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; Arslan, Mehmet; Siebel, Wolfgang; Sipahi, Ferkan; Ilbeyli, Nurdane; Temizel, Irfan

Late Cretaceous I-type plutons are widespread in the Eastern Pontides, NE Turkey. The studied Camiboǧazi pluton is a composite pluton consisting of diorite, tonalite, monzodiorite, monzonite, quartz monzonite, granite, and mafic microgranular enclaves (MMEs). Laser ablation ICP-MS U-Pb dating of zircon yielded crystallization ages of 76.21±0.79Ma, 75.65±0.50Ma, 75.04±0.83Ma, and 74.73±0.86Ma for diorite, monzodiorite, monzonite, and granite, respectively. The rocks of the pluton have I-type, high-K to shoshonitic and metaluminous character, displaying whole-rock geochemical features of arc-related granites. They are enriched in large-ion lithophile and light rare-earth elements, and depleted in high-field-strength elements. Major element variations can be attributed to fractionation of plagioclase, clinopyroxene, hornblende, and Fe-Ti oxides. The rocks show considerable variation in 87Sr/86Sr(i) (0.70498 to 0.70622), εNd(i) (-2.79 to -0.36), δ18O values (+6.3 to +11.4) and Nd model ages (TDM) (0.81Ga to 1.26Ga). Besides, they have (206Pb/204Pb)=18.44-19.09, (207Pb/204Pb)=15.64-15.69, and (208Pb/204Pb)=38.37-38.89. Although isotope signatures of the mafic microgranular enclaves (MMEs) (87Sr/86Sr(i)=0.70551 to 0.70622; εNd(i)=-2.9 to -1.23; δ18O=+8.3 to +9.7) are largely similar to the host rocks, MMEs are characterized by relatively high Mg-numbers (32-36), low contents of SiO2 (52-56wt.%) and low ASI (0.7-0.9). Estimated crystallization temperatures for the rocks of the pluton range from 735±58°C to 844±24°C and a shallow intrusion depth (<10km) is estimated from Al-in-hornblende thermobarometry. Whole-rock geochemical and isotopic data suggest magma generation by dehydration melting of an amphibolite-type lower crustal component with additional input of a subcontinental lithospheric mantle component. Furthermore, Sr-Nd isotope mixing model reveals ~30% to 40% lower crustal magma contribution to the mantle component.

Temizel, İrfan; Arslan, Mehmet; Abdioğlu, Emel; Yücel, Cem

Monzogabbro stocks including felsic enclaves (monzosyenite) around the Bafra (Samsun) area at the western edge of the Eastern Pontides cut Eocene-aged volcanic and sedimentary units. The monzogabbros contain plagioclase, alkali feldspar, clinopyroxene, olivine, hornblende, biotite, apatite, and iron-titanium oxides, whereas the felsic enclaves contain alkali feldspar, plagioclase, hornblende, biotite, clinopyroxene, and iron-titanium oxides. Mineral chemistry data suggest that magmas experienced hydrous and anhydrous crystallization in deep and shallow crustal magma chambers. Several thermobarometers were used to estimate temperatures of crystallization and emplacement for the mafic and felsic magmas. Clinopyroxene thermobarometry yielded 1100-1232 C and 5.9-8.1 kbar for monzogabbros, and 931-1109 C and 1.8-6.9 kbar for felsic enclaves. Hornblende thermobarometry and oxygen fugacity estimates reveal 739-971°C, 7.0-9.2 kbar and 10−9.71 for monzogabbros and 681-928°C, 3.0-6.1 kbar and 10−11.34 for felsic enclaves. Biotite thermobarometry shows elevated oxygen fugacity varying from 10−18.9-10−11.07 at 632-904°C and 1.29-1.89 kbar for monzogabbros, to 10−15.99 -10−11.82 at 719-873°C and 1.41-1.77 kbar for felsic enclaves. The estimated zircon and apatite saturation temperatures are 504-590°C and 693-730°C for monzogabbros and 765-775°C and 641-690°C for felsic enclaves, respectively. These data imply that several phases in the gabbroic and syenitic magmas did not necessarily crystallize simultaneously and further indicate that the mineral compositions may register intervals of disequilibrium crystallization. Besides, thermobarometry contrasts between monzogabbro and felsic enclave may be partly a consequence of extended interactions between the mafic and felsic magmas by mixing/mingling and diffusion. Additionally, the hot felsic magma was close to liquidus conditions (crystallinity < 30%) when injected into cooler mafic magma (crystallinity > 50%), and thus, the monzogabbro stocks reflect hybrid products from the mingling and incomplete mixing of these two magmas.

