Joint IGCP 499/SDS Meeting     

Peter konigshof Eberhard Schidler Volker Wilde Jurga Lazauskiene M.Namik Yalicn 《《幕》》2006,29(2):134-134

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Evolution of 2:1 layered silicates in low-grade metamorphosed Liassic shales of Central Switzerland     

K. J. T. LIVI  D. R. VEBLEN  J. M. FERRY  & M. FREY 《Journal of Metamorphic Geology》1997,15(3):323-344

White mica from the Liassic black shales and slates in Central Switzerland was analysed by transmission electron microscopy (TEM) and electron microprobe to determine its textural and compositional evolution during very low-grade prograde metamorphism. Samples were studied from the diagenetic zone, anchizone and epizone (T ≈100°–450 °C). Phyllosilicate minerals analysed include illite/smectite (I/S), phengite, muscovite, brammallite, paragonite, margarite and glauconite. Textural evolution primarily is towards larger, more defect-free grains with compositions that approach those of their respective end-members. The smectite-to-illite transformation reduced the amounts of the exchange components SiK_?1Al_?1, MgSiAl_?2, and Fe³⁺Al_?1. These trends continue to a lesser degree in the anchizone and epizone. Correlations between the proportion of smectite in I/S and the composition of I/S indicate that smectite layers may contain a high layer charge. Illite in I/S bears a compositional resemblance to macrocrystalline phengite in some samples, but is different in others. Paragonite first appears in the upper diagenetic zone or lower anchizone as an interlayer-deficient brammallite, and it may be mixed with muscovite on the nanometre scale. Owing to the small calculated structure factor for paragonite-muscovite superstructures, conventional X-ray powder diffraction cannot distinguish between mixed-layer structures and a homogeneous compositionally intermediate solid solutions. However, indirect TEM evidence shows that irregularly shaped domains of Na- and K-rich mica exist below 10 nm. Subsequent coarsening of domains at higher grades produced discrete paragonite grains at the margins of muscovite crystals or in laths parallel to the basal plane of the host muscovite. Margarite appears in the epizone and follows a textural evolution similar to paragonite in that mixtures of margarite, paragonite, and muscovite may initially occur on the nanometre scale. However, no evidence of interlayer-poor margarite has been found.  相似文献   

Rapid orbit determination of LEO satellites using IGS clock and ephemeris products   总被引：4，自引：2，他引：4  

Oliver Montenbruck  Eberhard Gill  Remco Kroes 《GPS Solutions》2005,9(3):226-235

Different types of GPS clock and orbit data provided by the International GPS Service (IGS) have been used to assess the accuracy of rapid orbit determination for satellites in low Earth orbit (LEO) using spaceborne GPS measurements. To avoid the need for reference measurements from ground-based reference receivers, the analysis is based on an undifferenced processing of GPS code and carrier-phase measurements. Special attention is therefore given to the quality of GPS clock data that directly affects the resulting orbit determination accuracy. Interpolation of clock data from the available 15 min grid points is identified as a limiting factor in the use of IGS ultra-rapid ephemerides. Despite this restriction, a 10-cm orbit determination accuracy can be obtained with these products data as demonstrated for the GRACE-B spacecraft during selected data arcs between 2002 and 2004. This performance may be compared with a 5-cm orbit determination accuracy achievable with IGS rapid and final products using 5 min clock samples. For improved accuracy, high-rate (30 s) clock solutions are recommended that are presently only available from individual IGS centers. Likewise, a reduced latency and more frequent updates of IGS ultra-rapid ephemerides are desirable to meet the requirements of upcoming satellite missions for near real-time and precise orbit determination.  相似文献   

The Depleted Mantle Component in Kerguelen Archipelago Basalts: Petrogenesis of Tholeiitic-Transitional Basalts From the Loranchet Peninsula     

DOUCET  SONIA; WEIS  DOMINIQUE; SCOATES  JAMES S.; NICOLAYSEN  KIRSTEN; FREY  FREDERICK A.; GIRET  ANDRE 《Journal of Petrology》2002,43(7):1341-1366

A geochemical study of 28 Ma tholeiitic to transitional basaltsfrom the Kerguelen Archipelago (Mont des Ruches and Mont Fontaine)indicates that three distinct magma types erupted within  相似文献   

The Belize margin revisited: 1. Holocene marine facies     

Edward G. Purdy  Eberhard Gischler 《International Journal of Earth Sciences》2003,92(4):532-551

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Metamorphic evolution and geochemistry of kyanite eclogites in central Rhodope,northern Greece   总被引：1，自引：0，他引：1  

A. Liati  Eberhard Seidel 《Contributions to Mineralogy and Petrology》1996,123(3):293-307

In central Rhodope of northern Greece, kyanite eclogites were discovered in the area of Thermes. They are strongly overprinted and exhibit a multi-stage development of minerals and mineral assemblages formed during successive stages of the exhumation. The initial high-pressure assemblage was garnet+omphacite+kyanite+zoisite+phengite+rutile+quartz. Corundum, Fe-Mg-spinel, sapphirine and högbomite occur as products of a first, high-temperature overprint, still at high pressures, whereas various symplectites [corundum-plagioclase (pl), spinel-pl, sapphirine-pl, clinopyroxene-pl, biotite-pl, amphibole-pl] grew during subsequent stages of the exhumation. Diablastic amphibole+plagioclase formed as end-products of the amphibolitization. According to geochemical data, the protoliths of the kyanite eclogites were basalts to basaltic andesites with “volcanic arc” affinities. For the high-pressure stage of metamorphism, minimum PT conditions were around 19 kbar, 700°C, while for the initial stages of the overprint, high-pressure granulite-facies conditions prevailed (T>800°C, at P>15 kbar). The PT conditions of the amphibolite facies were 8–11 kbar, 580–690°C. The kyanite eclogites of Thermes record the highest temperatures of metamorphism within the whole of Rhodope.  相似文献   

