Subduction-related Late Cretaceous high-K volcanism in the Central Pontides orogenic belt: constraints on geodynamic implications

Mineral chemistry, major and trace elements, ⁴⁰Ar/³⁹Ar age and Sr–Nd–Pb isotopic data are presented for the Late Cretaceous Hamsilos volcanic rocks in the Central Pontides, Turkey. The Hamsilos volcanic rocks mainly consist of basalt, andesite and associated pyroclastics (volcanic breccia, vitric tuff and crystal tuff). They display shoshonitic and high-K calc-alkaline affinities. The shoshonitic rocks contain plagioclase, clinopyroxene, alkali feldspar, phlogopite, analcime, sanidine, olivine, apatite and titanomagnetite, whereas the high-K calc-alkaline rocks contain plagioclase, clinopyroxene, orthopyroxene, magnetite / titanomagnetite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic matrix. Mineral chemistry data reveal that the pressure condition of the clinopyroxene crystallisation for the shoshonitic rocks are between 1.4 and 6.3 kbar corresponds to 6–18-km depth and the high-K calc-alkaline rocks are between 5 and 12 km. ⁴⁰Ar/³⁹Ar age data changing between 72 ± .5 Ma and 79.0 ± .3 Ma (Campanian) were determined for the Late Cretaceous Hamsilos volcanic rocks, contemporaneous with the subduction of the Neo-Tethyan Ocean beneath the Pontides. The studied volcanic rocks were enriched in the large-ion lithophile and light rare earth element contents, with pronounced depletion in the contents of high-field-strength elements. Chondrite-normalised rare earth element patterns (La_N/Lu_N = 6–17) show low to medium enrichment, indicating similar sources of the rock suite. Initial ⁸⁷Sr/⁸⁶Sr values vary between .70615 and .70796, whereas initial ¹⁴³Nd/¹⁴⁴Nd values change between .51228 and .51249. Initial ²⁰⁶Pb/²⁰⁴Pb values vary between 18.001 and 18.349, ²⁰⁷Pb/²⁰⁴Pb values between 15.611 and 15.629 and ²⁰⁸Pb/²⁰⁴Pb values between 37.839 and 38.427. The main solidification processes involved in the evolution of the volcanic rocks consist of fractional crystallisation, with minor amounts of crustal contamination ± magma mixing. According to geochemical evidence, the shoshonitic melts in the Hamsilos volcanic rocks were possibly derived from the low degree of partial melting of a subcontinental lithospheric mantle (SCLM), while the high-K calc-alkaline melts were derived from relatively high degree of partial melting of SCLM that was enriched by fluids and/or sediments from a subduction of oceanic crust.     

Late Triassic rifting and Jurassic–Cretaceous passive margin development of the Southern Neotethys: evidence from the Adıyaman area,SE Turkey

Evidence of rifting and continental break-up to form the S Neotethys is found within the volcanic-sedimentary Koçali Complex. This is a folded, thrust-imbricated succession that includes lavas, volcaniclastic sediments, pelagic carbonates, radiolarites and manganiferous deposits. Interbedded ribbon cherts contain radiolarians of Late Triassic to Late Jurassic age. The lower part of the succession of Mid?-Late Triassic age (Tarasa Formation) is dominated by enriched mid-ocean ridge basalt (E-MORB). The overlying Late Triassic to Mid-Jurassic interval (Konak Formation) is characterised by intercalations of ocean island basalt and E-MORB. Taking account of structural position, the basalts erupted within the outer part of a continent–ocean transition zone. Continental break-up probably occurred during the Late Triassic (Carnian–Norian). Early to Mid-Jurassic lavas and volcaniclastic sediments record volcanism probably after continental break-up. In addition, the Karadut Complex is a broken formation that is located at a relatively low structural position just above the Arabian foreland. Pelagic carbonates, redeposited carbonates and radiolarites predominate. Radiolarians are dated as Early to Mid-Jurassic and Late Cretaceous in age. The pelagic carbonates include planktic foraminifera of Late Cretaceous age. The Karadut Complex resulted from the accumulation of calcareous gravity flows, pelagic carbonate and radiolarites in a relatively proximal, base-of-slope setting. After continental break-up, MORB and ophiolitic rocks formed within the S Neotethys further north. Tectonic emplacement onto the Arabian platform took place by earliest Maastrichtian time. Regional interpretation is facilitated by comparisons with examples of Triassic rifting and continental break-up in the eastern Mediterranean region and elsewhere.     

