Dönmez, Cahit; Aral, Zehra Deveci; Saka, Samet; Günay, Kurtulus; Yildirim, Nail; Yildirim, Esra; Yagcioglu, Kiymet Deniz; Maqsud, Isoqov; Movlanov, Jakhongir; Dovronovich, Mamarozikov Usmonjon

The Central Asian Orogenic Belt's ophiolites lack a full ophiolitic succession and instead occur as irregular fragments and slices in tectonic melanges and accretionary complexes. The Teskuduk and Northern Nurata ophiolites in Uzbekistan comprise extensively serpentinized mantle rocks that contain minor podiform chromitites, situated in the western area of the southern Tien Shan belt. Chromites in this region are found in a very limited area, and this study aims to determine the geochemical properties and formation environments of chromites by conducting geochemical studies on a limited number of recently discovered chromitites. In this context, mineral chemistry and platinum group element (PGE) geochemistry analyses were carried out on chromites. For Teskuduk chromitites, the Cr2O3, Al2O3, and TiO2 contents range from 53.2 to 55.7wt%, 11.1 to 12.7wt%, and 0.14 to 0.20 wt%, respectively, whereas for Nurata chromitites, the corresponding values range from 36.2 to 37.2 wt%, 23.1 to 30.2 wt%, and 0.10 to 0.30 wt%. The Teskuduk and Nurata chromitites contain a total average of 370 ppb and 117 ppb PGEs, respectively. They are classified as unfractionated chromitites, with low Pd/Ir ratios (0.03-0.20). These chromitite samples have chondrite-normalized PGE patterns that are identical to Cr-rich mantle-derived chromitites found in subduction-related ophiolites. Collectively, these data suggest that the Teskuduk ophiolites formed in a forearc setting, whereas the Nurata ophiolites evolved in a back-arc setting within the same oceanic branch.

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.

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.

Sipahi, Ferkan

Skarn deposits are located in the NE Black Sea region of Turkey belonging to the Alpin metallogenic province. The Fe skarn deposit at Arnastal is hosted by Late Cretaceous carbonate rocks comprised of limestone and the skarn occurrence at Camibogazi dolomitic limestone, adjacent to the Eocene Zigana Granitoid. The prograde textures include rhythmic banding, spots, and mossiness, and the retrograde textures are shock-induced and brecciated. These are identified in the Fe skarn deposit at Arnastal, where there are mineral parageneses of andradite, actinolite, tremolite, epidote, quartz, magnetite, and hematite, and less pyrrboune and pyrite. Additionally, well-crystallized vesuvianite, well-crystallized phlogopite, and diopside in the skarn occurrence. at Camibogazi are identified. Some of the skarn minerals are calcic and have high Mg/(Mg + Fe) ratios. Clinopyroxene consists of diopside (Di(96.66-99.04)Hd(0.67-2.80)Jo(0.29-0.55)). Vesuvianite is mostly Mg-rich, and has a very low MnO content (<0.1 %). Other skarn minerals are Fe-rich. Garnet is characterized by oscillatory zoning and has an andradite composition (Ad(72)Gr(28) to Ad(98)Gr(2)). Epidote has an Fe content of 8.96 to 12.42 wt%. Magnetite is generally massive and sporadically banded with some martitization. The formation temperatures of skarn minerals range from 330 to 600 degrees C. In addition, mass change calculations from the granitoid and andesite toward the skarn zone indicate that there is considerable mass transfer of Si, Al, Fe, and Mg to the carbonate rocks during skarn formation. The average mass changes are estimated at a depletion of 41 g/100 g in granitoid and a gain of 8 g/100 g in andesite. Fe skarn deposit and skarn occurrence are characterized by early, high-temperature mineral assemblages dominated by the anhydrous minerals garnet and diopside and late low-temperature assemblages with hydrous minerals, such as vesuvianite, phlogopite, and epidote. The type of garnet and the abundance of magnetite with minor pyrite suggest that the Fe skarn deposit at Arnastal forms under relatively oxidized conditions. The type of clinopyroxene in the skarn occurrence at the Camibogazi shows oxidized skarns.

Eker, Cigdem Saydam; Korkmaz, Sadettin

This study focuses on Upper Cretaceous sandstones of the Eastern Pontides to identify the source area, subaerial weathering level, and tectonic environment. Thirty four sandstone samples from six stratigraphic sections were analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MC) and by petrographic investigation. The late Cretaceous sandstones are defined as lithic arenites and feldspathic wackes, and lithic wackes depending on mineralogical and matrix content. The sandstones have low to moderate SiO2 contents (25-59%; on average -56%). There are high positive correlations between SiO2 Al2O3, and TiO2 and negative correlations between SiO2 and K2O. Geochemically, the sandstones are classified mainly as grey wackes and lithic arenites. Chemical index of alteration (CIA) and chemical index of weathering (CIW) values for Upper Cretaceous sandstones vary from 19 to 48 % and 20 to 49 % respectively. The combination of CIW/CIA values suggests little transportation until final deposition. The ratios of Th/Sc (on average -0.42), La/Sc (-1.81), Co/Th (-5.05) and Zr/Hf (-39.1) of sandstone samples in the study area indicate a mafic source. Furthermore, high light rare earth elements (LREE)/heavy rare earth elements (HREE) ratios (on average -19.72) and negative Eu anomalies (except in the Dagbasi section) suggest a contribution from a felsic source. The lower trace element contents of the Upper Cretaceous sandstones in relation to the Post-Archean Australian Shale (PAAS), which are considered to be representative of the upper continental crust, show that the recycling processes in their source areas were probably less intense than those of the PAAS. SiGyAlA (3.2-7.9) and K2O/Na20 (0.3-1) ratios, together with the Th (on average -3.3 ppm), Zr (on average -91.9 ppm), Co (on average -15 ppm), and Sc (on average -12.6 ppm) contents of the late Cretaceous sandstones of the eastern Pontides indicate a magmatic arc origin. Sandstones of the Trabzon region were probably deposited in fore-arc basins, and those from the Gumushane and Giresun regions in back-arc basins.

