Late Cenozoic stress evolution along the Karasu Valley, SE Turkey

This study defines the Mio-Pliocene to present-day stress regime acting at the northeastern corner of the eastern Mediterranean region along the Karasu Valley (i.e., the Amanos Range), taking in the Antakya, Osmaniye and Kahramanmaras provinces. The inversion slip vectors measured on fault planes and chronologies between striations indicate that the stress regime varied from transpressional initially to transtensional, having consistent NW- and NE-trending σ_Hmax (σ₁) and σ_Hmin (σ₃) axes, respectively; there are significantly different mean stress-ratio (R_m) values however. The older mean stress state is characterized by N151±11°E-trending σ₁ and N59±12°E-trending σ₃ axes, and by a mean arithmetic R_m value of 0.76, indicating that the regional stress regime is transpressional. The younger stress regime is characterized by N154±8°E-trending σ₁ and N243±8°E-trending σ₃ axes, and by a mean arithmetic R_m value of 0.17, indicating a transtensional character for this regional stress regime. The low R values of the stress deviators related to the recent stress state reflect normal-component slips. The earthquake focal mechanism inversions confirm that the younger stress regime continues into the Recent. The inversion identifies a transtensional stress regime representing strike-slip and an extensional stress state with a consistent NE-trending σ_Hmin (σ₃) axis. These stress states are characterized by N66°E and N249°E-trending σ₃ axes, respectively. Both significant regional stress regimes induce left-lateral displacement along the southern part of the East Anatolian Fault (EAF, or Amanos Fault). The temporal change, probably in Quaternary time, within the regional stress regime—from transpression to transtension—resulted from the coeval influences of subduction processes in the west–southwest (i.e., along the Cyprus arc), continental collision in the east, and westward escape of the Anatolian block.     

Geoelectromagnetic and geothermic investigations in the Ihlara Valley geothermal field

The Ihlara Valley is situated within a volcanic arc that is formed by the collision of the eastern Mediterranean plate system with the Anatolian plate. In this study we will present data from a reservoir monitoring project over the Ihlara-Ziga geothermal field, located 22 km east of Aksaray, in central Anatolia.Although identified geothermal resources in the Ihlara Valley are modest, substantial undiscovered fields have been inferred primarily from the volcanic and tectonic setting but also from the high regional heat flow (150–200 mWm⁻²) on the Kir ehir Massif.In 1988 and 1990, geoelectromagnetic surveys were undertaken by MTA-Ankara to confirm the presence of a relatively shallow (≈ 0.5–1 km), hydrothermally caused conductive layer or zone. CSAMT and Schlumberger resistivity data show good correspondence with each other, and 2-D geoelectric models are also in harmony with geologic data and gravity anomalies.The depth of the resistive basement, which is interpreted as Paleozoic limestone, is 200–250 m in the western part and increases eastward (≈ 600–750 m). This may imply N-S-oriented normal faulting within the survey area. The parameters of the top layer are a resistivity of 25 to 95 ohm m and a thickness of between 100 and 250 m. The thickness of the conductive tuffs between the top layer and the basement, whose resistivity is about 4–5 o hmm, also increases eastward (from 100 to 450 m). The apparent resistivity maps for the frequencies between 32 and 2 Hz reveal a localized low resistivity anomaly to the east of Belisirma.     

Recent crustal deformation of İzmir, Western Anatolia and surrounding regions as deduced from repeated GPS measurements and strain field

To investigate contemporary neotectonic deformation in İzmir, Western Anatolia and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2001. Combination of three spatially dense GPS campaigns in 2001, 2003 and 2004 with temporally dense campaigns between 1992 and 2004 resulted in a combined velocity field representing active deformation rate in the region. We computed horizontal and vertical velocity fields with respect to Earth-centered, Earth-fixed ITRF2000, to Eurasia and to Anatolia as well.The rates of principal and shear strains along with rigid-body rotation rates were derived from velocity field. Results show east–west shortening between Karaburun Peninsula and northern part of İzmir Bay together with the extension of İzmir Bay in accordance with general extension regime of Western Anatolia and Eastern Agea. East–west shortening and north–south extension of Karaburun Peninsula are closely related to right-lateral faulting and a clockwise rotation. There exists a block in the middle of the peninsula with a differential motion at a rate of 3–5 ± 1 mm/year and 5–6 ± 1 mm/year to the east and south, respectively.As is in Western Anatolia, north–south extension is dominant in almost all parts of the region despite the fact that they exhibit significantly higher rates in the middle of the peninsula. Extensional rates along Tuzla Fault lying nearly perpendicular to İzmir Bay and in its west are maximum in the region with an extension rate of 300–500 ± 80–100 nanostrain/year and confirm its active state. Extensional rates in other parts of the region are at level of 50–150 nanostrain/year as expected in the other parts of Western Anatolia.     

Investigation of Crustal Thickness in Eastern Anatolia Using Gravity,Magnetic and Topographic Data

The tectonic regime of Eastern Anatolia is determined by the Arabia-Eurasia continent-continent collision. Several dynamic models have been proposed to characterize the collision zone and its geodynamic structure. In this study, change in crustal thickness has been investigated using gravity, magnetic and topographic data of the region. In the first stage, two-dimensional low-pass filter and upward analytical continuation techniques were applied to the Bouguer gravity data of the region to investigate the behavior of the regional gravity anomalies. Next the moving window power spectrum method was used, and changes in the probable structural depths from 38 to 52 km were determined. The changes in crustal thickness where free air gravity and magnetic data have inversely correlated and the type of the anomaly resources were investigated applying the Euler deconvolution method to Bouguer gravity data. The obtained depth values are consistent with the results obtained using the power spectrum method. It was determined that the types of anomaly resources are different in the west and east of the 40° E longitude. Finally, using the obtained findings from this study and seismic velocity models proposed for this region by previous studies, a probable two-dimensional crust model was constituted.     

Stratigraphy and tectono-sedimentary evolution of the Upper Cretaceous–Tertiary sequence in the southern part of the Malatya Basin, East Anatolia, Turkey

The Malatya Basin is situated on the southern Taurus-Anatolian Platform. The southern part of the basin contains a sedimentary sequence which can be divided into four main units, each separated by an unconformity. From base to top, these are: (1) Permo-Carboniferous; (2) Upper Cretaceous–Lower Paleocene, (3) Middle-Upper Eocene and (4) Upper Miocene. The Upper Cretaceous–Tertiary sedimentary sequence resting on basement rocks is up to 700 m thick.The Permo-Carboniferous basement consist of dolomites and recrystallized limestones. The Upper Cretaceous–Lower Paleocene transgressive–regressive sequence shows a transition from terrestrial environments, via lagoonal to shallow-marine limestones to deep marine turbiditic sediments, followed upwards by shallow marine cherty limestones. The marine sediments contain planktic and benthic foraminifers indicating an upper Campanian, Maastrichtian and Danian age. The Middle-Upper Eocene is a transgressive–regressive sequence represented by terrestrial and lagoonal clastics, shallow-marine limestones and deep marine turbidites. The planktic and benthic foraminifers in the marine sediments indicate a Middle-Upper Eocene age. The upper Miocene sequence consists of a reddish-brown conglomerate–sandstone–mudstone alternation of alluvial and fluvial facies.During Late Cretaceous–Early Paleocene times, the Gündüzbey Group was deposited in the southern part of a fore-arc basin, simultaneously with volcanics belonging to the Yüksekova Group. During Middle-Late Eocene times, the Yeşilyurt Group was deposited in the northern part of the Maden Basin and the Helete volcanic arc. The Middle-Upper Eocene Malatya Basin was formed due to block faulting at the beginning of the Middle Eocene time. During the Late Paleocene–Early Eocene, and at the end of the Eocene, the study areas became continental due to the southward advance of nappe structures.The rock sequences in the southern part of the Malatya Basin may be divided into four tectonic units, from base to top: the lower allochthon, the upper allochthon, the parautochthon and autochthonous rock units.     

Petrogenesis of oligocene plutonic rocks in western Anatolia (NW Turkey): Insights from mineral and rock chemistry,Sr-Nd isotopes,and U-Pb,Ar-Ar and (U-Th)/He geochronology

Northwestern Anatolia is characterized by voluminous Paleozoic to Cenozoic granitoid bodies with varying compositions. Most of them are composite plutons emplaced into western Anatolia orogenic crust during the Eocene, Oligocene and Miocene along the İzmir-Ankara-Erzincan suture zone. This paper reports systematic good quality mineral and bulk-rock chemistry, Sr-Nd isotope data, honblend Ar-Ar, zircon U-Pb and first apatite (U-Th)/He (AHe) ages to reveal possible source compositions of the Evciler and Eybek granitoids and petrogenetic/geodynamic processes involved during their genesis, and thermochronology of Oligocene magmatism in the NW Anatolia. The Evciler and Eybek granitoids are mainly granodiorite and composed of K-feldspar (usually orthoclase and rarely microcline), plagioclase (albite, oligoclase), hornblende, biotite, quartz and accessory minerals (e.g., titanite, zircon, apatite, opaque), and secondary minerals such as chlorite, sericite and clay minerals. Estimated temperature-pressure conditions are 690–770 ° C at 1.6–2.7 kbar for the Evciler granitoid and 690–760 ° C at 3.2–4.01 kbar for the Eybek granitoid. These two granitoids enriched in LILEs (e.g., U, Th, Rb, and K), LREEs and Pb, and depleted in HREEs (e.g., Nb, Ti) and Sr, Ba and P relative to LILEs, and display small negative Eu anomalies. They belong to calc-alkaline, high-K calc-alkaline and minor shoshonite series, and display metaluminous and I-type character. Their REE patterns show a large fractionation between LREE and HREE ((La/Yb)N = 4.6–21.4) and a small negative Eu anomaly (Eu* = 0.2–0.3). The Evciler granitoid has homogeneous ⁸⁷Sr/⁸⁶Sr = 0.7060−0.7063 and ¹⁴³Nd/¹⁴⁴Nd = 0.51259−0.51262, and the Eybek granitoid has ⁸⁷Sr/⁸⁶Sr = 0.7060−0.7080 and ¹⁴³Nd/¹⁴⁴Nd = 0.51243−0.51263. New precise ⁴⁰Ar/³⁹Ar age data of hornblende and ²⁰⁶Pb–²³⁸U ages of zircons and (U-Th)/He ages of apatites from the plutons allow a more accurate temporal reconstruction of the Cenozoic magmatism of the western Anatolia. ⁴⁰Ar/³⁹Ar dating of hornblendes from the Evciler and Eybek granitoids gave plateau ages of between ca. 28 Ma and 25 Ma. Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) ²⁰⁶Pb-²³⁸Pb ages of euhdral magmatic zircons from the samples of these granitoids yield between ca. 28 and 26 Ma. The new high-temperature age constraints indicate Oligocene emplacement ages for the two intrusive bodies. The closeness of the zircon U-Pb and the hornblende Ar-Ar ages show that they experienced quick post-crystallization cooling. However, the significant difference between the apatite (U-Th)/He ages of 19.8 Ma and 7.6 Ma obtained on the Evciler and Eybek granitoids warns that in the post-Oligocene times the two structural blocks had different exhumation histories.     

