Tectonics of the Aegean block: Rotation, side arc collision and crustal extension

A new tectonic model for the Aegean block is outlined in an effort to explain the widespread extension observed in this region. A key element in this model is the concept of “side arc collision” This term is used to describe the interaction of subducted oceanic lithosphere with continental lithosphere in a subduction arc in which oblique subduction occurs. In the Hellenic arc side arc collision is proposed for the northeast corner near Rhodes. The collision involves subducted African lithosphere, moving to the northeast almost parallel to the arc, with the continental mass of southwest Turkey. It affects the motion of the Anatolian-Aegean plate complex, but is not similar to continental collision since it occurs mostly at depth and involves only little, if any, of the shallow and rigid part of the continental lithosphere. The model assumes that Anatolia and the Aegean are part of one plate complex which undergoes counterclockwise rotation; if it were not for the side arc collision near Rhodes, the two blocks would exhibit similar deformation and might, in effect, be indistinguishable. At present, however, free and undisturbed rotation is possible only for the Anatolian block (excluding western Anatolia) where the motion is accommodated by subduction along the Cyprean arc. Further west the side arc collision inhibits this rotation along the subduction front. Still further west, undisturbed subduction along the central and western parts of the Hellenic arc is again possible and is well documented. On the other side of the Anatolian-Aegean plate complex, relatively free motion occurs along the North Anatolian fault zone including in the Aegean Sea. The combination of this motion in the north with the local obstruction of the rotation near Rhodes, must create a torque and a new pattern of rotation for the western part of the plate complex, thus creating a separate Aegean block. Since, however, the two blocks are not separated by a plate boundary, the Aegean block cannot move freely according to the new torque. Effective motion of the Aegean block relative to Europe and Anatolia, particularly in the north, is achieved through extension of the crust (lithosphere?). Thus the greatest amount of deformation (extension) is observed along the suture zone between the two blocks and, in particular, in the northeastern part of the Aegean block where motion relative to Anatolia must be greatest.     

Late Cenozoic tectonics and stratigraphy of northwestern Anatolia: the effects of the North Anatolian Fault to the region

In northwest Anatolia, there is a mosaic of different morpho-tectonic fragments within the western part of the right-lateral strike-slip North Anatolian Fault (NAF) Zone. These were developed from compressional and extensional tectonic regimes during the paleo- and neo-tectonic periods of Turkish orogenic history. A NE-SW-trending left-lateral strike-slip fault system (Adapazari-Karasu Fault) extends through the northern part of the Sakarya River Valley and began to develop within a N–S compressional tectonic regime which involved all of northern Anatolia during Middle Eocene to early Middle Miocene times. Since the end of Middle Miocene times, this fault system forms a border between a compressional tectonic regime in the eastern area eastwards from the northern part of the Sakarya River Valley, and an extensional tectonic regime in the Marmara region to the west. The extension caused the development of basins and ridges, and the incursions of the Mediterranean Sea into the site of the future Sea of Marmara since Late Miocene times. Following the initiation in late Middle Miocene times and the eastward propagation of extension along the western part of the NAF, a block (North Anatolian Block) began to form in the northern Anatolia region since the end of Pliocene times. The Adapazari-Karasu Fault constitutes the western boundary of this block which is bounded by the NAF in the south, the Northeast Anatolian Fault in the east, and the South Black Sea Thrust Fault in the north. The northeastward movement of the North Anatolian Block caused the formation of a marine connection between the Black Sea and the Aegean/Mediterranean Sea during the Pleistocene.     

Neotectonics of Turkey – a synthesis

Turkey forms one of the most actively deforming regions in the world and has a long history of devastating earthquakes. The better 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 contractional, the North Anatolian, the Central Anatolian ‘Ova’ and the West Anatolian extensional provinces. Each province is characterized by its unique structural elements, and forms an excellent laboratory to study active strike-slip, normal and reverse faulting and the associated basin formation.     

The termination of the North Anatolian Fault System (NAFS) in Eastern Turkey

ABSTRACT

The present-day tectonic framework of Turkey comprises mainly two strike-slip fault systems, namely dextral North Anatolian and sinistral East Anatolian faults. They are considered as the main cause of deformation patterns in Anatolia. These two mega shear systems meet at Kargapazar? village of Karl?ova county. The area to the east of the junction has a transpressional tectonic regime between the Eurasian and Arabian plates and is characterized, based on field observation, by a network of faults defining a typical horsetail splay structure. The horsetail splay is interpreted as marking the termination of the North Anatolian Fault System (NAFS), which continues eastward into the Varto Fault Zone (VFZ) and then dies out. The present study reveals that the VFZ is made up of two main parts, namely the principal displacement zone (PDZ) and the transpressional splay zone (TPSZ), both characterized by the right-lateral strike-slip with reverse motion. However, the area to the east of Varto is characterized dominantly by reverse-thrust faults and E–W-trending faults as shown by focal mechanism solutions. The generation of the VFZ as a transpressional termination to the NAFS can be related directly to the block movements of the Eurasian, Anatolian, and Arabian plates.     

