Temizel, İrfan; Arslan, Mehmet; Abdioğlu Yazar, Emel; Aslan, Zafer; Kaygusuz, Abdullah; Baki Eraydın, Tuğba

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[sbnd]Ti oxides, whereas the hornblende gabbro includes mainly plagioclase, hornblende, rarely biotite and Fe[sbnd]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[sbnd]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 (LaN/LuN = 0.94–2.56) with positive Eu anomalies (EuN/Eu* = 1.15–2.14; except for two pyroxene gabbro samples). The gabbroic rocks have 87Sr/86Sr(i) ratios (0.704533 to 0.706265), εNd(i) values (4.04–4.85), 206Pb/204Pb (18.56–18.68) and 207Pb/204Pb (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.

Temizel, Irfan; Arslan, Mehmet; Yücel, Cem; Abdioğlu Yazar, Emel; Kaygusuz, Abdullah; Aslan, Zafer

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.

Temizel, İrfan; Arslan, Mehmet; Yücel, Cem; Yazar, Emel Abdioğlu; Kaygusuz, Abdullah; Aslan, Zafer

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 (La N /Lu N = 10.3–10.7 for the Direkli pluton; La N /Lu N = 6.8–11.7 for the Yeniköy Tepe pluton) with negative Eu anomalies. The plutons have 87 Sr/ 86 Sr ratios (0.705368–0.706954), 143 Nd/ 144 Nd ratios (0.512600–0.512672), 206 Pb/ 204 Pb ratios (19.29–19.52) and 207 Pb/ 204 Pb 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.

Kaygusuz, Abdullah; Aslan, Zafer; Aydınçakır, Emre; Yücel, Cem; Gücer, Mehmet Ali; Şen, Cüneyt

This paper presents Sr-Nd-Pb isotopic and whole-rock geochemical data of Miocene to Pliocene volcanic rocks in the Eastern Anatolia (Turkey) aiming to unravel their sources and evolutionary history. The wide compositional range of lavas and pyroclastics includes basaltic andesite, basaltic trachyandesite, trachyandesite, andesite and trachydacite. These calc-alkaline volcanics are enriched in large ion lithophile elements and light rare earth elements and depleted in the high field strength elements. Sr-Nd isotope data indicate low values for 87Sr/86Sr(i) (0.70432–0.70464) and high values for 143Nd/144Nd(i) (0.51272–0.51282). Further, these data are within the mantle array of the isotope ratio diagram. The lead (Pb) isotopic compositions (206Pb/204Pb(i) = 18.33 to 18.62, 207Pb/204Pb(i) = 15.51 to 15.60, 208Pb/204Pb(i) = 38.10 to 38.45) reveals the presence of an enriched source. The main petrological processes involved fractional crystallization and the mixing of at least two fractionated magmas having same source characteristics. All evidence supports the findings that the Kandilli volcanic rocks were derived from a partial melting of the both spinel and garnet bearing subcontinental lithospheric mantle, which had been previously metasomatized by mostly fluids derived from subducted slab during the collisional and post-collisional extension-related geodynamic setting in the Eastern Anatolia region of Turkey.

Temizel, Irfan; Abdioǧlu Yazar, Emel; Arslan, Mehmet; Kaygusuz, Abdullah; Aslan, Zafer

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 NWSE 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 wholerock 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.

Gücer, Mehmet Ali; Aslan, Zafer

The Yoncayolu Metamorphic Rocks (YMR), exposed in the Sakarya zone (Erzincan, NE Turkey), consists mainly of greenschist rocks which are chlorite schists, muscovite-chlorite schists, metabasic rocks and lesser extent of pyhllites and calc-schists. All YMR are fine-grained, weakly foliated and often cut by quartz veins. The common mineral assemblage is chlorite+albite+epidote+quartz+/-clinozoisite+/-actinolite+/-opaques. Geochemically, protoliths of the YMR resemble calc-alkaline volcanic arc rocks. The YMR have high contents of large ion lithophile elements (LILEs) and low contents of high field strength elements (HFSEs) similar to mid-ocean ridge basalt (MORB). (La/Lu)(CN) values are between 0.26 and 6.16. The REE patterns show slight or no Eu anomalies (Eu-CN/Eu* of 0.48 to 1.13), suggesting minor plagioglase fractionation. 40Ar-39Ar dating on plagioclases from the metabasic samples of the YMR gave ages of 100.8+/-3.4 Ma (Albian) and 94.1+/-3.3 Ma (Cenomanian), suggesting that metamorphism was related to the closure of the Neo-Tethyan Ocean. Metamorphism took place during subduction of the Neo-Tethyan Ocean between similar to 90-70 Ma. Chlorite geothermometry yielded a temperature of 320-350 degrees C and a pressure around 4 kbar. All these findings lend support for greenschist facies metamorphic conditions during the formation of the YMR.

Aslan, Zafer; Arslan, Mehmet; Temizel, Irfan; Kaygusuz, Abdullah

Volcanic rocks from the Gümüşhane area in the southern part of the Eastern Pontides (NE Turkey) consist mainly of andesitic lava flows associated with tuffs, and rare basaltic dykes. The K-Ar whole-rock dating of these rocks range from 37.62 ± 3.33 Ma (Middle Eocene) to 30.02 ± 2.84 Ma (Early Oligocene) for the andesitic lava flows, but are 15.80 ± 1.71 Ma (Middle Miocene) for the basaltic dykes. Petrochemically, the volcanic rocks are dominantly medium-K calc-alkaline in composition and show enrichment of large ion lithophile elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magmas derived from an enriched mantle source. Chondrite-normalized rare-earth element patterns of the volcanic rocks are concave upwards with low- to-medium enrichment (LaCN/LuCN = 3.39 to 12.56), thereby revealing clinopyroxene- and hornblende-dominated fractionations for andesitic-basaltic rocks and tuffs, respectively. The volcanic rocks have low initial 87Sr/86Sr ratios (0.70464 to 0.70494) and εNd(i) values (+1.11 to +3.08), with Nd-model ages (TDM) of 0.68 to 1.02 Ga, suggesting an enriched lithospheric mantle source of Proterozoic age. Trace element and isotopic data, as well as the modelling results, show that fractional crystallization and minor assimilation played an important role in the evolution of the volcanic rocks studied. The Eocene to Miocene volcanism in the region has resulted from lithospheric delamination and the associated convective thinning of the mantle, which led to the partial melting of the subduction-metasomatized lithospheric mantle.

