The geochronology and origin of mantle sources for late cenozoic intraplate volcanism in the frontal part of the Arabian plate in the Karacadağ neovolcanic area of Turkey. Part 1. The results of isotope-geochronological studies

This paper considers results from isotope-geochronological (K-Ar) studies of the products of Neogene-Quaternary volcanism in the Karacada? area, which is situated within the northern frontal part of the Arabian plate. It was found that magmatic activity has been evolving at this location for at least the last 11–10 Myr and was distinctly discrete in character. Three stages of volcanism have been identified: (I) Early or Miocene, ～11–6.7 Ma; (II) Middle or Pliocene-Early Quaternary, 4–1 Ma; and (III) Late or Late Quaternary, 0.4–0.1 Ma. The most recent manifestations of magmatic activity in the region date back to about 100000 years ago. An analysis of the spatial distribution of volcanic centers of different ages in the Karacada? neovolcanic area shows that the magmatism of that region involved a lateral migration of activity from northwest to southeast along a major regional tectonic fault. The migration was caused by the movement of local tension zones where the lithosphere was thinner and deep-seated mantle magmas were ascending.     

Late Cenozoic stress states around the Bolu Basin along the North Anatolian Fault, NW Turkey

This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional transtensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively.The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trending σ_Hmax(σ₁) and σ_Hmin(σ₃) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending σ₃ axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trending σ₁ and σ₃ axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block.     

Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust,Eastern Turkey: Implications for crustal thickening to delamination

Early Cenozoic (48–50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO₂ contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high I_Sr (0.70474–0.70640) and low ε_Nd (50 Ma) values (? 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr–Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic.     

Identification and origin of bitumen in Neolithic artefacts from Demirköy Höyük (8100 BC): Comparison with oil seeps and crude oils from southeastern Turkey

Two ring-like artefacts from the aceramic Neolithic site of Demirköy Höyük in southeastern Turkey were analysed using geochemical techniques in order to determine whether they were prepared using a bitumen amalgam or not. The artefacts, dated 8100 BC, are early evidence of the innovative use of a petroleum-based material to prepare pieces of ornaments (beads, rings, etc.) for the elite of a Neolithic settlement. In order to trace the source of the presumed bitumen, two oil seeps, Boğazköy and Yeşilli, were sampled. To complete the genetic references, geochemical data on crude oils from the main oil fields from the area were compiled.Basic geochemical data show that bitumen is present in the artefacts. Sterane and terpane patterns, as well as carbon isotopic data on C₁₅₊ saturated and C₁₅₊ aromatic hydrocarbons, allowed us to conclude that the Demirköy Höyük bitumen and the Boğazköy oil seep were generated from a Silurian source rock. The detailed geochemical characteristics show, however, that the Demirköy Höyük bitumen does not correlate perfectly with the Boğazköy oil. This discrepancy suggests several explanations: the real bitumen source may be elsewhere in the vicinity and has not been discovered or was at the Boğazköy oil seep location but with slightly different properties in Neolithic times, or has disappeared. Another possibility is that the slight molecular differences are due to weathering effects, which affected the pristine bitumen within the archaeological sample.     

The changing world under the corona virus threat—from human needs to SDGs and what next?

The COVID-19(coronavirus)disease has affected over 100 countries in a matter of weeks.The way humans live and work on planet Earth has changed profoundly over the last months.Many lives and livelihoods have been lost.Ways of working,shopping,and social interactions are all vastly different for most of us.We do not know when the current crisis will end,or how far we will"return"to the way things were before the pandemic.The world is experiencing one of the most transformative moments of the last 100 years.The social,economic,and political influences of the COVID-19 crisis have already been hugely momentous,we do not utterly understand it.Looking ahead,we have inevitably had to make important public health,economic,governance,and ecological decisions with less information than usual and to reverse recently adopted policies,which can lead to an era of disruptive transformations to sustainability.During these historic times,we must understand the hidden reality of the earth system and attempt to transform our needs so that we all have a sustained future on our planet.     

