Neotectonic evolution of the northwestward arched segment of the Central Anatolian Fault Zone,Central Anatolia,Turkey

Abstract

Central Anatolia has undergone complex Neotectonic deformation since Late Miocene-Pliocene times. Many faults and intracontinental basins in this region were either formed, or have been reactivated, during this period. The eastern part of central Anatolia is dominated by a NE-SW-trending, left lateral transcurrent structure named the Central Anatolian fault zone located between Sivas in the northeast and west of Mersin in the southwest. Around the central part, it is characterized by transtensional depressions formed by left stepping and southward bending of the fault zone. Pre-Upper Miocene basement rocks of the region consist of the central Anatolian crystalline complex and a sedimentary cover of Tertiary age. These rock units were strongly deformed by N-S con- vergence. The entire area emerged to become the site of erosion and formed a vast plateau before the Late Miocene. A NE-SW- trending extensional basin developed on this plateau in Late Miocene-Early Pliocene times. Rock units of this basin are characterized by a thick succession of pyroclastic rocks intercalated with calcalkaline-alkaline volcanics. The volcanic sequence is uncon- formably overlain by Pliocene lacustrine-fluviatile deposits interrelated with ignimbrites and tuffs. Thick, coarse grained alluvial/colluvial fan deposits of marginal facies and fine grained elastics and carbonates of central facies display characteristic synsedimentary structures with volcanic intercalations. These are the main lines of evidence for development of a new transtensional H?rka— k?zd?rmak basin in Pliocene times. Reactivation of the main segment of the Central Anatolian fault zone has triggered development of depressions around the left stepping and southward bending of the central part of this sinistral fault zone in the ignimbritic plateau during Late Pliocene-Quaternary time. These transtensional basins are named the Tuzla Gölü and Sultansazl??? pull-apart basins. The Sultansazl??? basin has a lazy S to rhomboidal shape and displays characteristic morphologic features including a steep and stepped western margin, large alluvial and colluvial fans, and a huge composite volcano (the Erciyes Da??).

The geometry of faulting and formation of pull-apart basins can be explained within the framework of tectonic escape of the wedgelike Anatolian block, bounded by sinistral East Anatolian fault zone and dextral North Anatolian transform fault zone. This escape may have been accomplished as lateral continental extrusion of the Anatolian Plate caused by final collision of the Arabian Plate with the Eurasian Plate. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Mio-Pliocene basin development in the eastern part of the Cappadocian Volcanic Province (Central Anatolia,Turkey) and its implications for regional tectonics

The Cappadocian Volcanic Province (CVP) comprises predominantly of a thick succession of volcanogenic rocks and interbedded siliciclastic sediments of Middle Miocene to Recent age in Central Anatolia, Turkey. The conditions of basin development in the eastern part of the CVP have been elucidated by using sedimentological and geomorphological approaches. The prevailing tectonic regime, its extent and causes are also discussed. Sedimentological analysis supported by geomorphological observations revealed a major NE-trending probably normal, border fault and its several synthetics. This tectonic element constitutes the SE margin of the basin and divided the CVP from the Tauride range during Middle Miocene to Pliocene. The basin fill in the study area comprises gravelly alluvial fans near the border fault, while fluvial clastics and lacustrine carbonates dominate towards the centre. Some pyroclastic rocks and lava flows are also made part of the fill. The southeastern basin margin is characterized morphologically by a number of uplifted basement blocks, probably associated with synthetic faults, and some deeply incised canyons in the footwall. These canyons were subsequently filled with a Mid-Pliocene ignimbrite sheet, and represent the sediment supply conduits to the basin. The cessation of filling in the basin was determined by strike-slip faults that uplifted and detached the basin about 2.6 Ma. This date also marks the onset of the neotectonic period in the region. The overall extensional tectonic regime inferred for the eastern CVP appears coeval with events recognised in the southern basins, i.e. Adana and Mut Basins and the eastern Mediterranean. Some physical connections between these basins also have been demonstrated. It is suggested that the CVP and the southern basins were all created during a phase of extension resulting from continued northward subduction of the African plate beneath the Eurasia during the Late Cenozoic.     