Evaluation of tectonic structure of İskenderun Basin (Turkey) using steerable filters

In this paper, we demonstrate the effectiveness of steerable filters as a method of delineating the boundaries of subsurface geological structures. Steerable filters, generally used for edge detection on 2-D images, have the properties of band pass filters with certain directions and are applied to many image processing problems. We first tested the method on synthetic data and then applied it to the aeromagnetic data of İskenderun Basin and adjacent areas.İskenderun Basin is located in the Northeastern Mediterranean where African–Arabian and Anatolian plates are actively interacting. The basin fill records a complex tectonic evolution since the Early Miocene, involving ophiolite emplacement, diachronous collision of Eurasian and Arabian plates and subsequent tectonic escape related structures and associated basin formation. Geophysical investigations of the tectonic framework of İskenderun Basin of Turkey provide important insights on the regional tectonics of the Eastern Mediterranean and Middle East. In this study we show geological structures, which are responsible for the magnetic anomalies in İskenderun Basin and enlighten the structural setting of the Northeastern Mediterranean triple junction using steerable filters. We obtained a magnetic anomaly map of the region from the General Directorate of Mineral Research and Exploration as raw data and then evaluated this by steerable filters. We determined the magnetic anomaly boundaries for İskenderun Basin by using various types of steerable filters and correlated these to drilling data and seismic profiles from the Turkish Petroleum Corporation. The result of the steerable filter analysis was a clarified aeromagnetic anomaly map of İskenderun Basin. The tectonic structure of İskenderun Basin is divided into regions by an N–S trending oblique-slip fault defined by the steerable filter outputs. We propose a new tectonic structure model of İskenderun Basin and modify the direction of the East Anatolian Fault Zone. In our model, East Anatolian Fault Zone cross-cuts the basin as a narrow fault zone and continues towards the Cyprus arc.     

Turbidites and their association with past earthquakes in the deep Çınarcık Basin of the Marmara Sea

Two gravity cores (CAG-3 and C-15) from the tectonically active, 1,276-m deep Çınarcık Basin of the Marmara Sea each include three sandy turbiditic mud units (1 mm–2 cm thick) with sharp basal contacts. The high benthic foraminifer content of these units suggests that the sediments were transported by turbidity currents from the upper slope region. These units represent the thin edges of turbidites thickening towards the subsiding north-eastern part of the basin, and contain quartz, detrital calcite, intact shells and shell fragments, smectite, pyrite framboids, muscovite, biotite, epidote and garnet. Their clay fractions are more enriched in smectite than those of adjacent layers. AMS 14C ages (957±43 a.d. and 578±31 a.d.) of two upper and middle turbiditic units in core C15 overlap with the historical İstanbul-Thrace (intensity=10) and İstanbul-Kocaeli (intensity=9) earthquakes of 26 October 986 and 15 August 553, respectively. This overlap, together with sedimentological characteristics, strongly suggests that the turbiditic units are related to the tectono-seismic activity of the North Anatolian Fault. The age of the lowest turbiditic unit in core C-3 was found to be 6,573±87 a b.p. (calendar) by AMS 14 C. In terms of chronostratigraphic relationships and lithological composition, the turbiditic units in core CAG-3 cannot be correlated with those in C15. This can be explained by gravity-controlled sedimentation causing wedging out of turbidites towards the edge of the basin.     

Significance of the Felsic Sub–Volcanics in Development of Related Au–Ag Deposits at Maden Village (Bolkar Mountain Region), South Turkey: Constraints from Whole–Rock Geochemistry,Geochronology and Pb-S Isotopes

Geotectonics - The Horoz granitoid and related felsic sub–volcanics located in the Inner Tauride Belt are key igneous rocks for understanding and investigating the collision and closure...     

