Petrogenesis of extension-related alkaline volcanism in Karaburhan (Sivrihisar–Eskisehir), NW Anatolia, Turkey

Alkaline lavas were erupted as phonolites and trachytes around Karaburhan (Sivrihisar–Eskisehir, NW Anatolia) within the Izmir–Ankara–Erzincan suture zone. These volcanic rocks were emplaced as domes, close and parallel to the ophiolite thrust line. According to ⁴⁰Ar/³⁹Ar geochronological analyses of sanidine crystals from the phonolites, the age of the alkaline volcanics is 25 Ma (Late Oligocene–Early Miocene).The flow-textured phonolites are porphyritic and consist mainly of sanidine, clinopyroxene, and feldspathoid crystals. The clinopyroxenes show compositional zoning, with aegirine (Na_0.82–0.96Fe⁺³_0.68–0.83) rims and aegirine–augite cores (containing calcium, magnesium, and Fe⁺²). Some aegirine–augites are replaced with sodium-, calcium-, and magnesium-rich amphibole (hastingsite). Feldspathoid (hauyne) crystals enriched with elemental Na and Ca have been almost completely altered to zeolite and carbonate minerals. The fine-grained trachytes with a trachytic texture consist of feldspar (oligoclase and sanidine) phenocrystals and clinopyroxene microphenocrystals within a groundmass made up largely of alkali feldspar microlites.Although there are some differences in their element patterns, the phonolites and trachytes exhibit enrichment in LILEs (Sr, K, Rb, Ba, Th) and LREEs (La, Ce, Pr, Nd) and negative anomalies in Nb and Ta. These geochemical characteristics indicate a lithospheric mantle enriched by fluids extracted from the subduction component. In addition, the high ⁸⁷Sr/⁸⁶Sr (0.706358–0.708052) and low ¹⁴³Nd/¹⁴⁴Nd (0.512546–0.512646) isotope concentrations of the alkaline lavas reflect a mantle source that has undergone metasomatism by subduction-derived fluids. Petrogenetic modeling indicates that the alkaline lavas generated from the subduction-modified lithospheric mantle have undergone assimilation, fractional crystallization, and crustal contamination, acquiring high Pb, Ba, Rb, and Sr contents and Pb isotopic compositions during their ascent through the thickened crust in an extensional setting.     

The effects of climate change on historical and future extreme rainfall in Antalya,Turkey

Abstract

There is increasing concern that flood risk will be exacerbated in Antalya, Turkey as a result of global-warming-induced, more frequent and intensive, heavy rainfalls. In this paper, first, trends in extreme rainfall indices in the Antalya region were analysed using daily rainfall data. All stations in the study area showed statistically significant increasing trends for at least one extreme rainfall index. Extreme rainfall datasets for current (1970–1989) and future periods (2080–2099) were then constructed for frequency analysis using the peaks-over-threshold method. Frequency analysis of extreme rainfall data was performed using generalized Pareto distribution for current and future periods in order to estimate rainfall intensities for various return periods. Rainfall intensities for the future period were found to increase by up to 23% more than the current period. This study contributed to better understanding of climate change effects on extreme rainfalls in Antalya, Turkey.     

An inverse-modelling approach to assess the impacts of climate change in the Seyhan River basin,Turkey / Une approche de modélisation inverse pour évaluer les impacts du changement climatique dans le bassin versant de la Rivière Seyhan,Turquie