U/Th dating of the travertine deposited at transfer zone between two normal faults and their neotectonic significance: Cambazli fissure ridge travertines (the Gediz Graben-Turkey)

Abstract

The neotectonic characteristics of the travertines that outcrop near Cambazli Village to the west of the Gediz Graben in the Western Anatolia and the age determination of the travertine were carried out using the ²³⁰Th/^234,238U disequilibrium method. The Cambazli fissure ridge travertines represent the travertine depositions that develop at a transfer zone. The extent of these travertines is at NW-SE and NE-SW orientations and the ridge crest-trend of these travertines range between approximately 55° and 82° and they are located at an intersecting position. The evaluation of the fissure ridge travertine directions indicated that the compression stress that was responsible for the deposition of the Cambazli travertine was determined to be in the N-S orientation and the extensional stress was determined to be in the E-W orientation. The orientation of the dominant extension in Western Anatolia during the neotectonic period was N-S and this orientation is not in accordance with the directions of stress for the travertines. This situation indicates that the travertines were deposited along a transfer zone in N10W orientation between two normal faults. The travertines were determined to be active since the Upper Pleistocene as indicated by the age determination conducted using the ²³⁰Th/^234,238U disequilibrium method. The dilation rate of the travertines during dilation and the post-dilation period and the average dilation rate of the Cambazli travertines to the north of the Gediz Graben were calculated as 0.01–0.02 mm yr^?1 during deposition and as 0.05 mm yr^?1 during the post-dilation period. These dilation rates indicate lower tectonic activity along the northern ridge of the Gediz Graben than along the southern ridge.

© 2011 Lavoisier SAS. All rights reserved     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

Abstract

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and westdipping, N-S to N20°-30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacilar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of leftlateral oblique slip of approximately 4.1 mm?year^?1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Hydrogeochemical and Isotopic Study of Groundwater in a Semi-arid Region: Yeniceoba Plain (Cihanbeyli-KONYA), Central Anatolia,Turkey

Groundwater is the most important source of water supply in the Yeniceoba Plain in Central Anatolia,Turkey.An understanding of the geochemical evolution of groundwater is important for the sustainable development of water resources in this region.A hydrogeochemical investigation was conducted in the Plio-Quaternary aquifer system using stable isotopes(δ~(18)O andδD),tritium(~3H),major and minor elements(Ca,Na,K,Mg,Cl,SO_4,NO_3,HCO_3 and Br)in order to identify groundwater chemistry patterns and the processes affecting groundwater mineralization in this system.The chemical data reveal that the chemical composition of groundwater in this aquifer system is mainly controlled by rock/water interactions including dissolution of evaporitic minerals,weathering of silicates,precipitation/dissolution of carbonates,ion exchange,and evaporation.Based on the values of Cl/Br ratio(300 mg/l)in the Plio-Quaternary groundwater,dissolution of evaporitic minerals in aquifer contributes significantly to the high mineralization.The stable isotope analyses indicate that the groundwater in the system was influenced by evaporation of rainfall during infiltration.Low tritium values(generally1 tritium units)of groundwater reflect a minor contribution of recent recharge and groundwater residence times of more than three or four decades.     

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.     

Petrological and source region characteristics of ophiolitic hornblende gabbros from the Aksaray and Kayseri regions, central Anatolian crystalline complex, Turkey

Many Neo-Tethyan ophiolitic bodies are well exposed as thrust-slices in Central Anatolia and are predominantly represented by massive hornblende gabbros, most of which are cut by Supra Subduction Zone (SSZ) plagiogranites. The allochthonous gabbros are distinct from their autochthonous counterparts, with their mineralogy including both igneous hornblende, relict diopside rimmed by replacement hornblende and their chemical composition corresponding mostly to gabbro rather than diorite.The results of major and trace element analyses of forty-two samples, and REE analyses of nine samples, indicate that the hornblende gabbros are SSZ-type and formed from a wet magma by high-degree partial melting of peridotite possibly coupled with contamination by predominantly neighbouring-slab derived fluids within an intra-oceanic back-arc basin. The mafic magmas then underwent high-level fractional crystallization involving titaniferous magnetite, diopside, tschermakite and possibly olivine. Emplacement was followed by extensive ocean–floor metamorphism, which has induced crystallization (or recrystallization) of chlorite, biotite, amphiboles and mobilisation of most of the major elements such as alkali and alkali earth elements, and some LREE.     

