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  • 1
    Publication Date: 1980-09-01
    Description: The results of numerical models or of new observational programs are checked by comparing them with past observations. Also, it is desirable that the eddy diffusion coefficients used in two-dimensional models be derived from the same data set as the circulation statistics which the model outputs are checked against, so that all results refer to the same atmospheric conditions. For the first time, the three components of the eddy diffusion matrix, from 30–60 km, 80°N–10°S are computed, together with the means, variances and covariances of the wind and temperature through the same region using the same data set for 1960–76 and the same handling and analysis methods for all variables. Horizontal diffusivities, K yy , are obtained from the variance and integral time scale of the meridional wind speed. The present values are generally smaller than past estimates, presumably because temporal variations longer than a month have been removed in this work. Estimates of K yz are based on the tentative assumption that the diffusivity is proportional to the slope of isentropic surfaces, and estimates of K zz are based on the assumption that small-scale gravity waves are primarily responsible for vertical mixing. ©1980 Birkhäuser Verlag
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 1980-01-01
    Description: The southern Namib desert has a vegetation cover of mainly succulent plants in which species of the Mesembryanthemaceae are predominant. Climatically this area is characterized by hot and dry days, and cool and humid nights with episodic rainfalls only in winter. In this environment a great number of species perform a crassulaceaen acid metabolism (CAM). The responses of these plants to water stress as well as the regulation of CAM in the natural habitat are described and discussed. ©1980 Springer-Verlag
    Print ISSN: 0028-1042
    Electronic ISSN: 1432-1904
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 3
    Publication Date: 1981-06-01
    Description: Die postkretazische Entwicklung der Asiatischen Platte in Burma zeigt starke Beeinflussung durch die Spreizung des östlichen Indischen Ozeans und die Drift von „Groß-Indien“ nach Norden. Der westliche Abschnitt Burmas war während des frühen Mesozoikums ein Bereich, der klastische Sedimente aufnahm. Im späten Mesozoikum wurden die östlichen Teile Burmas landfest, während die westlichen Abschnitte von einem Shelfmeer eingenommen wurden, an welches sich gegen W eine Geosynklinale (Indoburman Geosyncline) anschloß, die langsam westwärts wanderte. Oberkretazische Flysche wurden hier nachgewiesen. Die Kollision der Indischen Platte mit der Asiatischen Platte veränderte die Sedimentationsbedingungen in Burma. Die Indoburmanischen Ketten tauchten während des Miozän auf, bildeten einen Äußeren Inselbogen und ließen die Bucht von Bengalen entstehen. Die Subduktion entlang der W-Küste von Burma änderte sich im N mit der Annäherung der kontinentalen Kruste Indiens und führte zu Überschiebungen im N-Teil der Indoburmanischen Ketten. Rezent scheint Subduktion nur südlich 18° N im östlichen Teil der Bucht von Bengalen aktiv zu sein. Die Öffnung der Andamanen-See fügt sich in die dynamische Entwicklung dieses Bereiches ein.The Post-Cretaceous evolution of the Asian Plate in Burma is strongly influenced by the spreading of the Eastern Indian Ocean and the movement of “Greater India” northward. The Western part of Burma apparently was an area which received clastic sediments during the early mesozoic times. During the end of the mesozoic the Eastern part of Burma emerged from the ocean. The Western part formed the shelf area with a slowly westwards migrating geosyncline (Indoburman Geosyncline) to the West of it. Flysch sediments of upper Cretaceous age have been found in this area. The collision of the Indian Plate with the Asian Plate changed the sedimentary conditions in Burma. The emergence of the Indoburman Ranges happened during the Miocene, generating an Outer Island Arc and forming the Bay of Bengal. The subduction along the W coast of Burma changed in the N with the approach of continental Indian crust and led to thrusts in the N part of the Indoburman Ranges. Today subduction appears to be active only S of 18° N in the Eastern Bay of Bengal. The opening of the Andaman Sea fits into the dynamical development of the area.RésuméL'évolution postcrétacée de la plaque asiatique en Birmanie est fortement influencée par l'accroissement de l'Océan Indien oriental