Aydin, Faruk; Oğuz Saka, Simge; Şen, Cüneyt; Dokuz, Abdurrahman; Aiglsperger, Thomas; Uysal, İbrahim; Kandemir, Raif; Karslı, Orhan; Sarı, Bilal; Başer, Rasim

The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks. The LCAVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the 87Sr/86Sr(i) (0.7044–0.7071) and ɛNd(i) values (−0.63 to + 3.47) as well as 206Pb/204Pb(i) (18.07–18.56), 207Pb/204Pb(i) (15.57–15.62) and 208Pb/204Pb(i) (37.12–38.55) ratios show very limited variation. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).

Aydınçakır, Emre; Şen, Cüneyt; Bak, Tülay; Yağcıoğlu, Ufuk Celal

Sakarya Zonunun güney kesiminde Bayburt, Amasya-Gümüşhacıköy ve Ankara-Kalecik lokasyonlarında ÜstKretase’nin son dönemlerinde benzer stratigrafik seviyelerde yüzeylenen alkalen volkanitler makroskobik olarak irianalsimleşmiş lösit porfirleri ve iri piroksen porfirleri içeren iki farklı litoloji sunarlar. Bu kayaçlar çarpışma öncesiyaşlı okyanus kabuğunun yitim açısının dikleşmesi sonucu, metasomatizmaya uğramış flogopitce zengin mantokayaçlarının düşük dereceli kısmi ergimesi sonucu oluşan kaynak magmalardan itibaren oluşmuşlardır. Oluşumlarınıizleyen süreçte alkalen magma, kabuk içerisindeki orta/sığ derinliklerdeki magma odalarında diferansiyasyonauğrayarak, iki farklı litolojide yeryüzüne ulaşmıştır.

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.

Sipahi, Ferkan; Sadiklar, M. Burhan; Şen, Cüneyt

The studied volcanic rocks are footwall and hanging wall dacites from the Murgul mine and the surrounding area. Moreover, the hanging wall dacites contain enclaves. Footwall dacite contains biotite, whereas hanging wall dacitic rocks contain hornblende as a ferromagnesian mineral. The enclaves in the hanging wall dacite have sizes that range from 1cm to 20cm and contain hornblende as a ferromagnesian mineral. The volcanic rocks show tholeiitic and transitional affinities. They are rich in large ion lithophile element and light rare earth element with pronounced depletion of high field strength elements. The chondrite-normalized rare earth element patterns (LaN/LuN=1.47-5.12) show low to medium enrichment, which reveal that the rocks were obtained from similar sources in Murgul volcanic rocks. The initial 87Sr/86Sr values range from 0.70442 to 0.70525, and the initial 143Nd/144Nd values range from 0.512741 to 0.512770. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallization with minor amounts of crustal contamination and magma mixing. All geochemical data support that these rocks originated from andesitic magma, and that the parental magma of the rocks were probably derived from an enriched upper mantle, previously modified by subduction-induced metasomatism in a geodynamic setting.

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; Şen, Cüneyt

The Köprübaşi{dotless} intrusion from the eastern Pontides of NE Turkey consists of granodiorite and monzogranite, and contains a number of mafic microgranular enclaves (MMEs). We report here U-Pb zircon age, geochemical and Sr-Nd isotopic data for these rocks in order to determining magma sources and magma production processes. On the basis of U-Pb zircon sensitive high-resolution ion microprobe dating (SHRIMP), the magma emplacement age of the granodiorite is 79.3±1.4Ma. The rocks of the pluton are calc-alkaline, metaluminous to peraluminous characteristics, and display features of I-type granites. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) with negative Eu anomalies (Eu/Eu*=0.60-0.76), but are depleted in high field strength elements (HFSE). They have small range of 87Sr/86Sr(i) (0.7067-0.7070) and e{open}Nd(i) (-3.2 to -4.4) values. Fractionation of plagioclase, hornblende and Fe-Ti oxides played an important role in the evolution of the Köprübaşi{dotless} intrusion. A relatively shallow intrusion depth (∼2-8km) was estimated from the Al-in-hornblende geobarometry. All these characteristics, combined with the low values of K2O/Na2O, SiO2, Al2O3/(FeOT+MgO+TiO2) and (Na2O+K2O)/(FeOT+MgO+TiO2), suggest an origin by dehydration melting from a metabasaltic lower crustal source.

