Eastern Pontides Orogenic Belt Research Articles

Late Triassic to Middle Jurassic magmatism in the Eastern Pontides (NE Türkiye): Evidence for divergent double subduction of Paleo-Tethys lithosphere

The Meso-Cenozoic geodynamic evolution of northern Türkiye remains a subject of debate primarily due to a lack of systematic geological, geochemical, geochronological, and geophysical investigations. This paper presents comprehensive geochronological and geochemical data on the Late Triassic andesite porphyry, andesite breccia and quartz diorite porphyry, and the Middle Jurassic diabase, and amphibole-poor and amphibole-rich andesite porphyry from Çevrepınar Igneous Complex (Gümüşhane) in the southern part of the Eastern Pontides Orogenic Belt (EPOB), a well-preserved continental arc in the Alpine-Himalayan orogen. Zircon U–Pb geochronology indicates crystallization ages of ∼208–202 Ma (Rhaetian) for the Late Triassic rocks and ∼175–172 Ma (Aalenian) for the Middle Jurassic rocks. Whole-rock geochemical and Sr-Nd-Pb isotopic data, and zircon εHf(t) data indicate that both the Late Triassic and the Middle Jurassic rocks originated by low-degree melting of a spinel lherzolite lithospheric mantle source modified by subduction-related fluids and/or melts. Based on the new and published data, we suggest that the Late Triassic to Middle Jurassic arc magmatism in EPOB occurred as a result of southward subduction of the Paleo-Tethys oceanic lithosphere beneath the northern margin of Gondwana-Land. Late Triassic to Jurassic arc magmatism and basin evolution occurred synchronously in the northern and southern peripheries of the present-day Eastern Black Sea Basin, indicating divergent double subduction of the Paleo-Tethys oceanic lithosphere beneath the northern margin of Gondwana and southern margin of Laurasia during the Early Mesozoic.

Petrogenesis of Late Cretaceous A-type plutonic rocks from the Eastern Pontides Orogenic Belt (NE Turkey): constraints from zircon U-Pb geochronology, zircon Lu-Hf and whole-rock Sr-Nd-Pb-Hf isotopes

ABSTRACT The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes.

Temporal and spatial radiogenic heat production rate of granitic plutons from the Eastern Pontides Orogenic Belt, NE Turkey: Constraints for the geothermal resources

The evaluation of the geothermal potential of the granitic rocks is important in long-term sustainable renewable energy projects due to increasing energy demand. The Eastern Pontides Orogenic Belt in NE Turkey contains a variety of granitic plutons changing in age, size, and composition. In this paper, we discussed the temporal and spatial distribution of radiogenic heat production by using the contents of heat-producing elements (U, Th, K) of the granitic plutons. The average U, Th, and K concentrations for the granitic plutons are 2.97 ± 0.95 ppm, 13.48 ± 3.48 ppm and 2.69 ± 0.47 wt% for Paleozoic plutons, 1.83 ± 0.98 ppm, 8.58 ± 5.10 ppm and 1.77 ± 0.80 wt% for Jurassic plutons, 5.24 ± 1.64 ppm, 26.02 ± 6.43 ppm and 3.17 ± 0.49 wt% for Cretaceous plutons, and 3.82 ± 0.90 ppm, 15.79 ± 4.27 ppm and 2.88 ± 0.40 wt% for Eocene plutons, respectively. Radiogenic heat production rates are 1.43–2.73 µW/m3 for Paleozoic plutons, 0.74–1.70 µW/m3 for Jurassic plutons, 0.66–6.28 µW/m3 for Cretaceous plutons and 1.15–5.22 µW/m3 for Eocene plutons. The studied plutons were classified as low- to moderate heat-producing granitoids. However, some Cretaceous and Eocene granitic plutons with radiogenic heat production values of 5.22–6.28 µW/m3 are considered as high heat-producing granitoids. The thermal indications in the region can be related to radiogenic heat generation and the neotectonic activity of the region. Considering the large volume of the Cretaceous- and Eocene- aged granitic plutons in the Eastern Pontides Orogenic Belt, the moderate to high radiogenic heat production of the granitic plutons in some areas has a significant geothermal impact and can be considered as the potential of enhanced geothermal systems for the future energy demand of the region.