Kaygusuz, Abdullah; Chen, Bin; Aslan, Zafer; Siebel, Wolfgang; Şen, Cüneyt

The petrogenesis and U-Pb SHRIMP zircon ages of the Late Cretaceous Sariosman pluton in the Eastern Pontides is investigated by means of whole-rock Sr-Nd isotope data with field, petrographic and whole-rock geochemical studies. The bulk of the I-type Sariosman pluton consists of biotite-hornblende monzogranite, with minor quantities of porphyritic hornblende-biotite monzogranite. The biotite-hornblende monzogranite contains a number of mafic microgranular enclaves (MMEs) of quartz monzodiorite composition. U-Pb zircon sensitive high-resolution ion microprobe dating (SHRIMP) dates the magma emplacement age of the biotite-hornblende monzogranite at 82.7±1.5 Ma. The rocks of the pluton show high-K calc-alkaline, metaluminous to slightly peraluminous characteristics, and are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE), thus displaying features of arc-related granitoids. Chondrite-normalised rare earth-element (REE) patterns have concave upward shapes (Lacn/Lucn= 10.1-17.4) with pronounced negative Eu anomalies (Eu/Eu*= 0.61-0.80). Initial εNd values vary between -3.0 and -4.1 and initial 87Sr/86Sr values between 0.7062 and 0.707. The MMEs are characterised by higher Mg-numbers (27-29) and lower values of both SiO2 (56-58 wt%) and aluminium saturation index (0.9-1.0), compared to the monzogranites. Fractionation of plagioclase, hornblende and Fe-Ti oxides played an important role in the evolution of the Sariosman pluton. The crystallisation temperatures of the melts ranged from 700 to 800 °C and a relatively shallow intrusion depth (~2 to 7 km) is estimated from the Al-in-hornblende geobarometry. The geochemical and isotopic compositions of the Sariosman pluton suggest an origin through dehydration melting of mafic lower crustal source rocks.

Aydin, Ali; Ferré, Eric C.; Aslan, Zafer

The magnetic susceptibility of rocks is determined by their bulk chemistry and magnetic mineralogy. In this case study of the Saruhan pluton in Turkey, a detailed survey based on 925 field measurements and 37 whole rock analyses, reveals a strong correlation between magnetic susceptibility and FeOt (R2 = 0.8). Petrographic observations and calculations based on whole-rock major element analyses indicate the presence of magnetite grains. Further calculations show that magnetite accounts for 88% of the magnetic susceptibility. The spatial correlation between FeOtotal and the magnetic susceptibility is particularly spectacular which suggests that Km is a proxy for geochemical differentiation. The zoning pattern of magnetic susceptibility across the pluton is concentric and reverse, with the highest values of magnetic susceptibility in the center. This type of zoning is consistent with a previously proposed petrogenetic model. The comparison of the Saruhan granites with a classic example of paramagnetic granites reveals two contrasted FeOt-Km trends. This suggests that these variations can be a useful tool to distinguish between leucocratic paramagnetic and leucocratic ferrimagnetic granites.

Arslan, M.; Aslan, Z.

Granitic intrusions in Eocene and post-Eocene volcanic rocks outcrop in the Northern and Southern Zones of the Eastern Pontides, NE Turkey. Intrusions in the Northern Zone extend NW-SE whereas those in the Southern Zone are nearly E-W orientated. The contacts of the intrusions with the volcanic rocks are sharp, epidotized and include volcanic xenoliths. The margins of Southern Zone intrusions often contain abundant angular mafic microgranular enclaves of diorite to quartz diorite composition. The rocks also show evidence of mingling and mixing between coeval mafic and felsic magmas. Field observations suggest a stopping type of ascent and emplacement style for the intrusions. Petrographically, intrusions show variations in both colour and mineralogy with fine to medium granular, monzonitic, poikilitic, rapakivi, anti-rapakivi and graphic textures. Based on modal mineralogy, the Northern rocks are monzonite, quartz monzonite, monzodiorite and quartz monzodiorite whereas the Southern samples are monzogranite and granodiorite. The rocks are generally calc-alkaline to mildly alkaline transitional and metaluminous, and show a CAFEMIC trend. The Northern Zone intrusions form a post-collisional, A-type, alkaline monzonitic association and Southern Zone intrusions form a post-collisional, I-type, granodioritic calc-alkaline-transitional association. Whole-rock compositional data indicate that differentiation occurred via fractional crystallisation with or without magma mixing. Incompatible and rare earth element patterns indicate that both the Northern and the Southern Zone intrusions were derived from melting of a mantle region enriched by subduction-related fluids but evolved differently during ascent and emplacement. U-Pb zircon dating in the Southern Zone yields an intrusion age of 44.4±0.3 Ma. Regional geodynamics indicates post-collisional extensional tectonics in the region. Crustal involvement and the level of emplacement may have been important for magmatic evolution, especially for the Southern Zone intrusions, after the cessation of subduction and subsequent crustal thickening.