Location of the River Euphrates in the Late Miocene; dating of terrace gravel at Shireen, Syria

International audienceWe report gravel of the River Euphrates, capped by basalt that is Ar-Ar dated to ~9 Ma, at Shireen in northern Syria. This gravel, preserved by the erosion-resistant basalt, allows us for the first time to reconstruct the history of this major river during the Late Miocene. In response to progressive regional surface uplift, the Euphrates extended SE by ~800 km between the early Middle Miocene, when the coast was near Kahramanmara? in southern Turkey, and the Pliocene, when it lay in western Iraq, east of the Arabian Platform uplands

Geochemistry, mineralogy and petrogenesis of the northeast Nigde volcanics, central Anatolia, Turkey

The volcanics exposed in the northeast Nigde area are characterized by pumiceous pyroclastic rocks present as ash flows and fall deposits and by compositions ranging from dacite to rhyolite. Xenoliths found in the volcanics are basaltic andesite, andesite and dacite in composition. These rocks exhibit linear chemical variations between end-member compositions and a continuity of trace element behaviour exists through the basaltic andesite-andesite-dacite-rhyolite compositional range. This is consistent with the fractionation of ferromagnesian minerals and plagioclase from a basaltic andesite or andesite parent. These rocks are peraluminous and show typical high-K calc-alkaline differentiation trends with total iron content decreasing progressively with increasing silica content. Bulk rock and mineral compositional trends and petrographic data suggest that crustal material was added to the magmas by subducted oceanic crust and is a likely contaminant of the source zone of the Nigde magmas. The chemical variations in these volcanics indicate that crystal liquid fractionation has been a dominant process in controlling the chemistry of the northeast Nigde volcanics. It is also clear, from the petrographic and chemical features, that magma mixing with disequilibrium played a significant role in the evolution of the Nigde volcanic rocks. This is shown by normal and reverse zoning in plagioclase and resorption of most of the observed minerals. The xenoliths found in the Nigde volcanics represent the deeper part of the magma reservoir which equilibrated at the higher pressures. Copyright © 2002 John Wiley and Sons, Ltd

A scanning electron microscope study of post-depositional changes in the northeast Nigde ignimbrites, South Central Anatolia, Turkey

The ignimbrites of the northeast Nigde area, which are subdivided into the Lower, Middle and Upper ignimbrites on the basis of their compositional and stratigraphical characteristics, display textural variations from the base to the top. A large proportion of these ignimbrites have been altered and recrystallized by the processes of compaction, welding and devitrification, and as a result of volatile movement. The alteration and recrystallization processes include four stages: hydration, glassy and spherulitic stages accompanied by vapour-phase crystallisation. In the early phases of devitrification, detailed shard shapes are easily recognisable with the scanning electron microscope, but as alteration proceeds clarity of detail disappears because compaction results in collapse of the structure of the rock. Spherulitic and vapour-phase crystallisation usually involves the growth of alkali feldspar and cristobalite. These later stages are more common in the Upper Ignimbrite than the Middle and Lower ignimbrites

Petrogenesis of basalts from southern Turkey: The Plio-Quaternary volcanism to the north of Iskenderun Gulf

The Quaternary volcanicity north of the Iskenderun Gulf in the eastern Mediterranean is represented by small basaltic scoria cones and flows. Approximately 115 km2 of land area is occupied by young basalts which straddle both the main (the Karatas-Osmaniye Fault Zone) strike-slip fault system which forms the Africa-Turkey Plate boundary and the suture of the southern arm of the former Neotethys Ocean. Detailed petrological and geochemical analyses of these rocks have been carried out, with the aim of trying to understand why they have erupted in this locality. The rocks consist mainly of basanites (43-46% silica; 3.9-6.5% alkalis) and some alkali olivine basalts (45% silica; 3.8-4.2% alkalis). Both the basanites and alkali olivine basalts are porphyritic, vitrophyric and highly vesiculated with euhedral and subhedral olivine (Fo82-Fo78) phenocrysts set in a fine-grained groundmass of olivine (Fo70), plagioclase (An71-An66), clinopyroxene and titanomagnetite. Olivine phenocrysts contain abundant Cr-spinel and titanomagnetite inclusions. Some geochemical characteristics of these basalts indicate similarity with extension-related alkali basalts; others indicate similarity with ocean island basalt; and yet others indicate subduction-related characteristics. This complexity leads to difficulties with interpretation, especially since there is no demonstrable local extension, subduction or mantle plume activity in the vicinity

Assessing the applicability of transcript conformation polymorphism for differentiation among Prunus necrotic ringspot virus isolates

