Petrology and geochemistry of post-collisional Middle Eocene volcanic units in North-Central Turkey: Evidence for magma generation by slab breakoff following the closure of the Northern Neotethys Ocean

The Eocene volcano-sedimentary units of Northern Anatolia are confined into a narrow zone trending parallel to the Intra Pontide and İzmir–Ankara–Erzincan sutures, along which the northern branch of the Neotethys Ocean was closed during a period between Late Maastrichtian and Paleocene. The Middle Eocene formations overlie both the imbricated and highly deformed units of the suture zone, which are Paleocene or older in age, as well as the formations of adjacent continental blocks with a regional disconformity. Therefore, they can be regarded to be post-collisional. These units are composed of subaerial to shallow marine sedimentary beds (i.e. the Örencik formation) at the base and a subaerial volcanic unit (i.e. the Hamamözü formation) in the middle and at the top. This sudden facies change from marine to subaerial environment in the Middle Eocene is a common phenomenon across northern Turkey, implying that a regional uplift event occurred possibly across the suture zone before the initiation of the volcanism during Lutetian. The Middle Eocene lavas span the whole compositional range from basalts to rhyolites and display a calc-alkaline character except for alkaline to mildly-alkaline lavas from the top of the sequence. All lavas display a distinct subduction signature. Our geochemical data indicate that calc-alkaline lavas were derived from a subduction-modified source, whereas alkaline to mildly-alkaline lavas of the late stage were possibly sourced by an enriched mantle domain. Magmas evolved in magma chambers emplaced possibly at two different crustal levels. Magmas in deeper (> 13 km) and possibly larger chambers fractionated hydrous mafic minerals (e.g. amphibole and biotite), two pyroxenes and plagioclase and assimilated a significant amount of crustal material. Intermediate to acid calc-alkaline lavas and pyroclastics were derived from these chambers. Magmas in the shallower chambers, on the other hand (~ < 12 km), crystallized anhydrous mineral assemblages, assimilated little or no crustal material and fed basic to intermediate lavas in the region. Both deep and shallow chambers were periodically replenished by mafic magmas. We argue that a slab breakoff model explains better than any alternative model (i) why the volcanism during the Middle Eocene was confined into a rather narrow belt along the suture zone, (ii) why it initiated almost contemporaneous with a regional uplift after the continental collision event, (iii) why it postdated arc volcanism along the Pontides in the north by 15–20 My, (iv) why it assimilated significant amount of crustal material, and (v) why alkalinity of lavas increased in time.     

Geotechnical Problems of Botan Bridge Piers Construction (Siirt,Turkey)

The Botan Bridge in Siirt (Turkey), now under construction, will carry a road across the River Botan and the lake which will be created by the Pervari Dam, 180 m high. The bridge has two piers with height of 115.88 m, and the total length of deck is 450 m which is built in accordance with the free cantilever method. The paper deals with foundations used in Botan Bridge for dam reservoir crossing bridge structures. Some of the geotechnical problems of construction of these foundations are highlighted. The slope debris deposits and basement rocks being ophiolite and the metamorphic rocks (calc schist, chlorite schist and meta-sediments) contribute to the geotechnical problems. Ophiolite, calc schist and chlorite schist, contains significant percentage of chlorite, feldspars, carbonates and serpentinites; their effect needs to be assessed in the interpretation of pier foundation construction and slope stability calculations. For this purpose, in situ and laboratory tests have been performed. Ophiolitic rock mass properties are an important factor for slope stability of rocks and foundation construction.     

Excavation Problem in Mixed Ground Conditions at the Kabatas–Mecidiyekoy Metro (Istanbul) Tunnels

Mechanized tunnelling is a well-established tunnel construction method which allows constructing tunnels in various conditions including mixed ground conditions as well as tunnels in vulnerable urban areas. The selection of the excavator suitable for the geological structure is important in terms of realizing an efficient tunnel excavation. Tunnel excavation studies of Istanbul Kabatas–Mecidiyeköy Metro tunnels are implemented as a double tube. Geology in this section is composed of sandstone, siltstone, mudstone interbedded or as separate units along with dyke intrusions. Calcareous clay, clayey limestone, clayey sand are also rarely observed. Between the Kabatas–Mecidiyekoy tunnels includes two types of mechanical excavation methods namely tunnel boring machine (TBM) and new Austrian tunnelling method (NATM). Main purpose of this study is mixed ground and their impacts on mechanized tunnelling. At the end, some issues have been presented which seems to be important for the success of TBM and NATM in the mixed grounds. As the tunnel excavation studies continued, the problem of collapse on the ground surface of Barbaros Boulevard in Besiktas station increased the importance of tunnel excavation under mixed ground conditions.     

Geomorphic evidence for active tectonic deformation in the coastal part of Eastern Black Sea,Eastern Pontides,Turkey

The Eastern Pontides (EP), which is the under transpressional deformation zone, is an active mountain belt that has been rising rapidly since the Cenozoic era because of the Arabian-Eurasian convergence. Morphometric studies have been performed to investigate the tectonic activity of this region and better understand the characteristics of the faults geomorphologically; the faults control the mountain fronts in the drainage basin of the EP. The results show the Hypsometric Curve (HC)-Hypsometric Integral (0.37-HI-0.67), Basin-Shaped Analysis (1.2-B_s-7), Valley-Floor-Width to Height-Ratio (0.4-V_f-1.2) and Asymmetry Factor (35-AF-81) applied to 46 drainage basins together with 9 tectonically controlled geomorphic indices (1.2-S_mf-1.5) and a Stream Length Gradient (30-S_L-120) indicate that the EP is tectonically active, and when the areas are evaluated according to S_mf and V_f analyses, the tectonic level is relatively high. According to our conceptual model for the uplifting of the EP, with respect to field studies and morphometric analysis, (i) the EP is the active deformation zone and has a “push-up” geometry in conjunction with the North Anatolian Fault; (ii) the EP is progressively uplifting at a rate of more than 0.5 mm/yr in along with the thrust faults of the Black Sea Fault (BSF) and Borjomi-Kazbegi Fault (BKF).     