Zircon U Pb geochronology and petrology of the tholeiitic gabbro from the Kovanlık (Giresun) area: Constraints for the Late Cretaceous bimodal arc magmatism in the Eastern Pontides Orogenic Belt, NE Turkey

Mafic intrusions of the Eastern Pontides Orogenic Belt (EPOB) in NE Turkey are found rarely in varying ages, sizes and compositions. Of these, tholeiitic gabbro stocks, namely Kovanlık gabbro, consist of pyroxene gabbro and minor hornblende gabbro with a mainly granular texture. The pyroxene gabbro contains plagioclase, clino- and ortho-pyroxene, olivine, and Fe Ti oxides, whereas the hornblende gabbro includes mainly plagioclase, hornblende, rarely biotite and Fe Ti oxides. The clinopyroxene compositions of the pyroxene gabbro exhibit arc-related tholeiitic magmas. The Kovanlık gabbroic rocks have high U/Yb zircon ratios, implying continental arc-related tectonic settings. Zircon U Pb dating on the Kovanlık gabbro yielded a concordia age of ~92 Ma (Turonian). Petrochemically, the gabbroic rocks have a tholeiitic character and show arc- and MORB-like signatures. The gabbroic rocks show positive Rb, Ba, K, Pb, Sr, Ti and negative Nb, Ce, Nd, Hf, Zr anomalies in N-MORB normalized diagrams. The chondrite-normalized REE plots of the rocks show flat to feeble right-dipping REE patterns (La N /Lu N = 0.94–2.56) with positive Eu anomalies (Eu N /Eu* = 1.15–2.14; except for two pyroxene gabbro samples). The gabbroic rocks have 87 Sr/ 86 Sr (i) ratios (0.704533 to 0.706265), εNd (i) values (4.04–4.85), 206 Pb/ 204 Pb (18.56–18.68) and 207 Pb/ 204 Pb (15.61–15.64) ratios. Low Nb/La and Nb/Y ratios, as well as high Sr/Yb and Ba/Rb ratios, indicate that source regions were modified by slab-derived fluids and/or melts. The obtained zircon dating, isotopic and geochemical data, as well as regional geology, revealed that the tholeiitic mafic magma derived from a spinel-lherzolite mantle at a relatively shallow depth, and the Kovanlık gabbro in the EPOB represents one of the first mafic intrusions of Late Cretaceous bimodal arc magmatism related to the roll-back of the northwards subducting Tethys oceanic plate. • The Kovanlık tholeiitic gabbro formed in a continental arc with a MORB-like source. • The zircon U Pb dating of the gabbro gave a concordia age of ~92 Ma (Turonian). • The parent magma originated by partial melting of a spinel lherzolite mantle source. • The gabbro evolved by fractional crystallization and lesser crustal assimilation. • Cretaceous bimodal arc magmatism is related to the rollback of the subducting slab.

Temporal and Spatial Radiogenic Heat Production Rate of Granitic Plutons from the Eastern Pontides Orogenic Belt, Ne Turkey: Implications for the Geothermal Potential

Temporal and Spatial Radiogenic Heat Production Rate of Granitic Plutons from the Eastern Pontides Orogenic Belt, Ne Turkey: Implications for the Geothermal Potential

Highly siderophile element and Os isotope systematics of the Cenozoic volcanic rocks from the Eastern Pontides, NE Turkey: Constraints on the origin and evolution of subcontinental mantle-derived magmas

The Cenozoic subalkaline to alkaline volcanic rocks from the Eastern Pontides Orogenic Belt (EPOB) in NE Turkey exhibit wide range of highly siderophile element (HSE) contents and Os isotope compositions that can be related to their mantle sources and parental melt evolution. Although some Eocene rocks show signs of late-stage modification, most of the studied volcanic rocks possess primary HSE and Os systematics. The Eocene volcanic rocks have largely variable PdN/IrN (~0.25–751), PdN/PtN (~0.25–87) and (187Os/188Os)i ratios (~0.113 to 0.51). The Miocene volcanic rocks have high PdN/IrN (~2.6–441), low PdN/PtN (~0.11–1.7) and radiogenic (187Os/188Os)i ratios ranging from ~0.166 to 0.52 while the Mio-Pliocene volcanic rocks show high PdN/IrN of ~7.2–29, low PdN/PtN (~1.2–2.7), and only mildly radiogenic (187Os/188Os)i values between ~0.132 and 0.177. Finally, the Quaternary volcanic rocks have low PdN/IrN (~2.3–3.6), PdN/PtN (~0.9–1.6) and radiogenic (187Os/188Os)i values ranging from ~0.133 to 0.194. Overall, the primitive mantle-normalized HSE patterns of the studied volcanic rocks are characterized by PPGE (Pt, Pd) and Re enrichment with respect to IPGE (Os, Ir, Ru). The variations in HSE and radiogenic Os isotope compositions of the relatively differentiated volcanic rocks indicate that crustal assimilation played active role in their parental melt evolution, especially in the Eocene and Miocene period. Besides, the obtained HSE data also suggest that the parental magmas of all the studied volcanic rocks were generated mainly in the S-saturated conditions. The temporal and spatial HSE and Os isotope variations observed in the studied Cenozoic volcanic rocks reflect the heterogeneity of the mantle source beneath the EPOB, which could be attributed to variations in response of different fluid/melt metasomatism of the underlying SCLM.