The applicability of single and double-stranded transcript conformation polymorphism (TCP) for differentiation among Prunus necrotic ringspot virus (PNRSV) isolates was evaluated and compared with other molecular differentiation procedures. Single-stranded TCP was found to be suitable to differentiate closely related virus isolates. However, due to its high variability, it was not suitable for grouping virus isolates. Double-stranded TCP, on the other hand, enabled the division of virus isolates into major groups. Restriction fragment length polymorphism (RFLP) of the PCR products confirmed the grouping of the virus isolates but this technique was limited in its ability to detect a wide range of nucleotide modifications. Nucleotide sequence analysis was essential for the detection of strain-specific sequences but did not clearly identify most other minor modifications that are necessary for virus classification. The combination of all methods is therefore sometimes required for complete analysis

Constraints on the timing and regional conditions at the start of the present phase of crustal extension in western Turkey, from observations in and around the denizli region

The chronology of extension of the continental crust in western Turkey has been the subject of major controversies. We suggest that these difficulties have arisen in part because of past misuse of dating evidence; and in part because the assumption often made, that deposition of major terrestrial sedimentary sequences implies crustal extension to create the necessary accommodation space, is incorrect. We report evidence that the present phase of extension began in the Denizli region at ~ 7 Ma, around the start of the Messinian stage of the Late Miocene. This timing matches the estimated start of right-lateral slip on the North Anatolian Fault Zone, and corresponds to a substantial increase in the dimensions of the Aegean extensional province to roughly its present size: beforehand, between ~ 12 Ma and ~ 7 Ma, extension seems to have only occurred in the central part of this modern province. In some localities, terrestrial sedimentation that began before this start of extension continued into this extensional phase, both within and outside normal fault zones. However, in other localities within the hanging-walls of normal faults, the start of extension marked the end of sedimentation. Relationships between sedimentation and crustal extension in this region are thus not straightforward, and a simple correlation should therefore not be assumed in structural interpretations. During the time-scale of this phase of extension, the Denizli region has also experienced major vertical crustal motions that are unrelated to this extension. The northern part of this region, in the relatively arid interior of western Turkey, has uplifted by ~ 400 m since the Middle Pliocene, whereas its southern part, closer to the Mediterranean Sea and with a much wetter climate, has uplifted by ~ 1,200 m since the Early Miocene, by up to ~ 900 m since the Middle Pliocene, and by an estimated ~ 300 m since the Early Pleistocene. This regional uplift, superimposed on the local effects of active normal faulting, is interpreted as a consequence of lateral variations in rates of erosion. A reliable chronology for this phase of extension in western Turkey, in relation to changes in the geometry of motions of adjoining plates and Late Cenozoic environmental change, is now in place. © 2005 Taylor & Francis Group, LLC

Timing of the quaternary Elazig volcanism, eastern Turkey, and its significance for constraining landscape evolution and surface uplift

The eastern part of the Anatolian plateau in eastern Turkey has experienced dramatic landscape evolution in the Late Cenozoic, surface uplift having been associated with the disruption of former lake basins and the development of the modern high-relief landscape, incised by the upper reaches of the River Euphrates and its major tributary, the Murat. Overall, the altitude of the plateau decreases gradually westward, and it has been assumed that uplift on any given timescale has varied regionally in a similar manner. However, using the Ar-Ar method, we have dated an episode of basaltic volcanism around the city of Elazig to -1.8-1.9 Ma (two alternative calculation procedures give ages of 1885±16 ka and 1839±16 ka; both ±2?. The disposition of this basalt indicates no more than -100 m of incision by the River Murat on this timescale in this area, in marked contrast to neighbouring localities where much more incision on similar timescales is indicated by the geomorphology. We interpret these variations as consequences of flow in the lower continental crust induced by surface processes, the flow being vigorous because the lower crust in this region is highly mobile due to the high Moho temperature. We thus suggest that the -1.8-1.9 Ma Elaz?g volcanism was triggered by outflow of lower crust following the emptying at -2 Ma of the adjacent Malatya lake basin; the resulting local removal of part of this lower-crustal layer can also account for the limited amount of subsequent net crustal thickening and surface uplift that has occurred locally. Local patterns such as this are superimposed onto the regional westward tilting of the surface of the Anatolian Plateau, which has facilitated the disruption of former lake basins such as this. Copyright © TÜBİTAK

Timing of the Quaternary Elazig volcanism, eastern Turkey, and its significance for constraining landscape evolution and surface uplift

