Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust,Eastern Turkey: Implications for crustal thickening to delamination     

Orhan Karsli  Abdurrahman Dokuz  İbrahim Uysal  Faruk Aydin  Raif Kandemir  Jan Wijbrans 《Lithos》2010,114(1-2):109-120

Early Cenozoic (48–50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO₂ contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high I_Sr (0.70474–0.70640) and low ε_Nd (50 Ma) values (? 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr–Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic.  相似文献   

Response and Stability of Underground Structures in Rock Mass during Earthquakes   总被引：1，自引：0，他引：1  

Ömer Aydan  Yoshimi Ohta  Melih Geniş  Naohiko Tokashiki  K. Ohkubo 《Rock Mechanics and Rock Engineering》2010,43(6):857-875

Underground structures are well known to be earthquake resistant. However, the recent earthquakes showed that underground structures are also vulnerable to seismic damage. There may be several reasons such as high ground motions and permanent ground movements. This study attempts to describe various forms of damage to underground structures such as tunnels, caverns, natural caves and abandoned mines during major earthquakes. Results of various model tests on shaking table are also presented to show the effect of ground shaking on the response and collapse of underground structures in continuum and discontinuum. Furthermore, some empirical equations are proposed to assess the damage to underground structures, which may be useful for quick assessments of possible damage.  相似文献   

Stratigraphic,sedimentological and palaeoenvironmental constraints on the rise of the Urgonian platform in the western Swiss Jura     

ALEXIS GODET  KARL B. FÖLLMI  STÉPHANE BODIN  ERIC De KAENEL  VIRGINIE MATERA  THIERRY ADATTE 《Sedimentology》2010,57(4):1088-1125

Urgonian‐type carbonates are a characteristic feature of many late Early Cretaceous shallow‐marine, tropical and subtropical environments. The presence of typical photozoan carbonate‐producing communities including corals and rudists indicates the prevalence of warm, transparent and presumably oligotrophic conditions in a period otherwise characterized by the high density of globally occurring anoxic episodes. Of particular interest, therefore, is the exploration of relationships between Urgonian platform growth and palaeoceanographic change. In the French and Swiss Jura Mountains, the onset and evolution of the Urgonian platform have been controversially dated, and a correlation with other, better dated, successions is correspondingly difficult. It is for this reason that the stratigraphy and sedimentology of a series of recently exposed sections (Eclépens, Vaumarcus and Neuchâtel) and, in addition, the section of the Gorges de l’Areuse were analysed. Calcareous nannofossil biostratigraphy, the evolution of phosphorus contents of bulk rock, a sequence‐stratigraphic interpretation and a correlation of drowning unconformities with better dated sections in the Helvetic Alps were used to constrain the age of the Urgonian platform. The sum of the data and field observations suggests the following evolution: during the Hauterivian, important outward and upward growth of a bioclastic and oolitic carbonate platform is documented in two sequences, separated by a phase of platform drowning during the late Early Hauterivian. Following these two phases of platform growth, a second drowning phase occurred during the latest Hauterivian and Early Barremian, which was accompanied by significant platform erosion and sediment reworking. The Late Barremian witnessed the renewed installation of a carbonate platform, which initiated with a phase of oolite production, and which progressively evolved into a typical Urgonian carbonate platform colonized by corals and rudists. This phase terminated at the latest in the middle Early Aptian, due to a further drowning event. The evolution of this particular platform segment is compatible with that of more distal and well‐dated segments of the same northern Tethyan platform preserved in the Helvetic zone of the Alps and in the northern subalpine chains (Chartreuse and Vercors).  相似文献   

Simulation of spatiotemporal dynamics of water fluxes in Germany under climate change     

Shaochun Huang  Valentina Krysanova  Hermann Österle  Fred F. Hattermann 《水文研究》2010,24(23):3289-3306

