Sipahi, Ferkan; Akpınar, İbrahim; Gücer, Mehmet Ali; Kaygusuz, Abdullah; Vural, Alaaddin; Saydam Eker, Çiğdem

The Kopuz Fe skarn deposit in the eastern Sakarya Zone is genetically associated with the 44–45 Ma Kopuz granitoid. The Fe ores are hosted within the contact zone between this granitoid and Jurassic Lower Cretaceous limestone. The deposit is characterized by both endo- and exoskarn zones, which exhibit a diverse range of minerals including clinopyroxene, plagioclase, amphibole, biotite, garnet, epidote, phlogopite, magnetite, hematite, pyrite, quartz, calcite, actinolite, limonite, and goethite. Magnetite and hematite, accompanied by small amounts of pyrite, are primarily ore minerals. Pyroxene types observed in the mineralization include diopsidic hedenbergite in the endoskarn zone and diopside in the exoskarn zone. Plagioclase in the endoskarn zone vary from oligoclase to Labrador in composition, which transition towards Na-rich plagioclase and orthoclase in the ore-bearing exoskarn zone. Amphiboles, primarily calcic in nature, are classified as Mg-hornblende and actinolite, with low F and Cl contents, indicating minimal F enrichment during Fe-skarn formation. Garnet is characterized by andradite in the exoskarn zone close to the endoskarn and grossular-andradite in the distal exoskarn zone. The increase of Ad/Gr ratios in zoned garnet indicate an increasing ƒO2 value outward from it. Considering that rare pyrite occur together with magnetite and hematite, we suggest that the deposit formed under conditions of low ƒS2 and high ƒO2 conditions. The homogenization temperature and salinity of the fluid inclusions in quartz from the exoskarn zone vary from 224 °C to 349 °C and 4.18 % (wt% NaCl equiv.), respectively. The oxygen isotope composition (5.10 ‰ to 7.86 ‰) of the fluids in equilibrium with magnetite and quartz minerals in the exoskarn zone supports a magmatic fluid origin. The oxygen isotopic signatures of epidote and amphibole further indicate a minor interaction with an additional source, likely meteoric waters. The sulfur isotope composition of pyrite (2.3 ‰) is consistent with a magmatic sulfur source. In summary, the middle Eocene-aged Kopuz Fe skarn deposit occurred a shallow depth within a magmatic arc, where oxidized conditions predominated.

Cimen, Okay; Gucer, Mehmet Ali; Akal, Cueneyt; Goncueoglu, Mehmet Cemal; Arslan, Mehmet; Simonetti, Antonio; Karaoglan, Fatih

The pre -Jurassic tectonic evolution of the Central Pontides in northern Turkey is still poorly understood due to the lack of detailed geochemical and geochronological data from the basement units. Therefore, this study reports for the first time combined whole rock geochemistry, trace element data and U-Pb ages for detrital zircons, and Ar-Ar geochronological data from the metasedimentary rocks of the Devrekani Massif, Geme Complex, and the Serve & ccedil;ay Unit to better understand their provenance, depositional age characteristics, and tectonic evolutions. The detrital zircon U-Pb data of metasedimentary units from the Devrekani Massif, Geme Complex, and the Serve & ccedil;ay Unit yield ca. 191, 185 and 298 Ma maximum depositional ages (youngest age peaks), respectively. The Devrekani Massif is dominated by Permo-Carboniferous-aged detrital zircons (67 %), whereas Neoproterozoic and Devonian -aged detrital zircons are more common in the Geme Complex (47 %) and the Serve & ccedil;ay Unit (53 %). These distinct age distributions clearly indicate that the Devrekani Massif may has been deposited in a dissimilar location compared to the Geme Complex and the Serve & ccedil;ay Unit. Furthermore, in contrast to the Devrekani Massif, the source area of the metasedimentary rocks from the Geme Complex is comparable with that of the Serve & ccedil;ay Unit. Lastly, the obtained detrital zircon U-Pb and mica Ar-Ar ages suggest that the Devrekani Massif and the Geme Complex were deposited and metamorphosed during the Early and Middle Jurassic, respectively. The Serve & ccedil;ay Unit was deposited and metamorphosed in the Permian.