et la dérive du continent Indien vers le nord. La partie occidentale de la Birmanie fût au début du Mésozoïque une aire de réception de sédiments clastiques. A la fin du Mésozoïque les parties orientales de la Birmanie se transformèrent en terre ferme, tandis que les régions occidentales furent submergées, formant une plate-forme continentale (shelf), à laquelle s'adjoignit vers l'ouest un géosynclinal (géosynclinal indobirman), progressant lentement vers l'ouest. Des flyschs d'âge crétacé supérieur ont été décrits dans cette zone. La collision entre la plaque Indienne et la plaque Asiatique changea les conditions de sédimentation en Birmanie. Les chaînes Indobirmanes firent leur émersion au cours du Miocène, en engendrant un arc insulaire externe, ainsi que le golfe du Bengale. La subduction le long de la côte occidentale Birmane se transforma au nord avec le rapprochement de la plaque Indienne et induisit des chevauchements dans la partie septentrionale des chaînes Indobirmanes. La subduction semble n'être active récemment qu'au sud de 18° N dans la partie orientale du golfe du Bengale. L'ouverture de la mer Andamane s'imbrique dans le développement dynamique de cette région.Краткое содержаниеПослемеловое развит ие азиатской платфор мы в Бирме характеризуется сильным слиянием рас ширения восточного И ндийского океана и дрейфом „великой Индии“ на се вер. Западная часть Би рмы была во время раннего мезозоя тем местом, ку да сносились кластич еские осадочные породы. В по зднем мезозое восточная Би рма оказалась сушей, в то время, как западную часть еë заняло шельф овое море, к которому п римыкала идущая на запад геосинклиналь (Индоб ирманская геосинкли наль), медленно сдвигающая ся на запад. Здесь устано влены верхнемеловые флиши. Коллизия индийской плиты с азиатской изм енила условия осадко накопления в Бирме. Во время миоцена появля ются индо-бирманские цепи гор, образуя внешнюю островную дугу, в резу льтате чего образует ся Бенгальский залив. Со сближением континентальной кор ы Индии изменяется за сасывание ее вдоль западного побережья Бирмы на севере и прив одит к появлению нарушений в северной части индо-бирманских гор. В наст оящее время субдукция каже тся активной только на юг от 18° северной широты в восточной части Бенгальской бухты. Открытие озера Андаманен связано с д инамикой развития в этой области. ©1981 Ferdinand Enke Verlag Stuttgart
    Print ISSN: 1437-3254
    Electronic ISSN: 1437-3262
    Topics: Geosciences
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  • 4
    Publication Date: 1983-06-01
    Print ISSN: 0165-0009
    Electronic ISSN: 1573-1480
    Topics: Geosciences , Physics
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  • 5
    Publication Date: 1984-09-01
    Description: Some workers have held that mid-ocean ridge basalts are fractionated from high pressure (15–30 kbar) picritic primary magmas whereas others have favored primary magmas generated at about 10 kbar with compositions close to those of mid-ocean ridge basalts. Of critical significance are presumed differences in composition between experimentally determined primary magmas and the least fractionated mid-ocean ridge basalts. To evaluate the significance of these differences, all based on electron microprobe analyses, we consider three sources of uncertainty: (1) analytical uncertainties for a single microprobe laboratory, (2) systematic interlaboratory analytical differences, and (3) real variations in the possible compositions of primary magmas that can be produced from a peridotite source at a given pressure. The first source of error is surprisingly large and can account for a substantial part of the total variation of normative quartz (hypersthene calculated as equivalent olivine and quartz) in FAMOUS basalts. The second is not as serious but remains undetermined for many laboratories. The third is potentially the largest but is not yet fully documented. The least fractionated FA-MOUS basalts have high mg numbers (70–73) compatible with derivation from the mantle by direct partial melting with little or no subsequent fractional crystallization. Because of the wide range of normative quartz content in these basalts, it appears necessary to consider them as representatives of multiple parental magmas. When all the sources of uncertainty are taken into account, we conclude that the experimental data by various investigators are all fairly consistent and favor derivation of the least fractionated mid-ocean ridge basalts by at most only a small amount of fractional crystallization from primary magmas having a wide range of normative quartz content and generated over a range of pressures from about 7–11 kbar. ©1984 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