In most of Europe, an increase in average annual surface temperature of 0·8 °C is observed, and a further increase is projected. Precipitation tends to increase in northern Europe and decrease in southern Europe, with variable trends in central Europe. The climate scenarios for Germany suggest an increase in precipitation in western Germany and a decrease in eastern Germany, and a shift of precipitation from summer to winter. When investigating the effects of climate change, impacts on water resources are among the main concerns. In this study, the first German‐wide impact assessment of water fluxes dynamics under climate change is presented in a spatially and temporally distributed manner using the state‐of‐the‐art regional climate model, Statistical Regional (STAR) model and the semi‐distributed process‐based eco‐hydrological model, soil and water integrated model (SWIM). All large river basins in Germany (lower Rhine, upper Danube, Elbe, Weser and Ems) are included. A special focus of the study was on data availability, homogeneity of data sets, related uncertainty propagation in the model results and scenario‐related uncertainty. After the model calibration and validation (efficiency from 0·6 to 0·9 in 80% of cases) the water flow components were simulated at the hydrotope level, and the spatial distributions were compared with those in the Hydrological Atlas of Germany. The actual evapotransipration is likely to increase in most parts of Germany, while total runoff generation may decrease in south and east regions. The results for the second scenario period 2051–2060 show that water discharge in all six rivers would be 8–30% lower in summer and autumn compared with the reference period, and the strongest decline is expected for the Saale, Danube and Neckar. Higher winter flow is expected in all of these rivers, and the increase is most significant for the Ems (about 18%). However, the uncertainty of impacts, especially in winter and for high water flows, remains high. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Paper II – Dirt,dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia,and their implications for sedimentary ancient DNA studies     

LEE J. ARNOLD  RICHARD G. ROBERTS  ROSS D. E. MACPHEE  JAMES S. HAILE  FIONA BROCK  PER MÖLLER  DUANE G. FROESE  ALEXEI N. TIKHONOV  ALLAN R. CHIVAS  M. THOMAS P. GILBERT  ESKE WILLERSLEV 《Boreas: An International Journal of Quaternary Research》2011,40(3):417-445

Arnold, L. J., Roberts, R. G., MacPhee, R. D. E., Haile, J. S., Brock, F., Möller, P., Froese, D. G., Tikhonov, A. N., Chivas, A. R., Gilbert, M. T. P. & Willerslev, E. 2010: Paper II – Dirt, dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia, and their implications for sedimentary ancient DNA studies. Boreas, Vol. 40, pp. 417–445. 10.1111/j.1502‐3885.2010.00181.x. ISSN 0300‐9483 The sedimentary ancient DNA (sedaDNA) technique offers a potentially invaluable means of investigating species evolution and extinction dynamics in high‐latitude environments. An implicit assumption of the sedaDNA approach is that the extracted DNA is autochthonous with the host deposit and that it has not been physically transported from older source deposits or reworked within the sedimentary profile by postdepositional mixing. In this paper we investigate whether these fundamental conditions are upheld at seven perennially frozen wetland sites across the Taimyr Peninsula and coastal lowlands of north‐central Siberia. Optically stimulated luminescence (OSL) and radiocarbon (¹⁴C) dating are used to constrain the ages of both the inorganic and organic fractions of perennially frozen deposits from which sedaDNA of extinct and extant species have been recovered. OSL and ¹⁴C age/depth profiles, as well as single‐grain equivalent dose (D_e) distribution characteristics, are used to assess the stratigraphic integrity of these sedaDNA sequences by (i) identifying the presence of primary or reworked organic and inorganic material, and (ii) examining the types of depositional and postdepositional processes that have affected specific sedimentary facies. The results of this study demonstrate that even though DNA preservation and stratigraphic integrity are commonly superior in perennially frozen settings, this does not, in itself, guarantee the suitability of the sedaDNA approach. The combined OSL and ¹⁴C chronologies reveal that certain perennially frozen sites may be poorly suited for sedaDNA analysis, and that careful site selection is paramount to ensuring the accuracy of any sedaDNA study – particularly for ‘latest appearance date’ estimates of extinct taxa.  相似文献   

Managing organizational change in an international scientific network: A study of ICES reform processes     

Kari Stange  Per Olsson  Henrik Österblom 《Marine Policy》2012,36(3):681-688

Organizations involved in the governance of natural resources are challenged to adjust to the call for more holistic management approaches. This often necessitates organizational change. Here change processes in the International Council for the Exploration of the Sea (ICES) during the years 1998–2009 are investigated using semi-structured interviews combined with observations and review of documents. Several organizational reforms were implemented during the time period studied. The major drivers were the need to improve efficiency and a striving for better integration between different components within the organization. The reform processes were driven forward by individuals who navigated between opportunities and constrains embedded in the network structure of ICES. This required good leadership and communication skills. Broad consultations were important to ensure support within the ICES community. By increasing the understanding of the dynamics of change in organizations, which operate at the science–policy interface developments in desired directions can be facilitated.  相似文献   

Hungarian icing activity survey     

Dr. I. Krmer 《Atmospheric Research》1995,36(3-4)

The paper summarizes the long term research and development efforts conducted in Hungary to provide reliable ice loading design data base of electricity transmission lines. After overviewing the country's climatic situation and the major synoptic conditions of rime formation, the author describes the main features of the long term national observation program. To remove uncertainity associated with quantifying the actual ice loads of overhead electricity lines, recently a comprehensive research program was carried out to improve the ice measuring methods and devices and to establish calibration methods between the ice accretion on the actual transmission line and that on the measuring device. The practical impact of the more consistent design data base is discussed.  相似文献   

