Erdinç Yiğitbaş

Ophiolitic and metamorphic assemblages of southeast Anatolia and their significance in the geological evolution of the orogenic belt

The southeast Anatolian orogen may be divided into three roughly east-west trending structural zones formed as a result of continental collision between the Taurus platform and the Arabian continent. Along the orogenic belt, metamorphic and ophiolitic rocks occur widely. The ophiolites represent remnants of the ocean or oceans which were totally consumed between these converging continental blocks during Late Cretaceous to Miocene period. Metamorphic rocks formed from the oceanic as well as the continental rocks which were incorporated into a nappe stack during the consumption of the oceanic lithosphere and the progressive southward advance of the nappes toward the Arabian continent. The metamorphic units, together with the ophiolite associations, provide stratigraphic and petrologic evidence indicating time, place, and environment of formation of these units; the metamorphic units also provide evidence of nappe transportation stages which are complementary to the data derived from the sedimentary successions in the evaluation of the orogenic evolution of southeast Anatolian orogen.

Geology of the Saros graben and its implications for the evolution of the North Anatolian fault in the Ganos–Saros region, northwestern Turkey

Abstract Palaeo- and neo-tectonic evolutions of the Gulf of Saros, northwestern Turkey, were investigated based on geological mapping, geomorphology, seismicity and GPS measurements. In this area three overlapping basins were differentiated: the Thrace, Enez and Saros basins. The Thrace basin opened during the middle Eocene on the continental Strandja Massif as a post-collisional, fault-controlled extensional basin after the closing of the Intra-Pontide Ocean to the south. This basin reached its greatest extent during the Late Eocene–Early Oligocene and then, turned into an intramontane terrestrial basin from the middle Miocene onwards. The Enez basin opened along the southern margin of the former Thrace basin as an E–W-trending half graben during the middle Miocene. The age and geometry of this basin corresponds to the extensional basins of the Aegean graben system to the south. Stratigraphy and structures related to the North Anatolian fault indicate that the fault started to be active since Pliocene and modified older structures. The fault zone evolved in two stages in and around the Gulf of Saros. During the initial stage the fault was trending as a single segment with a transpressional nature and without any stepping, and caused thrusting and folding subparallel to the main trace of the fault. Since the Late Pliocene the fault was left-stepping in the Saros area, giving rise to the Saros pull-apart basin. We modelled these two stages by using boundary element method, and found that there is a good correlation between the modelling results and geology and geomorphology.

Pre-Cenozoic tectono-stratigraphic components of the Western Pontides and their geological evolution

The Western Pontides of northern Turkey are a tectonic mosaic formed as a result of progressive welding of continental and oceanic fragments during the Palaeozoic and Mesozoic. In this region, three approximately east–west trending zones can be distinguished: the Pontide Zone representing the Pontides sensu stricto; the Sakarya Zone which is regarded as the southerly continental fragment; and the Armutlu–Ovacik Zone which is viewed as a tectonic mixture of the two zones. The Pontide Zone records development of an ensimatic island arc which are emplaced upon a continental fragment of Laurasian origin prior to the development of the Ordovician sediments. On top of this amalgamated basement, association thick sediments were deposited during the Palaeozoic and Early Mesozoic. During the Dogger, Palaeotethyan ophiolites were obducted onto the Pontides. The thick pile of cover sediments and the ophiolite slab were exhumed along a detachment surface while the underlying rocks were elevated to form a metamorphic core complex during the Early Cretaceous. The metamorphic rocks are exposed along the Ballidag, Sunnice, Almacik and Armutlu mountain ranges. This east–west trending structural high separated two coeval basins, the Ulus Basin and the Boyali Basin, which are located to the north and south respectively. During the Late Cretaceous, collision occurred between the Sakarya continent and the Pontide Zone. The continental convergence affected the region until the late Early Eocene. The present tectonic style of the region was established during this phase. From the Middle Eocene onwards only structural rearrangements have occurred. Copyright

New evidence and solution to the Maden complex controversy of the Southeast Anatolian orogenic belt (Turkey)

