排序方式： 共有44条查询结果，搜索用时 125 毫秒
21.
Abstract We review the carbon‐isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow‐ and intermediate‐spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The δ13C values of the bioaltered glassy samples from the CAO show a large range, between ?17 and +3‰ (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ?17‰ and ?7‰. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low δ13C values (less than ?7‰) are attributed to carbonate precipitated from microbially produced CO2 during oxidation of organic matter. Positive δ13C values >0‰ likely result from lithotrophic utilization of CO2 by methanogenic Archaea that produce CH4 from H2 and CO2. High production of H2 at the slow‐spreading CAO crust may be a consequence of fault‐bounded, high‐level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer‐cake pseudostratigraphy with much less faulting and supposedly less H2 production. A comparison of the δ13C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow‐spreading CAO crust, with a similar range in δ13C values of biogenic carbonates. The Late Ordvician Solund–Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate‐spreading mid‐ocean ridge and displays δ13C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate‐dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the δ13C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas. 相似文献
22.
Effect of heavy metal and alkali contamination on the swelling properties of kaolinite 总被引：2，自引：0，他引：2
Dilek Turer 《Environmental Geology》2007,52(3):421-425
One of the most important factors that determine engineering properties of soils are the type and the amount of clay present
in soil. Kaolinite being a very common and non-swelling clay mineral in soil was chosen as the medium, and significance of
the change in swelling property of kaolinite due to contaminant-clay interaction was investigated. The amount of change in
swelling percentages of the kaolinite due to contamination with 10,000 ppm solutions of Pb(NO3)2 and Zn(NO3)2 was determined using oedometers. For uncontaminated kaolinite, the amount of swell was determined as 2.2%. For Pb-contaminated
and Zn-contaminated kaolinite, these values reached to 5.8 and 5.3%, respectively. Besides heavy metals, kaolinite was also
contaminated with 4 N NaOH. The biggest change in the amount of swelling was obtained from NaOH-contaminated kaolinite which
is 13.9%. In addition to swelling percentages, swelling pressures were also determined. The swelling pressure of the uncontaminated
kaolinite was found as 1.06 N/cm2. For Zn and Pb-contaminated kaolinite, this value reached up to 2.0 and 2.6 N/cm2. The NaOH-contaminated kaolinite has the greatest swelling pressure which was 230 N/cm2. 相似文献
23.
24.
Zhi‐Xian Tian Yi Yan Chi‐Yue Huang Yildirim Dilek Meng‐Ming Yu Hai‐Quan Liu Xin‐Chang Zhang Yong Zhang 《地学学报》2021,33(1):21-29
Geochemical data compilation of Cenozoic basalts recovered from the South China Sea tectonic domain shows westward weakening of the influence of a focal zone‐like component in Nd–Hf, Nd–Pb and Sr–Pb, but not in Pb–Pb isotope spaces because the Pb isotopes are dominantly controlled by the high U/Pb component derived from the subducted Pacific oceanic slab. Low Th/U melt generated by recycling of marine carbonates, rather than the subduction‐related enriched mantle (EM2), signals the emplacement of the Hainan Plume at ~25 Ma. Radiogenic Hf in the pre‐existing ancient sub‐continental lithospheric mantle beneath the Cathaysia Block was greatly depleted by early‐stage magmatism influenced by the high U/Pb component. Hence, late Cenozoic basalts associated with the carbonatitic melts display contrasting Nd–Hf isotope covariations, with the Red River–Zhongnan Fault System as a dividing line, implying that the East and Southwest sub‐basins have been developed on the Cathaysia and Indochina Blocks respectively. 相似文献
25.
Multi-level geospatial modeling of human exposure patterns and vulnerability indicators 总被引：1，自引：0，他引：1
Christoph Aubrecht Dilek Özceylan Klaus Steinnocher Sérgio Freire 《Natural Hazards》2013,68(1):147-163
In the context of disaster risk management and in particular for improving preparedness and mitigation of potential impacts, information on socioeconomic characteristics including aspects of situation-specific human exposure and vulnerability is considered vital. This paper provides an overview on available multi-level geospatial information and modeling approaches from global to local scales that could serve as inventory for people involved in disaster-related areas. Concepts and applications related to the human exposure and social vulnerability domains are addressed by illustrating the varying dimensions and contextual implications. Datasets and methods are highlighted that can be applied to assess earthquake-related population exposure, ranging from global and continental-scale population grids (with a focus on recent developments for Europe) to high-resolution functional urban system models and space–time variation aspects. In a further step, the paper elaborates on the integration of social structure on regional scale and the development of aggregative social and economic vulnerability indicators which would eventually enable the differentiation of situation-specific risk patterns. The presented studies cover social vulnerability mapping for selected US federal states in the New Madrid seismic zone as well as the advancement of social vulnerability analysis through integration of additional economic features in the index construction by means of a case study for Turkey’s provinces. 相似文献
26.