    Topics: Geosciences
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  • 6
    Publication Date: 1984-01-01
    Description: The intrinsic oxygen fugacities of homogeneous, inclusion-free, megacryst ilmenites from the Frank Smith, Excelsior, Sekameng and Mukorob kimberlite pipes in southern Africa, and the alnöitic breccia in the Solomon Islands have been determined. Similar measurements have been made of the type A and B spinel peridotites from San Carlos in Arizona. The type A peridotites are characterised by oxygen fugacities close to the iron-wüstite buffer, similar to those of equivalent peridotite specimens from other continental and island arc environments. In strong contrast, the type B peridotites and all of the ilmenite megacrysts range between the oxygen fugacities defined by the nickelnickel oxide and fayalite-magnetite-quartz buffers. A close relationship between type B peridotites, oxidized metasomatizing fluids in the upper mantle and oxidized, silicaundersaturated magma types is suggested. It is unlikely that a solid elemental carbon phase can be an equilibrium crystallization product of kimberlite magmas if the ilmenite megacrysts represent the redox state of kimberlite melts. The ultimate source of the oxidizing fluids and the development of such a wide dispersion (〉4 orders of magnitude) in oxygen fugacities of the upper mantle is not clear, but may involve recycled lithosphere, fluids from the lower mantle or result from the relatively rapid diffusion of H_2, compared with other potential volatile species, in the mantle. ©1984 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
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  • 7
    Publication Date: 1983-06-01
    Description: Fenites associated with alkaline igneous rocks show a progression from a high temperature assemblage consisting of sodium-rich alkali feldspar + a sodium-ironrich mafic mineral, to an extreme end member assemblage consisting of pure potassium feldspar + iron oxide. The latter assemblage is only found in association with low temperature carbonatites. Segments of this distribution trend can be found in the contact aureole of single intrusive centers. In the east African Kisingiri nephelinite volcano, ijolite intruded a granodioritic basement, producing a fenitized contact aureole. During metasomatism of granodiorite, according to the mass balance model of Rubie (1982), feldspar only participated in an alkali exchange reaction, while quartz was replaced by sodic pyroxene. Outward from the intrusive contact, with decreasing temperature, feldspar became progressively K-enriched, while pyroxene was enriched in the acmite component. It is predicted that alkaliexchange reactions were controlled by NaCl0-KCl0 aqueous complexes close to the intrusive contact, while further out in the aureole Na+-K+ ions dominated at the lower temperatures and enhanced the level of potassium metasomatism of feldspar. With decreasing temperature in the aureole, the K/Na ratio of the fluid decreased and consequently the activity of acmite increased. Around carbonatites, where the level of CO2 in the escaping fluid can be expected to be high, Na_2CO _3 0 -K_2CO _3 0 complexes may dominate. Alkali exchange between feldspar and these aqueous species enhances, even further, the stabilization of pure potassium feldspar. Boiling may also play an important role in potassium metasomatism as carbonatites are frequently associated with pyroclastic rocks. Formation of hematite instead of sodic pyroxene may be attributed to low $$a_{SiO_2 } $$ , high $$a_{Fe{3 + } } $$ and a CO2-rich fluid. Important variables which determine the products of alkali metasomatism are shown to be temperature, pressure and CO2 content of the fluid, as well as the K/Na ratio of the fluid. ©1983 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
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  • 8
    Publication Date: 1981-10-01
