Erdin Bozkurt

Neotectonics of Turkey – a synthesis

AbstractTurkey forms one of the most actively deforming regions in the world and has a long history of devastating earthquakes. The belter understanding of its neotectonic features and active tectonics would provide insight, not only for the country but also for the entire Eastern Mediterranean region. Active tectonics of Turkey is the manifestation of collisional intracontinental convergence- and tectonic escape-related deformation since the Early Pliocene (~5 Ma). Three major structures govern the neotectonics of Turkey; they are dextral North Anatolian Fault Zone (NAFZ), sinistral East Anatolian Fault Zone (EAFZ) and the Aegean–Cyprean Arc. Also, sinistral Dead Sea Fault Zone has an important role. The Anatolian wedge between the NAFZ and EAFZ moves westward away from the eastern Anatolia, the collision zone between the Arabian and the Eurasian plates. Ongoing deformation along, and mutual interaction among them has resulted in four distinct neotectonic provinces, namely the East Anatolian contractiona...

Tectonics and Magmatism in Turkey and the Surrounding Area

This volume contains 23 papers from a range of international contributors, describing recent research into the tectonics and magmatism of Turkey and its surroundings. This region is sited at the collision zone between Eurasia and Afro-Arabia and, as such, provides an extraordinarily complete and well-exposed record of the staged tectonic evolution of this sector of the Alpine-Himalayan orogen. The geological history of this area involves separation of continental fragments from the margin of Gondwana, their migration across the Tethyan oceans, the subsequent closure of these oceans and, finally, the development of the neotectonic regime, which continues to evolve to the present day. Such a comprehensive record is relevant to the understanding of collisional zones worldwide. The volume is divided into five sections: Tethyan evolution, Neotethyan ophiolites, post-Tethyan basin evolution, neotectonics and igneous activity. The first two sections deal with Tethyan oceans, whose growth and subsequent closure dominated the geodynamic framework in the Mesozoic and Cenozoic. The subsequent sections deal with more recent geological developments from the Balkan Peninsula in the west to the Transcaucasus in the east that followed consumption of the Tethyan oceans. There is a broad mix of papers throughout the volume: wide-ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution, specific aspects of extensional and strike-slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area. Tectonics and Magmatism in Turkey and the Surrounding Area presents up-to-date results and ideas from a large number of international contributors on a wide range of current research activity in this region. It is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern Mediterranean geology.

Southern Menderes Massif: an incipient metamorphic core complex in western Anatolia, Turkey

In the southern sector of the Menderes Massif, north of Selimiye (Milas) augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed Palaeozoic ‘envelope’. The granitic rocks exhibit a moderately-dipping mylonitic foliation and NNE-SSW- trending mineral elongation lineation. The progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked, from bottom to top, by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite. The kinematic indicators exhibit a top-to-the south, down-dip sense of shear. These structures are attributed to exhumation of the granitic rocks of the massif along a major, south-dipping, normal-sense shear zone that accommodated crustal extension during Late Oligocene collapse of the orogen in western Turkey. Thus, the southern Menderes Massif may be interpreted as the exhumed footwall of a major extensional shear zone, and possibly as an incipient core complex.

Origin of NE-trending basins in western Turkey

Abstract The origin of NE-trending basins and their relation to the E–W-trending grabens in western Turkey have been the subject of long lasting debate. The stratigraphical and structural aspects of the basin fill in the E–W Gediz Graben and in the NE-trending Gordes, Demirci, Selendi and Usak-Gure basins located immediately to the north of the graben are reassessed here. The Gediz Graben is characterized by two contrasting sedimentary packages that are separated by an angular unconformity. These are: (1) a folded Miocene-Lower Pliocene megasequence, exhumed on the shoulders of the graben; and (2) nearly horizontal Plio-Quaternary sediments. In contrast, the NE-trending basins comprise solely Lower–Middle Miocene sediments and unconformably overlying Quaternary alluvium. The Miocene configuration of different trending basins shows close similarities, and suggests that they started to develop simultaneously during the Early Miocene. Miocene sedimentation in these basins occurred in the hanging-wall of a presently low-angle, north-dipping, major normal fault (detachment fault) that bounds the Gediz Graben to the south, while the metamorphic rocks of the Menderes Massif in the footwall were progressively deformed, uplifted and exhumed. The Miocene sediments in the NE-trending basins were also deformed along broad folds with axes parallel to the basin margins. The extension was therefore partially complemented by a horizontal shortening at high-angle to it, and the basin-bounding faults together with the blocks they bound have rotated around vertical axes. In this scenario, the NE-basins started to develop as ”Aegean type cross-grabens”, and the bounding structures are interpreted as ”rotational accommodation faults” that accommodate differential stretching in the hanging-wall of the major breakaway fault, accompanying the Early Miocene phase of extension in western Turkey. Later, during the neotectonic extensional period commencing in the Pliocene (5 Ma), the margin-bounding high-angle normal faults of the modern E–W Gediz Graben cut and displaced the presently low-angle breakaway fault. Some parts of the NE-trending basins were therefore trapped within the E–W graben and some other parts remained as hanging basins on the footwall of the normal fault, along the northern margin of the Gediz Graben. It is concluded that the classification of basins for the area of the Gediz Graben and those located to its north as ”replacement and revolutionary” structures is still valid. It is also confirmed that the latest Oligocene–Early Miocene back-arc extension and/or orogenic collapse cannot be responsible for the entire history of continental extensional tectonics and the extension in western Turkey is not a continuous event, but occurred in two stages separated by a short period (7–5 Ma); the second being the Plio-Quaternary phase of N-S extension related to the westward escape of the Anatolian block.

