Derya Cicerali

Posof (Ardahan, Türkiye) Yöresi Geç Miyosen-Kuvaterner Yaşlı Volkanik Kayaçların Petrografisi, Mineral Kimyası, Jeokimyası, Jeokronolojisi ve Petrojenezi irdelenmiştir. Üst Miyosen volkanik kayaçları (8.6-7.3 My) bazalttan bazaltik-andezite kadar değişen bileşimdedir ve plajiyoklaz+klinopiroksen+olivin+hornblend+opak mineralleriyle temsil edilir. Buna karşılık, adakit benzeri jeokimyasal özellik sergileyen Pliyosen-Kuvaterner volkanik kayaçları (5.2-0.73 My) andezit bileşiminde olup plajiyoklaz±hornblend±biyotit±opak mineralleriyle karakterizedir. Üst Miyosen volkanik kayaçların SiO2 içerikleri % 48.14-61.22, Al2O3 % 14.81-16.86, MgO % 3.01-8.13, Mg# 34.9-51.3, Sr/Y 13.45-69.73, La/Yb 3.91-39.23'tür. Pliyosen-Kuvaterner volkanik kayaçların SiO2 % 64.56-70.83, Al2O3 % 15.51-16.97, MgO % 0.25-1.34, Mg#10.68-33.20, Sr/Y 43.72-143.42, La/Yb 43.45-76.68'dir. Üst Miyosen volkanik kayaçlar hafif zenginleşmiş LaN/LuN (2.66-27.12), Pliyosen-Kuvaterner volkanik kayaçlar ise LaN/LuN (29.36-75.58) oranları ile yüksek oranda zenginleşmiş kondrite normalize nadir toprak element desenleri sergiler. Üst Miyosen volkanik kayaçların (87Sr/86Sr)i 0.703792-0.704395, (143Nd/144Nd)i 0.512796-0.512881; Pliyosen-Kuvaterner volkanik kayaçların (87Sr/86Sr)i oranları 0.704153-0.704506, (143Nd/144Nd)i 0.512740-0.512809'dur. Sonuç olarak, Üst Miyosen volkanik kayaçları oluşturan magmaların genişlemeli bir tektonik ortamda, yitimle zenginleşmiş bir manto kaynağından delaminasyon süreçleriyle litosferik incelme ve yükselen astenosfere bağlı oluşan kısmi ergimeler ve buna eşlik eden juvenil alt kabuk kökenli ergiyiklerin; Pliyosen-Kuvaterner volkanik kayaçlarının ise benzer jeodinamik koşullar altında juvenil alt kabukta gelişen kısmi ergimeler sonucunda oluşan magmaların kabuk içerisinde fraksiyonel kristallenme ve magma karışımı gibi magmatik süreçlerle son halini aldığı söylenebilir.

Cicerali, Derya; Yücel, Cem; Aydinçakir, Emre; Kaygusuz, Abdullah

This study aimed to constrain the crystallization and emplacement conditions of magmas that produced the Late Miocene volcanic rocks exposed at the junction of the Erzurum-Kars Plateau and the Eastern Pontides in the Northeastern Anatolia Region through a series of thermobarometric analyses. The volcanic succession unconformably overlies Oligocene mudstone, siltstone, and sandstone alternations, with limestone and cherty limestone at higher levels. Petrographically, they consist offine-to coarse-grained basalt, basaltic andesite, and andesite. Mineral compositions include plagioclase (An(16-77)), clinopyroxene (Wo(39-45)En(43-50)Fs(11-12)), orthopyroxene (Wo(3-4)En(73-82)Fs(14-24)), olivine (Fo(63-86)), hornblende (Mg#=0.62-0.79), and Fe-Ti oxides (Usp(0.05-1.44), Ilm(94.10-95.53)). The groundmass comprises microlites of these minerals and volcanic glass. The dominant textures are microlitic porphyritic, hyalomicrolitic, and microlitic porphyritic, while glomeroporphyritic, intergranular, pilotaxitic, subophitic, flow, and vesicular textures are also observed. Widely present disequilibrium features, such as zoning, sieve, and resorption, are common in plagioclase and clinopyroxene. Thermobarometric calculations indicate crystallization temperatures of 880-1230 degrees C, pressures of 0.73-8.71 kbar, oxygen fugacities between (-10.94) and (-8.92), and water contents of4.60-6.32 wt.%. These results suggest that the volcanic rocks crystallized under volatile-rich, oxidizing conditions across a broad depth range (similar to 2-32 km), at relatively high temperatures.