Petrology of ultramafic to mafic cumulate rocks from the G?ksun(Kahramanmaras) ophiolite,southeast Turkey

The G?ksun(Kahramanmaras)ophiolite(GKO),cropping out in a tectonic window bounded by the Malatya metamorphic unit on both the north and south,is located in the EW-trending lower nappe zone of the southeast Anatolian orogenic belt(Turkey).It exhibits a complete oceanic lithospheric section and overlies the Middle Eocene Maden Group/Complex with a tectonic contact at its base.The ophiolitic rocks and the tectonically overlying Malatya metamorphic(continental)unit were intruded by I-type calc-alkaline Late Cretaceous granitoid(~81-84 Ma).The ultramafic to cumulates in the GKO are represented by wehrlite,plagioclase wehrlite,olivine gabbro and gabbro.The crystallization order for the cumulate rocks is as follows:olivine±chromian spinel→clinopyroxene→plagioclase.The major and trace element geochemistry as well as the mineral chemistry of the ultramafic to mafic cumulate rocks suggest that the primary magma generating the GKO is compositionally similar to that observed in the modern island-arc tholeiitic sequences.The mineral chemistry of the ultramafic to mafic cumulates indicates that they were derived from a mantle source that was previously depleted by earlier partial melting events.The highly magnesian olivine(Fo77-83),clinopyroxene(Mg#of 82-90)and the highly Ca-plagioclase(An81-89)exhibit a close similarity to those,which formed in a supra-subduction zone(SSZ)setting.The field and the geochemical evidence suggest that the GKO formed as part of a much larger sheet of oceanic lithosphere,which accreted to the base of the Tauride active continental margin,including the ispendere,K?mürhan and the Guleman ophiolites.The latter were contemporaneous and genetically/tectonically related within the same SSZ setting during the closure of the Neotethyan oceanic basin(Berit Ocean)between the Taurides to the north and the Bitlis-Pütürge massif to the south during the Late Cretaceous.     

Early Miocene stratigraphy of central west Anatolia,Turkey: implications for the tectonic evolution of the eastern Aegean area

Small‐mammalian faunas enable the discrimination and correlation of uppermost Lower Miocene lacustrine sedimentary units in central western Anatolia. On the basis of sequential stratigraphic relationships, early Early Miocene and latest Early Miocene relative ages are suggested for the older lacustrine mass‐flow deposits and younger paper shale units, respectively, which are devoid of age‐diagnostic fossils. In central western Anatolia, the sequential differences between the uppermost Lower Miocene successions delineate a deformation zone of NE–SW‐trending fault blocks separated by vertical faults. This deformation zone, inherited from Late Oligocene tectonics, underwent an early Early Miocene sinistral transtension leading to pull‐aparts that were emplaced by granitoids. Limited extension caused the late Early Miocene repetitive up‐ and down‐wards motions of the fault blocks, with variable magnitudes. This led to contrasting subsidence histories in the relevant basinal system. During the latest Early Miocene, fault blocks coalesced into a regional body characterized by uniform slow subsidence and non‐extensional deformation facies. The general trend of the above tectonic events can be explained by lateral slab segmentation and progressive asthenospheric wedging, in response to NE‐directed and decelerated palaeosubduction in the Aegean. Copyright © 2007 John Wiley & Sons, Ltd.     

Quantitative relationship between surface sedimentary diatoms and water depth in North-Central Bohai Bay,China

To study the quantitative relationship between surface sedimentary diatoms and water depth, 67 surface samples were collected for diatom analysis on eight profiles with water depth variation from the muddy intertidal zone to the shallow sea area in North-Central Bohai Bay, China. The results showed that the distribution of diatoms changed significantly in response to the change in water depth. Furthermore, the quantitative relationship between the distribution of dominant diatom species, their a...