Orhan Tatar

Palaeomagnetic study of block rotations in the Niksar overlap region of the North Anatolian Fault Zone, central Turkey

Abstract This palaeomagnetic study investigates crustal deformation within, and adjacent to, the Niksar overlap area of the North Anatolian Fault Zone (NAFZ) in central-east Turkey. The studied rock formations comprise: (1) red limestones of Late Cretaceous age (3 sites); (2) mafic lavas of Eocene age on the north side (13 sites) and south side (9 sites) of the NAFZ; and (3) volcanic rocks of Pliocene-Quaternary age from the Niksar pull-apart basin within the NAFZ (8 sites). Comparisons with reference palaeofield directions computed from apparent polar wander paths of the Eurasian and Afro-Arabian plates identify two scales of regional and local tectonic rotation: 1. (1) A pre-tilting remanence in the Eocene volcanic rocks south of the NAFZ ( D I = 144.1 −47.5° , β95 = 7.6°) is interpreted to reflect counterclockwise rotation by 30–40° from the reference palaeofields. Contemporaneous volcanic rocks from the north side of the NAFZ have the same reverse polarity recorded in pre-tilting magnetisations. The remanence is also rotated counterclockwise ( D I = 152.4 −42.5° , α95 = 11.3°), but by about 8° less than the volcanics on the south side of the NAFZ. Hence similar amounts of rotation are observed on both sides of the NAFZ and are interpreted to reflect motions during the pre-Middle Miocene collisional history in this sector of the Pontides. No distributed clockwise rotations anticipated from subsequent dextral motion along the NAFZ intracontinental transform are observed. The slightly larger anticlockwise rotation found on the south side of the NAFZ probably records relative rotation of en-echelon wedges by continental escape during post-Middle Miocene strike slip along the transform. 2. (2) Within the narrow zone of intense deformation along the NAFZ, Cretaceous limestones appear to be rotated clockwise by dextral strike-slip motion whilst Plio-Quaternary lavas within a fault-bounded block in the overlap region associated with the Niksar pull-apart basin, have magnetisations consistently directed 240–270°E. Magnetic inclinations are not diagnostic of polarity but both polarity solutions identify rapid clockwise rotation at rates in excess of 50°/m.y. A normal polarity solution is favoured and implies that a block (ca. 5 km across) has undergone a strike-slip displacement of around 12 km within the NAFZ during the last polarity chron. Cretaceous-Eocene palaeolatitudes are closer to those predicted from Eurasia than Afro-Arabia, but a study of older rocks is required to resolve affinities of this sector of the Anatolian block. Theoretical models of crustal deformation across intracontinental transforms obeying power-law behaviour and treating the lithosphere as a viscous medium predict that distributed clockwise rotations should be observed about as broad across the NAFZ. These rotations are not observed. Instead intense clockwise rotation is confined to a narrow zone close to the major fault break. The concentration of historic seismic activity here also implies that the bulk of the dextral motion between the Eurasian Plate and the Anatolian block is accommodated by slip along faults close and parallel to the main trace of the NAFZ.

A comparison of landslide susceptibility mapping of the eastern part of the North Anatolian Fault Zone (Turkey) by likelihood-frequency ratio and analytic hierarchy process methods

