Arslan, Mehmet; Temizel, İrfan; Krmíček, Lukáš; Yücel, Cem

The Middle Eocene (~43 Ma) and Late Miocene (~6 Ma) lamprophyres cropping out as sills from NE Türkiye can be classified as alkaline lamprophyres. These lamprophyres exhibit moderate contents of K2O (2.22–2.59 and 2.58–2.98 wt%), K2O/Na2O ratios (0.78–1.14 and 0.62–0.94) and Mg# (40.55–46.32 and 56.93–61.52), respectively, and low concentrations of mantle compatible elements. The lamprophyres also have a moderate to relatively high abundance of rare earth elements (ΣREEs = 140–159 and 547–604 ppm, respectively) with significantly fractionated REE patterns (LaN/YbN = 6.82–9.10 and 65.17–71.31, respectively), and are enriched in large-ion lithophile and light REEs but depleted in high-field-strength and heavy REEs. The lamprophyres have homogeneous and moderately low (87Sr/86Sr)i of 0.705048–0.705474 and 0.705252–0.705401, and nearly uniform εNd(i) values varying from −0.47 to 0.20 and 0.54 to 0.79 and εHf(i) values varying from 4.51–6.71 and 5.83–6.18, respectively. They also have a narrow and moderately high Δ7/4Pb range of 6.19–15.41 and 10.62–10.88 and Δ8/4Pb range of 49.56–56.14 and 46.86–47.99, respectively. Petrological modelling suggests that the parental magmas of both the Eocene and Miocene lamprophyres were generated by the low-degree partial melting of phlogopite-bearing spinel-garnet and amphibole-bearing garnet lherzolite sources, respectively. By integrating whole-rock trace elements and isotope compositions with regional geological observations, we propose that the post-collisional Middle Eocene and Late Miocene lamprophyres in the Eastern Pontides Orogenic Belt originated from the juvenile subcontinental lithospheric mantle sources metasomatized initially by Neotethyan subduction-related fluids during the Eocene, and subsequently overprinted by delaminated lithosphere-derived carbonate components in the Miocene. The lamprophyres likely record a temporal magmatic response to lithospheric delamination and regional thermal upwelling associated with Eocene extensional tectonics, followed by lithospheric thinning during the Miocene in a post-collisional tectonic setting.

Arslan, Mehmet; Temizel, İrfan; Ackerman, Lukáš; Yücel, Cem; Yazar, Emel Abdioğlu

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.

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.

Kaygusuz, Abdullah; Arslan, Mehmet; Temizel, İrfan; CemYücel; Aydınçakır, Emre

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.

Kaygusuz, Abdullah; Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Yi, Keewook; Jeong, Youn-Joong; Siebel, Wolfgang; Sipahi, Ferkan

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.

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.

Çakmak, Gökhan; Temizel, İrfan; Kaygusuz, Abdullah; Arslan, Mehmet; Sipahi, Ferkan

Doğu Pontid güney zonunda (Bayburt) Eosen yaşlı intrüzif kayaçlar bulunmaktadır. Bu bölgede, bugüne kadar yaşları kesin olarak tanımlanamayan sokulumların ve içlerindeki mafik mikrogranüler anklavlar (MMA)?ın mineralojik bileşimleri, tüm kayaç jeokimyasal, Sr-Nd-Pb-O izotopik özellikleri ve radyometrik yaşları ortaya konulmuştur. İncelenen plütonik kayaçların U Pb SHRIMP zirkon yaşları 43.14 ± 0.54 ila 45.81 ± 0.48 My arasında değişir. Bu kayaçlar yaklaşık KD-GB uzanımlı olup, boyutları 3-22 km2 arasında değişir. Bileşimleri diyoritten granite kadar değişmekte olup, başlıca mineralleri plajiyoklas (An02-68), ortoklas (Or01-96), amfibol (Mg#=0.03-0.93), kuvars, biyotit (Mg#=0.49-0.62), piroksen (En37-57 Fs12-45 Wo2- 48), magnetit ve ilmenit oluşturur. Genel olarak I-tipi, düşük-yüksek K?lu kalk-alkali, genellikle metalümin az oranda da peralümin karakterlidirler. Kondirite göre normalleştirilmiş nadir toprak element dağılımları konkav şekilli (LaN/LuN=2.53?12.22) olup, negatif Eu anomalisi (Eu/Eu*=0.31?0.92) gösterirler. Ana ve iz element değişimleri, kayaçların gelişiminde plajiyoklas, amfibol, piroksen ve Fe-Ti oksit fraksiyonlaşmasının etkili olduğunu gösterir. Kayaçların ?Nd(i) değerleri ?1.34 ve 0.92, 87Sr/86Sr(i) değerleri 0.7049 ve 0.7056 arasındadır. 206Pb/204Pb(i), 207Pb/204Pb(i) ve 208Pb/204Pb(i) içerikleri sırasıyla 18.43?18.69, 15.59?15.63 ve 38.44?38.83 arasındadır. İncelenen örneklerdeki ?18O değerleri ? 4.8 ila ? 8.8 arasında olup, I-tipi granitoyidlere benzer bileşime sahiptirler. Tüm veriler, incelenen plütonik kayaçların ana magmasının litosferik mantodan türediğini, kabuksal kayaçların katkısının nisbeten az olduğunu gösterir. İncelenen plütonik kayaçların içindeki MMA?lar diyorit, gabrodiyorit ve tonalit bileşimli olup, orta-yüksek K?lu metalümin karakterde ve ana kayadan daha düşük A/CNK (0.77-0.97) ve SiO2 (% 55-64) ve daha yüksek Na2O/K2O (4.9-7.2) oranlarına sahiptirler. İzotopik özellikleri dikkate alındığında, MMA?lar ana kayaçlara benzer Sr-Nd-Pb-O izotopik bileşimlere sahip olup, onlara nazaran daha düşük 143Nd/144Nd(i) (0.51253-0.51263) ve ?18O (6.1-7.4) değerlerine sahiptirler. Tüm bu veriler dikkate alındığında, MMA?lar ana kaya içerisinde soğumuş olan eş yaşlı mafik magmanın küçük kütlelerini temsil eden magma karışım ürünleri olarak kabul edilebilirler. İncelenen plütonlar ve içlerindeki MMA?larda hesaplanan kristalizasyon basınçları birbirine yakın değerlerde olup, ana kayaçlarda 0.1?2.6 kbar, MMA?larda ise 0.1?2.9 kbar arasındadır. Kristallenme sıcaklıkları ise ana kayaçlarda 506-1172 °C, MMA?larda ise 467-1155 °C arasında değişmektedir. Tüm bu veriler Eosen yaşlı plütonik kayaçların nisbeten sığ derinliklere (~ 5 to 9 km) yerleşmiş olduklarını ifade eder.

Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Abdioğlu Yazar, Emel; Ruffet, Gilles

The Eocene and Miocene volcanic rocks between the cities of Trabzon and Giresun in the Eastern Pontides (NE Turkey) erupted as mildly and moderately alkaline magmas ranging from silica-saturated to silica-undersaturated types. 40Ar-39Ar dating and petrochemical data reveal that the studied volcanic rocks are discriminated in two: Lutetian (Middle Eocene) mildly alkaline, (basaltic rocks: 45.31 ± 0.18 to 43.86 ± 0.19 Ma; trachytic rocks: 44.87 ± 0.22 to 41.32 ± 0.12 Ma), and Messinian (Late Miocene) moderately alkaline volcanic rocks (tephrytic rocks: 6.05 ± 0.06 and 5.65 ± 0.06 Ma). The trace and the rare earth element systematic, characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios in the Eocene basaltic and trachytic rocks, high LREE/HREE ratios in the Miocene tephrytic rocks, and different degrees of depletion in Nb, Ta, Ti coupled with high Th/Yb ratios, show that the parental magmas of the volcanic rocks were derived from mantle sources previously enriched by slab-derived fluids and subducted sediments. The Sr, Nd and Pb isotopic composition of the Eocene and Miocene volcanic rocks support the presence of subduction-modified subcontinental lithospheric mantle. During the magma ascent in the crust, parental magmas of both the Eocene and Miocene volcanic rocks were mostly affected by fractional crystallisation rather than assimilation coupled with fractional crystallisation and mixing. The silica-undersaturated character of the Miocene tephrytic rocks could be attributed to assimilation of carbonate rocks within shallow-level magma chambers. The parental magmas of the Eocene volcanic rocks resulted from a relatively high melting degree of a net veined mantle and surrounding peridotites in the spinel stability field due to an increase in temperature, resulting from asthenospheric upwelling related to the extension of lithosphere subsequent to delamination. The parental magmas for the Miocene volcanic rocks resulted from a relatively low melting degree of a net veined mantle domain previously modified by metasomatic melts derived from a garnet peridotite source after decompression due to extensional tectonics, combined with strike-slip movement at a regional scale related to ongoing delamination.

Kaygusuz, Abdullah; Arslan, Mehmet; Sipahi, Ferkan; Temizel, İrfan

Numerous intrusive rocks of varying ages and compositions exist in the Paleozoic to Tertiary periods in the Eastern Pontides. Carboniferous intrusive rocks are commonly observed in the southern part of the Eastern Pontides. The nature of the rocks in the northern part of the region has not been determined because of Upper Cretaceous and Tertiary volcano-sedimentary units. Whole-rock geochemical, isotopic and geochronological data obtained from five different mapped granitoid bodies located in the northern part of the Eastern Pontides allow for the proper reconstruction of Carboniferous magmatism and the geodynamic evolution of the region. According to laser ablation ICP-MS U–Pb zircon dating, the Özdil, Soğuksu, Seslikaya, Kızılağaç and Şahmetlik plutons have similar 206Pb/238U vs. 207Pb/235U concordia ages of 340.7 ± 1.8 Ma and 323.1 ± 1.5 Ma, 348.4 ± 1.6 Ma, 335.4 ± 1.4 Ma, 337.2 ± 0.6 Ma and 334.5 ± 1.4 Ma, respectively. The aluminium saturation index (ASI) values of all of the samples from the plutons are between 1.0 and 1.32, which indicate peraluminous melt compositions. The plutons have SiO2 contents between 59 and 79 wt.% and show low- to high-K calc-alkaline characteristics. The plutons are enriched in large-ion lithophile and light rare earth elements and are depleted in high-field strength elements. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies, with LaCN/YbCN = 1.9–46.8 and EuCN/Eu* = 0.19–1.76. The studied plutons show considerable variations in 87Sr/86Sr(i) (0.70255 to 0.71006) and εNd(i) values (− 4.8 to − 7.1), as well as Nd model ages (1.15 to 2.47 Ga). The Pb-isotopic ratios are 206Pb/204Pb = 17.11–18.60, 207Pb/204Pb = 15.58–15.64 and 208Pb/204Pb = 36.95–38.62. The crystallization temperatures of the melts range from 676 to 993 °C, as determined by zircon and apatite saturation thermometry. These data suggest that the Carboniferous granitic magmas were produced by the partial melting of meta-mafic to meta-felsic lower crustal source rocks, with minor contributions from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the northern part of the Eastern Pontides.

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.