Tectonic evolution of the Gediz Graben: field evidence for an episodic, two-stage extension in western Turkey

Western Turkey is one of the most spectacular regions of widespread active continental extension in the world. The most prominent structures of this region are E–W-trending grabens (e.g. Gediz and Buyuk Menderes grabens) and intervening horsts, exposing the Menderes Massif. This paper documents the result of a recent field campaign (field geological mapping and structural analysis) along the southern margin of the modern Gediz Graben of Pliocene (~ 5 Ma) age. This work provides field evidence that the presently low-angle ductile-brittle detachment fault is cut and displaced by the high-angle graben-bounding normal faults with total displacement exceeding 2.0 km. The evolution of the N–S extension along the Gediz Graben occurred during two episodes, each characterized by a distinct structural styles: (1) rapid exhumation of Menderes Massif in the footwall of low-angle normal fault (core-complex mode) during the Miocene; (2) late stretching of crust producing E–W grabens along high-angle normal faults (rift mode) during Pliocene–Quaternary times, separated by a short-time gap. The later phase is characterized by the deposition of now nearly horizontal sediments of Pliocene age in the hanging walls of the high-angle normal faults and present-day graben floor sediments. The evolution of extension is at variance with orogenic collapse and/or back-arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the Aegean-Cyprean subduction zone. Consequently, it is misleading to describe the Miocene sediments exhumed on shoulders of the Gediz Graben as simple graben fill.

Timing of Extension on the Büyük Menderes Graben, Western Turkey, and Its Tectonic Implications

Abstract The Büyük Menderes Graben is one of the most prominent structures of western Anatolia (Turkey) and borders the Aegean. New structural and stratigraphic evidence demonstrates that the (?)Miocene fluvio-lacustrine, coal-bearing red clastic sediments exposed along the northern margin of the graben are northward back-tilted, locally folded and overlain unconformably by horizontal terraced Pliocene-Pleistocene sediments. Also, there is no evidence that these red clastics at the base of the Neogene sequence were deposited during neotectonic extension. It is suggested here that these sediments cannot be regarded as passive neotectonic graben-fill deposits. This new evidence further indicates that the age of the modern Büyük Menderes Graben is Pliocene, younger than previously considered (Early-Middle Miocene) and that initiation of north-south neotectonic extensional tectonics in the graben, and thus in western Anatolia, is unlikely to have resulted from orogenic collapse. The Pliocene estimate of the start of extension is in close agreement with the start of slip on the North Anatolian Fault Zone. The north-south extensional tectonics, and associated east-west faulting and basin formation, commenced during the Pliocene due to the effect of westward tectonic escape of the Anatolian block along the North and East Anatolian Faults. New mammal evidence also constrains the start of slip on the younger faults which bound the present-day graben floor to c. 1 Ma. The Büyük Menderes Graben has experienced a two-stage extension. An initial extension (latest Oligocene-Early Miocene) along initially moderately, steeply dipping normal faults was superseded by movement on steeper normal faults during the (?)Pliocene. The two phases of deformation appear to reflect significant changes in the tectonic setting of western Anatolia and are attributed to orogenic collapse followed by tectonic escape.

Introduction to the Geology of Turkey—A Synthesis

JUST AS ANATOLIA (Asia Minor) has had a rich cultural history as home to numerous and diverse civilizations, the geology of Turkey is a colorful, fascinating mosaic. Presently lying within the Alpine-Himalayan mountain belt near the junction of Eurasia, Africa, and Arabia, the landmass that underlies most of Turkey was once situated at the collisional boundary of two megacontinents—Gondwana in the south and Laurasia in the north. The geological framework of Turkey comprises many lithospheric fragments that were derived from the megacontinental margins and then were amalgamated during the Alpine orogeny when the Arabian plate collided with the Anatolian plate in the Late Cretaceous-Tertiary. As the rifts widened, the Tethyan oceans developed; when, subsequently, the megacontinents collided, these oceans closed sequentially.

Metamorphic history of the southern Menderes massif, western Turkey

Metamorphic mineral compositions and textures are integrated with microstructures to test tectonic models for the construction and exhumation of a mid-crustal terrane in western Turkey. The southern Menderes massif, part of the Alpine orogen, is composed of a tilted sequence of metasedimentary rocks that structurally overlies orthogneiss. Garnet-biotite equilibria for schists collected along north-south traverses consistently indicate temperatures of 430 °C for the southernmost, structurally highest garnet-bearing rocks, ∼500 °C for structurally intermediate rocks, and ∼550 °C for the structurally deepest rocks near the contact with the orthogneiss. There are no detectable discontinuities in metamorphic grade from north to south within the schist unit, or between the schist and overlying lower-grade and underlying higher-grade rocks. Pressure estimates are less certain; geobarometric results for the schists yield P ≈ 8 kbar, but mineral assemblages and structural data are consistent with lower pressures (≤6 kbar). Metamorphic textures and garnet zoning in the Menderes schists indicate metamorphism during a single thermal event accompanying development of the main penetrative foliation. Top-to-north fabrics formed during folding/thrusting and were synkinematic with garnet growth. Top-to-south chloritic shear bands truncate the earlier foliation and overprint peak-metamorphic assemblages and textures. We propose that these metamorphic features and structures indicate synmetamorphic shortening followed by extension during Alpine orogenesis.

The structure of the Palaeozoic schists in the Southern Menderes Massif, western Turkey: a new approach to the origin of the Main Menderes Metamorphism and its relation to the Lycian Nappes

The Early Eocene to Early Oligocene tectonic history of the Menderes Massif involves a major regional Barrovian-type metamorphism (M1, Main Menderes Metamorphism, MMM), present only in the Palaeozoic-Cenozoic metasediments (the so-called “cover” of the massif), which reached upper amphibolite facies with local anatectic melting at structurally lower levels of the cover rocks and gradually decreased southwards to greenschist facies at structurally higher levels. It is not present in the augen gneisses (the so called “core” of the massif), which are interpreted as a peraluminous granite deformed within a Tertiary extensional shear zone, and lie structurally below the metasediments. A pronounced regional (S1) foliation and approximately N-S trending mineral lineation (L1) associated with first-order folding (F1) were produced during D1 deformation coeval with the MMM. The S1 foliation was later refolded during D2 by approximately WNW-ESE trending F2 folds associated with S2 crenulation cleavage. It is now commonly believed that the MMM is the product of latest Palaeogene collision across Neo-Tethys and the consequent internal imbrication of the Menderes Massif area within a broad zone along the base of the Lycian Nappes during the Early Eocene-Early Oligocene time interval. However, the meso- and micro-structures produced during D1 deformation, the asymmetry and change in the intensity and geometry of the F2 folds towards the Lycian thrust front all indicate an unambiguous non-coaxial deformation and a shear sense of upper levels moving north. This shear sense is incompatible with a long-standing assumption that the Lycian Nappes were transported southwards over the massif causing its metamorphism. It is suggested here that the MMM results from burial related to the initial collision across the Neo-Tethys and Tefenni nappe emplacement, whereas associated D1 deformation and later D2 deformation are probably related to the northward backthrusting of the Lycian nappes.

The Kazova basin: an active negative flower structure on the Almus Fault Zone, a splay fault system of the North Anatolian Fault Zone, Turkey

Abstract The Kazova basin is located within the Almus Fault Zone (AFZ), a splay fault system of the North Anatolian Fault Zone, in the central Pontides, Turkey. It is a 0.7–10-km-wide, 60-km-long, wedge-shaped right-lateral strike-slip depression bounded by the Mercimekdaǧi-Camdere fault set in the north and the Tokat fault set in the south. The Kazova basin is superimposed on pre-Pliocene basement rocks while its basin fill comprises the Pliocene to lower Quaternary Kizkayasi and Cerci formations, and Quaternary alluvials. The Mercimekdaǧi-Camdere and Tokat fault sets of the AFZ, the basin-margin faults of the Kazova basin have a considerable amount of normal separation, and show a divergent character. Here, the Kazova basin is interpreted as an active negative flower structure, where the combination of normal movement (extension) along the different segments of the AFZ, and the oblique extension between its branching splays resulted from a natural response to the anticlockwise rotation along the AFZ are suggested basin-forming mechanism. This kind of basin is first from Turkey although different types of strike-slip basins, such as fault-wedge, pull-aparts, composite pull-aparts, are widely represented and well-known.