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.

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.

Kaygusuz, Abdullah; Siebel, Wolfgang; Şen, Cüneyt; Satir, Muharrem

The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO2 between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated Lacn/Lucn = 6.0-14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59-0.84). Initial εNd(i) values vary between -3.1 and -4.1, initial 87Sr/86 Sr values between 0.7058 and 0.7072, and δ18O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36-38, low contents of Na2O (2.3-2.5 wt%) and SiO2 (52-55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn = 2.8-3.3; (Tb/Yb)cn = 1.2] and show small negative Eu anomalies (Eu/Eu*= 0.74-0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher 87Sr/ 86Sr (0.7075-0.7079) and lower εNd(i) (-4.5 to -5.3). The syenogranites have high SiO2 (70-74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher Lacn/Lucn (12.9) and Eu/Eu* (0.76-0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [εNd(i) = -4.0 to -3.3; 87Sr/86Sr(i) = 0.7034-0.7060; δ18 O = + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe'Ti oxides played an important role in the evolution of Torul granitoids. The crystallization temperatures of the melts ranged from 800 to 900°C as determined from zircon and apatite saturation thermometry. All these characteristics, combined with low K2 O/Na2O, low Al2O3/(FeOT + MgO + TiO2), and low (Na2O + K2O)/ (FeOT + MgO + TiO2) ratios suggest an origin through dehydration melting of mafic lower crustal source rocks.

Karsli, Orhan; Chen, Bin; Aydin, Faruk; Şen, Cüneyt

The major and trace elements and Sr-Nd-Pb isotopes of the host rocks and the mafic microgranular enclaves (MME) gathered from the Dölek and Sariçiçek plutons, Eastern Turkey, were studied to understand the underlying petrogenesis and geodynamic setting. The plutons were emplaced at ∼ 43 Ma at shallow depths (∼ 5 to 9 km) as estimated from Al-in hornblende geobarometry. The host rocks consist of a variety of rock types ranging from diorite to granite (SiO2 = 56.98-72.67 wt.%; Mg# = 36.8-50.0) populated by MMEs of gabbroic diorite to monzodiorite in composition (SiO2 = 53.21-60.94 wt.%; Mg# = 44.4-53.5). All the rocks show a high-K calc-alkaline differentiation trend. Chondrite-normalized REE patterns are moderately fractionated and relatively flat [(La/Yb)N = 5.11 to 8.51]. They display small negative Eu anomalies (Eu/Eu* = 0.62 to 0.88), with enrichment of LILE and depletion of HFSE. Initial Nd-Sr isotopic compositions for the host rocks are εNd(43 Ma) = - 0.6 to 0.8 and mostly ISr = 0.70482-0.70548. The Nd model ages (TDM) vary from 0.84 to 0.99 Ga. The Pb isotopic ratios are (206Pb/204Pb) = 18.60-18.65, (207Pb/204Pb) = 15.61-15.66 and (208Pb/204Pb) = 38.69-38.85. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.70485 to 0.70517, εNd(43 Ma) - 0.1 to 0.8 and with Pb isotopic ratios of (206Pb/204Pb) = 18.58-18.64, (207Pb/204Pb) = 15.60-15.66 and (208Pb/204Pb) = 38.64-38.77. The MMEs have TDM ranging from 0.86 to 1.36 Ga. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data, in conjunction with the geodynamic evidence, suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, probably triggered by the upwelling of the asthenophere, and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on the Sr-Nd isotope data indicates that ∼ 77-83% of the subcontinental lithospheric mantle involved in the genesis. Consequently, the interaction process played an important role in the genesis of the hybrid granitoid bodies, which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation, en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime.