Halil Gürsoy

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.

Palaeomagnetic Study of the Erciyes Sector of the Ecemiş Fault Zone: Neotectonic Deformation in the Southeastern Part of the Anatolian Block

Abstract In the Turkish sector of the Afro-Eurasian collision zone, continuing northward motion of the Arabian promontory is extruding the Anatolian region to the west. Although the East Anatolian Fault Zone (EAFZ) is recognized as the southern boundary of this tectonic escape, distributed deformation is occurring across a broad zone extending for at least 300 km to the northwest, which includes a number of major dextral and sinistral fault lineaments. The longest of these lineaments is the Ecemiş Fault Zone, although the long-term significance of deformation, and specifically strike-slip, across this zone is disputed. This zone is also the locus of major volcanic activity in the Kayseri region. The present paper reports a palaeomagnetic study of young (1–2 Ma) lava flows which has aimed to identify recent block rotations resulting from regional deformation in this region. Rock magnetism shows the lavas to be dominated by low-Ti magnetite assemblages of primary cooling related origin. Although grain properties are predominantly multidomain, significant fractions of single domains are always present and responsible for a stable thermoremanence of normal and reversed polarity. Whilst group mean directions show that the blocks in this sector of Anatolia show the typical counterclockwise rotation resulting from tectonic escape, in this case by c. 10° during the last 1 Ma, larger differential rotations in both senses are identified across the Sultansazhği Depression. Comparable differential rotations recorded by the 2.8 ± 0.2 Ma Incesu Ignimbrite have resulted from the pull-apart in this sector of the Ecemiş Zone which has accommodated emplacement of the Erciyes volcanic centre since the termination of ignimbrite activity. Within the wedge-shaped terrane confined between the EAFZ in the south and the North Anatolian Fault Zone in the north, the degree of counterclockwise rotation during tectonic escape within the last 2–3 Ma has diminished from c. 25° in the east to c. 10° towards the southwest. This corresponds to a transition from highly strained to a less-strained lithosphere as the width of the semi-plastic Anatolian terranes confined between the Arabian-Eurasian pincer broadens out to the west.

Kinematics of Late Pliocene-Quaternary Normal Faulting in the Southeastern End of the Gediz Graben, Western Anatolia, Turkey

The kinematic analysis of fault-slip data obtained from lower Pliocene and Pleistocene deposits indicates two successive extensional events in the southeastern end of the Gediz graben. The late Pliocene N-S extensional phase was followed by a NNE-SSW extension in the Pleistocene. This change in extension direction from N-S to NNE-SSW is indicated by slip vectors on active fault planes and historic fault offsets. This younger extensional event is still active, as suggested by recent seismic activity and focal mechanisms of earthquakes in the region. The slip regime has important implications for the Neogene tectonic evolution of western Anatolia.

Two-phased evolution of the Suşehri Basin on the North Anatolian Fault Zone, Turkey

This study has aimed to evaluate the current tectonic structure of the Suşehri Basin located on the eastern part of the North Anatolian Fault Zone (NAFZ), one of the most important active faults in Turkey. The work extends earlier investigations of offset and seismicity on the NAFZ and tests a range of evolutionary models. In this study, buried faults have been determined from Ground penetrating radar and magnetic anomalies and possible discontinuities identified by interpolating these data in a region between Gölova and Suşehri. The discontinuities are shown to be linked to negative flower structures formed within the strike-slip fault zone. Quickbird satellite images have been used to map faults and produce kinematic analyses which show that the active stress regime is dominantly strike-slip. However, normal faults and oblique-slip faults are also observed in the basin together with strike-slip faults and the stress regime creating the strike-slip faults is shown to have formed under NW-SE directed transtension. In addition, oblique faults formed under an extensional regime with NNE-SSW direction also occur in the Suşehri Basin as subsets formed under the constraining strike-slip regime. We conclude that the Suşehri Basin started to grow as a fault wedge basin following which it transformed into a pull-apart basin by a south splay on the NAFZ so it is now dominantly a transtensional pull-apart feature.

Fossil findings from the Sıcak Çermik fissure ridge-type travertines and possible hominid tracks, Sivas, Central Turkey

Abstract Sıcak Çermik (Sivas) is an important geothermal and recent travertine formation area in Central Anatolia. The majority of travertines found in the region comprise fissure-ridge type travertines according to morphological classification. At the location called Tepe Çermik within the travertine area, fill containing fossil bone fragments of Equus sp., Bovidae and other abundant animals formed within the fracture axis of a N–S striking fissure-ridge travertine developed under control of tectonic forces. The finds of these fossils in fissure-ridge travertines linked to tectonic forces indicates formation of a unique fossil environment created under the control of these forces. The Accelerator Mass Spectrometry Radiocarbon Dating analyses of fossils from the study area determined the fills were older than 43,000 years. The U/Th age of a sample from the most recently-formed banded travertine in the axis of the fracture was identified as 278,540 ± 18,436 years. As a result, the ages of fossils found within this fill are thought to be between 43,000 and 278,540 ± 18,436 years old. The high amount of perissodactyla and artiodactyla fossils found within fill in the axis of the fissure-ridge travertine probably indicates the presence of hominids who chose the region for hunting or settlement. The Equus sp. and Bovidae fossil samples found in the axis of the fracture indicate that in the dry and cold glacial period the paleogeography in a large portion of Anatolia comprised desert-like steppe.