Kaygusuz, Abdullah; Güloğlu, Zikrullah Samet; Aydınçakır, Emre; Yücel, Cem; Vural, Alaaddin; Saydam Eker, Çiğdem; Cicerali, Derya

The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a well-preserved continental magmatic arc in the Alpine-Himalayan Orogenic Belt and contains many Eocene I-type high-K plutons. Employing LA-ICP-MS U-Pb zircon geochronology, the crystallization ages of the investigated Yaylalıköy and Taşbaşı plutons were established to be Lutetian (Middle Eocene), ranging from 47 Ma to 46 Ma. These plutons exhibit a compositional spectrum ranging from diorite to granodiorite, characterized by I-type, metaluminous, and high-K geochemical signatures. Notably, they are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), displaying pronounced negative Eu anomalies (EuN/Eu* = 0.58–0.96). Isotopic signatures reveal homogeneous and moderately low initial 87 Sr/86 Sr(i) ratios (0.704643–0.705034) and positive εNd(i) values (0.24 to 1.67) for the investigated plutons. These isotopic signatures are consistent with mantle origin, as evidenced by their position within the mantle array on isotope ratio diagrams. Lead isotope compositions exhibit limited variations, with initial ratios of 206 Pb/204 Pb(i) (18.55–18.64), 207 Pb/204 Pb(i) (15.61–15.64), and 208 Pb/204 Pb(i) (38.46–38.75). Zircon εHf(i) values are positive (2.32–6.20), plotting between the depleted mantle and chondritic evolution lines. Additionally, these rocks display low zircon δ18 O values (+4.54 to + 6.53‰), comparable to mantle composition. The petrographic characteristics of the investigated plutons suggest that fractional crystallization with minimal assimilation and/or magma mixing played a dominant role during their solidification. The integration of geochemical and isotopic data, alongside regional geological constraints, advocates for enriched lithospheric mantle as the source for the parental magmas of the studied plutons. These magmas subsequently underwent differentiation within a deep-seated magma chamber, followed by emplacement into the crust.

Yücel, Cem; Aydınçakır, Emre; Kaygusuz, Abdullah; Arslan, Mehmet; Yi, Keewook; Jeong, Youn-Joong; Cicerali, Derya

The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes.

Cicerali, Derya; Arslan, Mehmet; Yazar, Emel Abdioglu; Yücel, Cem; Temizel, Irfan; Park, Sohyun; Schroeder, Paul A.

Eocene vitric tuffs in the Bayburt area (NE Turkey) possess a dacite-rhyodacite composition and contain abundant altered glass shards and flattened fibrous pumice with lesser amounts of pyrogenic minerals (plagioclase, quartz, biotite, and sanidine). Zeolitization is common and generally develops in the glassy components. The main zeolite mineral found in the tuffs is clinoptilolite, with lesser amounts of analcime and mordenite (?). Smectite is the dominant clay mineral, with lesser amounts of kaolinite also present. Opal-CT, calcite, and dolomite occur as secondary minerals. Scanning electron microscopy studies reveal the dissolution of glass, with the development of popcorn-textured smectites and tabular clinoptilolites developed. The opal-CT spheres found on the clinoptilolite crystals appear to have crystallized simultaneously and are due to excess silica in the environment. Fibrous mordenite (?) also developed on the clinoptilolites. In the clinoptilolites R-r = 0.81-0.82, Si/Al = 4.20-4.70, and K+ is the dominant exchangeable cation (0.65-3.30) seen, together with lesser amount of Ca2+ (0.39-2.25) and Na+ (0.02-2.16). The degree of zeolitization increases with the content of glassy component in the tuffs. The formation of K-clinoptilolite is controlled by the SiO2/Al2O3 (4.9-7.0) and K2O/Na2O (0.8-10.8) ratios in the zeolitized tuffs. delta O-18(V-SMOW) and delta DV-SMOW values of clinoptilolite-rich tuffs range from 22 to 25.6960 and from -96 to -111 parts per thousand, respectively, which suggests that zeolitization occurred at low temperatures (30-55 degrees C) via fluid-rock interactions. Smectite was initially formed from the devitrification of glassy components and is associated with the increase in (Na+ +K+ +Ca2+)/H+ activity and the presence of high pH similar to-9-10) fluids. The zeolites subsequently developed within a saline-alkali shallow marine environment.