Petrology and Geochemistry of Post-Collisional Early Miocene Volcanism in the Karacada? Area (Central Anatolia, Turkey)

Early Miocene (ca.?21–18 Ma) volcanism in the Karacada? area comprises three groups of volcanic rocks: (1) calcalkaline suite (andesitic to rhyolitic lavas and their pyroclastics), (2) mildly-alkaline suite (alkali basalt, hawaiite, mugearite, benmoreite and trachydacite), and (3) a single trachyandesitic flow unit. Field observations, 40Ar/39Ar ages and geochemical data show that there was a progressive temporal transition from group 1 to 3 in a post-collisional tectonic setting. The calcalkaline suite rocks with medium-K in composition resemble those of subduction-related lavas, whereas the mildly-alkaline suite rocks having a sodic tendency (Na2O/K2O=1.5–3.2) resemble those of within-plate lavas. Incompatible element and Sr-Nd isotopic characteristics of the suites suggest that the lithospheric mantle beneath the Karacada? area was heterogeneously enriched by two processes before collision: (1) enrichment by subduction-related processes, which is important in the genesis of the calcalkaline volcanism, (2) enrichment by small degree melts from the astenosphere, which dominates the mildly alkaline volcanism. Perturbation of the enriched lithosphere by either delamination following collision and uplift or removal of the subducted slab following subduction and collision (i.e., slab breakoff) is the likely mechanism for the initiation of the post-collision volcanism.     

Geochemistry of Pliocene/Pleistocene basalts along the Central Anatolian Fault Zone (CAFZ), Turkey

Abstract

Pliocene-Pleistocene volcanism accompanied strike-slip-related transtensional deformation along the K?z?l?rmak fault segment of the Central Anatolian fault zone (CAFZ) in the west of ?ark??la (Sivas-central Turkey). These volcanic rocks are represented by alkali olivine basalts. They can be divided into four different sub-groups on the basis of their Zr, Nb, TiO₂ contents. A primitive mantle-normalized incompatible trace element diagram for four subgroups shows close similarity to typical OIB pattern. Some of the incompatible trace element ratios (Ce/Y, Zr/Nb, La/Ba, La/Nb) are also akin to OIB values. Highly fractionated REE patterns (La/Yb_N=24.7–9.2) with no Eu anomaly are the main features of the alkali basalts and are comparable to alkaline volcanism in continental rift zones. On the basis of Al₂O₃/TiO₂, Nb/Y, Zr/Y Zr/Nb ratios, the geochemical differences among four sub-groups can be explained by variable degrees of partial melting of compositionally similar mantle source. Th/Nb, Th/Y, Nb/Y ratios and the primitive mantle-normalized trace element diagram suggests significant amount of crustal involvement for most of the alkali olivine basalts erupted along the CAFZ. Rupture of the continental lithosphere by strike-slip-related transtensional deformation might have caused decompressional partial melting of the asthenospheric mantle and generating alkali olivine basalts in this region. © 2001 Éditions scientifiques et médicales Elsevier SAS.     

Geodynamic significance of granitoid magmatism in the southeast Anatolian orogen: geochemical and geochronogical evidence from Göksun–Afşin (Kahramanmaraş, Turkey) region

In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaraş–Malatya–Elazığ region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Göksun–Afşin in Kahramanmaraş, Doğanşehir in Malatya and Baskil in Elazığ) intrude all the former units in a NE–SW trending direction. The granitoid in Göksun–Afşin (Kahramanmaraş) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys.     

Petrogenesis of mafic microgranular enclaves (MMEs) in the oligocene-miocene granitoid plutons from northwest Anatolia,Turkey

