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651.
Wolfgang R. Dick 《Astronomische Nachrichten》1996,317(6):382-382
652.
Progressive crustal contamination of the Bushveld Complex: evidence from Nd isotopic analyses of the cumulate rocks 总被引:4,自引:2,他引:2
Wolfgang D. Maier Nicholas T. Arndt Edward A. Curl 《Contributions to Mineralogy and Petrology》2000,140(3):316-327
We report the first Nd isotopic data on the cumulate rocks of the Bushveld Complex, South Africa. We analysed 17 whole-rock
samples covering 4700 m of stratigraphy through the Lower, Critical and Main Zones of the intrusion at Union Section, north-western
Bushveld Complex. The basal ultramafic portions of the complex have markedly higher ɛNd(T) (−5.3 to −6.0) than the gabbronoritic
Main Zone (ɛNd(T) −6.4 to −7.9). The rocks of the Upper Critical Zone have intermediate values. These results are in agreement
with new Nd isotope data on marginal rocks and sills in the floor of the complex that are generally interpreted as representing
chilled parental magmas, and with published Sr isotopic data, all of which show a larger crustal component in the upper part
of the intrusion. In contrast, the concentrations of many highly incompatible trace elements are decoupled from the isotopic
signatures. The basal portions of the complex have higher ratios of incompatible to compatible trace elements than the upper
portions. The variations of isotopic and trace-element compositions are interpreted in terms of a change in the nature of
the crustal material that contaminated Bushveld magmas. Those magmas that fed into the lower part of the complex had assimilated
a relatively small amount of incompatible trace-element-rich partial melt of upper crust, whereas magmas parental to the upper
part of the complex had assimilated a higher proportion of the incompatible trace-element-poor residue of partial melting.
Received: 5 October 1999 / Accepted: 7 July 2000 相似文献
653.
We present the results of a re-examination of a [Ne II] line emission data cube (λ 12.8μm) and discuss the kinematic structure of the inner 3×4 pc of the Galaxy. The quality of [Ne II] as a tracer of ionized gas is examined by comparing it to radio data. A three-dimensional representation of the data cube allows us to disentangle features which are projected onto the same location on the sky. A model of gas streams in different planes is fitted to the data. We find that most of the material is located in a main plane which itself is defined by the inner edge of the Circum-Nuclear Disk in the Galactic Center. Finally, we present a possible three-dimensional model of the gas streams. 相似文献
654.
The Born approximation is applied to the modelling of the propagation of deeply turning longperiod body waves through heterogeneities in the lowermost mantle. We use an exact Green's function for a spherically symmetric earth model that also satisfies the appropriate boundary conditions at internal boundaries and the surface of the earth. The scattered displacement field is obtained by a numerical quadrature of the product of the Green's function, the exciting wavefield and structural perturbations. We study three examples: scattering of longperiod P waves from a plume rising from the coremantle boundary (CMB), generation of longperiod precursors to PKIKP by strong, localized scatterers at the CMB, and propagation of corediffracted P waves through largescale heterogeneities in D". The main results are as follows: (1) the signals scattered from a realistic plume are small with relative amplitudes of less than 2 per cent at a period of 20 s, rendering plume detection a fairly difficult task; (2) strong heterogeneities at the CMB of appropriate size may produce observable longperiod precursors to PKIKP in spite of the presence of a diffraction from the PKP B caustic; (3) corediffracted P waves ( P diff ) are sensitive to structure in D" far off the geometrical ray path and also far beyond the entry and exit points of the ray into and out of D"; sensitivity kernels exhibit ringshaped patterns of alternating sign reminiscent of Fresnel zones; (4) P diff also shows a nonnegligible sensitivity to shear wave velocity in D"; (5) down to periods of 40 s, the Born approximation is sufficiently accurate to allow waveform modelling of P diff through largescale heterogeneities in D" of up to 5 per cent. 相似文献
655.