Neogene tectono-sedimentary development of the western margin of the Çankırı Basin, central Turkey: reply to the comment of Kaymakçı 2003

The Neogene succession in the western margin of Çank?r? Basin is fragmented by a NNE‐trending tectonic sliver having normal faulted western and thrusted eastern margins. This newly recognized E‐vergent sliver was created by the NW–SE compression due to the North Anatolian and K?r?kkale–Erbaa Fault zones following late Pliocene, accommodating the internal deformation of the Anatolian plate. Determinations of the K?lçak, Kumarta? and Hançili formations on both sides of this tectonic sliver invalidate the stratigraphical, structural and basin evolution models previously proposed by Kaymakç?.     

Neotectonics of Turkey – a synthesis

Abstract

Turkey 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 contractional, the North Anatolian, the Central Anatolian ‘Ova’ and the West Anatolian extensional provinces. Each province is characterized by its unique structural elements, and forms an excellent laboratory to study active strike-slip, normal and reverse faulting and the associated basin formation. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Mantle flow-induced crustal thinning in the area between the easternmost part of the Anatolian plate and the Arabian Foreland (E Turkey) deduced from the geological and geophysical data

Eastern Anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the Arabian and Eurasian plates. This collisional and contractional zone is being accompanied by the tectonic escape of most of the Anatolian plate to the west by major strike-slip faulting on the right-lateral North Anatolian Transform Fault Zone (NATFZ) and left-lateral East Anatolian Transform Fault Zone (EATFZ) which meet at Karlıova forming an east-pointing cusp. The present-day crust in the area between the easternmost part of the Anatolian plate and the Arabian Foreland gets thinner from north (ca 44 km) to south (ca 36 km) relative to its eastern (EAHP) and western sides (central Anatolian region). This thinner crustal area is characterized by shallow CPD (12–16 km), very low Pn velocities (< 7.8 km/s) and high Sn attenuation which indicate partially molten to eroded mantle lid or occurrence of asthenospheric mantle beneath the crust. Northernmost margin of the Arabian Foreland in the south of the Bitlis–Pötürge metamorphic gap area is represented by moderate CPD (16–18 km) relative to its eastern and western sides, and low Pn velocities (8 km/s). We infer from the geophysical data that the lithospheric mantle gets thinner towards the Bitlis–Pötürge metamorphic gap area in the northern margin of the Arabian Foreland which has been most probably caused by mechanical removal of the lithospheric mantle during mantle invasion to the north following the slab breakoff beneath the Bitlis–Pötürge Suture Zone. Mantle flow-driven rapid extrusion and counterclockwise rotation of the Anatolian plate gave rise to stretching and hence crustal thinning in the area between the easternmost part of the Anatolian plate and the Arabian Foreland which is currently dominated by wrench tectonics.     

Insights into biaxial extensional tectonics: an examplefrom the Sandıklı Graben,West Anatolia,Turkey

West Anatolia, together with the Aegean Sea and the easternmost part of Europe, is one of the best examples of continental extensional tectonics. It is a complex area bounded by the Aegean–Cyprus Arc to the south and the North Anatolian Fault Zone (NAFZ) to the north. Within this complex and enigmatic framework, the Sandıklı Graben (10 km wide, 30 km long) has formed at the eastern continuation of the Western Anatolian extensional province at the north‐northwestward edge of the Isparta Angle. Recent studies have suggested that the horst–graben structures in West Anatolia formed in two distinct extensional phases. According to this model the first phase of extension commenced in the Early–Middle Miocene and the last, which is accepted as the onset of neotectonic regime, in Early Pliocene. However, it is controversial whether two‐phase extension was separated by a short period of erosion or compression during Late Miocene–Early Pliocene. Both field observations and kinematic analysis imply that the Sandıklı Graben has existed since the Late Pliocene, with biaxial extension on its margins which does not necessarily indicate rotation of regional stress distribution in time. Although the graben formed later in the neotectonic period, the commencement of extension in the area could be Early Pliocene (c. 5 Ma) following a severe but short time of erosion at the end of Late Miocene. The onset of the extensional regime might be due to the initiation of westward motion of Anatolian Platelet along the NAFZ that could be triggered by the higher rate of subduction at the east Aegean–Cyprus Arc in the south of the Aegean Sea. Copyright © 2003 John Wiley & Sons, Ltd.     

Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles

Turkey is moving westward relative to Eurasia, thereby accommodating the collision between Arabia and Eurasia. This motion is mostly taken up by strike-slip deformation along the North and East Anatolian Faults. The Sea of Marmara lies over the direct westward continuation of the North Anatolian Fault zone. Just east of the Sea of Marmara, the North Anatolian Fault splits into three strands, two of which continue into the sea. While the locations of the faults are well constrained on land, it has not yet been determined how the deformation is transferred across the Sea of Marmara, onto the faults on the west coast of Turkey. We present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep Marmara Sea basins of Çlnarclk, Central Marmara and Tekirdag, in order to determine how the deformation is distributed across the Sea of Marmara, and how it is taken up on the western side of the sea. The data show active dipping faults with associated tilting of sedimentary layers, connecting the North Anatolian Fault to strike-slip faults that cut the Biga and Gallipoli Peninsulas.     

Fault kinematic and Plio-Quaternary paleostress evolution of the Bakırçay Basin,Western Turkey

ABSTRACT

At the end of the Cenozoic, western Turkey was fragmented by intense intra-continental tectonic deformation resulting in the formation of two extensional areas: a transtensional pull-apart basin systems in the northwest, and graben systems in the central and southwest areas. The question of the connection of this Late Cenozoic extensional tectonics to plate kinematics has long been an issue of discussion. This study presents the results of the fault slip data collected in Bak?rçay Basin in the west of Turkey and addresses changes in the direction of extensional stresses over the Plio-Quaternary. Field observations and quantitative analysis show that Bak?rçay Basin is not a simple graben basin that has evolved during a single phase. It started as a graben basin with extensional regime in the Pliocene and was transformed into a pull-apart basin under the influence of transtensional forces during the Quaternary. A chronology of two successive extensional episodes has been established and provides reasoning to constrain the timing and location of subduction-related back-arc tectonics along the Aegean region and collision-related extrusion tectonics in Turkey. The first NW–SE trending extension occurred during the Pliocene extensional phase, characterized by slab rollback and progressive steepening of the northward subduction of the African plate under the Anatolian Plate. Western Turkey has been affected, during the Middle Quaternary, by regional subsidence, and the direction of extension changed to N–S, probably in relation with the propagation of the North Anatolian Fault System. Since the Late Quaternary, NE–SW extension dominates northwest Turkey and results in the formation and development of elongated transtensional basin systems. Counterclockwise rotation of Anatolian block which is bounded to the north by the right-lateral strike-slip North Anatolian Fault System, accompanies to this extensional phase.     

The origin of Neogene tectonic rotations in the Galatean volcanic massif, central Anatolia

A paleomagnetic study was carried out on Neogene volcanic rocks at 30 sites within the Galatean massif (40.4°N, 31.5°E) to determine possible block rotations due to stress variations. Two phases of rotation could be characterized as the result of Neogene volcanic activity. We suggest that the first stage of rotation was isolated in Early Middle Miocene calc-alkali rocks, with a relative counterclockwise rotation of R ± ΔR = −20.2 ± 9.3° with respect to Eurasia. This accommodates the south-westward rotational collapse of the Western Anatolia peninsula across a pole on the Bitlis suture. In the neotectonic period, on other hand, a relative clockwise rotation of R ± ΔR = 27.3 ± 6.4° with respect to Eurasia is predicted. In contrast to the uniform clockwise rotations, extremely large clockwise rotations up to 264° are restricted in a narrow zone between two dextral faults. We believe that the second stage rotations support the idea of individual microblock rotations due to deformation along the North Anatolian Fault zone.     

Rockfall avalanche deposits associated with normal faulting in the NW of Çanklrl basin: implications for the postcollisional tectonic evolution of the Neo-Tethyan suture zone

The NNE-trending Neo-Tethyan suture zone between Ankara and Çanklrl, thrusts eastward onto different stratigraphic levels of the Neogene succession; however, its western side shows a normal fault relationship. This E-vergent tectonic sliver was inactive during the accumulation of the Miocene–Lower Pliocene sedimentary succession and was created by the movement of the North Anatolian Fault Zone and its splay after the late Pliocene, indicating internal deformation of the Anatolian plate. These results are inconsistent with the previous suggestion that intracontinental convergence related to Neo-Tethyan orogeny continued until the Pliocene (Ankara Orogenic Phase).     