Mafic microgranular enclaves (MMEs) in host granitoids can provide important constraints on the deep magmatic processes. The Oligocene-Miocene granitoid plutons of the NW Anatolia contain abundant MMEs. This paper presents new hornblende Ar-Ar ages and whole-rock chemical and Sr-Nd isotope data of the MMEs from these granitic rocks. Petrographically, the MMEs are finer-grained than their host granites and contain the same minerals as their host rocks (amphibole + plagioclase + biotite + quartz + K-feldspar), but in different proportions. The Ar-Ar ages of the MMEs range from 27.9 ± 0.09 Ma to 19.3 ± 0.01 Ma and are within error of their respective host granitoids. The MMEs are metaluminous and calc-alkaline, similar to I-type granites. The Sr-Nd isotopes of MMEs are 0.7057 to 0.7101 for ⁸⁷Sr/⁸⁶Sr and 0.5123 to 0.5125 for ¹⁴³Nd/¹⁴⁴Nd, and are similar to their respective host granitoids. These lithological, petrochemical and isotopic characteristics suggest that the MMEs in this present study represent chilled early formed cogenetic hydrous magmas produced during a period of post-collisional lithospheric extension in NW Anatolia. The parental magma for MMEs and host granitoids might be derived from partial melting of underplated mafic materials in a normally thickened lower crust in a post-collisional extensional environment beneath the NW Anatolia. Delamination or convective removal of lithospheric mantle generated asthenospheric upwelling, providing heat and magma to induce hydrous re-melting of underplated mafic materials in the lower crust.     

Neotectonic and volcanic characteristics of the Karasu fault zone (Anatolia,Turkey): The transition zone between the Dead Sea transform and the East Anatolian fault zone

The Karasu Rift (Antakya province, SE Turkey) has developed between east-dipping, NNE-striking faults of the Karasu fault zone, which define the western margin of the rift and west-dipping, N–S to N20°–30°E-striking faults of Dead Sea Transform fault zone (DST) in the central part and eastern margin of the rift. The strand of the Karasu fault zone that bounds the basin from west forms a linkage zone between the DST and the East Anatolian fault zone (EAFZ). The greater vertical offset on the western margin faults relative to the eastern ones indicates asymmetrical evolution of the rift as implied by the higher escarpments and accumulation of extensive, thick alluvial fans on the western margins of the rift. The thickness of the Quaternary sedimentary fill is more than 465 m, with clastic sediments intercalated with basaltic lavas. The Quaternary alkali basaltic volcanism accompanied fluvial to lacustrine sedimentation between 1.57 ± 0.08 and 0.05 ± 0.03 Ma. The faults are left-lateral oblique-slip faults as indicated by left-stepping faulting patterns, slip-lineation data and left-laterally offset lava flows and stream channels along the Karasu fault zone. At Hacılar village, an offset lava flow, dated to 0.08 ± 0.06 Ma, indicates a rate of left-lateral oblique slip of approximately 4.1 mm·year^–1. Overall, the Karasu Rift is an asymmetrical transtensional basin, which has developed between seismically active splays of the left-lateral DST and the left-lateral oblique-slip Karasu fault zone during the neotectonic period.     

Source constraints for the young basaltic rocks from the northernmost end of Cappadocian region,Turkey: Melting evidence from peridotite and pyroxenite source domains

Widespread magmatic activity developed in the Middle Miocene in the Cappadocian Region of Central Anatolia in Turkey. Despite several previous studies that focus on the geochemical features of the magmatic rocks, the source components and development of melting conditions are still a matter of debate.Recent basaltic rocks from Karaburna and Gül?ehir (1228 and 96 Ka, respectively, Dogan, 2011) are considered as a part of the Central Anatolian Volcanic Province, situated at the northernmost end of the Cappadocian Region. These lavas have similar large ion lithophile (LIL) (except Rb) and high field strength (HFS) element abundances, however, Karaburna samples are more enriched in HFS elements, and both of the rocks suites reflect HFS depletions relative to the OIB signature.Karaburna and Gül?ehir basalts have low Nb/La (0.45–0.5; 0.35–0.5), Nb/Th (2.75–4.61; 1.26–2.85) values, respectively, suggesting contributions from crustal sources, whereas Zr/Ba ratios of these samples range between 0.32–0.93 and 0.4–0.88 and imply that these rocks appear to be derived from asthenospheric sources. These incompatible element ratios can be attributed to either different geochemical processes, or are related to melting from different source component(s).The ambient mantle source of the Cappadocian region appears to be consistent with spinel peridotite, but this domain is not solely satisfactory to represent the melting conditions in the light of new elemental data. Values of Tb/Yb(N) and Zn/Fe provide new constraints suggesting the magmas were generated from the asthenosphere. Tb/Yb(N) ratio separates garnet – spinel transition Tb/Yb_(N) (>1.8) and Zn/Fe ratio displays separation between the peridotite-derived (Zn/Fe <12) and pyroxenite-derived (13?20) melts.A melting model based on REE ratios and Zn/Fe, Co/Fe, Tb/Yb(N) values indicates that basaltic rocks were not derived from a single source component (peridotite). Instead, those values suggest substantial melting contributions from a pyroxenite source domain, which has not been discussed as a source component in previous studies. Melts, from both of the source domains, with the result of asthenospheric upwelling linked to the downgoing Aegean and Cyprean slabs, are distinct from the alkaline character frequently observed as the final products of recent volcanic activity in the Cappadocian region and also explains the different trace element variations observed in such a small scale.     