Xenoliths in Late Cretaceous to Early Paleocene adakites of the Eastern Pontides Orogenic Belt, NE Turkey

Late Cretaceous to Early Paleocene hypabyssal intrusives near Bayburt in northeastern Turkey, in the Eastern Pontides Orogenic Belt (EPOB), host a variety of xenoliths, including clinopyroxenite, hornblendite, hornblende- and plagioclase-rich gabbro, quartz diorite and amphibole-rich diorite, quartz syenite, and amphibolite. We report major and trace element data for both host rocks and xenoliths, along with zircon U-Pb and amphibole 40Ar/ 39Ar ages, zircon trace element data, mineral compositions, and Sr-Nd-Pb-Hf isotopic data. Host rock compositions range from trachyandesite to dacite and rhyodacite, but major element (e.g. Mg-number) and trace element systematics (e.g. La/YbN) indicate that they are not related by fractional crystallization. Host rocks belong to the high-K calc alkaline and calc-alkaline series, and have the signature of arc rocks (depleted Nb, Ta, Ti, and elevated Pb). Trace element data (Sr/Y and La/Yb) indicate that the dacitic rocks are adakitic. Host rock ages cluster around 70 ± 2 Ma; one intrusion contains zircons that suggest a ~62 Ma crystallization age. Hornblendite xenoliths show ages of 76, 78, and 81 Ma, whereas quartz syenites range from 66 to 70 Ma. The younger ages (62, 66, 70 Ma) fall in an apparent magmatic gap, and document the oldest adakitic magmatism in the EPOB. Mineral compositions indicate initiation of crystallization in the host rocks at ~9 kb and 1250 °C, with progressive crystallization continuing to ~2 kb and 800 °C. Host rocks and xenoliths have similar ranges of 87Sr/86Sri (0.7044–0.7062), 143Nd/144Ndi (−1.5 < εNd < 1.5), and Pbi (18.28 <206Pb/204Pb < 18.68) compositions. The clinopyroxenite, hornblendite, and gabbro xenoliths are broadly cognate with the host rocks, and are cumulate fragments from an arc-root magma system. The quartz diorite, quartz syenite, and amphibolite xenoliths have different histories. Some of the quartz syenites are near eutectic compositions in the H2O saturated q-or-ab system at ~5 kb. The host rocks and xenoliths derive from crustal magma chambers and dominantly crustal melting in the back-arc region of the EPOB.

U–Pb zircon ages and petrogenesis of the Late Cretaceous I-type granitoids in arc setting, Eastern Pontides, NE Turkey

The Eastern Pontides Orogenic Belt (EPOB) as a well-preserved ancient magmatic arc situated in the eastern part of the Sakarya Zone and has key importance to allow for proper reconstruction of the geodynamic evolution of the region. The region accepted as important part of Alpine–Himalayan Belt comprises of many granitoids of the Late Cretaceous age. This paper presents new mineral chemistry, bulk-rock petrochemistry, U-Pb geochronology and radiogenic and stable isotope geochemistry data from the Arpaköy and Oyman granitoids in the north part of the EPOB to interpretation of the igneous activity and geodynamic evolution of the region in Late Cretaceous era. Emplacement ages of 86.82 ± 0.58 Ma for the Oyman granitoid and 82.0 ± 2.3 Ma for the Arpaköy granitoid according to laser ablation ICP-MS U–Pb zircon dating. The Arpaköy granitoid are gabbro diorite, diorite and granite, whereas the Oyman granitoid are tonalite and granite in composition. They show metaluminous-peraluminous transitional (ASI = 0.79–1.20) low to medium-K calc-alkaline features. The rock samples from granitoids are characterized by enrichment in large ion lithophile elements (LILE) and high field strength elements (HFSE) depletion with concave-upward shapes (LaN/LuN = 1.88 to 6.04). The crystallization temperatures are 648 °C–913 °C and the pressure values are 0.2–3.0 kbar, which indicates emplacement depth of the studied granitoids varying from ~1 to 9 km correspond to shallow crustal depths. They show considerable variations in εNd(i) (−4.02 to 1.50) and 87Sr/86Sr(i) (0.70478–0.70689). The 206Pb/204Pb ratios are between 17.97 and 18.65, and δ18O are varying from +5.4 to +9.3‰. The parental magma of the Arpaköy and Oyman granitoids originated from a melt of the enriched lithospheric mantle and the fractional crystallization and lesser assimilation processes has important role on the evolution of magmas in the shallow crustal levels.

Eocene I-type magmatism in the Eastern Pontides, NE Turkey: insights into magma genesis and magma-tectonic evolution from whole-rock geochemistry, geochronology and isotope systematics

ABSTRACT The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikdağı, Aydıntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by significant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (87Sr/86Sr(i) = 0.70502 to 0.70560; εNd(i) = +0.9 to – 1.4; δ18O = +5.0 to +8.7‰, εHf(i) = – 2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (87Sr/86Sr(i) = 0.70508 to 0.70542; εNd(i) = +0.9 to −1.1; δ18O = +5.8 to +8.0, εHf(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers.