The volcanosedimentary units of Late Mesozoic-Tertiary age that outcrop in the Southeast Anatolian orogenic belt are commonly referred to as the Maden complex. There is a long-lasting controversy over its definition, age, stratigraphic and structural position, and the origin, and thus, the orogenic evolution. To solve this problem, large strips across the Southeast Anatolian orogenic belt have been studied extensively, and different rock groups which were regarded previously as the Maden unit have been differentiated. Their major characteristics and differences have been identified. The Maden unit sensu stricto is here redefined as a volcanosedimentary succession of Middle Eocene age representing a short-lived back-arc basin which reached the stage of an embryonic ocean. Presently, the Maden group occurs mainly within the lower nappe stack of the nappe zone of the Southeast Anatolian orogen. It rests stratigraphically on an amalgamated nappe package consisting of the different metamorphic tectonic units and, in turn, is overlain tectonically by the upper nappe units.

The Geology and Evolution of the Tokat Massif, South-Central Pontides, Turkey

The Tokat Massif is a major metamorphic complex of the south-central Pontides, the origin and development of which have long remained unknown. Recent detailed field-based mapping has revealed the major geological features of this complex. The Tokat Massif appears to be a tectonic mosaic composed of three major components: (1) the Yesilirmak Group; (2) the Turhal Metaophiolite; and (3) the Amasya Group. The Yesilirmak Group, which consists of a coherent lithoiogical sequence involving Paleozoic basement and overlying Triassic units, represents a short-lived basin assemblage. The Turhal Metaophiolite consists of an ophiolitic melange association and slices of a stratigraphically ordered ophiolite. The Amasya Group, the highest-standing tectonic unit, is represented by a lower Paleozoic clastic succession. The different major tectonostratigraphic assemblages of the Tokat Massif record a continent-continent collision between the Laurasian Amasya Group and the Gondwanan Yesilirmak Group. The Turhal Metaophioli...

Post-Late Cretaceous Strike-Slip Tectonics and Its Implications for the Southeast Anatolian Orogen, Turkey

The Southeast Anatolian orogen is a part of the eastern Mediterranean-Himalayan orogenic belt. Development of the Southeast Anatolian orogen began with the first ophiolite obduction onto the Arabian platform during the Late Cretaceous, and it continued until the Miocene. Its lingering effects continue to be discernible at present. During the Late Cretaceous-Miocene interval, three major deformational phases occurred, related to Late Cretaceous, Eocene, and Miocene nappe emplacements. The Miocene nappes are composed of ophiolites and metamorphic massifs. For a decade, field studies in the region have shown that strike-slip tectonics played a role complementary to the major horizontal effects of the nappe movement, as indicated by: (1) fault systems active during the Eocene; (2) different Eocene rock units composed of coeval continental and deep-sea deposits and presently tectonically juxtaposed; and (3) other stratigraphic and structural data obtained across the present strike-slip fault zones. These strik...

A geophysical approach to the igneous rocks in the Biga Peninsula (NW Turkey) based on airborne magnetic anomalies: geological implications

The Biga Peninsula, the complex geological structure of which has attracted intense attention so far, is located in the north-western part of Anatolia, Turkey. The Peninsula is tectonically very important region where different tectonic zones meet and comprises various kinds of sedimentary, metamorphic and igneous rocks. Among these rocks, igneous rocks occupy a considerably amount of areas in the Biga Peninsula and they are mostly associated with geothermal systems and mineral deposits, and therefore they play an important role in the geology of the Peninsula. In this paper, derived results concerning the geological features and subsurface structures of the igneous rocks in the Peninsula are presented based on analyzing the airborne magnetic anomalies. To this end, a MATLAB-based toolkit named as Gravity and Magnetic Interpretation (GMINTERP) that is composed of a set of linked functions in conjunction with a graphical user interface was developed and used for the interpretation of the airborne magnetic anomalies. Some linear transformations and derivative-based techniques were performed to process the potential field data-set and also to help build a general understanding of the geological details. The close agreement between the derived geophysical anomaly maps and the well-known surface geology map of the Biga Peninsula helped us discuss the geological implications of the geophysical traces. This study also indicated that the developed interactive data processing toolkit may assist geological interpretation even in the areas whose subsurface structure is poorly known.