Kaygusuz, Abdullah; Aydingakir, Emre

Zircon U-Pb ages, major and trace elements, and Sr-Nd isotope data are reported for the Late Cretaceous Dagbasi pluton from the eastern Pontides, NE Turkey. This pluton has calc-alkaline affinity and displays typical features of volcanic arc granitoids. It is a composite pluton consisting of tonalite, granodiorite, and monzogranite, all containing mafic microgranular enclaves (MMEs). Based on U-Pb zircon SHRIMP dating, magma emplacement ages of the tonalite, granodiorite, and monzogranite are 88.1 ± 1.7 Ma, 86.0 ±2.0 Ma, and 82.9 ± 1.3 Ma, respectively. The tonalites have low SiO2 (60-64 wt%) and display metaluminous to peraluminous characteristics. They have similar Lacn/Lucn (1.5-7.3) and Eu/Eu* (0.65-0.88) values compared to granodiorites and monzogranites. The isotopic signatures of these rocks εNd(i) = -1.4 to -1.7; 87Sr/86Sr(i) = 0.7056-0.7060) are largely similar to granodiorites and monzogranites. Samples from the granodiorites and monzogranites have SiO2 between 69 and 76 wt% and display peraluminous to slightly metaluminous characteristics. Chondrite-normalized REE patterns are characterized by moderate Lacn/Lucn ratios (1.6-7.1), with pronounced negative or positive Eu anomalies (Eu/Eu* = 0.46-1.11). Radiogenic isotope signatures of granodiorites and monzogranites show overlapping 87Sr/86Sr(i), (0.7057-0.7067) and εNd(i) (-3.2 to + 1.5) values. The MMEs have similar geochemical and isotopic features as the host rocks. All plutonic rocks are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE). Fractionation of plagioclase, hornblende, and Fe-Ti oxides played an important role in the evolution of Daǧbasi granitoids. All these geochemical and isotopic characteristics suggest an origin by dehydration melting of an amphibolitic 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

The Neogene Ilica volcanics in eastern Anatolia are of sub-alkaline affinity and present features of post-collisional volcanism. The lava flows in the Ilica area reveal K/Ar ages ranging from 13.9 ± 0.5 to 4.4 ± 0.3 Ma, corresponding to the Miocene- and Pliocene age. The volcanic rocks are composed of calc-alkaline basaltic trachyandesitic-, trachyandesitic-, andesitic- and minor dacitic lavas associated with pyroclastics, with the andesitic lavas being volumetrically the most abundant. Some special textures, such as the dissolution/melting and poikilitic type, and the normal, reverse, and oscillatory zoning in the plagioclase- and pyroxene phenocrysts are attributable to disequilibrium crystallization related to magma mixing. The rocks are characterized by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), with pronounced depletion of high field strength elements (HFSE). They show depletion in Nb and Ta, indicating the role of crustal contamination. The rocks also have moderately fractionated rare earth elements (REE) patterns with (La/Lu)N ratios of 10-19 for andesitic- and dacitic rocks, and 7-10 for basaltic trachyandesitic- and trachyandesitic rocks. Basaltic trachyandesites show slightly positive Eu anomalies, whereas the deepening of Eu through gradual increase from trachyandesite to dacite, indicating a genetic link between the basaltic trachyandesite and the dacites. The main solidification processes consist of magma mixing and fractional crystallization with minor amounts of crustal contamination which were operative during the solidification of the volcanic rocks. All evidences support the theory that Ilica volcanic rocks were derived from partial melting of lower continental crust, having undergone interaction with subcontinental lithospheric mantle in a post-collisional geodynamic setting.

Demir, Yilmaz; Uysal, Ibrahim; Sadiklar, M. Burhan; Sipahi, Ferkan

Vein type Köstere ores were deposited along cracks formed as a result of NE-SW fault system in the late Cretaceous felsic volcanic rocks in the northeastern Black Sea Region of Turkey. Total silver content of the Köstere ore is controlled by total silver content of the hydrothermal solution, homogenization temperature of the ore minerals and modal abundances of the tetrahedrite-tennantite serie minerals. The Zn/Cd ratios of sphalerites from the Köstere deposit are close to those of granite-related classical vein-type hydrothermal deposits. Furthermore Co/Ni ratio in pyrite separates, higher than unit, suggests an acidic source for the ore forming fluids. Homogenization temperatures of 200-370 °C and salinity of 0-9.85 eq. wt% NaCl were obtained on the basis of fluid inclusions studies measured in quartz minerals. These data indicate that ore formation conditions for the Köstere ore are similar with the vein-type epithermal-mesothermal deposits, related to the magmatic fluids. The overall low salinities of fluids (on average: 5.4 eq. wt% NaCl) suggest that meteoric waters were involved in mineralization. The possibility of interactions between ascending hydrothermal fluids and dilute meteoric waters is supported by geological features and mineralogical data which indicate a shallow depth of mineralization. Torul Pluton, which is the younger acidic unit (72 my) in the area, is suggested to be related to the formation of Köstere deposit.