Palaeomagnetically defined rotations of fault-bounded continental blocks in the North Anatolian Shear Zone, North Central Anatolia

The 1200 km-long North Anatolian Transform Fault connects the East Anatolian post-collisional compressional regime in the east with the Aegean back-arc extensional regime to the west. This active dextral fault system lies within a shear zone reaching up to 100 km in width, and consists of southward splining branches. These branches, which have less frequent and smaller magnitude earthquake activity compare to the major transform, cut and divide the shear zone into fault delimited blocks. Comparison of palaeomagnetic data from 46 sites in the Eocene volcanics from different blocks indicate that each fault-bounded block has been affected by vertical block rotations. Although clockwise rotations are dominant as expected from dextral fault-bounded blocks, anticlockwise rotations have also been documented. These anticlockwise rotations are interpreted as due to anticlockwise rotation of the Anatolian Block, as indicated by GPS measurements, and the effects of unmapped faults or pre-North Anatolian Fault tectonic events.     

Neotectonic deformation in the western sector of tectonic escape in Anatolia: palaeomagnetic study of the Afyon region, central Turkey

Following final closure of the Neotethyan Ocean during the late Miocene, deformation in central Turkey has led to crustal thickening and uplift to produce the Anatolian Plateau followed by westward extrusion of terranes by strike–slip. Widespread volcanism has accompanied this latter (neotectonic) phase, and palaeomagnetic study of the volcanism shows a coherent record of differential block rotations, indicating that the Anatolian region is not a plate (or ‘platelet’) sensu stricto but is undergoing distributed internal deformation. To evaluate the scale of neotectonic rotations in the transition zone near the western limit of tectonic escape and the border of the extensional domain in central-west Turkey, we have studied the palaeomagnetism at 82 sites in volcanic suites distributed along a 140-km lineament with north–south trend and ranging in age from 18 to 8 Ma. Comparable deflection of magnetic remanence from the present field direction is identified along the full length of the lineament. A mean clockwise rotation of 12.3±4.2° is determined for this western sector of the Anatolian strike–slip province. Since similar rotations are observed in the youngest and oldest units, this cumulative rotation occurred after the late Miocene. When interpreted together with results elsewhere in Anatolia, it is inferred that the rotation is later than crustal thickening and uplift of the Anatolian Plateau and entirely a facet of the tectonic escape. Inclinations are mostly 10° shallower than the predicted Miocene field and are considered to reflect the presence of a persistent inclination anomaly in the Mediterranean region. Larger rotations departing from the regional trend are also observed within the study region, but are confined to the vicinity of major faults, notably those bounding the Afyon-Ak ehir Graben.The pattern of neotectonic declinations across Anatolia identifies strong anticlockwise rotation in the east near the Arabian pincer with progressive reduction in the amount of rotation towards the west; it becomes zero or slightly clockwise at the western extremity of the accreted terrane collage. Rotations also appear to become generally younger towards the south. Crustal deformation has therefore been distributed, and the net effect of terrane extrusion to the west and south has been to expand the curvature of the Tauride Arc. The westward radial expansion of the extruded terranes is inferred to combine with backroll on the Hellenic Arc to produce the contemporary extensional province in western Turkey.     

Palaeomagnetically defined rotations of fault-bounded continental blocks in the North Anatolian Shear Zone,North Central Anatolia

The 1200 km-long North Anatolian Transform Fault connects the East Anatolian post-collisional compressional regime in the east with the Aegean back-arc extensional regime to the west. This active dextral fault system lies within a shear zone reaching up to 100 km in width, and consists of southward splining branches. These branches, which have less frequent and smaller magnitude earthquake activity compare to the major transform, cut and divide the shear zone into fault delimited blocks. Comparison of palaeomagnetic data from 46 sites in the Eocene volcanics from different blocks indicate that each fault-bounded block has been affected by vertical block rotations. Although clockwise rotations are dominant as expected from dextral fault-bounded blocks, anticlockwise rotations have also been documented. These anticlockwise rotations are interpreted as due to anticlockwise rotation of the Anatolian Block, as indicated by GPS measurements, and the effects of unmapped faults or pre-North Anatolian Fault tectonic events.     