Skamletz Jörg Korn Michael Forkmann Bernhard Göthe Wolfgang 《Studia Geophysica et Geodaetica》2000,44(2):142-157
Since December 1997 a network of 10 autonomously recording digital seismic stations operates in W-Saxony to monitor microseismic activity generated by tectonic movements in the Gera-Jáchymov fault zone and induced by the flooding of the uranium mining area near Aue. Further goals to be followed with these data are the in situ verification of engineering seismological parameters and the study of the transmission properties of seismic waves across the Gera-Jáchymov fault zone to improve seismic risk evaluation.
So far 19 tectonic and more than 50 induced events have been located and source parameters have been determined. Event clusters near Zwickau and within the Aue mining area could be spatially resolved with a master event technique. The cluster near Zwickau occured on a common fault plane striking parallel to the Gera-Jáchymov fault zone and dipping at an angle of about 60° towards ENE. The induced events near Aue occured within a volume of approximately 5 km
3
. The majority of these events were located in the granite body underneath the mining area. Fault plane solutions show a variety of focal mechanisms with no clear relation to the regional stress field. 相似文献
656.
Distribution of Natural and Synthetic Estrogenic Steroid Hormones in Water Samples from Southern and Middle Germany Natural and synthetic hormones can reach surface waters via domestic sewage effluents. For drinking water production, bank filtration of river waters is a common procedure and hormone contaminations can potentially reach groundwater levels and drinking water sources. In order to analyse steroid hormones in the different aquatic compartments (raw sewage and effluent, surface water, groundwater, raw and drinking water) of South and Middle Germany, a sensitive analytical method was developed and employed to detect the natural steroid hormones estradiol (E2) and estrone and the synthetic estrogen ethinylestradiol (EE2). Samples which were taken in two subsequent series were subjected to clean‐up and enrichment procedure and subsequently analysed by HPLC‐MS. The limit of quantitation for the method was determined to be 0.05 to 0.5 ng/L, depending on the matrix. By treating the samples with glucuronidases/arylsulfatases, conjugates were amenable to analysis and the sum of conjugates and unconjugated steroids was calculated. In raw sewage, the median of the concentrations of the unconjugated steroids was 7 ng/L for EE2, 1.5 ng/L for E2, and 5.5 ng/L for estrone. After cleavage of conjugates, the medians of total steroids were 9.5 ng/L (EE2), 3 ng/L (E2), and 13 ng/l (estrone). Conjugates therefore contributed up to 50 % of the total steroid concentration in raw sewage. In treated effluents, the concentrations of steroids were much lower than in the raw sewage. The medians of free steroids were determined to be 0.3 ng/L for EE2, 0.2 ng/L for E2, and 2.5 ng/L for estrone. Overall the medians in the effluent were thus less than 10% of those in the influent. Conjugates still contributed significantly (40% and more) to the steroid concentrations (medians: EE2: 0.5 ng/L, E2: 0.8 ng/L, and estrone: 8 ng/L). 相似文献
657.
The k-ε turbulence model which relates the eddy viscosity to turbulent kinetic energy, k, and to the rate of its dissipation, ε, and determines the distribution of these two quantities from modeled transport equations, is employed in calculating the vertical structure of wave-induced turbulent flows in two-dimensional estuaries. The empirical constants in this model are given the standard values cited in the literature and used successfully for calculating a large variety of steady flows; they are not tuned to the oscillating flows. The free surface elevation and the eddy-viscosity distribution are also calculated as a part of the solution. First, calculations performed for oscillatory laminar flows are compared with analytic solutions to ensure the proper performance of the numerical scheme. The turbulent flow in a laboratory-estuary model with one end closed, and in the Humber Estuary is simulated with the numerical model, and the results are compared with the corresponding flume and field measurements. The influence of frequency and roughness is thereby investigated. The results indicate that the time and space variation of the velocity field and the phase lag between the surface slope and the horizontal velocity can be predicted satisfactorily in wave-induced turbulent flows. 相似文献
658.