On the determination of the closure parameters in higher-order closure models     

Marion Wichmann  Eberhard Schaller 《Boundary-Layer Meteorology》1986,37(4):323-341

In higher-order closure models at least the pressure redistribution and the dissipation of the turbulent kinetic energy and the temperature variance have to be parameterized. Due to this, the introduction of proportionality coefficients — the so-called closure parameters — is forced, which have to be determined before the model is used. We compare a group of models which use the return-to-isotropy hypothesis (Rotta, 1951) to describe the pressure redistribution and assume local isotropy for the smallest eddies in order to parameterize the dissipation. Special concern is given to the method of Mellor and Yamada (1982). Some of the closure parameters are re-derived on the basis of sensitivity studies requiring that both shear production and buoyancy behave in a realistic way if pressure redistribution or dissipation is changed by varying the closure parameters. This set of parameters is compared with those obtained by fitting to experimental data, by use of the Monin-Obukhov similarity theory and by considering ratios of variances, covariances and mean flow gradients, respectively. It is shown that the various sets of closure parameters are at least of the same order. The differences give some insight into the advantages and disadvantages of the various determination procedures. However, the general accordance of the different parameter sets supports the assumption of universal constants.  相似文献   

Direct measurements of volume transports through Fram Strait   总被引：9，自引：1，他引：9  

Eberhard Fahrbach  Jens Meincke  Svein Østerhus  Gerd Rohardt  Ursula Schauer  Vigdis Tverberg  Jennifer Verduin 《Polar research》2001,20(2):217-224

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.  相似文献   

Ground-based remote sensing of the atmospheric boundary layer: 25 years of progress   总被引：1，自引：0，他引：1  

J. M. Wilczak  E. E. Gossard  W. D. Neff  W. L. Eberhard 《Boundary-Layer Meteorology》1996,78(3-4):321-349

The role of ground-based remote sensors in boundary-layer research is reviewed, emphasizing the contributions of radars, sodars, and lidars. The review begins with a brief comparison of the state of remote sensors in boundary-layer research 25 years ago with its present-day status. Next, a summary of the current capabilities of remote sensors for boundary-layer studies demonstrates that for boundary-layer depth and for profiles of many mean quantities, remote sensors offer some of the most accurate measurements available. Similar accuracies are in general not found for most turbulence parameters. Important contributions of remote sensors to our understanding of the structure and dynamics of various boundary-layer phenomena or processes are then discussed, including the sea breeze, convergence boundaries, dispersion, and boundary-layer cloud systems. The review concludes with a discussion of the likely future role of remote sensors in boundary-layer research.  相似文献   

Die Strukturgeschichte der Zentralsahara     

Prof. Dr. Eberhard Klitzsch 《International Journal of Earth Sciences》1970,59(2):459-527

The author has investigated paleogeographic and structural problems in the middle part of the Sahara desert since 1959. Detailed studies of thickness changes, of disconformities and unconformities and of structural events resulted in the definition of the different tectonical eras and their individual paleogeographic elements. The middle part of North Africa is characterized by three major periods of structural development:

1. Folding and consolidation in Precambrian time.
2. Formation of NW to NNW striking horsts during Cambrian time, which became the core of uplifts (separated by troughs) in Silurian and Devonian time. This structural relief of the early Paleozoic era possibly is the result of regional stretch in NE-SW direction.
3. Formation of uplifts and troughs striking NE during late Paleozoic and Mesozoic time. Blockfaulting occurred along the edge of some uplifts during Jurassic time or at the Jurassic-Cretaceous transition. These movements were the result of regional compression from SE toward NW. The formation of this large scale undulation of the earth's crust coincides with the separation of the Sahara platform from the so-called Tethys (geosynclinal area in NW Africa, the Mediterranean and parts of Asia). This separation most probably began in Northwest Africa during late Carboniferous or early Permian time, it reached Northeastern Libya in Jurassic time. The Sirte grabens were formed as the result of east-west shearing movements, during Upper Cretaceous. Finally, in late Tertiary to Pleistocene time, volcanic activity formed large basalt plateaus. Volcanism occurs mainly along well defined old structural elements.

The results of this analysis were used to interpret structural aspects of larger parts of Africa. The structural relief of the early Paleozoic Era seems to extend far southeast into areas of the old African shield indicating that there is no principal structural difference between the shield and the Sahara platform. The orientation of the late Paleozoic to Mesozoic large scale undulation indicates that the reason for the SE-NW compression is the rotation tendency of Africa which began in late Carboniferous time and culminated during the Tertiary, when Africa was separated from Asia along the Red Sea graben. At approximately the same time, the Atlas area of Northwest Africa was folded.  相似文献