Abstract

One of the most significant anticipated consequences of global climate change is the change in frequency of hydrological extremes. Predictions of climate change impacts on the regime of hydrological extremes have traditionally been conducted by a top-down approach that involves a high degree of uncertainty associated with the temporal and spatial characteristics of general circulation model (GCM) outputs and the choice of downscaling technique. This study uses the inverse approach to model hydrological risk and vulnerability to changing climate conditions in the Seyhan River basin, Turkey. With close collaboration with the end users, the approach first identifies critical hydrological exposures that may lead to local failures in the Seyhan River basin. The Hydro-BEAM hydrological model is used to inversely transform the main hydrological exposures, such as floods and droughts, into corresponding meteorological conditions. The frequency of critical meteorological conditions is investigated under present and future climate scenarios by means of a weather generator based on the improved K-nearest neighbour algorithm. The weather generator, linked with the output of GCMs in the last step of the proposed methodology, allows for the creation of an ensemble of scenarios and easy updating when improved GCM outputs become available. Two main conclusions were drawn from the application of the inverse approach to the Seyhan River basin. First, floods of 100-, 200- and 300-year return periods under present conditions will have 102-, 293- and 1370-year return periods under the future conditions; that is, critical flood events will occur much less frequently under the changing climate conditions. Second, the drought return period will change from 5.3 years under present conditions to 2.0 years under the future conditions; that is, critical drought events will occur much more frequently under the changing climate conditions.     

Evaluation of environmental parameters in logistic regression models for landslide susceptibility mapping

Abstract

The aim of this study was to determine how well the landslide susceptibility parameters, obtained by data-dependent statistical models, matched with the parameters used in the literature. In order to achieve this goal, 20 different environmental parameters were mapped in a well-studied landslide-prone area, the Asarsuyu catchment in northwest Turkey. A total of 4400 seed cells were generated from 47 different landslides and merged with different attributes of 20 different environmental causative variables into a database. In order to run a series of logistic regression models, different random landslide-free sample sets were produced and combined with seed cells. Different susceptibility maps were created with an average success rate of nearly 80%. The coherence among the models showed spatial correlations greater than 90%. Models converged in the parameter selection peculiarly, in that the same nine of 20 were chosen by different logistic regression models. Among these nine parameters, lithology, geological structure (distance/density), landcover-landuse, and slope angle were common parameters selected by both the regression models and literature. Accuracy assessment of the logistic models was assessed by absolute methods. All models were field checked with the landslides resulting from the 12 November 1999, Kayna?li Earthquake (Ms = 7.2).     

Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area,eastern Pontides,Turkey

The northern and southern zones of the eastern Pontides (northeast Turkey) contain numerous plutons of varying ages and compositions. Geochemical and isotopic results on two Hercynian granitoid bodies located in the northern zone of the eastern Pontides allow a proper reconstruction of their origin for the first time. The intrusive rocks comprise four distinct bodies, two of which we investigated in detail. Based on LA–ICP–MS U–Pb zircon dating, the Derinoba and Kayadibi granites have similar ²⁰⁶Pb/²³⁸U versus ²⁰⁷Pb/²³⁵U Concordia ages of 311.1 ± 2.0 and 317.2 ± 3.5 million years for the former and 303.8 ± 1.5 million years for the latter. Aluminium saturation index values of both granites are between 0.95 and 1.35, indicating dominant peraluminous melt compositions. Both intrusions have high SiO₂ (74–77 wt.%) contents and show high-K calc-alkaline and I- to S-type characteristics. Primitive mantle-normalized element diagrams display enrichment in K, Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies with La_cn/Yb_cn?=?4.6–9.7 and Eu_cn/Eu*?=?0.11–0.59 (Derinoba), and La_cn/Yb_cn?=?2.7–5.5 and Eu_cn/Eu*?=?0.31–0.37 (Kayadibi). These features imply crystal-melt fractionation of plagioclase and K-feldspar without significant involvement of garnet. The Derinoba samples have initial ?Nd values between –6.1 and –7.1 with Nd model ages and T _DM between 1.56 and 2.15 thousand million years. The Kayadibi samples show higher initial ?Nd_(I) values, –4.5 to –6.2, with Nd model ages between 1.50 and 1.72 thousand million years. This study demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios were lowered in some samples by hydrothermal interaction or alteration. Isotopic and petrological data suggest that both granites were produced by the partial melting of early Palaeozoic lower crustal rocks, with minor contribution from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.     