The North Anatolian Fault is known as one of the most active and destructive fault zones which produced many earthquakes with high magnitudes both in historical and instrumental periods. Along this fault zone, the morphology and the lithological features are prone to landslides. Kuzulu landslide, which is located near the North Anatolian Fault Zone, was triggered by snow melting without any precursor, occurred on March 17, 2005. The landslide resulted in 15 deaths and the destruction of about 30 houses at Kuzulu village. There is still a great danger of further landslides in the region. Therefore, it is vitally important to present its environmental impacts and prepare a landslide susceptibility map of the region. In this study, we used likelihood-frequency ratio model and analytical hierarchy process (AHP) to produce landslide susceptibility maps. For this purpose, a detailed landslide inventory map was prepared and the factors chosen that influence landslide occurrence were: lithology, slope gradient, slope aspect, topographical elevation, distance to stream, distance to roads, distance to faults, drainage density and fault density. The ArcGIS package was used to evaluate and analyze all the collected data. At the end of the susceptibility assessment, the area was divided into five susceptibility regions, such as very low, low, moderate, high and very high. The results of the analyses were then verified using the landslide location data and compared with the probability model. For this purpose, an area under curvature (AUC) and the seed cell area index assessments were applied. An AUC value for the likelihood-frequency ratio-based model 0.78 was obtained, whereas the AUC value for the AHP-based model was 0.64. The landslide susceptibility map will help decision makers in site selection and the site-planning process. The map may also be accepted as a basis for landslide risk-management studies to be applied in the study area.

Palaeomagnetic study of the Karaman and Karapinar volcanic complexes, central Turkey: neotectonic rotation in the south-central sector of the Anatolian Block

Abstract In the Anatolian sector of the Afro–Eurasian collision zone a palaeotectonic collisional phase (Paleocene to Miocene) responsible for emplacement of the Pontide and Tauride orogens has been replaced by a neotectonic phase of continental deformation (Late Miocene/Early Pliocene to Recent). The latter phase appears to have been accommodated mainly by crustal thickening during Late Miocene and Pliocene times, but was succeeded by complex differential rotations of fault blocks during crustal extrusion in Late Pliocene and Quaternary times. In this study we have investigated palaeomagnetism of Miocene–Recent volcanic rocks comprising the western extension of the Central Anatolian Volcanic Province located in the south-central part of the Anatolian Block with the aim of resolving deformations near to the border with the Tauride orogen. Rock magnetic investigations identify low-Ti magnetite assemblages of primary cooling-related origin. These have predominant multidomain structures but significant fractions of single domains are always present; low-temperature alteration is largely absent. The Karaman Volcanic Complex (Late Pliocene) shows a net rotation of −5.7±6.9° not significantly different from the regional field axis during Recent times. The Karapinar Volcanic Field (Brunhes epoch) identifies a larger net rotation of −23.1±12.0° in a restricted sample. The adjoining Karacadag Volcanic Complex (Late Miocene–Pliocene) and Middle Miocene lavas beneath the Hasandag Complex define net rotations of −8.1±5.9° and −16.4±8.9° respectively. Analysis of palaeomagnetic results from Late Cretaceous–Recent rock units emplaced in Anatolia during the palaeotectonic and neotectonic regimes shows that rates of rotation have accelerated in post-Pliocene times as crustal thickening has given way to tectonic escape. A near-uniform anticlockwise rotation of 25–35° has characterised much of this block during the most recent phase of deformation and appears to have occurred in common with the Eurasian Plate to the north of the North Anatolian Fault Zone. Whilst this rotation appears to extend south eastwards across the Ecemis Fault Zone towards the East Anatolian Fault, the present study shows that smaller differential anticlockwise rotations have characterised the south-central region of the block where it has interacted at its southwestern margin with oroclinal bending focussed on the Isparta angle.

Deformational behaviour of continental lithosphere deduced from block rotations across the North Anatolian fault zone in Turkey