The Strandja Massif and the İstanbul Zone were once parts of the same palaeotectonic unit: new data from Triassic detrital zircons

Spatially continuous rock assemblages that share similar environmental evolution or structural features can be classified as a single tectonic unit. This approach enables to link dispersed units or massifs with each other and sometimes can be subjective, depending on the classification criteria. The relationship and the nature of the contact between the Strandja Massif and the ?stanbul Zone have been controversial due to the Cainozoic cover. Amalgamation of these units was claimed as early as the Aptian-Albian.

Lower Triassic sedimentary rocks, which are overlain by the Carboniferous flysch with a N-verging thrust fault are exposed NW of the ?stanbul Zone. This study reveals the spatial relationship between the Strandja Massif and the ?stanbul Zone deduced from the U-Pb dating and Lu-Hf isotopes of the detrital zircons from these Lower Triassic clastics. Our results show that the early Triassic basin was fed from a provenance that included arc-related Upper Carboniferous-Lower Permian magmatic rocks which is much more likely to be the Strandja Massif than the ?stanbul Zone. The second outcome of this study is that a unit that previously assigned to Palaeozoic turned out to be Triassic, which brings the Strandja Massif farther to the east, into the northern ?stanbul Zone.     

Evaluation of sustainable water supply alternatives in karstified rock masses using GIS and AHP methodology for Antalya (Turkey) urban area

The demand for water by growing populations and agricultural operations in the Antalya urban area is expected to increase significantly in the near future. For that reason, alternative water sources are important to the future of Antalya. There are a large number of water sources around Antalya to meet the water needs of the city. These are classified as surface water, groundwater, and reclaimed water. One of the options considered is the provision of water from rock pores. Rock pore water has been adopted as a potential alternative for water resources in the area. It is proposed to drill horizontal galleries using the microtunnel machine to the rock masses in carbonate aquifers to obtain new water resources. This study presents a useful method to find water supply alternatives for urban areas like Antalya. In this study, karstified rock masses have been evaluated for the karst hydrosystems and water source from rock pores using geographic information systems and analytical hierarchy process. Additionally, this study discusses the practical value of the provision of water from rock pores, as well as the possibility of application and selection of potential areas.     

Evaluation of an abandoned aggregate quarry used for uncontrolled waste disposal using remote sensing technologies (Atabey,Isparta-Turkey)

Today, waste is an important environmental problem that needs to be solved. The way it is collected and managed should be considered with respect to the negative impact on the environment. Although the Atabey aggregate quarry was operated with natural sand-gravel until 2 years ago, it was closed due to technological renovation in the crushing-screening unit and uneconomic production. This area was later used by the Atabey Municipality as a waste storage area. Thus, uncontrolled storage occurred at the quarry site. As a result, new, more intensive environmental problems have emerged in the area, such as visual pollution and the pollution of groundwater. This paper evaluates the impact of municipal solid waste disposal in an abandoned quarry site on groundwater, land surface temperature, land surface moisture, and vegetation cover using GIS (Geographic Information Systems) and remote sensing technologies. According to the obtained results, the solid wastes stored in the area caused groundwater pollution, increased surface temperature, and reduced soil moisture.     

Secondary toppling failure analysis and optimal support design for ignimbrites in the Ihlara Valley (Cappadocia,Turkey) by finite element method (FEM)

Geotechnical and Geological Engineering - Kizilkaya ignimbrite, characterized by a blocky structure in the Ihlara Valley (Cappadocia, Turkey), poses many hazards to visitors and the human-made...     

North Atlantic Oscillation influences on Turkish lake levels

The North Atlantic Oscillation (NAO) is a large‐scale mode of natural climate variability governing the path of Atlantic mid‐latitude storm tracks and precipitation regimes in the Atlantic and Mediterranean sectors. The primary focus of this study is to investigate the variability of lake levels in seven lakes scattered across Turkey using the method of continuous wavelet transforms and global spectra. The long winter (December, January, February and March) lake‐level series and the NAO index (NAOI) series were subjected to wavelet transform. The global wavelet spectrum (energy spectrum of periodicities) of lake levels and winter NAOI anomalies, in most cases, revealed a significant correlation. It was shown that the Tuz, Sapanca, and Uluabat lakes reflect much stronger influences of the NAO than the other four lakes. In contrast, weak correlations were found in the coastal areas of the Mediterranean and eastern Turkey. The periodic structures of Turkish lake levels in relation to the NAO revealed a spectrum between the 1‐year and 10‐year scale level. Although the periodicities of more than 10‐year scale levels were detected, explaining significant relations between the NAO and these long‐term periodicities remains a challenging task. The results of this study are consistent with the earlier studies concerning the teleconnection between the NAO and climate variables in Turkey. Copyright © 2009 John Wiley & Sons, Ltd.