Tectonic Setting and Evolution of the Sivas Basin,Central Anatolia,Turkey

The Sivas Basin is one of several Central Anatolian basins. It developed mainly after the closure of the northern branch of Neotethys. Its location between the Kirsehir Massif and the Taurides implies that it should not be confused with the Inner Tauride ocean located south of the Eastern Taurides. The basement of the Sivas Basin consists of ophiolitic nappes and melanges that were thrust toward the margins of the continental blocks present in this area—the Pontide belt to the north and the Anatolide-Tauride platform to the south. The basin was initiated by tectonic subsidence at the end of the Cretaceous, and it can be compared to a foreland basin during Paleocene and early to middle Eocene time. It was emergent during late Eocene and Oligocene time, although it continued to subside. A transgression in some parts of the basin occurred during the Oligocene and early Miocene (maximum flooding). During the Pliocene, it was affected by regional compression directed toward the NNW, which resulted from convergence of the Arabian and Eurasian plates. This basin may have developed as an intracontinental basin within the Tauride platform and probably never had an oceanic basement. As a result of this work, the general paleogeographic organization of Central Anatolia and Northern Tethys during the Mesozoic should to be revised.     

Geochemical and Sr–Nd isotopic evidence for the genesis of the Late Cainozoic Almopia volcanic rocks (Central Macedonia, Greece)

Summary ?Major and trace element contents and Sr–Nd isotope ratios of selected volcanics of Pliocene age from the Almopia area, central Macedonia, Greece, have been determined. These rocks are mainly distinguished as two groups based on geographical, petrological and isotopic data: a) the east–central western group (E–CW) and b) the south western group (SW). The absence of contemporaneous basic volcanics in the Almopia area coupled with the considerable scatter of elements in variation diagrams rule out fractional crystallization as the dominant differentiation process. Instead, disequilibrium textures along with the positive correlation of Sr-isotope ratios with differentiation suggest mixing between a basic and an acid component combined with assimilation and fractionation. The spider diagrams of the most silica-poor volcanics show evidence of subduction-related processes, indicating that the parental magmas may have been derived from partial melting of mantle wedge enriched in LILE and LREE by subducted slab-derived fluids. Previous data on the oxygen isotope composition of the same volcanics are consistent with this genetic hypothesis. Lastly, the relatively high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd ratios (0.7080 and 0.512370, respectively) of the volcanic sample inferred to be compositionally the closest one to the parental magma of Almopia rocks suggest that the incompatible element enrichment of the mantle source is old, probably of Proterozoic age. Received December 12, 2001; revised version accepted June 20, 2002 Published online November 29, 2002     

Geotechnical evaluation of Miocene gypsum from Sivas (Turkey)

Gypsum is widely distributed in Sivas (Turkey), occurring chiefly in the formations of Miocene age. The gypsum is generally of the alabastrine type with a little of the porphiroblast type and contains traces of clay minerals, anhydrite and calcite. It is a moderately strong rock in terms of its unconfined compressive strength which is related to the crystal size. Strength increases as the crystal size decreases. The strength of gypsum was reduced by approximately 55%, when the samples were kept in the water for 20 days. Most samples exhibit plastic–elastic–plastic deformation. The gypsum has a high modulus ratio, and is a moderately deformable rock. High lateral deformations and low vertical deformations are observed under the vertical stress conditions in accordance with the relationship between modulus ratio and strain.     

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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C, O, S and Sr isotope studies on the genesis of Fe-carbonate and barite mineralizations in the Attepe iron district (Adana, Southern Turkey)

The Attepe district consists of Precambrian, Lower–Middle Cambrian, Upper Cambrian–Lower Ordovician and Mesozoic formations. It contains several iron deposits and occurrences. Three types of iron-mineralizations can be distinguished in the area; (i) Sedimentary Fe-sulfide in Precambrian bituminous metapelitic rocks, and Fe-oxides in Precambrian metasandstones (SISO), (ii) vein-type Fe-carbonate and oxides composed of mainly siderite, ankerite and hematite including barite in Lower–Middle Cambrian metacarbonates of the Çaltepe Formation (HICO), (iii) karstic Fe-oxides and hydroxides essentially in the Lower–Middle Cambrian metacarbonates and the unweathered Fe-carbonates (KIO). The latter type is more widespread and located at the upper parts of the most important mineable iron deposits like Attepe deposit.