Impact of climate change on meteorological and hydrological droughts for Upper Coruh Basin,Turkey

Natural Hazards - Environmental changes have led to non-stationary flood risks in coastal cities. How to quantitatively characterize the future change trend and effectively adapt is a critical...     

A New Natural Secondary Reference Material for Garnet U-Pb Dating by TIMS and LA-ICP-MS

Gem quality andradite-rich garnet (IUC-1), obtained from the Miocene trachyte dome near Ankara city (Turkey), has been identified as a potential natural secondary reference material for U-Pb dating. In this study, U-Pb dating was performed in five different laboratories using isotope dilution TIMS and laser ablation ICP-MS to determine the homogeneity of euhedral garnet crystals. The U-Pb ID-TIMS data for IUC-1 yielded ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ages of 20.9 ± 0.4 and 20.6 ± 0.8 Ma respectively, and these values are consistent with U-Pb LA-ICP-MS analyses, in which different garnet crystals yielded ages of 20.8 ± 0.1, 20.7 ± 0.1, 20.7 ± 0.2 and 20.2 ± 0.1 Ma. An andradite (IUC-2) from the Serçeören wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID-TIMS data yielded ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ages of 20.4 ± 0.4 and 20.9 ± 1.0 Ma respectively, and yielded U-Pb ages on different grains of 20.5 ± 0.1, 20.7 ± 1.0, 20.8 ± 1.7 and 20.9 ± 1.6 Ma. The assigned weighted mean age of IUC-1 (20.4 ± 0.5 Ma, 2s) is proposed as a 2023 reference value. IUC-1 garnet is expected to contribute significantly to rapidly developing garnet geochronology in the near future.     

Using tree-ring signals and numerical model to identify the snow avalanche tracks in Kastamonu,Turkey

Many parts of our planet are exposed to natural disasters such as snow avalanches, floods and earthquakes. Detailed knowledge on these natural disasters is crucial for human safety. On December 25–26, 1992, two avalanches occurred at Kayaarkası-Kastamonu in northern Turkey. The first avalanche took place at night of 25–26 December and caused no damage. The second avalanche took place at morning of 26 December, killed four people and did damage to properties. The purpose of the present study is to determine the effects of the snow avalanches on tree rings and to investigate the boundaries and velocities of the avalanches using a numerical simulation model and the tree-ring data. Increment cores from 71 trees in the avalanche-impacted area and the control site were sampled to obtain individual standard chronologies. In the analyses, trees were grouped as (1) heavily damaged by the avalanche, showing a decrease in tree-ring widths since the event, (2) trees heavily damaged by the avalanche, showing an increase in tree-ring widths a couple of years later the event and (3) trees that were not damaged by the avalanche. In this study, one of the most important results is the precise determination of the temporal and spatial patterns of the undocumented avalanche (the first avalanche) event. Avalanches were numerically simulated using dynamical avalanche simulation software ELBA+. Comparison of the simulation model with tree-ring analysis revealed valuable results about the boundaries of the zone of influence of the avalanches.     

A simultaneous spectroscopic and photometric study of two eclipsing binaries: V566 Oph and V972 Her

In this study, we have performed simultaneous solutions of light and radial velocity curves of two eclipsing binary systems, V566 Oph and V972 Her. We observed both systems spectroscopically with a very recently installed spectrograph on the 40 cm telescope, T40, located in Ankara University Kreiken Observatory (AUKR), for the first time. We made use of the photometric data from the Hipparcos satellite for V972 Her, while we obtained the photometric observations of V566 Oph by using the 35 cm telescope, T35, located also in our observatory campus. We derived the absolute parameters for both systems and discussed their evolutionary states. In addition to the simultaneous analysis, we have also analyzed the change in mid-eclipse times for V566 Oph, and found cyclic variations, for which we have discussed light-time effect and magnetic activity as their potential origin, superimposed on a secular change due to a mass transfer between the components of the binary.