Abstract Theoretical considerations of lithosphere deformation across transform plate boundaries predict an expression in terms of 3istributed deformation. The magnitude of rotation is expected to diminish away from the fault zone in a way which depends on the length of the fault, the amount of displacement, and the ductility of the lithosphere. Palaeomagnetic studies across the North Anatolian transform fault zone, which separates the Eurasian Plate and Anatolian Block in northern Turkey, show that clockwise rotations predicted from the sense of dextral motion are indeed present and have attained finite rotations of up to 270° during the ∼ 5 Ma history of Neotectonic deformation. Such rotations are, however, confined to narrow ( ∼ 10 km wide) zones between system-bounding faults and appear to have resulted from rotation in ball-bearing fashion of equidimensional blocks a few kilometres in size. Outside of this zone only anticlockwise rotations are observed; these are unrelated to deformation across the fault zone and record regional anticlockwise rotation of Turkey which is complementing clockwise rotation of Greece and accompanying Neogene opening of the Aegean Sea. The observed behaviour of continental lithosphere satisfies no plausible value of power law behaviour. We therefore conclude that relative motion across this transform boundary occurs as a discrete zone of intense deformation within a brittle layer comprising the seismogenic upper crust. This is presumed to be detached from a continuum deformation response to shearing in the lower crust and mantle beneath.

A PALAEOMAGNETIC STUDY OF THE SIVAS BASIN, CENTRAL TURKEY : CRUSTAL DEFORMATION DURING LATERAL EXTRUSION OF THE ANATOLIAN BLOCK

Abstract The Sivas Basin is a complex collage of Eocene and younger rocks located within the wedge-shaped eastern margin of the Anatolian Block between the (dextral) North Anatolian Fault Zone and the (sinistral) Eastern Anatolian Fault Zone. It has been subject to ongoing deformation by movement of the Arabian Block into Eurasia and concomittant sideways expulsion of the Anatolian Block. Post-collisional deformation since mid-Miocene times has been dominated by NS to NWSE compression expressed by thrusting and strike-slip faulting. Cretaceous and Eocene rocks were magnetically overprinted to variable degrees during the collisional phase although these overprints have since been rotated mostly anticlockwise. Rocks emplaced during the neotectonic history are high-fidelity palaeomagnetic recorders of subsequent block movements. Regional anticlockwise rotation is recognised across the basin with differential rotation of fault and thrust-bounded blocks. An absence of perceptible differences between group mean rotations identified from Miocene, Pliocene and Quaternary units shows that most regional rotation has been concentrated within the latest phase of the neotectonic history during Quaternary times at an average rate of ∼ 10°/Ma. Commencement of this rotation postdates initiation of the North Anatolian Fault Zone implying that compression following collision was accomodated initially by crustal thickening during Late Miocene and Pliocene times. Subsequent anticlockwise rotations have resulted from sideways expulsion of blocks to the south of the Central Anatolian Thrust along major NESW sinistral faults to achieve the crustal shortening resulting from NS compression. These fault orientations and their sense of motion are explained by a Prandtl model involving deformation of a triangular plastic terrane (the Anatolian Block) between two rigid plates (Eurasia and Afro-Arabia). The variations in regional rotation identified by palaeomagnetism show that average contemporary anticlockwise rotation of Anatolia revealed by GPS data (∼ 1.2°/Ma) is achieved by variable, and locally large, block rotations between major thrusts and strike-slip faults.

Rate of strike-slip motion on the Amanos Fault (Karasu Valley, southern Turkey) constrained by K–Ar dating and geochemical analysis of Quaternary basalts

The left-lateral Amanos Fault follows a ∼200-km-long and up to ∼2-km-high escarpment that bounds the eastern margin of the Amanos mountain range and the western margin of the Karasu Valley in southern Turkey, just east of the northeastern corner of the Mediterranean Sea. Regional kinematic models have reached diverse conclusions as to the role of this fault in accommodating relative motion between either the African and Arabian, Turkish and African, or Turkish and Arabian plates. Local studies have tried to estimate its slip rate by K–Ar dating Quaternary basalts that erupted within the Amanos Mountains, flowed across it into the Karasu Valley, and have since become offset. However, these studies have yielded a wide range of results, ranging from ∼0.3 to ∼15 mm a−1, which do not allow the overall role and significance of this fault in accommodating crustal deformation to be determined. We have used the Cassignol K–Ar method to date nine Quaternary basalt samples from the vicinity of the southern part of the Amanos Fault. These basalts exhibit a diverse chemistry, which we interpret as a consequence varying degrees of partial melting of their source combined with variable crustal contamination. This dating allows us to constrain the Quaternary slip rate on the Amanos fault to ∼1.0 to ∼1.6 mm a−1. The dramatic discrepancies between past estimates of this slip rate are partly due to technical difficulties in K–Ar dating of young basalts by isotope dilution. In addition, previous studies at the key locality of Hacilar have unwittingly dated different, chemically distinct, flow units of different ages that are juxtaposed. This low slip rate indicates that, at present, the Amanos Fault takes up a small proportion of the relative motion between the African and Arabian plates, which is transferred southward to the Dead Sea Fault Zone. It also provides strong evidence against the long-standing view that its slip continues offshore to the southwest along a hypothetical left-lateral fault zone located south of Cyprus.