Dokuz, Abdurrahman; Alçiçek, Mehmet Cihat; Tunçdemir, Vahdet; Kandemir, Raif; Aydinçakir, Emre

The processes that caused removal of the upper Carboniferous to Permian sediments in the eastern Sakarya Zone, Turkey, are modeled by using of geochemical data and LA-ICP-MS U-Pb ages from detrital zircons. A felsic provenance and passive margin setting during the deposition of the upper Carboniferous catalcesme sediments are inferred from the geochemistry of sandstones (SiO2 > 85 wt%). Chemical Index of Alteration (CIA) values (75 - 81) indicate warm and humid climatic conditions and tectonic tranquility during deposition. Fifty-three (58%) concordant zircon grains produce a youngest age population in the range of 308.7 +/- 4.4 to 342.1 +/- 6.9 Ma, typical for the Variscan events. The burgundy color and upward-fining in clast size and bed thickness are the most prominent features of the concordantly overlying Hardisi Formation. Geochemistry (SiO2 = 66-81 wt%) and CIA values (58-65) of the clastic rocks point to a subduction-related tectonic setting and increasing rate of erosion in the source area. We highlight that the catalcesme sediments were deposited in a back-arc basin opened to the south of a continental ribbon separated from Gondwana. Approaching of the Paleotethyan mid-ocean ridge to the subduction zone was resulted in flattening in subducting slab, which in turn caused the back-arc basin to migrate into the interior parts of Gondwana and the former back-arc basin to evolve into a lacustrine setting. Increase in the elevation of source areas was resulted in an increase in the rate of physical erosion and trans-portation of burgundy Hardisi clastic sediments into the lacustrine basin.

Karsli, Orhan; Dokuz, Abdurrahman; Aydin, Faruk; Uysal, Ibrahim; Sengün, Firat; Kandemir, Raif; Santos, Jose Francisco; Andersen, Tom

The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.

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).

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.

Öztürk, Serkan; Şahin, Şakir

In this study, a detailed space-time-magnitude assessment on the aftershock sequence of July 21th, 2017, M W 6.5, Bodrum-Kos earthquake (Turkey) is carried out by focusing on the analyses of aftershock parameters: b-value, p-value, Dc-value and Mamax. b-value is estimated as 0.90 ± 0.05 with a completeness magnitude Mc = 1.6 and this relatively small b-value may be resulted from the abundance of aftershocks with magnitude M L ≥ 4.0. However, it is well represented by the Gutenberg-Richter law with a typically b ≈ 1.0. p-value is estimated as 1.04 ± 0.02 with a c-value = 0.224 ± 0.039 and is well characterized nearly close to the global p ≈ 1.0. This relatively high p-value may be a result of the relative fast decay rate of the aftershock activity. Dc-value is calculated as 1.74 ± 0.09 and it means that aftershocks are homogeneously distributed. Temporal distribution of b-value shows that small b-values may be due to a stepwise increase in effective stress before the occurrence of larger aftershocks. Regional changes range from 0.5 to 1.2 in b-value, from 0.4 to 1.3 in p-value and from 3.0 to 5.2 in Mamax. The smallest b-values are found in and around mainshock, including Karaada, Bodrum, Akyarlar and Turgutreis, and these regions have high stress as well as coseismic deformation. The largest p-values are found in and around the mainshock epicenter including Karaada, and it is interpreted that this situation may be caused by coseismic deformation. Mamax values larger than 4.4 are observed in and around mainshock epicenter, including Bodrum and Akyarlar, and there is a clear correlation between spatial variations of b-values and Mamax. These results show that stress changes and coseismic deformation seem highly effective on b and p-value variations. Therefore, a special interest needs to be given to these anomaly regions since aftershock hazard is highly associated with these parameters and may be developed considering their space-time-magnitude distribution.

Gücer, Mehmet Ali; Arslan, Mehmet; Çimen, Okay; Sherlock, Sarah C.

The Devrekani Massif in the northern part of the Central Pontides (Northern Turkey) provides important clues to the regional tectonics and geodynamic processes associated with Jurassic high grade metamorphic conditions. This study reports new paragenetic assemblages, mineral compositions, whole-rock geochemistry and 40Ar-39Ar geochronological data from the paragneisses in the massif, and, discusses the P–T conditions and geodynamic implications of the Jurassic metamorphism during continental extension in the Central Pontides. Upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif. Within these, there are five different mineral parageneses with diagnostic mineral assemblages of: quartz, K-feldspar (An0-1Ab4-26Or73-96), plagioclase (An18-35), biotite [XPhl: 0.28–0.57; Mg/(Mg + Fe2+): 0.33–0.61], sillimanite, cordierite [Mg/(Mg + Fe2+): 0.48–0.71] and garnet (Alm43-80Grs0-18Prp5-23And0-4Sps10-33) with minor hercynite. Based on Na-in-Crd thermometry and GASP barometry results, the peak metamorphic conditions are 775 ± 25 °C and 6 ± 1 kbar in the massif. The field relations, petrography and bulk chemical data suggest that the paragneisses, derived from shale-wackestone and pelitic sedimentary protoliths, are typical rock lithologies of an active continental margin. They display enrichments in LILE over HFSE, coupled with negative Nb and Ti anomalies, which are geochemical signatures of subduction-related sources. It is likely that the peak metamorphism took place during the Middle–Upper Jurassic period (ca. 174–156 Ma), suggesting that the metamorphic rocks cooled to 300–350 °C at ca. 156 Ma. The mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite-garnet-K-feldspar zone. The petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano-sedimentary successions. We conclude that the Devrekani Massif represents the products of pre-Jurassic sedimentation, and Permo-Carboniferous continental arc magmatism, overprinted by Jurassic metamorphism.