Geology, fluid inclusion, and stable isotope (O, H, S, C) characteristics of the Hazinemağara (Gümüşhane) lead-zinc deposit, NE Turkey

The Hazinemağara (Gümüşhane) Pb-Zn deposit is located in the southern part of the Eastern Pontides Orogenic Belt in northeastern Turkey. It occurs as irregularly shaped ore bodies with breccia fill structure within the intraformational breccia or brecciated horizons of limestone in the Upper Jurassic-Lower Cretaceous Berdiga Formation. The dominant ore minerals are pyrite, sphalerite, galena, and tetrahedrite, and the major gangue minerals are calcite, quartz, and barite. Microthermometric investigations of the fluid inclusions show that the ore-forming fluids contain CaCl2 and MgCl2 in addition to NaCl. The salinity of the fluid ranges from 1.7% to 9.2% with an average of 5.7% (wt.% NaCl equivalent) (n = 93). The homogenization temperature of the fluid ranges from 160.0 to 386.0 °C with an average of 263.5 °C (n = 98). The plots of the δD values of water trapped in fluid inclusions hosted by barite and quartz (in the range of 92‰ to 81‰) and the δ18O values calculated for water in equilibrium with these minerals (4.1‰ to 18.5‰) are closer to the magmatic range than any other water sources and suggest the presence of magmatic water in hydrothermal fluid with some modifications by interaction with fluid from surrounding sedimentary rocks. The sulfur isotope composition of sulfide minerals (in the range of -7.8‰VCDT to +5.4‰VCDT, avg.: -2.0‰; n = 13) indicates a magmatic source for sulfur. It is concluded that the magmatic water derived from deep-seated Eocene plutonic rocks (Kaçkar Granitoids-I and -II) possibly carried metals and the sulfur derived from the source magma or leached from magmatic rocks on the pathway along the fault zones and precipitated mainly within voids between limestone fragments in intraformational breccia horizons of the Berdiga Formation. The Berdiga Formation is observed in large areas within the Eastern Pontide region and the intraformational breccia horizons could provide large stratabound ore potential.

Eocene tonalite–granodiorite from the Havza (Samsun) area, northern Turkey: adakite-like melts of lithospheric mantle and crust generated in a post-collisional setting

ABSTRACT Eocene intermediate to felsic plutons of different sizes and compositions are widespread in the Eastern Pontides Orogenic Belt in northern Turkey. Of these, the Taşlık Tepe pluton in the Havza (Samsun) area is fine-to-medium-grained, with granular, porphyritic, and micrographic textures, and include mafic microgranular enclaves (MMEs). LA-ICP-MS U-Pb zircon dating yielded emplacement ages of 42.9 (± 1.4) and 40.5 (± 1.3) Ma for the host granodioritic pluton and the dioritic MMEs, respectively. Petrochemically, the host pluton has I-type, high-K calc-alkaline, and metaluminous-to-slightly peraluminous features (A/CNK = 0.95–1.06). The host pluton also shows geochemical features of adakite-like rocks with high SiO2 (67–68 wt%) and Al2O3 (15.5–16.0 wt%) content and Ba/La (17–23), Sr/Y (40.7–61.6), and LaN/YbN (14.4–23.7) ratios and low Y (8.2–9.9 ppm) and YbN (3.1–4.4) contents. Whole-rock major and trace element variations suggest that fractional crystallisation played a significant role in the pluton evolution. The N-MORB normalised trace element patterns of the pluton are similar to those of MMEs with enrichment in large-ion lithophile elements, Th and Ce, and negative Nb and Ti anomalies. Chondrite-normalised rare earth element plots show moderate-to-highly enriched concave patterns (LaN/LuN = 14.2–21.6) with insignificant negative Eu anomalies (EuN/Eu* = 0.86–1.14), all of which imply hornblende fractionation during magmatic evolution. The pluton samples have 87Sr/86Sr ratios of 0.704767 to 0.704927, 143Nd/144Nd ratios of 0.512767–0.512774, εNd values of (+2.52) – (+2.65), and δ18O values of 7.9–9.7‰. The isotopic compositions of the host pluton and MMEs are similar to I-type granitoids derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. Combined with regional studies, these new data suggest that the parental magma of the studied adakite-like pluton was generated from the lithospheric mantle and then modified by fractional crystallisation and assimilation in a post-collisional setting.

Investigation of the crustal and upper-mantle structure of the eastern Pontides orogenic belt (NE, Turkey): a receiver-function study

In this study, we use teleseismic P and S receiver functions (i.e., S-to-P and P-to-S converted signals) and their joint inversions to determine seismic discontinuities in the crust and upper mantle. Eight permanent broadband stations from the KOERI (Kandilli Observatory and Earthquake Research Institute) that are distributed along the eastern Pontides orogenic belt (EPOB), NE, Turkey, comprise our database. Inversion is performed by using a simulated annealing technique with and without travel time residuals. Our inversion results reveal the Moho depth, a high S velocity lid, a low-velocity zone, and the underlying upper mantle layer. The studied area is divided into two regions based on the station locations: (a) a northern region and (b) a southern region. The inversion results from the northern area produce crustal models that indicate that the uppermost crust is represented by a low P and S wave velocity (Vp = ~ 5.0 km/s and Vs = ~ 2.8 km/s). These velocities are clear evidence of (1) the sedimentary and volcanic rocks that widely crop out in the region and (2) a thinner uppermost crust, whereas the velocities of the southern region (Vp = ~ 6.0 km/s and Vs = ~ 3.1 km/s) indicate a thicker uppermost crust (~ 7 km). Our calculated Vp/Vs velocity ratio in the lower crust is approximately 1.90 and 1.80 in the northern and southern regions, respectively. These ratios are generally attributed to mafic rocks. Beneath the northern stations, the crustal thicknesses are 30, 33, 37, and 40 km from east to west, while the depths of the Moho are 46, 42, 39, and 44 km beneath the southern stations. Some velocity histograms show a transition from the high S velocity mantle lid to the low-velocity zone, which is known as the lithosphere–asthenosphere boundary. A representative value of the boundary’s depth is around 83 km in the north and ~ 88 km in the south. The hypothesis of some researchers regarding the existence of southward subduction beneath the eastern Pontides orogenic belt during the Late Mesozoic–Cenozoic is supported by our 2-D and 3-D velocity-depth models.

U-Pb geochronology, bulk-rock geochemistry and petrology of Late Cretaceous syenitic plutons in the Gölköy (Ordu) area (NE Turkey): Implications for magma generation in a continental arc extension triggered by slab roll-back

Late Cretaceous felsic plutons in the Eastern Pontides orogenic belt of Turkey are found in varying ages, sizes and compositions. The Late Cretaceous syenitic bodies, namely Direkli and Yeniköy Tepe plutons in the Ordu area, intruded into the Late Cretaceous volcanics and volcanoclastics, and compositionally consist of syenite and minor quartz-syenite with mainly granular and rarely porphyric, poikilitic and perthitic textures. The studied plutons contain K-feldspar, plagioclase, quartz, clinopyroxene, biotite and minor hornblende, and Fe-Ti oxide, apatite, and zircon. Mineral thermobarometer estimations imply that the syenitic plutons were crystallized in P-T conditions representing mid to shallow crustal levels. Petrochemically, these syenitic plutons show I-type, metaluminous-peraluminous transitional (A/CNK = 0.85–1.04) and shoshonitic features. LA-ICP-MS U-Pb zircon dating on the syenitic plutons yielded weighted mean ages of 78.5–72 Ma. Primitive mantle-normalized trace element patterns of the studied plutons are characterized by negative anomalies of Ba, Sr, Nb, Ta and Ti, and enrichment in Rb, Th, K, Ce and La. The chondrite-normalized rare earth element (REE) plots of the studied plutons show moderately enriched concave-shaped patterns (LaN/LuN = 10.3–10.7 for the Direkli pluton; LaN/LuN = 6.8–11.7 for the Yeniköy Tepe pluton) with negative Eu anomalies. The plutons have 87Sr/86Sr ratios (0.705368–0.706954), 143Nd/144Nd ratios (0.512600–0.512672), 206Pb/204Pb ratios (19.29–19.52) and 207Pb/204Pb ratios (15.65–15.67). The geochemical data, as well as regional geology, suggest that the Late Cretaceous syenitic plutons have formed in an extensional continental arc setting triggered by slab roll-back. The parental magma of syenitic plutons was derived from melts of lower crustal materials (metabasalt/metaandesite) and lithospheric mantle component.

