 °C 1000 °C 400 °C 900 °C 1000 °C 396,000 1484 270,000 1370

1400 °C 1400 °C 1100 °C 600 °C 950 °C 1000 °C 396,000 1484 354,000 1388

Compositional Parameters

Magma initial concentration (ppm), Cmo Magma isotope ratio, £m Magma distribution coefficient, Dm Assimilant initial concentrations (ppm) Cmo Assimilant isotope ratio, £a Assimilant distribution coefficient, Da

Crust 1

Crust 2

Sr

Nd

Sr

Nd

1612

67.4

1612

67.4

0.703992 0.512795 0.703992 0.512795 0.9 0.1 0.9 0.1 506 24 506 24 0.707355 0.512704 0.707355 0.512704 1.5 0.25 0.5 0.2

et al., 2007; Hirose, 1997), hornblendite melts, cpx- hornblendite melts and hornblendite-DMM1 sandwich melts (Pilet et al., 2008) in FC3MS space (Fig. 12). FC3Ms values of carbonated peridotites are too low to be source for the Çatak lavas. Hornblendite and phlogopite peridotite melts display consistency with Çatak basanites in their FC3MS value combined with MgO and Na2O + K2O contents. However, in Fig. 12 FC3MS versus La/Yb ratios are plot on/between experimental melts from PM-like garnet peridotite melts and metasomatised garnet peridotite melts (FC3MS ratiosN0.65 characterize hornblendite and pyroxenite melts, Yang and Zhou, 2013) reflecting basanites result from metasomatised peridotite in garnet stability field. Metasomatism of upper mantle by hydrous or carbonate-rich fluids/ melts may be one of the precursors to the alkaline magmatism. Alkali elements such as K, Rb, Ba and water are stored in phlogopite and amphibole within metasomatized upper mantle during melting (Adam et al., 1993; Dalpé and Baker, 1994; LaTourrette et al., 1995) This effect appears as negative K-anomalies on primitive mantle normalized spider diagrams (Fig. 8) The depletion of Rb, TiO2, K2O, Pb, and SiO2 gives some clues about the type of the metasomatism and that could be the presence of residual phlogopite and/or amphibole in the mantle. Recent experiments on the melting phlogopite bearing peridotites (Condamine et al., 2016; Condamine and Médard, 2014) have resulted in potassic or ultrapotassic melts, however, Na2O + K2O contents of the Çatak basanites are ranging between 5.95 and 7.38 wt% characterized by high Na2O contents up to 5. 92 wt%. It seems that melting of phlogopite bearing peridotite alone would not be source for the Çatak lavas. Melting of amphibole bearing metasomatic veins and their interaction with the surrounding mantle proposed source for the low silica alkaline melts (Pilet et al., 2008). In order to reproduce the incompatible trace element variation we modeled non-modal batch melting of hydrous, anhydrous lherzolite (garnet and spinel) and hornblendite (Fig. 13). with different source and melt models (Table 2). Source compositions are hornblendite (AG4, French Pyrenees, Pliet et al., 2008) and peridotite (primitive mantle, Sun and McDonough, 1989). The former is used since it repsesents amphibole bearing hydrous veins in lithospheric mantle. For the dry peridotite component neither spinel facies peridotite nor garnet facies peridodite is capable of generating K/La and Tb/Yb ratios of Çatak basanites (Fig. 13). Since the FC3MS values of the Çatak basanites have similarities with experimental melts of hornblendite and phlogopite peridotites (Fig. 12), we also plot the melting curves of those components

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Fig. 11. Rare earth element inversions for Çatak ne-basanites calculated by inversion method Mckenzie and O'nions (1991).

in our model (Fig. 13). Çatak basanites plot between these two curves and can be interpreted as result of mixing between 0,5-0,75% melting of phlogopite bearing garnet peridotite and 20–30% melting of hornblendite. Melting model also suggests an ~ 50% (an average) contribution of hornblendite veins in the source of the Çatak basanites. Our findings have similarities with the study of Pilet et al. (2008), Pilet (2015) and Ma et al. (2011) that low silica basaltic rocks are products of melting of metasomatic lithospheric (amphibole ± phlogopite rich veins) mantle. 5.4. Geodynamic aspects The Bitlis Suture Zone which hosts the Çatak ne-basanites comprises an accumulation of Precambrian to Cretaceous metamorphic rocks, Late Cretaceous – Eocene and Middle Eocene volcano-sedimentary units. They all thrust over the Arabian platform between late Eocene and Middle Miocene (Şengör et al., 2003) after the convergence between Anatolian and Arabian plates. Thus the volcanism responsible for postcollisional Çatak basanites was originated from the northeastern edge of the Arabian mantle component beneath the Bitlis Suture Zone. Late Cenozoic volcanism in eastern Anatolia would be differentiated into two main groups in space; i) volcanism on the Anatolian Plate, situated northern parts of the Bitlis Suture Zone and extent to Lesser Caucasus ii) volcanism on Arabian Foreland (northern edge of Arabian Plate). The time-space distribution and origin of the volcanism northern parts of

the Bitlis Suture Zone is still in controversy. Those have similarities to the ocean island basalts and volcanic arcs, many models have been proposed for the origin of these volcanics. Regarding the basaltic rocks, generally, highly alkaline members are absent (except Tendürek volcano; Lebedev et al., 2016), most of them have mildly alkaline affinities. Most of the studies on post-collisional volcanics in eastern Anatolia and Lesser Caucasus have consensus on the inherited subduction component/metasomatic origin in the mantle source of these rocks (e.g. Allen et al., 2013; Keskin, 2003, 2007; Lebedev et al., 2016; Neill et al., 2013; Oyan et al., 2016, 2017; Özdemir et al., 2006, 2011; Özdemir and Güleç, 2014; Pearce et al., 1990; Şengör et al., 2008; Yılmaz et al., 1998). Melts with/without subduction component have been proposed to be originated from lithosphere, asthenosphere or mixing melts from both of them. However, volcanism on Arabian foreland, such as Karacadağ volcano is devoid of such a metasomatism (subduction influence) and originated from the garnet stability field of the lithospheric mantle by localized lithospheric extension (e.g. Ekici et al., 2014). Similarly a number of studies have recognized potential mantle sources for volcanism on the Arabian Plate such as convecting upper mantle, mantle out flow from Afar triple junction flow and variably metasomatised lithospheric mantle (e.g. Bertrand et al., 2003; Camp and Roobol, 1992; Çapan et al., 1987; Ekici et al., 2012; Krienitz et al., 2006, 2007, 2009; Lustrino et al., 2010; Ma et al., 2011; Pearce et al., 1990; Şen et al., 2004; Shaw et al., 2003; Weinstein et al., 2006). The heterogeneous nature of Arabian lithosphere is thought to result of earlier

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Fig. 12. FeOT/CaO-3*MgO/SiO2 versus MgO, Na2O + K2O and La/Yb of experimental melts (modified from Yang et al., 2016; Yang and Zhou, 2013) together with Çatak basanites. Data source for experimental melts are from Condamine et al. (2014;2016), Dasgupta et al. (2007), Hirose, (1997), Pilet et al. (2008), Yang et al. (2016). Triangles represent Çatak ne-basanites.

Fig. 13. Tb/Yb vs La/Yb and K/La vs La/Yb for Çatak ne- basanites. Nonmodal batch melting models for spinel, garnet peridotite and hornblendite. PM composition and hornblendite are from McDonough and Sun (1995) and Pilet et al. (2008) respectively. Source, melt modes and partition coefficients are given in Table 2. Dashed lines corresponds to mixing between Ph-Grperidotite and hornblendite. Sp, Gr, Ph represent; spinel, garnet and phlogopite respectively.

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Table 2 . Mineral-melt partition coefficients and source modes used in partial melting modeling. Source and melt modes for mantle peridotites are from 1- Thirwall et al. (1994); 2- Pilet et al. (2008), Ma et al. (2011); 3- Barry et al. (2003) and Kaczmarek et al. (2016). Partition coefficients used in this partial melting model curves are from a- Kelemen et al. (1993); b-Adam and Green (2006); c-Hart and Dunn (1993); d- van Westrenen et al. (2000) and e- Tiepolo et al. (2007). PM (Primitive mantle) and AG-4 (hornblendite source) are taken from Sun and McDonough (1989) and Pilet et al. (2008), respectively. Source modes

Source mode1 Melt mode1

Olivine

Orthopyroxene

Clinopyroxene

Garnet Peridotite 0.598 0.05 Hornblendite

0.211 0.2

0.076 0.3

Spinel

Garnet

Source mode1 Melt mode1

0.18 0.40

0.95 1

1 1

0.05 0.20

0.119 0.5

0.033 0.13

Clinopyroxene

Spinel

0.01 0.10

1 1 1 1

Partition coeffficient Olivine La Yb Tb K

Source Comp. Orthopyroxene

a

0.0000007 0.023 a 0.0015b 0.000000001a

Sum 1 1

0.05 Phlogopite-Garnet-Peridotite 0.56 0.20 0.10 0.20 Spinel Peridotite 0.578 0.27 0.10 0.27

Phologopite

0.115 0.45

Source mode2 Melt mode2 Source mode3 Melt mode3

Amphibole

a

0.0005 0.1 a 0.019 b 0.00001 a

c

0.0536 0.43c 0.31 b 0.0072 a

silicate/carbonate melt or fluid-related metasomatism. Several chemically distinct lithospheric components has been proposed for the source region of the volcanism on the northern Arabian Plate. These are amphibole-rich veins (Ma et al., 2011), phlogopite-rich domains (Ekici et al., 2014) and carbonatite impregnations (Shaw et al., 2007). Mantle source of the Çatak basanites located at the north-eastern edge of the Arabian plate seems to have amphibole and phlogopite in garnet stability field. Thermobarometric calculations using the Lee et al. (2009) yield mantle potential temperatures between 1331 and 1369 °C with an average of 1353 °C and pressures between 2.64 and 3.04 GPa with an average of 2.85 Gpa. The obtained mantle potential temperatures are not consistent with stability of phlogopite from the experimental study of Condamine et al. (2016; stability of phlogopite reaches up to ~ 1300 °C at 3 Gpa). However, have consistency with the studies of Modreski and Boettcher (1972) and Sato et al. (1997) which yields higher temperatures and pressures for the stability of the phlogopite in the mantle. The lithospheric thickness has important effect on the stability of the hydrous phases (Lloyd and Bailey, 1975). Such as amphibole is stable up to 3.0 Gpa, while stability of phlogopite can be reach 8 Gpa if the lithosphere is too thick (Harlow and Davies, 2004; Rapp, 1995). A recent study by McNab et al. (2018) subjected on the Neogene uplift and magmatism of Anatolia suggests 1400 °C (+90,−40) mantle potential temperatures for the eastern Anatolia, which are nearly, overlap our results. They also argue that the lithospheric thickness is about 60 km beneath the volcanic regions and asthenospheric thermal anomalies play a significant role in generating regional uplift and basaltic magmatism. Studies on lithospheric structure (e.g. Al-Lazki et al., 2003; Gök et al., 2003; Vanacore et al., 2013; Zor, 2008; Zor et al., 2003) (e.g. Zor et al., 2003; Zor, 2008; Vanacore et al., 2013;Al-Lazki et al., 2003; Gök et al., 2003) point out crust is not thick as expected and a thin lithospheric mantle beneath the region. The average thickness of crust under Eastern Anatolia, northern Arabian platform and Caucasus are represented by 45, 38 anf 44 km respectively (Komut (2015)). Despite the known crustal thickness under the region knowledge about the thickness of the lithospheric mantle is limited. The lithosphere-asthenosphere boundary beneath the East Anatolia has been observed at 60–80 km depth by the study of (Angus et al., 2006); Kind et al. (2015) propose a depth of lithosphere between 80 and 100 km for whole Anatolia. A more recent study by Mahatsente et al. (2018) suggests thinner lithospheric thickness for the Eastern

Garnet a

0.0006 0.0045 a 0.01 b 0.17 a

d

0.0018 5.14d 0.75 b 0.013 b

Amphibole e

0.117 0.684e 0.83 b 1.36b

Phologopite b

0.007 0.005b 0.0001 b 4.1b

PM

AG-4

0.687 0.493 0.108 250

52.7 2.540 1.26 10125

Anatolia than the Arabian Plate. They invoke gravity data modeling and suggest 62–74 km lithospheric thickness for the north of the Bitlis Suture Zone and 84–95 km for suture zone and the Arabian plate. Our thermobarometric results of 2.85 Gpa corresponds to a depth of ~85 km beneath the Bitlis Massif which refers to the base of the Arabian lithospheric mantle in the region. The temperature and pressure results getting from thermobarometer of Lee et al. (2009) are in a good agreement with the geophysical data (Fig. 14). The P-T estimates are also compatible with the INVMEL results which support generation of the lavas from garnet peridotite stability field (Fig. 11). Çatak basanites exposed on the Bitlis Massif were reached surface from a north-south trending fissure zone. This can be interpreted as localized lithospheric

Fig. 14. Pressure-temperature diagram (modified from Jung et al., 2012) for illustrating the probable source region of the Çatak ne-basanites. Dry mantle solidus is from Mckenzie and Bickle (1988). Stability field for garnet and spinel peridotite in upper mantle rocks are from Falloon and Green (1990), Foley (1991). Solidus for peridotite after Hirschmann (2000) and solidus for garnet pyroxenite after Kogiso et al. (2003). Lithosphere astenosphere boundry under Bitlis Massif and northern parts of the Arabian Plate is at about 84–95 km taken by geophysical data (Mahatsente et al., 2018). White area represents Çatak ne-basanites (filled square represents average).