An unsuccessful attempt at U/Th dating of soil calcretes from the Doukkâli area (western Morocco) and environmental implications

A large number of calcrete samples from topsoils of the Doukkâli area, western Morocco, were studied by U-disequilibrium series methods. The ²³⁰Th/²³⁴U ages are rather uniformly distributed between>350 and 2 ka BP. Homologous samples for occurrence and structure display quite different ages, the ²³⁰Th/²³⁴U ages are considered apparent. This is explained by repeated deposition of secondary calcite in the calcrete pores, which caused lowering of the original ages. However, the apparent ages may be considered minimum ages of the calcrete formation, indicating that calcium carbonate mobilization and deposition has been taking place repeatedly since >350 ka.

The age range obtained is quite comparable with that of calcretes from southern Spain, suggesting similar conditions for the calcrete formation in the two areas.     

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.     

Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation

The Central Pontides (northern Turkey) is one of the key localities to understand the geodynamic evolution of the Palaeo- and Neotethyan oceans. It consists of the pre-Jurassic basement units, the Early Jurassic and the Early Cretaceous accretionary complexes, the widespread Middle Jurassic continental arc magmatics and the Late Jurassic to Tertiary cover units. The Early Cretaceous accretionary complex is represented by the Central Pontide Structural Complex and includes the Middle Jurassic oceanic units, which were metamorphosed during the Early Cretaceous. Apart from these oceanic units, a few metaophiolite and serpentinite fragments have been recognized within the basement units, which may represent the remnants of an older ocean. The pre-Middle Jurassic Devrekani Metaophiolite is the largest oceanic fragment and tectonically intercalated within/between the Devrekani Metamorphics and the Çangaldağ Metamorphic Complex. It is mainly composed of harzburgites, dunites with chromite veins and metagabbros, and cut by metabasaltic andesites and metadacites. Petrographically, the gabbro consists mainly of plagioclase and clinopyroxene, and displays phaneritic/porphyritic texture. In contrast, the metabasaltic andesite includes plagioclase and mica phenocrysts within a fine-grained groundmass. Also, the metadacite is composed predominantly of quartz, plagioclase, and mica minerals. Two different magmatic groups belonging to completely different tectono-magmatic settings have been geochemically determined based on the immobile trace element systematics. The metadacites and metabasaltic andesites are akin to continental arc magmatics and characterized by negative Nb and Ta anomalies and depleted HFSE relative to Th and La contents. However, the metagabbro samples display the geochemical signatures of boninitic rocks and characterized by highly depletion in HFSEs and REEs relative to N-MORB. The Devrekani Metaophiolite in the Central Pontides may represent another remnant of pre-Middle Jurassic oceanic crust generation and can be north-eastward continuation of the Permian-aged Almacık complex and the Boğazköy Metaophiolite fragment in the western Sakarya Composite Terrane. It may have been cut by intrusions of the extensive Middle Jurassic continental arc magmatism after its imbrication within the basement unit. The presence of pre-Middle Jurassic oceanic units may indicate that the Paleozoic ocean may have survived as the Jurassic Intra-Pontide Ocean between the Scythian Platform and Sakarya Composite Terrane during the Mesozoic time. Thus, the Intra-Pontide Suture may normally include the Palaeozoic and Mesozoic remnants of the long-lived northward subducting Tethyan ocean.     