Uysal, Ibrahim; Dokuz, Abdurrahman; Kapsiotis, Argyrios; Saka, Samet; Karsli, Orhan; Kaliwoda, Melanie; Mueller, Dirk

The eastern Orhaneli ophiolite in NW Anatolia (Turkey) consists of voluminous dunite and minor harzburgite intruded by clinopyroxenite veins. Harzburgite contains spinel of low Cr# [100 x Cr/(Cr + Al) = 40-45] and diopside of low Al2O3 and TiO2 contents, whereas dunite contains spinel of higher Cr# (62-82) and diopside (blebs) (even more) depleted in Al2O3 and TiO2 (than harzburgite). The concentrations of Heavy Rare Earth Elements (HREE) in harzburgite are consistent with derivation of this type of peridotite from 19% dry melting of a fertile mantle protolith at a MOR regime. Dunites have lower concentrations of HREE than harzburgite implying that dunites were generated by higher degrees (> 30%) of (cumulative) melting of the same protolith. Furthermore, the characteristic U-shapes of the chondrite-normalized REE-patterns of dunites indicate the involvement of hydrous melt-peridotite interaction processes in their genesis. Nevertheless, a set of mosaic-in texture dunite samples contain olivine that has lower Fo# [100 x Mg/(Mg + Fe2+)] and NiO contents than olivine in harzburgite. These dunites are probably of cumulate origin as it is also indicated by their enrichment in Pt and Pd (<= 17.92 ppb). Micro-textural and Re-Os isotopic data support that clinopyroxenite intrusions do not have a pure magmatic origin and their formation was partly controlled by metasomatic processes. Overall data indicate that the eastern Orhaneli ultramafic rocks have a complex petrological history including various stages of partial melting, metasomatism and magmatism in an evolving from MOR to SSZ geotectonic setting.

Akaryali, Enver; Akbulut, Kübra

The Eastern Pontide Orogenic Belt (EPOB) constitutes one of the best examples of the metallogenic provinces in on the Alpine-Himalayan belt. This study focuses on the genesis of the Ünlüpinar Pb-Zn. ±. Au deposit in the southern part of the Eastern Pontide Orogenic Belt. The main lithological units in the study area are the Early Carboniferous Kurtoğlu Metamorphic Complex the Late Carboniferous Köse Granitoid and the Early-Middle Jurassic Şenköy Formation. The studied deposit is hosted by the Şenköy Formation, which consists predominantly of basaltic-andesitic rocks and associated pyroclastic rocks that are calc-alkaline in composition. Silicic, sulfidic, argillic, chloritic, hematitic, carbonate and limonite are the most obvious alteration types observed in the deposit site. Ore microscopy studies exhibit that the mineral paragenesis in deposits includes pyrite, chalcopyrite, sphalerite, galena, gold, quartz and calcite. Electron microprobe analyses conducted on sphalerite indicate that the Zn/Cd ratio varies between 84 and 204, and these ratios point at a hydrothermal deposit related to granitic magmas. Fluid inclusion studies in calcite and quartz show that the homogenization temperature of the studied deposit ranges between 90-160. °C and 120-330. °C respectively. The values of sulfur isotope analysis of pyrite, sphalerite and galena minerals vary between 1.6‰ and 5.7‰, and the results of oxygen and carbon isotope analysis range between 8.4‰ and 18‰ and -5‰ and -3.6‰, respectively. The average formation temperature of the ore was calculated as 264. °C with a sulfur isotope geothermometer. All of the data indicate that the Ünlüpinar deposit is an epithermal vein-type mineralization that was formed depending on the granitic magmatism.