Late Cretaceous I- and A-type magmas in eastern Turkey: Magmatic response to double-sided subduction of Paleo- and Neo-Tethyan lithospheres

We provide geochronological (zircon UPb) and geochemical data (whole rock major and trace elements, Sr-Nd-Pb isotopes, mineral compositions, zircon trace elements) for Late Cretaceous I- and A-type granitoids and associated gabbros from three areas (Dereli, Şebinkarahisar, Divriği), along a north-south traverse in eastern Turkey from the northern part of the Eastern Pontides Orogenic Belt to the Anatolide-Tauride Block, and from two locations (Sökmen and Pırnallı) that are situated away from the traverse line. Our aim is to interpret the tectonic environment in which the granitoids formed. Late Cretaceous plutonic activity began ~ 90 Ma and continued uninterruptedly for about 20 my. The Dereli suite and the Asarcık intrusion at Şebinkarahisar are I-type granitoids; the others are A-type granitoids. The A-type classification of these rocks is ambiguous; they are A-typerelative to other coeval granitoids in eastern Turkey. The Şebinkarahisar, Murmana (Divriği), and Pırnallı granitoids evolved primarily by closed-system fractional crytallization. At Şebinkarahisar, I- and A-type intrusions are isotopically indistinguishable, and must share the same source. Open system, AFC processes affected the other granitoids. Crustal components contributed to all of the granitoids. The Dereli granitoids have an old component (1.2 < TDM < 1.75 Ga) that is unusual among Turkish igneous rocks. No mantle component is recognizable in the A-type granitoids, but the low SiO2 content of some granitoids requires a mantle-derived component. Arc-like geochemical features may be inherited from a mid-crustal source component, in addition to contributions from the arc environment active at the time of magmatism. A petrogenetic relation cannot be demonstrated between the Divriği gabbros and their contemporaneous granitoids. The gabbros require a subcontinental lithospheric mantle source. Trace elements in zircon track fractional crystallization paths within suites, and faithfully map the arc-related petrogenesis of the granitoids, but do not mirror trace element distributions in zircons from other A-type suites. Available data indicate that Late Cretaceous plutonic activity began at about ~90 Ma in both the northern part of the Eastern Pontides Orogenic Belt and the southern part of the Anatolide-Tauride Block. Magma compositions began to change at ca. 80 Ma, and transformed successively into high-K I-type and shoshonitic A-type activity, and magmatism continued until ~ 70 Ma. We interpret this 20 my interval to be the subduction-dominated, arc-construction phase in the Eastern Pontides. The distribution of I-type magmas in eastern Turkey is best explained by double-sided, initially shallow-angle subduction of Paleo- and Neo-Tethyan lithospheres, with subsequent steepening of the subducted slabs leading to an extensional regime and the generation of A-type magmas. This hypothesis also explains the origin of Late Cretaceous I- and A-type Central Anatolian granitoids.

Discovery of Latest Cretaceous OIB-type alkaline gabbros in the Eastern Pontides Orogenic Belt, NE Turkey: Evidence for tectonic emplacement of seamounts

The Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt, a mountain chain extending parallel to the southeastern margin of the Black Sea, has been controversial for the last forty years. Here we present data for a newly discovered alkaline gabbro body and its surrounding basaltic rocks in the northern part of the Eastern Pontides Orogenic Belt. We also provide a comprehensive assessment of the Late Mesozoic-Cenozoic geodynamic evolution of the Eastern Mediterranean region. The gabbroic body is bounded by reverse faults along its northern and southern borders and is surrounded by vesicular, pillow-fragment breccias and pillow basalts. Mineral compositions suggest that crystallization of the gabbros began at about 1170 °C, and the lowest preserved crystallization T is near 1000 °C. Estimated pressure at the beginning of crystallization is 5.7–7.4 kb. The 40Ar/39Ar dating of kaersutite and plagioclase and UPb dating of titanite indicated that the Hayrat gabbro crystallized at ~67 Ma (Late Maastrichtian). Whole rock major-trace-rare earth element and Sr-Nd-Pb isotope data indicate that the gabbros and basalts have different origins. The gabbros are alkaline and exhibit the geochemical features of OIB, whereas the basalts are tholeiitic and reveal depletions of HFSE that are similar to those of arc rocks. The gabbros are strongly fractionated, and derive from an enriched, lithospheric mantle source, with partial melting occurring in a garnet-stable environment. The basalts are less fractionated, and probably derive from a shallower source in which spinel peridotite was the predominant lithology. Considering all new and old geological, geochemical, geochronological and geophysical data from the Black Sea Basin and the Eastern Pontides-Lesser Caucasus-Alborz Orogenic Belt, we suggest that the alkaline Hayrat gabbro formed in an oceanic intraplate setting, and was accreted to the forearc region of the Eastern Pontides Orogenic Belt during southward subduction of Paleotethyan lithosphere. It was later tectonically juxtaposed with subaqueously erupted, arc-related basalts.