Palaeomagnetic study of crustal deformation across an intracontinental transform: the North Anatolian Fault Zone in Northern Turkey

Abstract Eocene volcanic rocks spanning the North Anatolian Fault Zone in north central Turkey have a common reversed polarity and appear to record a short term volcanic episode useful for identifying subsequent tectonic rotations. Although regional differences are present, no distributed clockwise rotations caused by dextral motion across the fault zone since mid-Miocene times are found. Instead variable anticlockwise block rotations demonstrate that this fault system does not obey theoretical models for crustal behaviour across continental transforms. Deformation is found to be highly inhomogeneous with a narrow zone of intense clockwise rotation recognised within blocks bounded by strike-slip faults above, and parallel to, the fundamental lineament. Further from the lineament no systematic rotations with respect to the major bounding plates are detected. A zone of c. 30° anticlockwise rotation in the east may be either a consequence of emplacement of the Pontides or an ongoing consequence of continental collision. Slightly larger rotations south of the fault probably record block rotations into Anatolia as this region is being extruded westwards by continuing impingement of Afro-Arabia into the Eurasian Plate.

Palaeomagnetism and magnetic properties of the Cappadocian ignimbrite succession, central Turkey and Neogene tectonics of the Anatolian collage

Abstract The Cappadocian ignimbrite succession of central-southern Anatolia comprises at least nine major and two minor calc-alkaline rhyolitic sheets emplaced at 1–2-Ma intervals between 11.2 and 1.1 Ma. It records the last phase of Neotethyan subduction during final emplacement of the Tauride orogen in southern Turkey. This study reports magnetostratigraphy and describes associated rock magnetic properties. Remanence resides in Ti-poor titanomagnetites. Haematisation is locally produced by post-emplacement oxidation but does not contribute significantly to the palaeomagnetic signature although secondary processes within the ignimbrite sheets have produced composite isothermal remanent magnetisation spectra and variable intensities of magnetisation. Weak anisotropy of magnetic susceptibility describes tensors with maximum axes close to bedding and minimum axes perpendicular to this plane. Directions of kmax with weak imbrication mostly suggest flow away from centres of eruption located by gravity and remote sensing. Older ignimbrites (Upper and Lower Goreme, Akdag-Zelve) from the Cardak Centre are all of normal polarity. Later ignimbrites, partly erupted from the Derinkuyu Centre, comprise the Sarimaden (R), Cemilkoy (R), Tahar (R), Kizilkaya (R), Incesu (N) and Valibaba-Sofular (R) ignimbrites. The overall (reversed) group mean is D/I=174/−51° (N=10 units, R=9.84, α95=6.6°, k=55) and all magnetisation directions from the Upper Goreme (9.0 Ma) onwards are rotated anticlockwise with respect to Eurasian and African palaeofields. This sense of rotation characterises most of central Anatolia and averages 9±5° in this sector. The rotation rate from 8 to 1 Ma BP was ∼1.25°/Ma but it appears to have accelerated during the latter part of the Quaternary to about an order higher than rates determined from GPS. Rotation has resulted from extrusion of fault blocks during tectonic escape of the Anatolian collage to the southwest and followed crustal thickening as the Afro-Arabia Plate has continued to impinge differentially into Eurasia. Cenozoic magnetic inclinations are systematically shallower across Anatolia than inclinations expected from the geocentric dipole model and the apparent polar wander of bordering major plates. Only part of this difference (∼400 km) can be accommodated by northward movement and crustal thickening in Central Anatolia since mid-Miocene times. Shallow inclinations observed in the Aegean region extend into Turkey; they are observed in young volcanics and appear to reflect a regional geomagnetic anomaly. The pattern of neotectonic declinations across Anatolia shows rotations that are strongly anticlockwise rotated in the east near the Arabian pincer but diminish towards the west to become zero or slightly clockwise at the western extremity of the collage. Rotations also seem 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 and, by inference, the Cyprus Arc.