Exchange times in the Pacific Equatorial Current system     

Rana A. Fine  H. Göte Östlund 《Earth and Planetary Science Letters》1980,49(2):447-452

Tritium data from the GEOSECS eastern and western track stations sampled in the thermocline of the North Equatorial Counter Current (NECC) showed high values, which are indicative of the contribution of the North Equatorial Current (NEC) to the equatorial region. A tritium front at 6°N is evidence of the penetration of northern latitude water into the NECC. The results of a two-? model show no net flux between NEC and NECC and a lower bound estimate of five years for an exchange time scale between the NEC and NECC in the thermocline; this is consistent with a horizontal diffusivity of 5 × 10⁷ cm²/s.  相似文献   

Fault kinematic and Plio-Quaternary paleostress evolution of the Bakırçay Basin,Western Turkey     

Ercan Sangu  Ömer F. Gürer  Aysan Gürer 《International Geology Review》2020,62(10):1245-1261

ABSTRACT

At the end of the Cenozoic, western Turkey was fragmented by intense intra-continental tectonic deformation resulting in the formation of two extensional areas: a transtensional pull-apart basin systems in the northwest, and graben systems in the central and southwest areas. The question of the connection of this Late Cenozoic extensional tectonics to plate kinematics has long been an issue of discussion. This study presents the results of the fault slip data collected in Bak?rçay Basin in the west of Turkey and addresses changes in the direction of extensional stresses over the Plio-Quaternary. Field observations and quantitative analysis show that Bak?rçay Basin is not a simple graben basin that has evolved during a single phase. It started as a graben basin with extensional regime in the Pliocene and was transformed into a pull-apart basin under the influence of transtensional forces during the Quaternary. A chronology of two successive extensional episodes has been established and provides reasoning to constrain the timing and location of subduction-related back-arc tectonics along the Aegean region and collision-related extrusion tectonics in Turkey. The first NW–SE trending extension occurred during the Pliocene extensional phase, characterized by slab rollback and progressive steepening of the northward subduction of the African plate under the Anatolian Plate. Western Turkey has been affected, during the Middle Quaternary, by regional subsidence, and the direction of extension changed to N–S, probably in relation with the propagation of the North Anatolian Fault System. Since the Late Quaternary, NE–SW extension dominates northwest Turkey and results in the formation and development of elongated transtensional basin systems. Counterclockwise rotation of Anatolian block which is bounded to the north by the right-lateral strike-slip North Anatolian Fault System, accompanies to this extensional phase.  相似文献   

The distribution of inselbergs and their relationship to geomorphological, structural and lithological controls in Southern Zimbabwe     

Wolfgang Rmer 《Geomorphology》2005,72(1-4):156-176

The gneissic-granitic basement of southern Zimbabwe is characterized by a wide variety of inselbergs, preferentially developed on the granitoid rocks. However, there are significant differences in the frequency of inselbergs and most inselbergs occur in the younger granitoid rocks, particularly in rocks with microcline as the dominant K-feldspar, but their distribution is not uniform. Completely isolated inselbergs are rare and most inselbergs are arranged in clusters or are associated with plateaus or they occur as the detached ends of spurs and ridges.Chemical and mineralogical investigations indicate significant differences in the composition of the older and younger granitoid rocks. The latter are characterized by a higher content of alkali feldspars and a lower content of plagioclase and mafic minerals.The influences of texture, fabric and fracture characteristics on the resistance of the rocks vary. In the southern part of the study area the majority of rock domes is associated with porphyritic granites and fine-grained granites, whilst inselbergs of the large batholith complexes in the northern part of the study area show virtually no relationships to the grain-size of the rocks.Thin-sections analysis indicate, that the rocks of the terrains with a higher density of inselbergs are characterized by an intense intergrowth of minerals and a higher number of contacts between quartz and alkali feldspars. Particularly in the case of the porphyritic granites the influence of texture on the frequency of rock domes is linked with two factors. These are a high content of microcline minerals that have filled the interstices of the surrounding mineral framework and enclosed the surrounding minerals. Overgrowths and replacement micro-structures indicate a long lasting crystallization, which appears to be responsible for a lower density of cooling fractures. Enclosure of the more vulnerable minerals in the more resistant microcline megacrysts retards the loosening of the rock constituents.The marked differences in the lithological and structural characteristics of the various granitoid rocks influence the weathering behaviour of the rocks and illustrate that the divergent weathering characteristics of the rocks are strongly dependent on lithological and structural factors.  相似文献