Yücel, Cem; Temizel, Irfan; Abdioʇlu, Emel; Arslan, Mehmet; Yaʇcioʇlu, Ufuk Celal

Silica-undersaturated mafic volcanic rocks of Tertiary age in form of lava flows, dikes and sills of tephritic compositions extend along the northern part of the Eastern Pontides. These rocks typically contain Ca-clinopyroxene (Wo32-53En26-54Fs8-24), analcime, Fe-Ti oxides, apatite and minor olivine, plagioclase (An49 - 94), K-feldspar (Or29 - 66), hornblende and phlogopite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic textures. Petrochemical features of the studied rocks, such as enrichment in LILE, depletion in Nb, Ta and Ti and moderate or high LREE/HREE ratios, provide strong evidence for melt production from a subduction-metasomatized lithospheric mantle. Besides, the rocks are characterized by their low K2O contents and low K2O/Na2O ratios as a result of analcimization. Analcime detected in these rocks appears to have formed by pseudomorphic mineral replacement reactions. Euhedral or anhedral analcime crystals, 100 - 600 um in diameter, are set in groundmass and display six-sided polygon or rounded shape and irregular cracks. The analcime pseudomorphs are colourless, milky white to grey and occur in clinopyroxene or in the groundmass. Based on the electron microprobe results, analcimes contain a minor amount of cations other than Na and probably represent the remnants of leucite as marked by K-zoning. X-ray diffraction studies of the analcime-bearing samples confirm the presence of cubic and tetragonal analcime crystals in addition to tetragonal leucite. The presence of Ca-clinopyroxene and plagioclase rather than their sodic equivalents, presence of anhydrous mineral phases and lack of Na differentiation trend as well as partial alteration of the rocks likely supports the secondary growth of analcime either during cooling or after magma solidification.

Kaygusuz, Abdullah; Arslan, Mehmet; Sipahi, Ferkan

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Kaygusuz, Abdullah; Sipahi, Ferkan; Ilbeyli, Nurdane; Arslan, Mehmet; Chen, Bin; Aydinçakir, Emre

A series of Cretaceous plutons is present in the eastern Pontides of northeastern Turkey. The Turnagöl intrusion is the least studied and, thus, the least understood plutons in the orogen. This intrusion consists of hornblende-biotite granodiorites emplaced at 78 Ma based on LA-ICP-MS U-Pb zircon dating. It is of sub-alkaline affinity, belongs to the medium- to high-K calc-alkaline series, and displays features typical of I-type granites. The rocks of the intrusion are enriched in large-ion lithophile elements and light rare earth-elements with negative Eu anomalies (Eu/Eu* = 0.69-0.82), but are deficient in high-field-strength elements. They have a small range of ( 87Sr/86Sr)i (0.7060-0.7063), ÉNdi(-2.6 to -3.1), and δ18O (+8.1 to +9.1) values. Their Pb isotopic ratios are 206Pb/204Pb = 18.63-18.65, 207Pb/ 204Pb = 15.62-15.63, and 208Pb/204Pb = 38.53-38.55. The fractionation of plagioclase, hornblende, and Fe-Ti oxides had key functions in the evolution of the Turnagöl intrusion. The crystallization temperatures of the melts ranged from 758 to 885 C as determined by zircon and apatite saturation thermometry. All these characteristics, combined with the low values of K2O/Na2O and (Na 2O + K2O)/(FeOt + MgO + TiO2), as well as the high values of (CaO + FeOt + MgO + TiO2), suggest an origin by dehydration melting from a metabasaltic lower crustal source.