The eastern part of the Anatolian plateau in eastern Turkey has experienced dramatic landscape evolution in the Late Cenozoic, surface uplift having been associated with the disruption of former lake basins and the development of the modern high-relief landscape, incised by the upper reaches of the River Euphrates and its major tributary, the Murat. Overall, the altitude of the plateau decreases gradually westward, and it has been assumed that uplift on any given timescale has varied regionally in a similar manner. However, using the Ar-Ar method, we have dated an episode of basaltic volcanism around the city of Elazığ to ~1.8-1.9 Ma (two alternative calculation procedures give ages of 1885±16 ka and 1839±16 ka; both ±2s). The disposition of this basalt indicates no more than ~100 m of incision by the River Murat on this timescale in this area, in marked contrast to neighbouring localities where much more incision on similar timescales is indicated by the geomorphology. We interpret these variations as consequences of flow in the lower continental crust induced by surface processes, the flow being vigorous because the lower crust in this region is highly mobile due to the high Moho temperature. We thus suggest that the ~1.8-1.9 Ma Elazığ volcanism was triggered by outflow of lower crust following the emptying at ~2 Ma of the adjacent Malatya lake basin; the resulting local removal of part of this lower-crustal layer can also account for the limited amount of subsequent net crustal thickening and surface uplift that has occurred locally. Local patterns such as this are superimposed onto the regional westward tilting of the surface of the Anatolian Plateau, which has facilitated the disruption of former lake basins such as this

Late Cenozoic uplift of western Turkey: Improved dating of the Kula Quaternary volcanic field and numerical modelling of the Gediz River terrace staircase

A set of 13 new unspiked K-Ar dates has been obtained for the Quaternary basaltic volcanism in the Kula area of western Turkey, providing improved age control for the fluvial deposits of the Gediz River that underlie these basalt flows. This dating is able, for the first time, to resolve different ages for the oldest basalts, assigned to category ß2, that cap the earliest Gediz deposits recognised in this area, at altitudes of ~140 to ~210 m above present river level. In particular, the ß2 basalt capping the Sarni{dotless}ç Plateau is dated to 1215 ± 16 ka (± 2?), suggesting that the youngest underlying fluvial deposits, ~185 m above present river level, are no younger than marine oxygen isotope stage (MIS) 38. In contrast, the ß2 basalt capping the adjacent Burgaz Plateau is dated to 1014 ± 23 ka, suggesting that the youngest underlying fluvial deposits, ~140 m above present river level, date from MIS 28. The staircase of 11 high Gediz terraces capping the latter plateau is thus dated to MIS 48-28, assuming they represent consecutive ~40 ka Milankovitch cycles, although it is possible that as many as two cycles are missing from this sequence such that the highest terrace is correspondingly older. Basalt flows assigned to the ß3 category, capping Gediz terraces ~35 and ~25 m above the present river level, have been dated to 236 ± 6 ka and 180 ± 5 ka, indicating incision rates of ~0.15 mm a- 1, similar to the time-averaged rates since the eruptions of the ß2 basalts. The youngest basalts, assigned to category ß4, are Late Holocene; our K-Ar results for them range from zero age to a maximum of 7 ± 2 ka. This fluvial incision is interpreted using numerical modelling as a consequence of uplift caused by a regional-scale increase in spatial average erosion rates to ~0.1 mm a- 1, starting at ~3100 ka, caused by climate deterioration, since when a total of ~410 m of uplift has occurred. Parameters deduced on this basis from the observed disposition of the Early Pleistocene Gediz terraces include the local effective viscosity of the lower crust, which is ~2 × 1018 Pa s, the Moho temperature of ~660 °C, and the depth of the base of the brittle upper crust, which is ~13 km. The thin lithosphere in this area results in high heat flow, causing this relatively shallow base of the brittle upper crust and the associated relatively thick lower-crustal layer, situated between depths of ~13 and ~30 km. It estimated that around 900 ka, at the start of the ~100 ka Milankovitch forcing, the spatial average erosion rate increased slightly, to ~0.12 mm a- 1; the associated relatively sluggish variations in uplift rates are as expected given the relatively thick lower-crustal layer. This modelling indicates that the growth of topography since the Pliocene in this study region has not involved a steady state. The landscape was significantly perturbed by the Middle Pliocene increase in erosion rates, and has subsequently adjusted towards-but not reached-a new steady state consistent with these increased erosion rates. It would not be possible to constrain what has been occurring from the Middle to Late Pleistocene or even the Early Pleistocene uplift response alone; information regarding the starting conditions is also essential, this being available in this region from the older geological record of stacked fluvial and lacustrine deposition. This result has major implications for the rigorous modelling of uplift histories in regions of rapid erosion, where preservation of information to constrain the starting conditions is unlikely. © 2006 Elsevier B.V. All rights reserved