The late Pan-African intracontinental linear fold belt of the Eastern Hoggar (Central Sahara,Algeria): geology,structural development,U/Pb geochronology,tectonic implications for the Hoggar shield

The structural development of the Tiririne Belt, located in the eastern Hoggar, central Sahara, Algeria has been entirely controlled by a high-strain, now vertical, N—S-trending zone, along which metamorphism and deformation gradually appear to the north in the Tiririne Formation, a clastic unit up to 8000 m thick whose sedimentological environment is described. U/Pb geochronology on zircons from a pretectonic sill within the Tiririne Formation indicates a pre-660 Ma depositional age. This intracontinental belt has been formed during the ‘late Pan-African’, as shown by the 604 and 585 Ma U/Pb zircon ages obtained on syn- to late-kinematic granitic phases from a circular pluton emplaced in the belt (using λ₈ = 0.155125 · 10^?9 y^?1 and λ₅ = 0.98485 · 10^?9 y^?1). The tectonic implications are discussed in the light of the structural and geochronological data. They suggest an eastwards younging of the peak of Pan-African deformation towards the East-Saharan craton, which has been stable for more than 660 Ma.     

Oligocene deposits of the Zara-Hafik region (Sivas,Central Turkey): evolution from storm-influenced shelf to evaporitic basin

New stratigraphical and micropalaeontological data, supplemented by detailed sedimentological and petrographical observations, have been obtained from an almost completely exposed Oligocene-Miocene succession near Celalli in the Zara-Hafik basin, which forms part of a long-lived zone of subsidence associated with the North Anatolian Fault system. Four laterally extensive lithostratigraphical units have been distinguished and ostracod microfaunas indicate that the lower two units are of Middle Oligocene age, while bivalve/brachiopod faunas from the third unit are also Oligocene. The status of the uppermost unit of redbeds remains equivocal, but microfaunas from the capping marls are of lowermost Miocene age.The basal brown sandstone unit was formed in a shallow marine environment dominated by southwards transport of sand by offshore-directed storm-surges, with associated east-west longshore movement also important. The discordantly succeeding limestone unit records a phase of carbonate bar migration across the basin while the third formation (in which medium-scale facies cyclicity is prominent) was formed in a southwards-prograding coastal plain complex, following a renewal of terrigenous supply to this region. The late Oligocene-Miocene redbed unit resulted from continued terrestrial progradation and is characterised by alluvial deposits formed by small, southwards-flowing streams of high sinuosity, ultimately succeeded by carbonate and evaporitic deposits marking the early Miocene marine transgression.Stratigraphical analysis of sandstone petrography reveals a gradual change in provenance through the Oligocene, from sources of »oceanic« character (rich in ophiolitic rocks) to those of »continental« nature (with silicic metamorphics and sedimentary cover-rocks prominent), and the compositional data thus accord with models suggesting closure of a small oceanic or arc-related basin in this region during the late Palaeogene.

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Zusammenfassung Aus einer nahezu vollständig aufgeschlossenen Schichtenfolge des Oligozän und Miozän im Gebiet von Celalli im Zara-Hafik-Becken/Türkei werden neue Daten zur Stratigraphie und Mikropaläontologie vorgestellt. Diese werden ergänzt durch sedimentologische und petrographische Beobachtungen. Das Becken ist Teil einer Zone mit lange anhaltender Subsidenz, die mit dem System des Nordanatolischen Lineaments in Verbindung steht. Es lassen sich vier lateral aushaltende lithostratigraphische Einheiten unterscheiden, von denen die beiden unteren mit Ostracoden-Mikrofaunen in das Mittel-Oligozän eingestuft werden. Nach Muschel- und Brachiopoden-Faunen ist die dritte Einheit ebenfalls oligozänen Alters. Das Alter der obersten Einheit von Rotsedimenten ist nicht genau bekannt, doch besitzen die Mikrofaunen der hangenden Mergel ein tiefstmiozänes Alter.Der basale braune Sandstein wurde in einem flachmarinem Milieu gebildet, das von einem südwärts gerichteten Sandtransport durch ablandige Sturmwellen beherrscht wird. Zusätzlich ist eine ost-west-gerichtete Küsten-Längsdrift von Bedeutung. Die diskordant darüber lagernde Kalkfolge wurd durch eine Phase von durch das Becken wandernden karbonatischen Bänken aufgebaut. Die dritte Einheit (in der eine Fazies-Zyklizität mittlerer Größe vorherrscht) baute sich in dem südwärts vorschreitenden Komplex einer Küstenebene auf, die einer neuerlichen terrigenen Schüttung in diesem Gebiet folgt. Die spätoligozän-miozäne Einheit von Rotsedimenten ist das Ergebnis weiter voranschreitender terrestrischer Sedimente. Sie besteht aus alluvialen Ablagerungen von kleinen nach Süden fließenden Flüssen mit hoher Sinuosität, gefolgt von karbonatischen und evaporitischen Bildungen, die die frühmiozäne Transgression anzeigen.Die stratigraphische Analyse der Sandstein-Petrographie offenbart einen allmählichen Wandel der Provenienz im Oligozän, der von »ozeanischem« Liefergebiet (reich an ophiolithischen Gesteinen) zu »kontinentalem« (mit vorherrschend kieseligen Metamorphiten und sedimentärer Bedeckung) überwechselt. Die Zusammensetzung stimmt mit Modellen überein, die die Schließung eines kleinen ozeanischen oder inselbogen-artigen Beckens während des späten Paläogens nahelegen.