İlbeyli, Nurdane; Kaygusuz, Abdullah; Arslan, Mehmet; Sipahi, Ferkan

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Kaygusuz, Abdullah; Arslan, Mehmet; Siebel, Wolfgang; Sipahi, Ferkan; Ilbeyli, Nurdane

The northern and southern zones of the eastern Pontides (northeast Turkey) contain numerous plutons of varying ages and compositions. Geochemical and isotopic results on two Hercynian granitoid bodies located in the northern zone of the eastern Pontides allow a proper reconstruction of their origin for the first time. The intrusive rocks comprise four distinct bodies, two of which we investigated in detail. Based on LA-ICP-MS U-Pb zircon dating, the Derinoba and Kayadibi granites have similar 206Pb/ 238U versus 207Pb/ 235U Concordia ages of 311.1 2.0 and 317.2 3.5 million years for the former and 303.8 1.5 million years for the latter. Aluminium saturation index values of both granites are between 0.95 and 1.35, indicating dominant peraluminous melt compositions. Both intrusions have high SiO 2 (74-77 wt.%) contents and show high-K calc-alkaline and I-to S-type characteristics. Primitive mantle-normalized element diagrams display enrichment in K, Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies with L acn/Y bcn=4.6-9.7 and E ucn/Eu*=0.11-0.59 (Derinoba), and L acn/Y bcn=2.7-5.5 and E ucn/Eu*=0.31-0.37 (Kayadibi). These features imply crystal-melt fractionation of plagioclase and K-feldspar without significant involvement of garnet. The Derinoba samples have initial Nd values between-6.1 and-7.1 with Nd model ages and T DM between 1.56 and 2.15 thousand million years. The Kayadibi samples show higher initial Nd (I) values,-4.5 to-6.2, with Nd model ages between 1.50 and 1.72 thousand million years. This study demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios were lowered in some samples by hydrothermal interaction or alteration. Isotopic and petrological data suggest that both granites were produced by the partial melting of early Palaeozoic lower crustal rocks, with minor contribution from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.

Arslan, Mehmet; Şen, Cüneyt; Kaygusuz, Abdullah; Siebel, Wolfgang

Doğu Pontidlerde Eosen yaşlı Torul volkanitlerinin ana, iz element, K-Ar yaş ve Sr-Nd izotop verileri incelenmiştir. İncelenen volkanitler, bazaltik andezit, andezit, trakiandezit ve az oranda da trakidasit ve bunların piroklastiklerinden oluşurlar. Volkanitler plajiyoklas (An2–44), hornblend (Mg#= 0.78–0.98), klinopiroksen (Wo ₄₃₋₄₆ En ₄₁₋₄₃ Fs ₁₀₋₁₅), biyotit, kuvars ve az oranda da sanidin fenokristallerinden oluşurlar. Hornblendlerdeki K-Ar yaşları, 43.99 (±2.59) – 33.45 (±2.32) My aralığında olup, Torul volkanitlerinin Orta–Geç Eosen zamanında oluştuklarını göstermektedir. Torul volkanitleri kalk-alkalen karakterli olup orta–yüksek K içeriğine sahiptirler. Volkanitler büyük iyon yarıçaplı elementler (LILE) ve hafif hafif nadir toprak elementlerce (LREE) zenginleşmiş, yüksek çekim alanlı elementlerce (HFSE) tüketilmişlerdir. Kondrite normalize edilmiş nadir toprak element dağılımları, düşük–orta derecede zengileşmeyle konkav şekilli olup (La _cn/Lu _cn= 4.0–9.8), volkanitleri oluşturan kayaçların benzer kaynaktan itibaren oluştuklarını düşündürmektedir.⁸⁷Sr/⁸⁶Sr(i) değerleri 0.70457–0.70511 arasında olup ¹⁴³Nd/¹⁴⁴Nd(i) değerleri 0.70457–0.70511 arasındadır. Volkanitlerin gelişiminde başlıca fraksiyonel kristallenme, daha az oranda da kabuksal kirlenme ± magma karışımı rol oynamıştır. Tüm bu veriler, volkanitlerin köken magma(lar)sının muhtemelen daha önceki yitim akışkanları tarafından metasomatizmaya uğratılmış zenginleşmiş bir üst manto kaynağından, çarpışma sonrası jeodinamik bir ortamda türeyebileceklerini ifade etmektedir.