    Description: The Edgecumbe volcanic field is a Holocene volcanic province located on Kruzof Island, SE Alaska. Exposed within the 260 km2 field are basalt, andesitic basalt, andesite, dacite and rhyodacite. The rhyodacites were erupted after the basalts and before the andesites. The volcanics, which are Al-rich (14–18 wt%) and lack an iron enrichment trend, range from tholeiites (47 wt% SiO_2) through rhyodacites (72%), but a compositional gap of approximately 9 wt% separates the dacites and rhyodacites. Initial 87Sr/86Sr ranges from 0.70297 in the basalts to 0.70440 in a pyroxene andesite. δ 18O increases across the suite: 5.8‰ to 7.9‰. Plagioclase (An_32–86) is the dominant phenocryst in all but one lava. Olivine (Fo_58–86) occurs in the basic lavas (〈53 wt% SiO_2), but is replaced by orthopyroxene (En_43–73) and clinopyroxene (En_31Wo_41-En_48Wo_40) in the more siliceous volcanics. In the basalts and rhyodacites, plagioclase is weakly zoned, but extreme zoning (〈30 mole% An) is characteristic of phenocrysts in the intermediate lavas. Fractionation of the observed phenocryst assemblages could not have produced the more silicous volcanics. Instead they were generated by partial melting of intrusive basement (87Sr/86Sr=0.70487; δ 18O: 8.7–9.3) by basaltic magma and subsequent assimilation. Mass balance calculations show the rhyodacites are almost pure partial melt (〈5% basaltic component) whereas the intermediate lavas contain between 30 and 60% partial melt. ©1981 Springer-Verlag
    Print ISSN: 0010-7999
    Electronic ISSN: 1432-0967
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  • 9
    Publication Date: 1981-09-01
    Description: Experiments carried out on the system SiO_2-NaAlSi_3O_8-KAlSi_3O_8(Qz-Ab-Or) at 1 kbar in the presence of H_2O and F show that the quartz-alkali feldspar field boundary is progressively displaced towards the feldspar join as F contents increase from 0 to 4 wt. %F. Increasing $$P_{H_2 O} $$ , in the absence of F, has already been shown to have a similar effect (Tuttle and Bowen 1958; Luth, Jahns, and Tuttle 1964). The increased size of the quartz field in the F-bearing system compared to the hydrous system is believed to be caused by progressive removal of Al from the tetrahedral network of the melt by complexing with F. The residual network in the melt is thus enriched in Si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions. The common presence of quench cryolite (Na_3AlF_6) in certain experiments carried out with 4 wt.% F supports this interpretation and indicates that some Al in the melt may be present in six-fold coordination with F−. The effect of H_2O in the absence of F may be similar, with Al being progressively removed from four-fold coordination as more H_2O is dissolved in the melt. Although a proportion of Al in hydrous melts may occur in six-fold coordination, dry melts predominantly contain Al in four-fold coordination. This major difference in Al complexing may be one of the main causes for differences in the high-pressure phase relations of wet and dry Albearing silicate systems. ©1980 Springer-Verlag
    Print ISSN: 0010-7999
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  • 10
    Publication Date: 1980-04-01
    Description: Current methods of geothermometry and geobarometry applicable to garnet lherzolite are reviewed with reference to recent experimental studies of the equilibration of natural garnet lherzolite and it is concluded that the Wells and Mori-Green formulations of the two pyroxene solvus provide the most reasonable temperature estimates. Pressures are best estimated by using these temperatures with Wood's formulation of the orthopyroxene-garnet geobarometer without chromium corrections. Pipe 200 garnet lherzolites are considered to have equilibrated at 907°–950° C at 30.0–34.5 kb. It is shown that the transport times of xenoliths from the mantle are sufficiently long (0.5–24 h) to allow thermal equilibration with kimberlite but are too short to allow chemical re-equilibration to occur. Xenolith suites therefore retain information regarding the pressure/temperature history of the upper mantle despite being heated to the temperature of the kimberlite magma during transport. The Pipe 200 xenolith suite indicates that the upper mantle beneath Lesotho has been perturbed to temperatures slightly above those defined by steady state geotherms. The Pipe 200 suite is derived from a narrow depth range (90–110 km) and derivation of chromite and garnet lherzolites from similar depths implies that the mantle is heterogeneous over short vertical distances. No simple stratigraphy, in which chromite lherzolites overlie garnet lherzolites is evident. Comparison with other suites of Lesotho garnet lherzolites shows that it is not possible to construct an upper mantle stratigraphy except in the most general terms because of the prevailing lateral and vertical heterogeneity and apparent limited depth range represented by the xenolith suites. ©1980 Springer-Verlag
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