Paleomagnetic constraints on neotectonic deformation in the Kashi depression of the western Tarim Basin,NW China

A paleomagnetic study is reported of Eocene to Pliocene formations from the Kashi depression, which aims to constrain the pattern of neotectonic deformation within the western sector of the Tarim Basin in northwest China. With the exception of Pliocene specimens from one locality (East Kulukeqiati) which show large within site-mean variations in declination, most sites from five sampled formations yield well-grouped characteristic remanent magnetizations and positive fold tests and are of probable post-depositional detrital origin. First-order consistency of paleomagnetic results from a range of rock ages and localities demonstrates that only small inter-locational vertical-axis rotation has occurred here and indicates that the Kashi depression is decoupled from the remainder of Tarim to the east and has behaved as a quasi-rigid block which has rotated by 20–30° counterclockwise relative to Eurasia and North China since the late Pliocene. The crustal-scale Talas-Ferghana Fault cuts the Tian Shan and meets the Kashi depression in the region immediately to the northwest of the study region and we find no paleomagnetic evidence for differential rotations to suggest that this fault zone extends southwards across the Kashi depression to link with the North Pamir Thrust Fault (NPTF). Instead, we argue that the southern extension of this zone is a transform-orogen junction with southward motion of the eastern wall accommodated by southward thrusting at the margins of the south Tian Shan and the Tarim Basin. We propose that dextral transpression around the margins of the crustal block incorporating the Kashi depression was responsible for the contrasting amounts of thrusting on the NPTF in the southwest and the South Tian Shan Thrust Fault in the north. Extensive evidence for neotectonism in the bordering zones of this block, as well as some paleomagnetic evidence from low unblocking temperature components, indicates that the deformation produced by block rotation is ongoing.     

The North Anatolian fault and complexities of continental escape

Before the Plio-Pleistocene, the proto North Anatolian fault zone was occupied by two separate faults: a WNW-striking right-lateral eastern segment which extended to the Black Sea, and a WSW-striking left-lateral western segment. During the Plio-Pleistocene most of the right-lateral displacement on the eastern fault was transferred from the Black Sea extension to the western fault, converting the latter to a right-lateral structure, and giving rise to the modern North Anatolian fault zone. This model explains the evidence first reported by Hancock & Barka for an apparent Plio-Pleistocene reversal of displacement along the western part of the fault. The model may also account for the Plio-Pleistocene change in regional stress in southwestern Anatolia.     

The role of thrust ramp reactivation in pull-apart mechanism of the Erzincan basin,North Anatolian Fault Zone,Turkey

The new field data obtained from the southwestern margin of the Erzincan pull-apart basin located on the eastern segment of North Anatolian Fault Zone indicate that the opening of the basin is not only controlled by pull-apart mechanism but also by a lateral ramp structure associated with SSE-NNW Late Miocene thrusting along the Sivas Basin. The fault bordering the southwestern margin of the basin is the lateral part of the Karada thrust that is the roof thrust of the Sivas fold-thrust system, rather than a segment of the North Anatolian Fault Zone. The Erzincan basin was nucleated as a lateral ramp basin during the Pliocene on the lateral ramp-related folds and expanded by the pull-apart opening mechanism between two segments of the North Anatolian Fault Zone. The WSW-ENE pull-apart opening of the basin was recorded by the Pliocene lacustrine-fluvial sediments and Quaternary volcanics as listric normal faulting.     

The AD 365 Crete earthquake and possible seismic clustering during the fourth to sixth centuries AD in the Eastern Mediterranean: a review of historical and archaeological data

Historical and archaeological data are used to test geological claims that, in the fourth to sixth centuries AD, the Eastern Mediterranean experienced an unusual clustering of destructive earthquakes (the ‘Early Byzantine Tectonic Paroxsym’). A review of historical accounts of a notable earthquake at this time, that of 21 July AD 365, indicates that this event destroyed nearly all the towns in Crete and was followed by a tsunami which devastated the Nile Delta. The AD 365 event was also probably responsible for reported or observed destruction in ancient towns of west Cyprus and Libya. This earthquake is most likely to be identified with a Hellenic Arc subduction-zone event of ‘great’ (M>8) magnitude, as testified by up to 9 m of uplift in western Crete dated by previous geological studies to around this time. Historical and archaeological data also support the hypothesis that the fourth to sixth centuries AD was a period of abnormally high seismicity in the Eastern Mediterranean. The high seismicity rates of this period may reflect a reactivation of all plate boundaries in the region (Dead Sea Transform, East Anatolian Fault, North Anatolian Fault, Hellenic Arc, Cyprus Arc Fault).