MINERAL CHEMISTRY, WHOLE-ROCK GEOCHEMISTRY AND PETROLOGY OF EOCENE I-TYPE SHOSHONITIC PLUTONS IN THE GÖLKÖY AREA (ORDU, NE TURKEY)

The Eocene intermediate to felsic plutons are widespread in varying sizes and compositions throughout the Eastern Pontides Orogenic Belt in NE Turkey. Of these, two monzonitic bodies (namely the Eriko Tepe and Göl Tepe Plutons) in the Gölköy (Ordu) area, extend nearly in the orientation of NW-SE and E-W and were emplaced into the Upper Cretaceous and/or Eocene volcanic and sedimentary rocks. Petrographically, the studied monzonitic plutons are compositionally fine to medium grained monzonite, monzodiorite and subordinate quartz-monzonite. They consist of plagioclase (An35-67), K-feldspar (Or61-96), quartz, clinopyroxene (Wo28-49En35-51Fs10-25), biotite (Mg#: 0.53-0.73) ± hornblende (Mg#: 0.65-0.82), Fe-Ti oxide with monzonitic, poikilitic, perthitic, rare antirapakivi and graphic textures. Mineral thermobarometer estimations imply that the plutons were crystallized in P-T conditions of mid to shallow crustal levels. Petrochemically, these monzonitic plutons show post-collisional, I-type, metaluminous (A/CNK=0.76-0.93) and shoshonitic features. The whole-rock major oxide and trace element variations suggest that fractionational crystallization played a significant role in the evolution of these monzonitic plutons. The primitive mantle-normalized trace element patterns of the studied plutons are similar to each other with enrichment in large ion lithophile elements, Th, Ce and negative Nb and Ti anomalies. Moreover, the chondrite-normalized rare earth element plots of the plutons show moderately enriched concave-shaped patterns (LaN/LuN=9.3-12.6) with negative Eu anomalies (EuN/Eu*=0.69-0.84), all of which imply plagioclase and clinopyroxene ± hornblende fractionations during their evolution. The geochemical data suggest that the monzonitic plutons have evolved from parental magmas derived from the melts of enriched lithospheric mantle in a post-collisional setting.

The final pulse of the Early Cenozoic adakitic activity in the Eastern Pontides Orogenic Belt (NE Turkey): An integrated study on the nature of transition from adakitic to non-adakitic magmatism in a slab window setting

The Eastern Pontides Orogenic Belt, one of the best examples of a fossil continental arc in the Alpine-Himalayan system, is characterized by adakitic magmatism during the Early Cenozoic. Popular models correlate the adakitic magmatism to syn- or post-collisional processes occurring after the collision between the Eastern Pontides Orogenic Belt and the Tauride Platform at the end of Late Mesozoic and/or beginning of the Cenozoic. We present new geological, petrological and chronological data from andesites and felsic tuffs exposed in the Bayburt area, in the southern part of the Eastern Pontides Orogenic Belt, and discuss the nature of the transition from adakitic to non-adakitic activities in a continental arc. Major, trace and rare earth element concentrations of both andesites and felsic tuffs clearly suggest that they are related to arc magmatism in a continental arc with adakitic composition. The isotopic compositions are permissive of mixing between a component similar to depleted mantle and a second component that is either mafic lower crust or subducted oceanic crust. 39Ar/40Ar hornblende and U/Pb zircon dating indicate that this adakitic magmatism in the Bayburt area ended by about 47Ma, and transformed into non-adakitic, granitoid arc magmatism in the area immediately north of Bayburt in the Lutetian (∼46Ma). Based on our new results in conjunction with available data, we propose that the beginning of northward rollback of a south-directed subducting slab, and simultaneous opening of a slab window related to ridge subduction, triggered both adakitic magmatism for approximately a 10Myr period between 57.6 and 47Ma and arc-parallel extension that caused the opening of the Early Cenozoic sedimentary basins. We also suggest that the shallow marine environment, in which Nummulite-bearing sandy limestones accumulated in the Early Cenozoic, was transformed into a saline-lake environment during the pyroclastic activity that produced the studied felsic tuffs at ∼47Ma.

Petrology and Ar/Ar Chronology of Erdembaba and Kuyucak Volcanics Exposed along the North Anatolian Fault Zone (Eastern Pontides, NE Turkey): Implications for the Late Cenozoic Geodynamic Evolution of Eastern Mediterranean Region

Abstract The Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt (EPOB), which geographically corresponds to the northeastern part of Turkey, is still controversial due to lack of systematic geological, geochemical and chronological data. This paper provides new geochemical and chronological data from the Kuyucak and Erdembaba volcanics exposed along the North Anatolian Fault Zone, which is one of the most seismically-active intracontinental strike-slip fault systems on the globe, in the Reºadiye (Tokat) area that is situated in the southern part of the EPOB. Kuyucak volcanics consist predominantly of basaltic rocks including mainly olivine, augite and plagioclase. Erdembaba volcanics comprise mainly dacite and minor trachydacite-trachyandesite that are composed mainly of augite, plagioclase, hornblende and rarely biotite. The Geochemical properties of the Erdembaba volcanic define small amounts of magma mixing events and it follow a linear trend from a primitive end member through to upper crustal evolution. The 40Ar/39Ar age determinations of whole rock of volcanic rock samples yielded the ages ranging from 1.33 to 6.31 Ma (late Miocene-Pleistocene). Both groups display an enrichment in LIL and LREE elements relative to HFS and HREE elements, strong negative Nb and Ti anomalies. All geochemical and Ar/Ar chronological data indicate that the late Miocene Kuyucak volcanic rocks, which are characterized by low concentrations of SiO2 (&amp;lt;50 wt.%), were generated by mantle-derived magmas that underwent contamination processes during their transfer to the surface. Whereas, Erdembaba volcanic rocks including high concentrations of SiO2 were derived from partial melting of the plunging continental crust beneath the Eurasian plate in Pliocene, after closure of Neotethys ocean that was situated in the southern part of the EPOB.

