排序方式： 共有103条查询结果，搜索用时 15 毫秒
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Mualla Cengiz Cinku Dieter Rammlmair Mümtaz Z. Hisarli Naci Orbay 《Studia Geophysica et Geodaetica》2009,53(4):475-494
Upper Cretaceous volcanic rocks were collected at 24 sites along the Pontides, N-NE Turkey, for rock magnetic and geochemical
studies. Rock magnetic and petrographic methods showed that the lavas are characterized predominantly by titanomagnetites
with a mixture of pseudo-single and multi-domain grains, whereas in tephrite single domain titanohematite was dominant. Measurements
of magnetic susceptibility and the geochemical properties on different volcanic rock types provide important knowledge about
the magnetic stability of the rocks. The magnetic properties are interpreted in terms of the composition, concentration, magma
generation. Tephrite and phonotephrites with the highest intensities (5200 mA/m) and high magnetic susceptibility values (2585
× 10−5), largest grain sizes and Fe/Ti values, showing minor or no alteration are the most magnetic stable samples in contrast to
dacites with the lowest intensity-magnetic susceptibility (520 mA/m − 573 × 10−5) and high alteration degree. The basanite samples show very low NRM (48–165 mA/m) but very high magnetic susceptibility (2906–3100
× 10−5) values suggesting the alteration of Fe-Ti minerals. It is shown that the magnetic properties of the basic to acidic rocks
show a systematic variation with magma differentiation and could be related to fractional crystallization. Major and trace
elements revealed that the lavas are compatible with complex magma evolution, with mineral phases of olivine+magnetite+clinopyroxene
in basic series, amphibole+ +clinopyroxene in intermediate rocks and plagioclase+clinopyroxene+biotite in acidic series. 相似文献
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Using simulation results from three different regional ocean models (HOPS, ROMS and FVCOM) we show that only a few spatio-temporal POD (proper orthogonal decomposition) modes are sufficient to describe the most energetic ocean dynamics. In particular, we demonstrate that the simulated ocean dynamics in New Jersey coast, Massachusetts Bay and Gulf of Maine is energetically equivalent to the wake dynamics behind a cylinder at low Reynolds number. Moreover, the extrema of the POD spatial modes are very good locations for sensor placement and accurate field reconstruction. We employ a modified POD theory to incorporate a limited number of measurements in reconstructing the velocity and temperature fields, and we study systematically the corresponding reconstruction errors as a function of the sensor location, number of sensors, and number of POD modes. This new approach is quite accurate in short-term simulation, and hence it has the potential of accelerating the use of real-time adaptive sampling in data assimilation for ocean forecasting. 相似文献
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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
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Tamer Coskun Asuman Yildirim Cigdem Balcik Neslihan Manav Demir Eyup Debik 《洁净——土壤、空气、水》2013,41(5):463-468
In the following study, two methods were employed in which olive mill wastewaters were treated by using reverse osmosis membranes (BW30 and XLE). In the first, wastewater was centrifuged and then passed through the reverse osmosis whereas in the second, an ultrafiltration was placed between the centrifuge and the reverse osmosis. The reverse osmosis experiments were conducted under 10, 15, 20, and 25 bar. The chemical oxygen demand (COD) removal efficiencies under 25 bar were found to be 97.5% for both BW30 and XLE membranes. The highest conductivity removal rates obtained under 25 bar for BW30 and XLE membranes were found to be 95.6 and 96.2%, respectively. As for the highest permeation flux values obtained under 25 bar, they were separately determined for BW30 and XLE as 15.3 and 21.2 L m?2 h?1, respectively. The performances of the membranes were also evaluated in terms of their mass transfer coefficients. According to this, all mass transfer coefficients were found to be <1 and also in proximate to one another; this clearly reflects the results as COD and conductivity removals were approximate and there was a lack of any significant difference, whether ultrafiltration was applied or not. 相似文献
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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
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Havvanur Kılıç Saadet Arzu Berilgen Perihan Biçer Mustafa Yildirim 《Marine Georesources & Geotechnology》2013,31(4):303-323
Istanbul, the largest city in Turkey and one of the major metropolitan areas in the world, cleaned one of its environmentally polluted areas—Golden Horn—by dredging 5 million m3 of the bottom sediments and pumping the resulting sludge to a storage area behind a dam built at an abandoned rock quarry site in Alibey district. The reclamation of the land that formed over the storage area of Golden Horn dredged material is socially and economically very desirable. In this paper, results from experimental studies that are focused on determining the shear strength behavior of the dredge material and undisturbed soil are presented. Slurry consolidometer test, large model tests and small model tests are used to consolidate the dredged soil samples from Halic to simulate the natural consolidation behavior of these soils. Shear strength parameters are determined by laboratory vane tests; unconfined compression tests; undrained-unconsolidated (UU) and consolidated-undrained (CU) triaxial tests on samples that are obtained through in situ undisturbed samples and laboratory model tank and slurry consolidation. Moreover, the effects of fly ash and lime additives on the undrained shear strength were determined by mixing the materials with the dredged clay from Golden Horn during the model experiments conducted in the laboratory. Based on these findings, equations are proposed that govern the relationships between undrained shear strength and water content value. 相似文献