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tension related volcanism during Quaternary. Adıyaman and Chorowicz (2002) have proposed that initiation of the Eastern Anatolian fault zone has caused east-west tension and volcanism on the northern edge of the Arabian Plate (e.g. Karacadağ Volcano). 6. Conclusions Çatak volcanics representing the firstly observed post-collisional rocks on the Bitlis Suture Zone consist of silica undersaturated nebasanites. They cross-cut the rocks of Bitlis Suture Zone which trust over the Arabian lithosphere between late Eocene and Middle Miocene. K\\Ar ages yield 0.63–0.66 My, the volcanism was initiated with scoria falls, bombs and ended up with lava flows. The ne-basanites are generally fine-grained with minerals of olivine+clinopyroxene+nepheline +Cr spinel+magnetite. Independent barometers indicate that crystallization takes place over a wide range of pressure 8–20 kbar and melt cooled from about 1301 °C -1035 °C. EC-AFC modeling of isotope and trace element compositions point to no/minor crustal contamination during their en route to the surface. Thermobarometric calculations (without olivine adding) reveal the melting pressure and temperature an average of 2.85 kbar and 1353 °C respectively. FC3MS (wt% FeO/ CaO-3*MgO/SiO2) parameter, inverse (INVEL), forward modelings using REE suggest Çatak basanites are products of amphibole and phlogopite bearing metasomatised lithospheric mantle in garnet stability field. Results of thermobarometric calculations together with the recent geophysical data point out melting originated from the base of Arabian lithospheric mantle. Acknowledgements This work has been funded by both Van-Yüzüncü Yıl University Scientific Research Project Foundation (2013-FBE-YL024) and TUBITAK the Scientific and Technological Research Council of Turkey (Project No. 113Y406). Authors gratefully thank to Dan Mckenzie for his help in carrying out INVMEL. We also thank to Orhan Karslı, Zong-Feng Yang and Chief-Editor Nelson Eby for their constructive comments which helped in improving our paper. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.lithos.2019.01.020. References Adam, J., Green, T.H., Sie, S.H., 1993. Proton microprobe determined partitioning of Rb, Sr, Ba, Y, Zr, Nb and Ta between experimentally produced amphiboles and silicate melts with variable F content. Chemical Geology 109, 29–49. https://doi.org/10.1016/00092541(93)90060-V. Adıyaman, Ö., Chorowicz, J., 2002. Late cenozoic tectonics and volcanism in the northwestern corner of the Arabian plate: a consequence of the strike-slip Dead Sea fault zone and the lateral escape of anatolia. Journal of Volcanology and Geothermal Research 117, 327–345. https://doi.org/10.1016/S0377-0273(02)00296-2. Aktürk, A., 1985. Tectonics and Stratigraphy of Çatak-Narlı (Van). Fırat University, Elazığ. Ali, S., Ntaflos, T., Upton, B.G.J., 2013. Petrogenesis and mantle source characteristics of quaternary alkaline mafic lavas in the western carpathian-pannonian region, styria austria. Chemical Geology 337–338, 99–113. https://doi.org/10.1016/j.chemgeo. 2012.12.001. Alıcı, P., Temel, A., Gourgaud, A., 2002. Pb-Nd-Sr isotope and trace element geochemistry of Quaternary extension-related alkaline volcanism : a case study of Kula region (western Anatolia , Turkey). Journal of Volcanology and Geothermal Research 115, 487–510. Al-Lazki, A.I., Seber, D., Sandvol, E., Turkelli, N., Mohamad, R., Barazangi, M., 2003. Tomographic Pn velocity and anisotropy structure beneath the anatolian plateau (eastern Turkey) and the surrounding regions. Geophysical Research Letters 30, 8043. https://doi.org/10.1029/2003GL017391. Allen, M.B., Kheirkhah, M., Neill, I., Emami, M.H., McLeod, C.L., 2013. Generation of arc andwithin-plate chemical signatures in collision zone magmatism: quaternary lavas from kurdistan province Iran. Journal of Petrology 54, 887–911. https://doi.org/ 10.1093/petrology/egs090. Angus, D.A., Wilson, D.C., Sandvol, E., Ni, J.F., 2006. Lithospheric structure of the Arabian and Eurasian collision zone in eastern Turkey from S-wave receiver functions.

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