Geochemical, fluid inclusion and isotopic (O, H and S) constraints on the origin of Pb–Zn ± Au vein-type mineralizations in the Eastern Pontides Orogenic Belt (NE Turkey)

The mineralization area (Altınpınar, Torul–Gümüşhane) is situated in the Southern Zone of the Eastern Pontides Orogenic Belt (EPOB), which is one of the important metallogenic provinces in the Alpine–Himalayan belt and is intruded by the late Carboniferous granitic rocks (Gümüşhane Granitoid), an early to middle Jurassic volcano-sedimentary unit consisting mainly of basaltic–andesitic volcanic and pyroclastic rocks (Şenköy Formation) and Eocene basaltic–andesitic volcanic rocks (Alibaba Formation). The studied Pb–Zn±Au mineralizations are related to silica veins ranging from a few millimeters to a maximum of 40cm in thickness and are localized within fracture zones developed along the contact between the Gümüşhane Granitoid and Şenköy Formation. Silicic, sulfidic, hematitic, argillic, intense chloritic and carbonate alteration are the most common types from the fault lines toward the outer zones. Cavity filling and banded structures are widely observed. The mineral paragenesis comprises galena, sphalerite, pyrite, chalcopyrite, tennantite and quartz. Mineral chemistry studies indicate that ion exchange occurs between Zn and Fe in sphalerites, and the Zn/Cd ratio of sphalerites varies between 50.65 and 144.64. The homogenization temperatures measured from fluid inclusions vary between 170°C and 380°C, especially between 250°C and 300°C, and the wt.% NaCl eqv. salinity of ore-forming fluids is between 2.4 and 7.3 (4.7 on average), supporting an epithermal system in their origin. The values of sulfur isotopes, which are obtained from pyrite and galena minerals, range between −8.3‰ and −2.3‰, indicating that sulfur, which enables mineral formation, originates from magmatic genesis. The average formation temperature of the ore is 317°C as determined with a sulfur isotope geothermometer. The values of oxygen and hydrogen isotopes vary between 8.5‰ and 10.2‰ and −91‰ and −73‰, respectively. With regard to the compositions of oxygen and hydrogen isotopes, fluids comprising the mineralization are formed by the mixture of magmatic water and meteoric water. This situation is supported by the fact that the increase in the homogenization temperature indicates dilution with surface water but depends on the increase in the salinity of fluid inclusions. Considering all the data, it is clear that the studied mineralization is an epithermal vein-type mineralization that is related to granitic magmas.

Where are the remnants of a Jurassic ocean in the eastern Mediterranean region?

The subduction polarity of Tethyan oceanic lithosphere during Jurassic is a controversial topic in relation to the geodynamic evolution of the Alpine–Himalayan system. We present new geological, geochemical and zircon U–Pb data from four different regions of the Eastern Pontides Orogenic Belt, a key area of the Alpine–Himalayan system. We discuss the origin of the magmatism and also the existence of an ocean in the eastern Mediterranean region during the Jurassic period. Jurassic intrusions, predominantly gabbro, tonalite and minor diorite, are well exposed in the southern and axial zones of the orogenic belt. Thermobarometry indicates that high-pressure (6–10kb) crystallization of these intrusions occurred at temperatures of 1183–1250°C. Zircon U–Pb dating from 10 samples show ages between 195 and 165Ma, indicating that magmatism occurred between Sinemurian and Callovian time. We characterize the intrusions from electron microprobe, zircon geochronology, and whole rock and Sr, Nd, and Pb isotopes. Our data show that the studied intrusions are broadly tholeiitic, except for two calc-alkaline bodies, and formed in an arc-related setting with minimal involvement of older crust or sediment.The most widely accepted model proposes that the ultramafic–mafic rocks exposed between the Pontide arc and the Tauride belt are remnants of a Jurassic Penrose-type and/or suprasubduction zone ophiolite. However, new zircon U–Pb age data from mafic lithologies cutting the Kop ultramafic massif do not support this model and clearly indicate that the ultramafic lithologies are Paleozoic or older in age and are not remnants of a Jurassic ocean that known as ‘’Northern Branch of Neotehtys”.