Yazarlar

• Dokuz, Abdurrahman(3)
• Kandemir, Raif(2)
• Algur, Bahadırhan Sefa(1)
• Alçiçek, Mehmet Cihat(1)
• Aydin, Faruk(1)
• Aydinçakir, Emre(1)
• Budakoglu, Murat(1)
• Gücer, Mehmet Ali(1)
• Hisarlı, Z. Mümtaz(1)
• Karsli, Orhan(1)
• Kayın, Sercan(1)
• Ketenci, Murat(1)
• Kumral, Mustafa(1)
• Tunçdemir, Vahdet(1)
• Uysal, Ibrahim(1)
• İşseven, Turgay(1)

• MakaleAçık Erişim2025/r/gumushane/14346
  Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

  Kayın, Sercan; Hisarlı, Z. Mümtaz; İşseven, Turgay; Dokuz, Abdurrahman; Algur, Bahadırhan Sefa

  The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

  İncele
• MakaleYalnız künye2023/r/gumushane/16186
  Post-Variscan autochthonous cover in the eastern Sakarya Zone, Turkey: Evolution of the late Carboniferous back-arc ocean to the Triassic Karakaya Ocean

  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.

  İncele
• MakaleYalnız künye2021/r/gumushane/14839
  Origin, petrogenesis and geodynamic implications of the early Eocene Altınpınar adakitic andesites in the eastern Sakarya Zone, northeastern Turkey

  Gücer, Mehmet Ali

  Early Cenozoic magmatism in the eastern Sakarya Zone (NE Turkey) provides an important constraint on the regional tectono-magmatic evolution of the region. Early Eocene syn-collisional adakitic rocks are observed as small stocks with outcropping areas commonly less than 10 km2. This study presents petrography, whole-rock geochemistry and Sr-Nd-Pb isotope data, as well as in-situ 40Ar/39Ar age constraints on one of these adakitic andesites in the Altınpınar area of Gümüşhane, and discusses source region, petrological processes and geodynamic setting prevailed during their genesis. Andesites commonly show microlitic porphyric and vitrophyric porphyric textures, and include significant amounts of mafic microgranular enclaves (MMEs). Plagioclase, hornblende, Fe-Ti oxides and minor pyroxene are the main mineral phases. In-situ 40Ar-39Ar amphibole dating constrains the cooling age of andesites into a time span from 52.8 ± 1.3–48.8 ± 1.9 Ma. Andesites are medium to high-K calc-alkaline and display most of the signatures typical of those of the adakites. They are characterized by moderate MgO (1.7–4.1 wt%), low Y (9−14 ppm), Yb (0.9–1.5 ppm), and HREE and high Sr (325−964 ppm) contents, and high Sr/Y (36–76) ratios. 87Sr/86Sr(t) (0.704948−0.705100) and 143Nd/144Nd(t) (0.512588−0.512628) ratios are in the isotopic range of the adakites. All these geochemical and isotopic data suggest that the parental magma of adakitic andesites has been produced by partial melting of oceanic basalts under amphibole-eclogite facies conditions during the breakoff of the northern Neotethyan oceanic slab.

  İncele
• MakaleYalnız künye2018/r/gumushane/15299
  Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

  Karsli, Orhan; Aydin, Faruk; Uysal, Ibrahim; Dokuz, Abdurrahman; Kumral, Mustafa; Kandemir, Raif; Budakoglu, Murat; Ketenci, Murat

  An integrated study of comprehensive geochronological, geochemical, and Sr-Nd-Hf isotopic data was undertaken for the A-type Topcam pluton that intruded within the Sakarya Zone (NE Turkey) with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous A-type granites. New LA-ICP-MS zircon U-Pb crystallization ages of 72 and 73 Ma indicate emplacement in the Late Cretaceous time, just after extensive metaluminous I-type magmatism in the area. The pluton consists mainly of alkali feldspar, quartz, plagioclase, amphibole, and biotite with accessory minerals such as magnetite, apatite, and zircon. The outcrop is composed of granite, syenite, monzonite, and quartz monzonite and possesses a wide range of SiO2 content (57–70 wt%) with elevated Ga/Al ratios and low Mg# (mostly < 43). The pluton is metaluminous to weakly peraluminous, with aluminium saturation index (ASI) (molar Al2O3/[CaO + K2O + Na2O]) values of 0.82 to 1.18, and belongs to the shoshonitic and ultra-potassic series. All the samples exhibit relative enrichment in light rare earth elements (LREE) and significant negative Eu (Eu/Eu* = 0.31 to 0.86) anomalies on the chondrite-normalized REE diagram. The rocks are enriched in some large ion lithophile elements (e.g., Rb, Th and Ba), and spidergrams show a relative depletion in Nb, Ti, and Sr. The granitic rocks of the pluton have identical 87Sr/86Sr(i) ratios ranging from 0.70518 to 0.70716, relatively low εNd (t) values varying from − 5.5 to − 0.4, and TDM ages (0.82–1.19 Ga). In situ zircon analyses show that the rocks have variable negative and positive εHf (t) values (− 5.5 to 5.9) and Hf two-stage model ages (742 to 1468 Ma), which are indicative of minor addition of juvenile material. Sr-Nd isotope modelling suggests mixing of 70–90% of lower crustal-derived melt with ~ 10–30% of mantle-derived melt at lower crust depths. The heat source for partial melting is provided by upwelling of hot asthenosphere triggered by slab roll-back events. Geochemical and isotopic data reveal that metaluminous A2-type granites were derived from partial melting of the Paleozoic lower continental crust dominated by mafic rocks in amphibolitic composition, with minor input of subcontinental lithospheric mantle-derived magma followed by subsequent limited fractional crystallization to generate a variety of rock types. From integrating all available data with the regional tectonic evolution in the Sakarya Zone and adjacent regions, we attribute generation of aluminous A2-type granites to a back-arc extension in the subduction zone, which is induced by the roll-back of the Neo-Tethyan oceanic slab around 72 Ma. Consequently, we conclude that these A-type granites were related to intensive extension tectonic, which peaked during the late Cretaceous (Maastrichtian) in response to the roll-back of the Neo-Tethyan oceanic slab, which is indicative of the final-stage subduction-related magmatism in the Sakarya Zone.

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