A field application for lime stabilization

This study presents the improvements achieved as a result of the lime stabilization application conducted by the joint effort of the Turkish Association of Lime Industrialists and the General Directorate of Rural Services on the 200 m long section of the Ankara Province Yukar? Yurtçu Village road where green and brown clays are dominant. The study also numerically demonstrates the impacts of these improvements on the road section based on the results of various laboratory and field tests. The lime stabilization in field conditions was performed with 5% lime for both clays and was applied as a 30 cm thick single layer. In the soaked California bearing-ratio (CBR) tests conducted in the laboratory, increases that reach up from 16 and 21 times compared to initial soaked CBR values were observed in green and brown clays, respectively, at the end of 28 days. The high increases observed in soaked CBR values would reduce the upper layer thickness of the roads. The similar improvements are also achieved in unconfined compression and plate loading tests. The comparisons performed with the plate loading tests clearly demonstrated the behavior of the surface to lime and its cure impact.     

Analysis of Ezinepazarı–Sungurlu Fault Zone (Turkey) using Landsat TM data and its kinematic implications

The study area is located between Çorum and Amasya along the Ezinepazar?–Sungurlu Fault Zone (ESFZ) which is regarded as the splay of the North Anatolian Fault Zone (NAFZ). By this study, the 1/25,000 scaled geological map of the study area was prepared, and its stratigraphic and tectonic characteristics were unraveled as a result of palaeontological and petrographical analyses of the samples collected from different rock units. Particularly, geologic ages of the Late Jurassic–Early Cretaceous Ferhatkaya and Carcurum and Middle Eocene Çekerek formations were provided from palaeontological determinations. Using Landsat TM and Shuttle Radar Topography Mission 3 (SRTM 3) data of the region, the borders between the rock units and the tectonic characteristics in the study area were clarified by spectral and spatial enhancement methods. Kinematic characteristics of ESFZ obtained from the young sedimentary rocks along both sides of the fault zone were also inferred in this study. Understanding the kinematic and geometrical characteristics of the faults is important in terms of the seismotectonics of the region. In the statistical study conducted on the basis of the directions of the lineaments indicates the highest concentrations in general between N 50° - 60° E and N 60° - 70° E. Band 7 of the study area was enlightened in SE direction taking into consideration the relation of the geologic structures in the region with NAFZ and ESFZ and their general strike directions. Along with the formation of NAFZ, the region has undergone a counterclockwise rotation of approximately 20°–30°, which has developed between the “splay” faults in the south block of that fault. These faults are strike-slip faults formed under the compressional regime roughly in a NW–SE direction. It is noted that this tectonic regime has developed under compression in NW–SE direction, which was dominant in similar kinematic analysis studies conducted on NAFZ.     

Numerical Simulation of Small Perturbation on an Accretion Disk Due to the Collision of a Star with the Disk Near the Black Hole

In this paper, perturbations of an accretion disk by a star orbiting around a black hole are studied. We report on a numerical experiment, which has been carried out by using a parallel-machine code originally developed by Dönmez (2004). An initially steady state accretion disk near a non-rotating (Schwarzschild) black hole interacts with a “star”, modeled as an initially circular region of increased density. Part of the disk is affected by the interaction. In some cases, a gap develops and shock wave propagates through the disk. We follow the evolution for order of one dynamical period and we show how the non-axisymetric density perturbation further evolves and moves downwards where the material of the disk and the star become eventually accreted onto the central body. When the star perturbs the steady state accretion disk, the disk around the black hole is destroyed by the effect of perturbation. The perturbed accretion disk creates a shock wave during the evolution and it loses angular momentum when the gas hits on the shock waves. Colliding gas with the shock wave is the one of the basic mechanism of emitting the X-rays in the accretion disk. The series of supernovae occurring in the inner disk could entirely destroy the disk in that region which leaves a more massive black hole behind, at the center of galaxies.