28 March 1970 Gediz earthquake fault,western Turkey: palaeoseismology and tectonic significance

On 28 March 1970, an unexpected and destructive earthquake (Ms = 7.2) originated along the Erdo?mu? fault (EF), which forms the southern margin of the modern Erdo?mu?–Yenigediz graben in the central part of the Ak?ehir–Simav fault system. The EF is a N-dipping normal fault, ～12 km long, generally E–W-trending, and characterized by a minor right-lateral strike–slip component. To determine its past activity, a palaeoseismological exploratory trenching study was conducted. Two trenches (EFT-1 and EFT-2) were excavated on the ground surface rupture of the 1970 Gediz earthquake near Erdo?mu? village. Based on the relative displacement between units observed and mapped in EFT-1, at least three events were identified. Two events were also identified in EFT-2. Only one of the events in EFT-1 can be dated via ¹⁴C. The estimated recurrence interval on the EF is ～910 ± 40 years.     

H020U井钻进所遇问题及处理方法

土耳其贝帕扎里天然碱矿H020U井在造斜钻进和水平钻进过程中遇到井漏、钻头钻遇硅化灰岩层磨损严重、未绕过第一靶点V020而打中套管、井涌、仪器掉入裸眼、钻遇未知溶腔导致顶角下降,方位偏离而导致未直接连通第二靶点等问题。针对这些问题进行了分析,并提出了相应的处理方法,最后成功地使H020U井连通第一靶点V020井和第二靶点V020U井。     

Tree-ring reconstructions of May–June precipitation for western Anatolia

In this study, we aim to examine past dry and wet events for the western Anatolia, performing local and spatial reconstructions. 17 new black pine site chronologies were developed, May–June precipitation time series were reconstructed for four localities, and the first spatial May–June precipitation reconstruction was achieved for western Anatolia. The long-term local May–June precipitation reconstructions contain mostly one-year and, less commonly, two-year drought events. The longest consecutive dry period (AD 1925–1928) in the reconstructed time series for Kütahya lasted four years. Spatial reconstructions revealed that between AD 1786 and 1930 the extreme dry years for all of western Anatolia were AD 1887, 1893, 1794 and 1740. The driest year during the 215-year-long period under consideration was 1887. The wettest years for the entire western Anatolia were determined to be AD 1835, 1876, 1881 and 1901. There is a big overlap between agricultural famine years and dry years as determined from reconstructions. In this context, our study provides a basis for understanding agricultural drought and better management of regional water resources.     

Palaeomagnetic investigation of Cenozoic volcanic rocks bordering the North Anatolian Fault Zone,Reşadiye and Koyulhisar Districts,central-east Anatolia,Turkey

A palaeomagnetic study is reported from the lavas of Eocene, Miocene and Pliocene age cropping out immediately to the north of the North Anatolian Fault Zone (NAFZ) in the Re?adiye–Mesudiye region of central-eastern Anatolia. Rock magnetic investigations identify a high percentage of multi-domained magnetite as the dominant ferromagnet in these rocks and this probably accounts for a relatively poor response to alternating field and thermal demagnetisation. Thirty of 37 units yielded acceptable groupings of characteristic magnetisation directions. An earlier study indicated small anticlockwise crustal block rotation in this region since Upper Cretaceous times (D/I?=?347/50°), and our study indicates that this was overtaken by clockwise rotation in Eocene times (D/I?=?40/47°), although sample size control from the Palaeogene is poor. Results from later Miocene (D/I?=?2/62°) and Pliocene (D/I?=?0/53°) volcanic rocks indicate that no significant tectonic rotation has occurred in the north of the NAFZ in Neogene times. This contrasts with rotations in the weaker crust comprising the Anatolian collage south of the NAFZ, where differential and sometimes large anticlockwise rotations occurred during the latter part of the Neogene.     

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