We combine a geological, geochemical and tectonic dataset from 118 ophiolite complexes of the major global Phanerozoic orogenic belts with similar datasets of ophiolites from 111 Precambrian greenstone belts to construct an overview of oceanic crust generation over 4 billion years. Geochemical discrimi- nation systematics built on immobile trace elements reveal that the basaltic units of the Phanerozoic ophiolites are dominantly subduction-related （75%）, linked to backarc processes and characterized by a strong MORB component, similar to ophiolites in Precambrian greenstone sequences （85%）. The remaining 25% Phanerozoic subduction-unrelated ophiolites are mainly （74%） of Mid-Ocean-Ridge type （MORB type）, in contrast to the equal proportion of RiftlContinental Margin, Plume, and MORB type ophiolites in the Precambrian greenstone belts. Throughout the Phanerozoic there are large geochemical variations in major and trace elements, but for average element values calculated in 5 bins of 100 million year intervals there are no obvious secular trends. By contrast, basaltic units in the ophiolites of the Precambrian greenstones （calculated in 12 bins of 250 million years intervals）, starting in late Paleo- to early Mesoproterozoic （ca. 2.0-1.8 Ga）, exhibit an apparent decrease in the average values of incom- patible elements such as Ti, P, Zr, Y and Nb, and an increase in the compatible elements Ni and Cr with deeper time to the end of the Archean and into the Hadean. These changes can be attributed to decreasing degrees of partial melting of the upper mantle from HadeanJArchean to Present. The onset of geochemical changes coincide with the timing of detectible changes in the structural architecture of the ophiolites such as greater volumes of gabbro and more common sheeted dyke complexes, and lesser occurrences of ocelli （varioles） in the pillow lavas in ophiolites younger than 2 Ga. The global data from the Precambrian ophiolites, representative of nearly 50% of all known worldwide greenston 相似文献
27.
Ductilely deformed veins consisting of quartz+andalusite, in which the andalusite is partially replaced by fibrous sillimanite, locally occur in garnet–sillimanite schist near a margin of the Niğde metamorphic core complex in south-central Turkey. Mineral assemblages, reaction textures and structural features of the veins record low-pressure–high-temperature deformation during exhumation of mid-crustal rocks. The partial replacement of andalusite by sillimanite may indicate a late-stage increase in temperature and/or fluid pressure, possibly related to Miocene magmatism, during extensional unroofing of the core complex. Aluminosilicate-bearing veins are observed at the eastern margin of the massif where metapelitic rocks were deformed during unroofing of the core complex. Veins formed in aluminous rocks where deformation-enhanced permeability allowed fluid flow during extensional shear. The cm-scale veins are typically boudinaged and form asymmetric lenses concordant with the host rock foliation and are parallel to the down-dip lineation defined by sillimanite and stretched biotite. Aluminosilicate-bearing boudins record top-to-the-east shear sense, which is compatible with the extensional shear sense displayed by structures in the host rock. 相似文献
28.
Atila Yildiz Ahmet Aksoy Gul Nilhan Tug Cemil Islek Dilek Demirezen 《Journal of Atmospheric Chemistry》2008,60(1):71-81
The objective of this study was to determine the air pollution level of Ankara and to generate the air pollution map of this
city by using Pseudevernia furfuracea (L.) Zopf as a biomonitor. Lichen samples were collected from unpolluted area at Yaprakli Mountains, Cankiri in November
2002 and transplanted to 27 localities in Ankara. Lichen samples were retrieved following an exposure of 3 and 6 months. Heavy
metal, Cu, Mn, Ni, Pb and Zn, contents were determined by using inductively coupled plasma spectrometry (ICP). The chlorophyll
a and b contents were determined by using DMSO method. The increase in Ni, Pb, Zn and chlorophyll a content of the specimens
were statistically important. All the increases and decreases in the variables could be explained by the environmental stress
like pollution, but it is hard to say that this is the only reason of these changes, also climatic conditions, seasons, strength
of the light and the physiological status of the plant itself effective on these changes. According to the results of heavy
metal analysis Pseudevernia furfuracea continued to accumulate heavy metals and worked well as a biomonitor. The air pollution level of Ankara shows great variations
because of the great area of the city. 相似文献
29.
Mine
zdemir Dilek ak&#x;r &#x;lker K&#x;pak 《International Journal of Mineral Processing》2009,93(2):209-212
The recovery of magnesium from magnesite tailings in aqueous hydrochloric acid solutions by acid leaching was studied in a batch reactor using hydrochloric acid solutions. Subsequent, production of magnesium chloride hexahydrate (MgCl2.6H2O) from leaching solution was also investigated. The effects of temperature, acid concentration, solid-to-liquid ratio, particle size and stirring speed on the leaching process were investigated. The pseudo-second-order reaction model seemed to be appropriate for the magnesium leaching. The activation energy of the leaching process was estimated to be 62.4 kJ mol− 1. Finally, MgCl2.6H2O in a purity of 91% was produced by evaporation of leaching solution obtained at a temperature of 40 °C, 1.0 M acid, solid-to-liquid ratio of 10 g/L, particle size of 100 µm, stirring speed of 1250 rpm and leaching time of 60 min. 相似文献
30.
Estimation of evaporation is important for water planning, management, and hydrological practices. There are many available methods to estimate evaporation from a water surface, comprising both direct and indirect methods. All the evaporation models are based on crisp conceptions with no uncertainty element coupled into the model structure although in daily evaporation variations there are uncontrollable effects to a certain extent. The probabilistic, statistical, and stochastic approaches require large amounts of data for the modeling purposes and therefore are not practical in local evaporation studies. It is therefore necessary to adopt a better approach for evaporation modeling, which is the fuzzy sets and adaptive neural-based fuzzy inference system (ANFIS) as used in this paper. ANFIS and fuzzy sets have been evaluated for its applicability to estimate evaporation from meteorological data which is including air and water temperatures, solar radiation, and air pressure obtained from Automated GroWheather meteorological station located near Lake E?irdir and daily pan evaporation values measured by XVIII. District Directorate of State Hydraulic Works. Results of ANFIS and fuzzy logic approaches were analyzed and compared with measured daily pan evaporation values. ANFIS approach could be employed more successfully in modeling the evaporation process than fuzzy sets. 相似文献