Features of the tertiary volcanism around sea of Marmara

International audienceIn the region around the sea of Marmara, limited by the boundaries of the 1:500 000 scale Istanbul Quadrangle,the volcanism starting in Upper Cretaceous and intermittently continuing through the end of Upper Miocene has beendifferentiated into five different stages, namely Upper Cretaceous, Eocene, Oligocene, Lower-Middle Miocene and UpperMiocene, and the volcanic outcrops situated in the region have been dated. Together with the detailed petrographic studies, ninesamples from different areas and stages have been dated by K/Ar method, resulting in that the oldest and the youngest lava isof 74.3 ± 1.0 million years old (Upper Cretaceous) and 8.9±0.2 years old (Upper Miocene), respectively. Of these, belonging tothe first four stages are mostly calcalkaline (some of the Eocene aged samples are tholeiitic) and are of basalt, basaltic andesite,trachyandesite, andesite, dacite, rhyolite type, whereas that of belonging to the fifth stage are alkaline and of basanite, basaltand trachybasalt types. The pyroclastics of various size and the tuffs of the first four volcanism stages crop out in a wide area.The Upper Cretaceous volcanics have completely formed beneath the sea. On the other hand, some of Eocene volcanics haveformed beneath the sea which are seen intercalated with sediments while the others have formed on land. The lavas ofOligocene, Lower-Middle Miocene and Upper Miocene age have formed on land and are observed to be intercalated withlacustrine sediments, in places. Of the lavas stranded along the Black sea coast, the Upper Cretaceous aged ones have formedin a group of island arc volcanics and have been produced in a subduction zone and the Eocene, Oligocene and Lower-MiddleMiocene aged ones have formed in an environment of compression during and after the collision and have been produced froma material of crust and mantle mixture. It is proposed that the Upper Miocene aged alcaline basaltic volcanics have formed in anenvironment of extension by the uplift of mantle after the change of tectonic regime in Middle Miocene

Geological and hydrogeochemical properties of geothermal systems in the southeastern region of Turkey

Yesilnacar, Mehmet Irfan/0000-0001-9724-8683; UZELLI, TAYGUN/0000-0003-0846-5921; BABA, ALPER/0000-0001-5307-3156WOS: 000458467900021The Anatolia region is one of the most seismically active regions in the world. It has a considerably high level of geothermal energy potential thanks to its geological and tectonic settings. The Southeastern Anatolia Region (GAP) is located in the south of Bitlis-Zagros Suture Zone (BZSZ) which is in the Arabian foreland. During the neotectonic period, the folded structures have been developed under the influence of tectonic compression from the Upper Miocene in the GAP Region where it is closely related to active tectonics. These tectonic activities produce more geothermal resources. Few studies have been carried out in this region for geothermal energy. Limited portions of the geothermal resources have been used both for thermal tourism and greenhouses in the GAP region. The aim of this study is to determine geological, tectonic and hydrogeochemical properties of a geothermal system in the GAP Region. The result indicates that the surface temperatures of geothermal fluids are from 20 to 84.5 degrees C A large number of abandoned oil wells, whose temperature reaches 140 degrees C, are found in the region. Also, hydrogeochemical results show that deep circulated geothermal fluids are enriched with Na-Cl and shallow geothermal system fluids have Na - HCO3 and Ca-SO4 characters because of cold water mixing and water-rock interaction. Cold waters are generally of Ca-Mg - HCO3 and Ca - HCO3 type. Cation geothermometers were used for determining reservoir temperature of the geothermal resources in the region. The results show that the reservoir temperature of these geothermal resources ranges from 50 degrees C to 200 degrees C. The isotope data (oxygen-18, deuterium and tritium) suggests that geothermal fluid is formed by local recharge and deep circulation

Genesis of collision volcanism in Eastern Anatolia, Turkey

Late Cenozoic volcanism in Eastern Anatolia extends in a broad SW - NE trending belt across the Arabia - Eurasia collision zone, from the Arabian foreland basin in the southwest and to the Kars Plateau and Lesser Caucasus in the northeast. Foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic - alkaline composition. Volcanism on the thickened crust north of the Bitlis Thrust Zone varies from the mildly alkaline volcano, Nemrut, and older Mus volcanics in the south, through the transitional calc-alkaline/alkaline volcanoes Bingöl and Süphan and the alkaline volcano Tendürek to the calc-alkaline volcano Ararat and older Kars plateau volcanics in the north. Isotope (Sr, Nd) and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the Arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time; and that lavas from the alkaline volcanic area around Mus, and the volcanoes Nemrut and Tendürek north of the Bitlis Thrust Zone were derived from a lithospheric source of similar composition, either from the same, underthrust, Arabian continent or from the Bitlis Massif microcontinent. By contrast, the transitional lavas from Bingöl and Süphan and the calc-alkaline lavas from Ararat and Kars were derived from lithosphere carrying a distinct subduction signature inherited from pre-collision subduction events. Positive correlations between 87Sr/86Sr and SiO2 and Rb/Nb and SiO2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone. Trace element covariation diagrams such as Y-Rb indicate the importance of hornblende crystallization at depth (and orthopyroxene at shallow levels) within the calc-alkaline provinces, in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas. Trace element diagrams, based on the covariation of compatible and incompatible elements, point to moderate - low degrees of partial melting with residual clinopyroxene throughout, and residual garnet in the foreland province. Consideration of mineral stabilities, mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths, probably beneath the amphibole and dolomite breakdown curves. Perturbation of the thickened lithosphere by delamination of the thermal boundary layer, perhaps coupled with local stretching associated with pull-apart basins on strike-slip fault systems, is then sufficient to generate melt, the composition of that melt being largely dependent on the enrichment history of the lithosphere in question. In Eastern Anatolia, volcanism appears to have started between about 8 and 6 Ma ago, some 5 Ma after the start of rapid uplift of the East Anatolian Plateau

Slip partitioning in the Sea of Marmara Pull-Apart determined from GPS velocity vectors

Dislocation modelling is used to examine the GPS velocity vectors for the Marmara Sea region. First, the vectors due to the known Anatolia/Eurasia rotation are reproduced by introducing structures that approximate the large-scale tectonics. Observed features of the smaller scale fault system in the Marmara region are then progressively included with slip amplitudes and directions adjusted to fit an 80-vector subset of the GPS data. The motion in the Marmara Sea region is partitioned with the faults that bound the north of the basin carrying more strike-slip motion than predicted from the Anatolia-Eurasia plate motion and faults to the south having a greater perpendicular component. Taken together however, there is no net opening across the Marmara Sea perpendicular to the overall trend of the boundary and thus deformation in the Marmara region results only from the pull-apart geometry of the North Anatolian fault. No extension related to the Aegean system is needed to explain the observations. The GPS results are consistent with motion over the last 5 Myr that has been determined from geological reconstructions