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Résumé De nouvelles données stratigraphiques et micropaléontologiques, associées à des observations sédimentologiques et pétrographiques détaillées ont été recueillies dans une série oligocène-miocène exposée de manière presque complète près de Celalli dans le bassin de Zara-Hafik, lequel fait partie d'une zone de subsidence de longue durée associée au système de failles de l'Anatolie du Nord. Quatre unités lithostratigraphiques d'extension latérale notable ont été distinguées. Les deux unités inférieures sont datées de l'Oligocène moyen par une microfaune à Ostracodes, et la troisième de l'Oligocène par une faune à brachiopodes et autres bivalves; l'âge de l'unité supérieure reste incertain, mais les marnes terminales renferment une microfaune éo-miocène.L'unité inférieure, constituée de grès bruns, s'est formée dans un milieu marin peu profond dans lequel le sable était transporté à la fois vers le large (vers le Sud), par des vagues de tempête, et vers l'Ouest parallèlement au rivage. La deuxième unité, discordante et de nature calcaire, témoigne de la migration d'une barre carbonatée à travers le bassin. La troisième unité, caractérisée par une disposition cyclique des faciès à moyenne échelle, a été élaborée dans un complexe de plaine côtière progressant vers le Sud, comme suite à de nouveaux apports terrigènes. La quatrième unité (Oligocène tardif-Miocène), formée de couches rouges, résulte d'une sédimentation continentale continue et consiste en alluvions déposées par de petits cours d'eau très sinueux coulant vers le Sud; ces couches sont surmontées finalement de dépôts carbonates et évaporitiques marquant la transgression éo-miocène.L'analyse pétrographique du grès, opérée en fonction de la stratigraphie, révèle au cours de l'Oligocène un changement graduel de provenance, depuis un domaine nourricier de type »océanique« (riche en ophiolites) jusqu'à un domaine de type »continental« (à dominance de roches métamorphiques et sédimentaires siliceuses). Ces données sont en accord avec un modèle suggérant la fermeture d'un petit bassin océanique ou d'arc insulaire pendant le Paléogène tardif.

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Pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the Velay region (Massif Central,France)

In the volcanic region of Velay (Massif Central, France), lake sediment sequences derived from maar craters situated close to one another (Ribains, Praclaux and Lac du Bouchet) have been correlated on the basis of tephrostratigraphical analyses. This has enabled the construction of a sequence (2980 pollen spectra) that begins during the glaciation preceding the Holsteinian and ends in the present. This sequence covers the period from 450 ka, i.e. from the end of marine oxygen isotope stage 12, to the present time, and includes five climatic cycles. The study of a second core from the Praclaux site completed the long Velay sequence. The biostratigraphy of the whole sequence is described in detail and illustrated by a synthetic and simplified pollen diagram. Thirteen temperate forest episodes (interglacials or interstadials) and as many cold periods (glacials or stadials) are defined. Each temperate episode is characterised by particular forest development and vegetation dynamics, and all of them, with the exception of the Holocene, begin and end with a Pinus forest. The vegetation dynamics observed during the Holocene resemble more closely those recorded during the interstadials than during the interglacials. Copyright © 2000 John Wiley & Sons, Ltd.