Guillaume Backé Graham Baines David Giles Wolfgang Preiss Andrew Alesci 《Marine and Petroleum Geology》2010
The Adelaide Basin in Australia is a complex of late Neoproterozoic to Early Cambrian rift and sag basins which was inverted during the Cambro–Ordovician Delamerian Orogeny. The deposition of evaporitic sediments during the earliest stage of basin development in the late Neoproterozoic (Willouran age) played a major role in the subsequent tectonic evolution of the basin. Previous studies have shown that early mobilization, vertical transport and withdrawal of the evaporites influenced the sedimentation during the late Neoproterozoic and Early Cambrian. The evaporites also influenced deformation during the inversion of the basin and the development of the Delamerian fold and thrust belt. However, the control exerted by basement structures in the deposition of the evaporitic beds and the role of these tectonic structures in the later inversion of the basin have been poorly constrained. 相似文献
659.
River discharges of water and nutrients to the Mediterranean and Black Sea: Major drivers for ecosystem changes during past and future decades? 总被引:2,自引:0,他引:2
Wolfgang Ludwig Egon Dumont Michel Meybeck Serge Heussner 《Progress in Oceanography》2009,80(3-4):199-217
Rivers are important sources of freshwater and nutrients for the Mediterranean and Black Sea. We present a reconstruction of the spatial and temporal variability of these inputs since the early 1960s, based on a review of available data on water discharge, nutrient concentrations and climatic parameters. Our compilation indicates that Mediterranean rivers suffer from a significant reduction in freshwater discharge, contrary to rivers of the Black Sea, which do not have clear discharge trends. We estimate this reduction to be at least about 20% between 1960 and 2000. It mainly reflects recent climate change, and dam construction may have reduced discharge even further. A similar decrease can also be expected for the fluxes of dissolved silica (Si), strongly controlled by water discharge and potentially reduced by river damming as well. This contrasts with the fluxes of nitrogen (N) and phosphorus (P) in Mediterranean and Black Sea rivers, which were strongly enhanced by anthropogenic sources. Their total inputs to the Mediterranean Sea could have increased by a factor of >5. While N still remained at elevated levels in 2000, P only increased up to the 1980–1990s, and then rapidly dropped down to about the initial values of the 1960s. With respect to the marine primary production that can be supported by the riverine nutrient inputs, Mediterranean and the Black Sea rivers were mostly phosphorus limited during the study period. Their anthropogenic nutrient enrichment could only have had a fertilizing effect before the general decline of the P loads. When also considering Si as a limiting element, which is the case for siliceous primary producers such as diatoms, silica limitation may have become a widespread phenomenon in the Mediterranean rivers since the early 1980s. For the Black Sea rivers, this already started the late 1960s. Gross primary production sustained by rivers (PPR) represents only less than 2% of the gross production (PP) in the Mediterranean, and less than 5% in the Black Sea. Possible ecological impacts of the changing river inputs should therefore be visible only in productive coastal areas, such as the Gulf of Lions, where PPR can reach more than two thirds of PP. Reported ecosystem changes both in the Adriatic Sea and the Black Sea are concomitant with major changes in the reconstructed river inputs. Further work combining modelling and data collection is needed to test whether this may also have been the case for coastal ecosystems at other places in the Mediterranean and Black Sea. 相似文献
660.
Ian McCallum Wolfgang Wagner Christiane Schmullius Anatoly Shvidenko Michael Obersteiner Steffen Fritz Sten Nilsson 《Carbon balance and management》2009,4(1):8-14
Production efficiency models (PEMs) are based on the theory of light use efficiency (LUE) which states that a relatively constant
relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however
in the application of the PEM methodology to global net primary productivity (NPP) monitoring. The objectives of this review
are as follows: 1) to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS) identified
in the literature; 2) to review each model to determine potential improvements to the general PEM methodology; 3) to review
the related literature on satellite-based gross primary productivity (GPP) and NPP modeling for additional possibilities for
improvement; and 4) based on this review, propose items for coordinated research. 相似文献