Oxygen-, carbon-, sulfur- and strontium-isotope studies have been performed on siderites and barites in the vein-type ores, and on calcites in the recrystallized Çaltepe Limestones to investigate the sources and formation mechanism of primary ore-forming constituents. The δ¹³C values of siderites and calcites in limestones of the Çaltepe Formation range from −10.10‰ to −8.20‰, and from −0.8‰ to 2.30‰. Both carbonate minerals show δ¹⁸O values between 17.50–18.30‰ and 16.20–23.00‰, respectively. The δ¹³C and δ¹⁸O isotopic variations do not indicate any direct or linear relations between siderites and limestones. However, it is possible that the carbon and oxygen isotopic compositions of carbonate minerals could be changed to some extent, when limestones were subjected to hydrothermal processes or thermal alterations during metamorphism.

The isotopic values of barites display 32.40–38.30‰ for δ³⁴S and 12.20–14.70‰ for δ¹⁸O. The strontium isotope ratios (0.717169–0.718601) of barites and the sulfur isotope compositions of barites and pyrites suggest that there are no direct linkages of ore-forming compounds neither with a magmatic source nor with sedimentary pyrite formations in the Precambrian bituminous shales of the Attepe formation.

According to the field observations and the stable isotope data, siderites and ankerites should be formed by interaction between iron-rich hydrothermal fluids and Çaltepe limestones, whereas isotope ratios of barites indicate that they were formed by mixing of sulfur-rich meteoric waters and deeply circulated hydrothermal solutions.     

Investigation of the deep structure of the Sivas Basin (innereast Anatolia, Turkey) with geophysical methods

Sivas Basin is the easternmost and third largest basin of the Central Anatolian Basins. In this study, gravity, aeromagnetic and seismic data are used to investigate the deep structure of the Sivas Basin, together with the well seismic velocity data, geological observations from the surface and the borehole data of the Celalli-1 well. Basement depth is modeled three-dimensionally (3D) using the gravity anomalies, and 2D gravity and magnetic models were constructed along with a N–S trending profile. Densities of the rock samples were obtained from the distinct parts of the basin surface and in-situ susceptibilities were also measured and evaluated in comparison with the other geophysical and geological data. Additionally, seismic sections, in spite of their low resolution, were used to define the velocity variation in the basin in order to compare depth values and geological cross-section obtained from the modeling studies. Deepest parts of the basin (12–13 km), determined from the 3D model, are located below the settlement of Hafik and to the south of Zara towns. Geometry, extension and wideness of the basin, together with the thickness and lithologies of the sedimentary units are reasonably appropriate for further hydrocarbon exploration in the Sivas Basin that is still an unexplored area with the limited number of seismic lines and only one borehole.     

Examination of the structural characteristics arising in gypsums by the GPR and MASW methods (Sivas,Turkey)

This study was performed at an area of 50?×?48 m² being defined as a new settlement in the northeast of Sivas. In the study, the discontinuities that are not deep and their geophysical characteristics were examined by the GPR and MASW methods. For interpretation, GPR cross sections were prepared as 2D–3D, and MASW cross sections were prepared as 2D. As for geophysical cross sections, about 10 m depth was examined. It was understood that the reflections observed in the form of hyperbolas in GPR cross sections correspond to areas having low S wave velocity (V_s) in MASW cross sections. It was understood that the S wave velocities are lower than 653 m/s, that the seismic velocities in between 653 and 275 m/s indicate partially deteriorated areas and that the S wave velocities of unweathered gypsums are higher than 1275 m/s at these low-velocity zones. Thus, it was thought that the fill material that may arise in the fracture, crack and deterioration areas arises from intercalation and clastic gypsum units, and that it plays a role in having low value S wave velocities. In all the geophysical cross sections, it was understood that the structures with gypsum are intense at the initial 5 m. And a fracture at the south of the study area, that it was estimated might be longer than 40 m, was determined as the largest gypsum structure. It was understood that this fracture starts from a depth of about 5 m in the west and that it slopes down to 7 m depth in the east. According to these results, it was understood that the damage amount arising in time in the gypsum structures from the effect of water may increase, the study area was defined as risky, and the required importance should be attached to these structures especially in foundation engineering.     

