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

Ar-Ar dating of late Cenozoic basaltic volcanism in northern Syria: Implications for the history of incision by the River Euphrates and uplift of the northern Arabian Platform

Ar-Ar dating of basalt flows capping terrace deposits of the River Euphrates in northern Syria has provided a new quantitative chronology for the late Cenozoic evolution of this important river system and for the associated history of surface uplift of the northern Arabian Platform through which it flows, a region of relatively strong crust that has experienced only slow deformation. Notably, fluvial deposits ~65 m above the Euphrates are overlain by basalt dated to 2717 ± 20 ka, those ~45 m above the river are overlain by basalt dated to 2116 ± 39 ka, and those 8-9 m above the river are overlain by basalt dated to 402 ± 11 ka. These new dates require the previous dating scheme, based on Paleolithic archaeology, to be revised; the Euphrates terrace deposits and the associated incised valley are much older than was previously thought. Rates of incision by the Euphrates, providing a proxy for regional surface uplift that is inferred to be the isostatic response to regional erosion, have varied significantly over the past ~3 Ma, with indications that between ~1.2 and ~0.9 Ma, there was regional subsidence, which gave rise to fluvial aggradation. This unusual pattern, involving reversals in the sense of vertical crustal motions, is interpreted to be a consequence of a relatively cold and thin mobile lower crustal layer, no more than ~5 km thick, evidently due to the presence of a much thicker underlying layer of mafic underplating at the base of the crust. This study thus indicates previously unsuspected complexity in the isostatic response to regional erosion in an area of high crustal stability. Copyright 2007 by the American Geophysical Union