On the effectiveness of directional derivative based filters on gravity anomalies for source edge approximation: synthetic simulations and a case study from the Aegean graben system (western Anatolia, Turkey)

Approximating the locations and lateral boundaries of anomalous bodies (i.e. geological structures or contacts) is an important task in the interpretation of gravity field data. Edge-approximating algorithms based on the computation of directional derivatives are widely used for enhancing the gravity anomalies of the source bodies. These algorithms effectively aid geological mapping and interpretation by locating abrupt lateral changes in density, and may also bring out subtle details in the data without specifying any prior information about the nature and type of the sources. Therefore, some model parameters of source bodies may be estimated in this way, which may guide the inverse modelling procedure. In this paper we aim to review the effectiveness of the commonly used edge-approximating algorithms such as vertical derivative, total horizontal derivative, analytic signal, profile curvature, tilt angle and theta map in terms of their accuracy on the determination of locations and lateral boundaries of source bodies. These detections were performed on both noise-free and noisy synthetic gravity data. Additionally, a real gravity data set from a well-known geological setting, the Aegean graben system (western Turkey), was considered and the derived anomaly maps were compared with known mapped geology.

Interpretation of gravity anomalies to delineate some structural features of Biga and Gelibolu peninsulas, and their surroundings (north-west Turkey)

On the basis of gravity data, derived anomaly traces were presented for the interpretation of some shallow structural features of Biga and Gelibolu peninsulas. Since building general understanding of subtle details about subsurface geology is of great importance considering that the study area is tectonically important, some advanced data processing techniques were implemented to gravity anomalies in a detailed manner. The procedures were performed using a MATLAB-based software package (Gravity and Magnetic Interpretation – GMINTERP). First, a finite element method was utilised to produce the residual data-set which is expected to reflect short wavelength anomalies arising from shallower geological structures, and thereafter some derivative-based algorithms were executed to analyse the residual data. The general anomaly patterns obtained from the applications clearly corresponded to the well-known surface geology map of the study area. Derivative-based anomaly maps put forward some findings about the existence of an old caldera structure in the western part of the Biga Peninsula. Additionally, abrupt lateral changes in anomaly amplitudes indicated the presence of some major structural discontinuities. Thus, findings yielded to make significant geological interpretations that might be important for further investigations. This study also showed that GMINTERP software package proved useful in assisting geological interpretation using geophysical potential field data-sets.

Petrology and geochemistry of eclogites from the Biga Peninsula, Northwest Turkey

The Biga Peninsula in northwest Turkey contains high-pressure metabasic eclogite that occur in two localities; as lenses within a 2 km long, 500 m thick quartz-phengite schist slice that is in turn found in the greenschist-facies metasedimentary rocks of the Çamlıca metamorphics, in Çamlıca area, and in two north-south elongated eclogites occurring as a tectonic slice between Kazdağ Massif and Çetmi Group, in Çetmi area. The P-T conditions under which these two exposures of eclogites formed are important to quantify the tectonic processes of subduction, exhumation and emplacement that high-pressure rocks of the Biga Peninsula record. New geochemical data suggest that both protoliths were N-type MORB basalt with high TiO2 and K2O–Na2O content and Nb/Y ratios. Most eclogite samples have tholeiitic signatures volcanic arc settings. ∑REE abundances range from 47.55 to 107.4 ppm. Europium anomalies are slightly variable (Eu/Eu* = 0.9–1.1) and trace element contents are similar to typical MORB based on tectonic discrimination diagrams. All eclogite protoliths were probably derived from depleted mantle source, modified by fluids within the subduction zone. The high-P mineral assemblage in eclogites from both regions is omphacite + garnet + glaucophane + phengite + epidote + zoisite + quartz. The inclusions in garnet are glaucophane, quartz, phengite, Ca-amphibole and rutile. P-T conditions are similar to each other and constrained at 550–700 °C and 16–24 kbar. Geochemical data and mineral chemistry indicate that the eclogites in the Biga Peninsula represent oceanic crust processed at significant depths (50–80 km) within the subduction channel and were juxtaposed with greenschist facies as a tectonic slice in the accretionary complex at higher structural levels.