Geochemical characteristics of ophiolitic rocks from the southern margin of the Sivas basin and their implications for the Inner Tauride Ocean,Central-Eastern Turkey

Number of dismembered ophiolite bodies crop out between Sivas and Malatya on the top of the Eastern Tauride platform in the central-eastern Turkey. One of which at the southern margin of the Sivas basin in the Tecer Mountain area comprises melange and the lower part of an oceanic lithospheric section on top of the Tauride platform. The mantle tectonites are characterized by variably serpentinized harzburgites and dunites, and are intruded by numerous isolated dykes. The gabbroic cumulates consist of olivine gabbro, gabbro and gabbronorite. The major and trace element geochemistry of the mafic cumulate rocks suggests that the primary magma was compositionally similar to those observed in modern island-arc tholeiitic sequences. The isolated dykes are exclusively basaltic in composition and display geochemically two distinct subgroups: Group I is represented by high TiO₂ (.87–1.47 wt.%) and other incompatible elements, whereas Group II is characterized by low TiO₂ (.36–.66 wt.%) and other incompatible elements. The Group I isolated diabase dykes have flat to slightly LREE-depleted profiles (La/Yb_N = .32–.79), whereas the Group II isolated diabase dykes are more depleted in general and have a LREE-depleted character (La/Yb_N = .19–.49). This suggests that the isolated dykes were derived from an island arc tholeiitic magma (Nb/Y = .02–.05) with different degrees of partial melting (Group II > Group I) and relatively high oxygen fugacity in intra-oceanic subduction zone. The ophiolitic rocks in the study area may well be compared with the Divri?i ophiolite to the southeast. All the evidence suggests that the isolated dykes in the Tecer Mountain area differ from the alkaline isolated dykes cutting the Divri?i ophiolite. Since the late stage dykes (~76 Ma) in the Divri?i area are alkaline, the tholeiitic isolated dykes in the present study should have been emplaced prior to the alkaline dykes during Late Cretaceous SSZ-spreading (~90 Ma) within the Inner Tauride Ocean.     

Collapse dolines in miocene gypsum: an example from SW Sivas (Turkey)

 This study investigated the formation mechanism of dolines. Dolines are caused by dissolution of gypsum in the study area, 50–220 m in diameter. Two systems were applied to determine the support necessary for natural underground opening of given span in a given rock mass. From the characteristics of the rock mass, a 5 m-wide unsupported span in the gypsum can be expected to stand up for over 9 years. The designed span of an artificial opening would normally be considerably less than the span of a collapsed natural opening in the same rock. Dolines in the study area play an important role in the groundwater flow system. Received: 10 November 1995 · Accepted: 4 January 1996     

Structural,geomorphological and geomechanical aspects of the Koyulhisar landslides in the North Anatolian Fault Zone (Sivas,Turkey)

. Recently, numerous landslides occurred in the northern part of Koyulhisar. In 1998 and 2000, which were very wet years, landslides in different masses affected the geological formations which are well known for being prone to slope movements. Detailed geological, geomorphological and geotechnical surveys were carried out, and stability conditions in Koyulhisar village, located NE of Sivas (Turkey), are discussed in this paper. Kinematical analyses showed that the potential slope instabilities are in two main directions: the first direction is SE and the second is SW, these directions corresponding to the dominant slope directions of the study area. Geomechanic surveys confirmed that most of the rock slopes analysed are highly prone to instability. The SMR criterion gave results which correspond well with real stability conditions. Jointing and faulting, steep topography, water incisions, and heavy rainfall played a significant role in the occurrence of the landslides.     