Kaygusuz, Abdullah; Arslan, Mehmet; Siebel, Wolfgang; Şen, Cüneyt

Major, trace element, K -Ar age and Sr-Nd isotopic data are presented for the Eocene Torul volcanics in the eastern Pontide orogenic belt (NE Turkey). The studied rocks are composed of basaltic andesitic, andesitic, trachyandesitic, and minor trachydacitic lavas associated with their pyroclastics. These rocks contain plagioclase (An2-44), hornblende (Mg#= 0.78-0.98), clinopyroxene (Wo43-46 En41-43 Fs10-15), biotite, quartz, and minor sanidine phenocrysts. K-Ar ages on hornblendes ages range from 43.99 (±2.59) to 33.45 (±2.32) Ma, within the Middle to Late Eocene. The volcanic rocks show calc-alkaline affinities and have medium to high K contents. They are enriched in large ion lithophile (LILE) and light rare earth elements (LREE), with pronounced depletion of high field strength elements (HFSE). The chondrite-normalized REE patterns (Lacn/Lucn= 4.0-9.8) show low to medium enrichment, indicating similar sources for the rock suite. Initial 87Sr/86Sr values vary between 0.70457 and 0.70511 and initial 143Nd/144Nd values between 0.51264 and 0.51278. The main solidification processes involved in the evolution of the volcanics consist of fractional crystallization with minor amounts of crustal contamination ± magma mixing. All evidence supports the conclusion that the parental magma(s) of the rocks probably derived from an enriched upper mantle, previously modified by subduction- induced metasomatism in a post-collisional geodynamic setting.

Kaygusuz, Abdullah; Siebel, Wolfgang; Ilbeyli, Nurdane; Arslan, Mehmet; Satir, Muharrem; Şen, Cüneyt

Convergent plate margins are the most intense areas of granitoid magmatism on Earth. The Eastern Pontide Magmatic Belt in NE Turkey represents a paleo-arc with numerous quartz diorite to syenite intrusions, ranging in age from 142 to 56 Ma and being composed of K-feldspar, plagioclase, quartz, pyroxene, hornblende, biotite, and Fe-Ti oxides. The granitoids exhibit low- to high-K calc-alkaline, metaluminous to slightly peraluminous I-type features and contain abundant mafic magmatic enclaves (MME). They are characteristically enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE). Chondrite-normalized REE patterns are fractionated (LaN/LuN= 1.49-17.4) with pronounced negative Eu anomalies (Eu/Eu* = 0.46-1.77). Initial 87SrZ86Sr values are between 0.7056 and 0.7079, and εNd(1) values between -5.3 and 1.6. Fractional crystallization, magma mixing/mingling and crustal contamination played an important role during magma evolution. All these characteristics, combined with the low values of K2O/Na2O, Mg-number, ASI and ratios Of Al 2O3/ (FeOT+MgO+TiO2) and (Na 2O+K2O)/(FeOT+MgO+TiO2), suggest an origin by dehydration melting of mafic (amphibolitic) or tonalitic lower crustal source rocks.