Regional Significance of Neotectonic Counterclockwise Rotation in Central Turkey

Counterclockwise rotation is a characteristic feature of the results of most paleomagnetic studies of the Pontides and Anatolides of central Turkey, applicable to regions both north and south of the North Anatolian fault zone. In this paper, we report new data from Eocene volcanics and assess existing data from the calc-alkaline volcanic suites of this age. Although there are regional variations, probably resulting from rotations of individual fault blocks, an average counterclockwise rotation of ∼33° is identified across a region extending from 34° to 38° E Long. A mean Eocene paleolatitude of 27° N is compatible with ongoing northward movement and residual closure of a few degrees across the Pontide orogen during the latter part of its paleotectonic history. It seems probable that this rotated domain extends as far west as the Aegean graben system of western Turkey and as far south as the Taurides. Paleomagnetic evidence from younger volcanics suggests that the bulk of the rotation occurred during Quate...

Differential neotectonic rotations in Anatolia and the Tauride Arc: palaeomagnetic investigation of the Erenlerdaǧ Volcanic Complex and Isparta volcanic district, south–central Turkey

Abstract: In the Anatolian sector of the Alpine–Himalayan collisional belt a palaeotectonic phase of terrane accretion has been succeeded by a neotectonic phase of intracontinental deformation as the Afro-Arabian plate has continued to impinge differentially into the accreted collage. The resulting tectonic escape has, during the last few million years, extruded and rotated blocks in a southwesterly direction. This paper reports a palaeomagnetic investigation of the Erenlerdaǧ Volcanic Complex and Isparta alkaline volcanic district undertaken to extend analysis of crustal rotation into the southwestern part of the Anatolian region, and investigate the interaction with the Isparta angle and the extensional province of western Turkey. The Erenlerdaǧ volcanism comprises three phases of volcanism. The oldest Sille volcanics (11.7–11.4 Ma) yield a mean D=150° I=−52° rotated anticlockwise during early stages of crustal thickening and deformation before a later Miocene episode (c. 10.9–8.9 Ma, D=183°, I=−47°) and a Mio-Pliocene episode (D=179°, I=−51°). The latter two episodes indicate that no significant rotation has resulted during the neotectonic crustal extrusion in this southwestern sector of Anatolia. Further to the west within the Isparta Angle a 4.7–4.0 Ma alkaline episode yields a mean of D=186°, I=−53° rotated slightly clockwise. The pattern of palaeomagnetic declinations across Anatolia shows rotations that are strongly anticlockwise in the east near the Arabian pincer and diminish towards the west to become zero or slightly clockwise at the western extremity of the collage. The timing of rotation also appears to become 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 and, by inference, the Cyprian Arc. Where good age control exists in Cappadocia and the Sivas Basin rotations are found to be concentrated within the last few million years and are up to an order higher than rates deduced from global positioning system. The palaeomagnetic data imply that the neotectonic deformation following collision initially produced crustal thickening resulting in uplift of the Anatolian Plateau and was only subsequently accommodated by major differential block rotation during tectonic escape.