The 17 March 2005 Kuzulu landslide (Sivas, Turkey) and landslide-susceptibility map of its near vicinity

Landslides are common natural hazards in the seismically active North Anatolian Fault Zone of Turkey. Although seismic activity, heavy rainfall, channel incisions, and anthropogenic effects are commonly the main triggers of landslides, on March 17, 2005, a catastrophic large landslide in Sivas, northeastern of Turkey, the Kuzulu landslide, was triggered by snowmelt without any other precursor. The initial failure of the Kuzulu landslide was rotational. Following the rotational failure, the earth material in the zone of accumulation exhibited an extremely rapid flow caused by steep gradient and high water content. The Agnus Creek valley, where Kuzulu village is located, was filled by the earth-flow material and a landslide dam was formed on the upper part of Agnus Creek. The distance from the toe of the rotational failure down to the toe of the earth flow measured more than 1800 m, with about 12.5 million m³ of displaced earth material. The velocity of the Kuzulu landslide was extremely fast, approximately 6 m/s. The main purposes of this study are to describe the mechanism and the factors conditioning the Kuzulu landslide, to present its environmental impacts, and to produce landslide-susceptibility maps of the Kuzulu landslide area and its near vicinity. For this purpose, a detailed landslide inventory map was prepared and geology, slope, aspect, elevation, topographic-wetness index and stream-power index were considered as conditioning factors. During the susceptibility analyses, the conditional probability approach was used and a landslide-susceptibility map was produced. The landslide-susceptibility map will help decision makers in site selection and the site-planning process. The map may also be accepted as a basis for landslide risk-management studies to be applied in the study area.     

Geochemical and geochronological evidence for Early Triassic calc-alkaline magmatism in the Menderes Massif, western Turkey

Pan-African basement rocks and a Paleozoic cover series, which were intruded by the protoliths of leucocratic orthogneisses, have been recognized in the Menderes Massif, located in the western part of the Alpine orogenic belt of Turkey. This geochemical and geochronological study focuses on the evolution of the Menderes Massif at the end of Paleozoic time. Geochemical data suggest that the crustally derived leucocratic orthogneisses have chemical composition typical of calc-alkaline and S-type granite. Zircon grains which are euhedral with typical igneous morphologies were dated by the ²⁰⁷Pb/²⁰⁶Pb evaporation method. Single-zircon dating of three samples yielded mean ²⁰⁷Pb/²⁰⁶Pb ages of 246LJ, 241LJ and 235Lj Ma. These ages are interpreted as the time of protolith emplacement in Triassic. Geological and geochronological data suggest that leucocratic granites were emplaced in a period following a metamorphic event related to the closure of the Paleo-Tethys. The leucocratic granites were metamorphosed during the Alpine orogenesis and transformed into orthogneisses. The similar Triassic magmatic event at 233DŽ Ma was also occurred, using single-zircon evaporation method, from granitic gneisses which rest upon the migmatites with tectonic contacts in Naxos, Cycladic complex. This indicates that the Menderes Massif and Cycladic complex had a common pre-Early Triassic magmatic evolution.     

Contribution to the genesis of the SEDEX-type mineralizations of the Rhenish Massif (Germany) — implications for future Pb-Zn exploration

