Güloğlu, Zikrullah Samet; Kaygusuz, Abdullah

The Middle Eocene Arslandede Pluton, exposed in the Bayburt region on the southern margin of the Eastern Pontides (NE Turkey), has been investigated in terms of its geology and mineral chemistry. The pluton exhibits a NW-SE elongation and covers an area of approximately 7 km². It comprises a broad compositional spectrum ranging from monzodiorite to quartz monzonite. Major rock-forming minerals include plagioclase (An25-48), orthoclase (Or69-88), quartz, amphibole (Mg# = 0.63-0.73), biotite (Mg# = 0.52-0.62), pyroxene (Mg# = 0.70-0.75), and Fe-Ti oxides. Crystallization conditions, estimated via amphibole-plagioclase thermometry and Al-in-hornblende barometry, suggest crystallization temperatures of 737-812 °C and pressures of 0.09-1.61 kbar, corresponding to depths of 0.3-6.0 km. These results indicate that the pluton was emplaced at shallow crustal levels and subsequently solidified under low-pressure conditions. Comparison with other Middle Eocene plutons in the region reveals similar crystallization conditions, suggesting a common tectonic setting during the post-collisional extensional regime in the Eastern Pontides.

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.

Güloğlu, Zikrullah Samet; Kaygusuz, Abdullah

The Kazıkbeli pluton, located in the Kürtün (Gümüşhane) region of the Eastern Pontides, NE Turkey, was studied by employing zircon U-Pb geochronology, whole-rock geochemistry, Sr-Nd-Pb and zircon Lu-Hf isotope geochemistry. LA-ICP-MS U-Pb zircon dating revealed that the gabbroic diorite and granodiorite components of the pluton solidified during the Lutetian epoch of the Middle Eocene, at approximately 46.10 ± 0.26 Ma and 45.37 ± 0.29 Ma, respectively. The pluton is composed of calc-alkaline rocks, ranging from gabbroic diorite to granite (SiO2 = 55.3 to 72.4 wt%). These I-type rocks are typically metaluminous but exhibit peraluminous tendencies in some cases. They are enriched in large ion lithophile elements and display concave chondrite-normalized rare earth element patterns (LaN/YbN = 4.39 to 6.67) with negative Eu anomalies (EuN/Eu* = 0.45 to 0.80). The initial εNd values ranged from 1.85 to 2.24, and the initial 87Sr/86Sr(i) ratios ranged from 0.70458 to 0.70484, consistent with a mantle source in the isotope ratio diagram. The initial 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) ratios ranged from 18.505 to 18.571, 15.595 to 15.601, and 38.560 to 38.590, respectively. They have positive εHf(i) values (5.75 to 8.03), located between depleted mantle and chondrite evolution values. Fractional crystallization of plagioclase, hornblende, and Fe-Ti oxide minerals played a significant role in the magma evolution, while assimilation and magma mixing may have had a minor influence. Collectively, the evidence suggests that the primary magma source for these plutonic rocks was an enriched lithospheric mantle. Subsequent differentiation within crustal magma chambers, with limited crustal contamination, shaped the final magmatic evolution.

Kaygusuz, Abdullah; Güloğlu, Zikrullah Samet; Aydınçakır, Emre; Yücel, Cem; Vural, Alaaddin; Siebel, Wolfgang; Jeong, Youn-Joong

The Eastern Pontide Orogenic Belt (EPOB) hosts numerous plutonic bodies with different dimensions, compositions and ages ranging from Paleozoic to Late Eocene in NE Turkey. U-Pb zircon dating suggests that the Arslandede pluton crystallized at 44.50 ± 0.29 Ma, corresponding to the Lutetian (Middle Eocene) period. Rocks of this pluton have monzonitic character, with compositions ranging from monzodiorite to granite (SiO2 = 49˗71 wt%). The studied monzonitic rocks have I-type, metaluminous and shoshonitic character and are enriched in large-ion lithophile elements (LILEs). The rare earth elements (REEs) have concave up shape (LaN/YbN = 6.64–11.57) and show negative to slightly positive Eu anomalies (EuN/Eu* = 0.37–1.24). 87Sr/86Sr(i) values of 0.704801–0.705102 and εNd(i) values of 1.01–1.34 correspond to the mantle series on isotope ratio diagrams. Positive εHf(i) values (5.01–14.91) plot between the depleted mantle and the chondritic evolution lines. The petrological features of the rocks from the Arslandede pluton show that fractional crystallization with low rates of assimilation and/or magma mixing were effective during crystallization. All data show that the magma source of the pluton derived from an enriched lithospheric mantle and emplaced into the crust after differentiation in a deep seated magma chamber contaminated by relatively small proportions of crustal rocks.

Güloğlu, Zikrullah Samet; Kaygusuz, Abdullah; Aydinçakir, Emre; YÜCELc, Cem

The Eastern Pontides host a diverse suite of plutonic rocks spanning a wide range of ages and compositions. Among these, the Middle Eocene Kazıkbeli pluton, located in the Kürtün district of Gümüşhane, stands out due to its distinctive petrological characteristics. This study aims to unravel the petrological implications of petrographic and mineral chemical data to determine the physicochemical conditions (temperature, pressure, oxygen fugacity) under which the Kazıkbeli magma crystallized and was emplaced. By integrating mineral chemical data, we seek to quantify emplacement pressure, crystallization temperature, and oxygen fugacity. A comprehensive understanding of the genetic relationships and physicochemical properties of the Kazıkbeli pluton rocks, as determined through geological, petrographic and mineral chemistry, is crucial for elucidating the geological evolution of the Eastern Pontides. The Kazıkbeli Pluton exhibits a predominant NE-SW orientation and encompasses an area of roughly 46 km2. Modal mineralogical analysis reveals a compositional spectrum ranging from gabbroic diorite to monzogranite, with granodiorite and tonalite being the most prominent rock types. Textural variations encompass fine-to medium-grained, porphyritic, poikilitic, and occasionally graphic textures. The primary mineral assemblage of the pluton comprises plagioclase, orthoclase, quartz, amphibole, biotite, and Fe-Ti oxides. Accessory minerals include zircon, apatite, sphene, and allanite. Plagioclases are labradorite to oligoclase (An26 to An66) in composition. K-feldspar minerals exhibited an orthoclase composition (Or80 to Or97). All amphiboles belong to the calcic amphibole field and exhibit a magnesio-hornblende (Mg#=0.63-0.73) composition. Biotites crystallized as solidified melt products with compositions between annite and phlogopite endmembers, plotting close to the magnesium-rich (Mg#=0.52-0.58) end of the phlogopite solid solution series. Calculated crystallization temperatures derived from amphibole and biotite data range from 712°C to 824°C. Pressure estimations calculated using amphibole-plagioclase, amphibole and biotite suggest a range of 0.04 to 2.06 kbar. Oxygen fugacity (ƒO2) values calculated using amphibole and biotite fall between -12.5 and -16.1. Amphibole-based water content estimations indicate a range of 3.7% to 5.7% for the pluton. Biotite compositions within the studied Kazıkbeli pluton rocks exhibit characteristics suggestive of a potential mantle origin. Geobarometric calculations based on mineral chemistry data with geological and petrographic features indicate the emplacement of the Kazıkbeli Pluton at relatively shallow depths within the crust (~1 to 8 km).