The Meggen orebody and the number of subeconomic sediment-hosted mineralizations at Plettenberg-Affeln, Oberhundem, and Günterod (eastern Rhenish Massif) are considered to be typical members of the large SEDEX family, i.e., submarine-hydrothermal Zn-Pb orebodies. Examples such as Howards Pass (Canada), McArthur River and Broken Hill (Australia), and Navan (Ireland) formed between the Middle Proterozoic and Carboniferous as a consequence of slow continental extension, long-term elevated heat flow and basin dewatering, enhanced and focused along deeply penetrating synsedimentary fault zones. Volcanic activity bound to these fractures has no direct genetic relationship to SEDEX mineralization. Based on structural and detailed stratigraphic correlation and facies analysis it can be shown that all SEDEX-type mineralizations of the Rhenish Massif are bound to one and the same synsedimentary fault zone, named here the Balve-Oberscheld fault zone, which was reactivated during Variscan compressional and extensional movements. The trend of this tectonic lineament (termed »Menden-Oberscheld lineament«) can be even recognized on maps depicting crustal gravity patterns and the configuration of the Moho. Illite crystallinity measurements in Devonian shales along profiles crosscutting the lineament evidence increased Variscan to early post-Variscan metamorphism in the fault system, which already had promoted the synsedimentary heat flow. Indications were found that the metalliferous brines escaping into the Meggen basin were bound to a synsedimentary fault situated at the western margin of the Meggen basin. The widespread Zn-Pb-Ba mineralizations and anomalies in the middle to upper Givetian shales in the Plettenberg-Affeln area are likewise bound to horst-and-graben tectonism along the Balve-Oberscheld fault zone. Based on data from economic and scientific research in the Rhenish Massif, the application of paleostructural methods for future basemetal exploration is discussed.

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Zusammenfassung Der Meggener Zn-Pb-Ba Erzkörper und die stratiformen Pyrit-Baryt- und Buntmetallvorkommen der Gebiete Plettenberg-Affeln, Oberhundem und Günterod (rechtsrheinisches Schiefergebirge) gehören wie die berühmten Vererzungen von Howards Pass (Kanada), McArthur River und Broken Hill (Australien) und Navan (Irland) zur bedeutsamen Gruppe der SEDEX-Mineralisationen. Diese submarin-hydrothermalen Vererzungen sind an epikontinentale klastische Sedimente des Mittelproterozoikums bis Karbons gebunden. Die Hydrothermentätigkeit erfolgte während langanhaltender, moderater Dehnungstektonik, die durch beckenweite Blocktektonik und erhöhten Wärmefluß gekennzeichnet war. Der Entwässerungsstrom der Becken wurde durch tiefreichende synsedimentäre Störungssysteme örtlich fokussiert. Der an diese Bruchstrukturen gebundene Vulkanismus steht nicht in unmittelbarer genetischer Beziehung zur Vererzung. Es kann für das Rheinische Schiefergebirge gezeigt werden, daß alle SEDEX-Mineralisationen sowie zwei Eisenerzdistrikte vom Lahn-DillTypus auf der NNW-SSE-verlaufenden synsedimentären Balve-Oberscheld-Störungszone liegen. Diese wurde im Zuge variszischer und saxonischer Tektonik zu einem Lineament umgeformt, das seinen Ausdruck auch auf Karten der Erdschwere und der Mohokonfiguration hat. Die Untersuchung der Illitkristallinität devonischer Tonschiefer konnte zeigen, daß der permokarbone Wärmefluß — wie zuvor der synsedimentäre Wärmefluß — auf diesem »Menden-Oberscheld-Lineament« erhöht war. Geochemische und paläogeographische Untersuchungen machen wahrscheinlich, daß der Aufstieg der metallhaltigen Hydrothermen im Ober-Givetmm im Bereich der westlichen Beckenrandstörung des Meggener Beckens erfolgte. In einem ca. 1,5 km breiten NNW-SSE-gerichteten synsedimentären Graben, der im Gebiet Plettenberg-Affeln rekonstruiert werden konnte, kam es während des Mittel- bis Ober-Givetiums ebenfalls zur stratiformen Zn-Pb-Ba-Mineralisation. Anhand der Ergebnisse aus dem Rheinischen Schiefergebirge wird der Einsatz paläostruktureller Arbeitsmethoden für künftige Explorationsprogramme diskutiert.

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Résumé L'association minéralogique Zn-Ba-Pb de Meggen ainsi que les gisements de pyrite-barite stratiformes de Plettenberg-Affeln, Oberhundem et Günterod sont interprétés comme appartenant au large groupe des minéralisations de type SEDEX parmi lesquelles figurent les célèbres gisements de Howards Pass (Canada), McArthur River, Broken Hill (Australie) et Navan (Irlande). Les minéralisations hydrothermales sous-marines de type SEDEX sont liées aux sédiments clastiques épicontinentaux datant du Protérozoïque moyen jusqu'au Carbonifère. Leur formation s'est effectuée durant une longue période de tectonique de distension modérée, caractérisée par des systèmes de blocs à l'échelle du bassin rhénan et un flux de chaleur élevé. L'élimination de l'eau interstitielle des sédiments a été favorisée et localement focalisée par des systèmes synsédimentaires de failles profondes. L'activité volcanique accompagnant ces systèmes n'est cependant pas à relier directement à la genèse des minéralisations SEDEX. Dans le cas du Massif Schisteux Rhénan, on peut démontrer que toutes les minéralisations de type SEDEX, ainsi que deux districts à gisement de fer de type Lahn-Dill, s'alignent le long de la zone failleuse synsédimentaire NNW-SSE de Balve-Oberscheld. Celle-ci fut réactivée durant les phases tectoniques varisque et saxonne, donnant naissance à un linéament, visible sur la carte gravimétrique et sur celle de la profondeur du Moho. L'analyse de la cristallinité de l'illite montre que le flux de chaleur permo-carbonifère — ainsi qu'auparavant le flux de chaleur synsédimentaire — était relativement élevé à l'endroit de ce »Menden-Oberscheld lineament«. Les résultats des recherches géochimiques et paléogéographiques suggèrent que l'ascension de l'hydrotherme métallifère s'est effectuée durant le Givetien supérieur dans la zone de la faille située en bordure ouest du bassin de Meggen. D'autre part, dans un fossé d'effondrement long d'environ 1,5 km et d'orientation NNW-SSE, qui a pu être reconstitué dans la région Plettenberg-Affeln, on observe également des minéralisations Zn-Pb-Ba stratiformes datant du Givetien moyen à supérieur. Etant donné que les méthodes conventionnelles de prospection ont échoué dans la recherche de nouveaux gisements de type Meggen-Rammelsberg et comme toutes les minéralisations SEDEX connues au Canada, en Australie et en Europe sont liées à des zones de failles synsédimentaires, on propose, dans le cadre de programmes de recherches ultérieurs, l'application de méthodes de travail basées sur la paléotectonique.

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Assessment of naturally occurring arsenic contamination in the groundwater of Sarkisla Plain (Sivas/Turkey)

High arsenic levels in groundwater of the aquifers, belonging to the Pliocene terrestrial layers and Quaternary alluvial sediments, have become a significant problem for the inhabitants living in Sarkisla (Turkey). The main objective of this study was to determine the origin and arsenic contamination mechanisms of the Sarkisla drinking water aquifer systems. The highest arsenic concentrations were found in Pliocene layers and alluvial sediments with concentrations ranging from 2.1 to 155 mg/kg. These rocks are the main aquifers in the study area, and most of the drinking groundwater demand is met by these aquifers. Groundwater from the Pliocene aquifer is mainly Ca-HCO₃ and Ca-SO₄ water type with high EC values reaching up to 3,270 μS/cm, which is due to the sulfate dissolution in some parts of the alluvial aquifer. Stable isotope values showed that the groundwater was of meteoric origin. Tritium values for the groundwater were between 8.31 and 14.06 TU, representing a fast circulation in the aquifer. Arsenic concentrations in the aquifers were between 0.5 and 345 μg/L. The highest arsenic concentrations detected in the Pliocene aquifer system reached up to 345 μg/L with an average value of 60.38 μg/L. The arsenic concentrations of the wells were high, while the springs had lower arsenic concentrations. These springs are located in the upper parts of the study area where the rocks are less weathered. The hydrogeochemical properties demonstrated that the water–rock interaction processes in sulfide-bearing rocks were responsible for the remarkably high groundwater arsenic contamination in the study area. In the study area, the arsenic levels determined in groundwater exceeded the levels recommended by the WHO. Therefore, it is suggested that this water should not be used for drinking purposes and new water sources should be investigated.     

苏鲁造山带胶南区段片麻岩原岩的成因:地球化学及Nd同位素证据

出露于苏鲁造山带胶南区段的片麻岩主要包括三种类型黑云斜长片麻岩、二长花岗片麻岩和A型花岗质片麻岩,地球化学判别结果表明它们的原岩均为火成岩.不同类型片麻岩的地球化学特征各不相同,反映它们的原岩具有不同的形成与演化历史.其中黑云斜长片麻岩以负Eu异常弱,甚至出现明显的正异常(δEu=0.60～1.45)、强的Ba正异常、无明显的Sr异常为特征而明显不同于其它类型的片麻岩.其地球化学的总体特征类似于扬子克拉通北缘新元古代双峰式火山岩的酸性端元;与黑云斜长片麻岩类似,二长花岗片麻岩中轻、重稀土元素之间的分馏程度也较强(LaN/YbN=6.3～17.2),但以强的负Eu异常(δEu=0.27～0.54)、强的Sr负异常和弱的Ba负异常为特征明显不同于黑云斜长片麻岩;A型花岗片麻岩的稀土模式及蛛网图的形态类似于二长花岗片麻岩,所不同的是前者Nb、Ta负异常相对较弱.区内几种类型片麻岩的εNd(t)值差别不大,反映它们的原岩之间可能有一定的成因联系.它们的Nd同位素模式年龄TDM都集中在2.0Ga左右,表明它们的源区主要为早元古代的地壳物质,且岩性比较均一.推测二长花岗片麻岩与黑云斜长片麻岩的原岩是同源异相,而A型花岗岩是在大规模Ⅰ型花岗质岩浆形成后,由脱水的紫苏辉石质残留下地壳物质再次发生部分熔融形成的.     

Mineralogy and major-trace element geochemistry of the Haymana manganese mineralizations,Ankara, Turkey

The study area comprises Çayirli, Harapa?illari and Ortabel (ÇHO) districts in the Haymana town 25 km SW of the Ankara city. In this study, geologic setting, mineralogical and geochemical characteristics of manganese mineralizations are examined and their origin is discussed. Data were obtained from field observations, various polished and thin section determinations and chemical analyses of 25 ore samples. Major and trace element analyses were conducted with ICP-ES and ICP-MS methods at ACME Laboratories (Canada). ÇHO manganese ores are found in reddish radiolarites and partly interbedded marls of the Ankara ophiolitic melange of lower Cretaceous-upper Senonian age. In these extremely folded rocks, manganese is observed as band and lenses. All samples are composed of pyrolusite and quartz. Circular pyrolusites around the gangue form a ring texture and radiolarite ores yield spherical sections. In addition, breccia-like texture is observed between pyrolusite and quartz. Geologic setting, mineralogical and textural data indicate an exogene environment. Major and trace element abundances and correlation among them imply that ÇHO mineralizations are of hydrothermal origin and linked to the same source. Evaluation of all these data shows that ÇHO manganese mineralizations are of hydrothermal type sedimentary mineralization and they were deposited in distal part of the source.     

Geochemical characterization of the Biga Peninsula thermal waters (NW Turkey)

Thermal water chemistry from the Biga Peninsula (NW Turkey) was investigated in order to discriminate among hydrochemical facies, and isotopic groups and identify the major geochemical processes. A systematic hydrogeochemical survey was carried out, incorporating new data as well as results from the previous studies. Results were used to further develop hydrogeological and geochemical models. Thermal water compositions were classified into four groups and the processes affecting evolution of water compositions were interpreted. Types 1, 2 and 3 are representatives of water corresponding to sulfate dominant fluids (mainly NaSO₄-type), chloride dominant fluids (mainly NaCl-type), and bicarbonate dominant fluids (Na- or CaHCO₃-type), respectively. Group 4 comprises the fluids with compositions that are not dominated by any distinctive anion. Groundwater infiltrates and circulates through the marbles of the Paleozoic basement. The isotopic composition of thermal waters revealed that deep infiltration of meteoric water took place in periods of changed climatic conditions.