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41.
Akiho Miyashiro Fumiko Shido Maurice Ewing 《Contributions to Mineralogy and Petrology》1969,23(1):38-52
On cursory examination of hand specimens and thin sections, the abyssal tholeiite in a dredge haul may appear to be uniform in composition. Chemical analyses of a considerable number of fragments, however, have always revealed the existence of regular compositional variation in them. The MgO content decreases with increasing SiO2. In abyssal tholeiites with relatively low Al2O3 contents, the SiO2, total iron, Na2O and P2O5 contents tend to increase and the MgO content tends to decrease with increasing iron/magnesia ratio, probably owing to crystallization differentiation.In a certain dredge haul, high-alumina abyssal tholeiites (with Al2O3 contents near or over 17%) occur in association with low-alumina abyssal tholeiites. The magma of high-alumina abyssal tholeiites would be generated from that of low-alumina abyssal tholeiites by differentiation at a depth around 30 km.In pillow lavas of abyssal tholeiite free from weathering and metamorphism, the chilled rim of the pillow usually has virtually the same chemical composition as the more crystalline core except for a decrease of K2O content toward the rim. On the other hand, the weathered rim of pillow lavas shows marked compositional change. The Fe2O3/FeO ratio of unweathered abyssal tholeiite is in the range of 0.1 to 0.3. This ratio and the H2O– and H2O+ contents increase with advancing weathering.Lamont-Doherty Geological Observatory Contribution No. 1339 相似文献
42.
43.
Laurel L Wilking Gerald F Herman Edward Anders 《Geochimica et cosmochimica acta》1973,37(7):1803-1810
Cosmogenic 26A1 activities have been measured by γ-γ coincidence counting in the three ureilites which had not previously been studied. The values in dpm/kg are: Dingo Pup Donga, 38.4 ± 2.4; North Haig, 39.3 ± 4.8; Dyalpur, 55.8 ± 4.8. Five of the six known ureilites thus have lower 26A1 contents, 63 per cent to 77 per cent, than the calculated saturation values, in marked contrast to most other stony meteorites. This cannot be attributed to short cosmic ray exposure ages. Nor do size and depth effects account for the narrow range of 26A1 activities, because a nuclear particle track study indicates that preatmospheric radii were highly variable, from ≥ 40 cm for Goalpara to only a few cm for Dingo Pup Donga. By default, the most likely explanation is that the ureilites had much smaller or much larger orbits than all other stony meteorites. 相似文献
44.
Gary Latham Maurice Ewing James Dorman Yosio Nakamura Frank Press Nafi Toksőz George Sutton Fred Duennebier David Lammlein 《Earth, Moon, and Planets》1973,7(3-4):396-421
Analysis of seismic signals from man-made impacts, moonquakes, and meteoroid impacts has established the presence of a lunar crust, approximately 60 km thick in the region of the Apollo seismic network; an underlying zone of nearly constant seismic velocity extending to a depth of about 1000 km, referred to as the mantle; and a lunar core, beginning at a depth of about 1000 km, in which shear waves are highly attenuated suggesting the presence of appreciable melting. Seismic velocitites in the crust reach 7 km s–1 beneath the lower-velocity surface zone. This velocity corresponds to that expected for the gabbroic anorthosites found to predominate in the highlands, suggesting that rock of this composition is the major constituent of the lunar crust. The upper mantle velocity of about 8 km s–1 for compressional waves corresponds to those of terrestrial olivines, pyroxenites and peridotites. The deep zone of melting may simply represent the depth at which solidus temperatures are exceeded in the lower mantle. If a silicate interior is assumed, as seems most plausible, minimum temperatures of between 1450°C and 1600°C at a depth of 1000 km are implied. The generation of deep moonquakes, which appear to be concentrated in a zone between 600 km and 1000 km deep, may now be explained as a consequence of the presence of fluids which facilitate dislocation. The preliminary estimate of meteoroid flux, based upon the statistics of seismic signals recorded from lunar impacts, is between one and three orders of magnitude lower than previous estimates from Earth-based measurements.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973. 相似文献
45.
On the physics of the Atlantic Multidecadal Oscillation 总被引:1,自引:0,他引:1
The Atlantic Multidecadal Oscillation (AMO) is a pronounced signal of climate variability in the North Atlantic sea-surface temperature field. In this paper, we propose an explanation of the physical processes responsible for the timescale and the spatial pattern of the AMO. Our approach involves the analysis of solutions of a hierarchy of models. In the lowest member of the model hierarchy, which is an ocean-only model for flow in an idealized basin, the variability shows up as a multidecadal oscillatory mode which is able to destabilize the mean thermohaline circulation. In the highest member of the model hierarchy, which is the Geophysical Fluid Dynamics Laboratory R30 climate model, multidecadal variability is found as a dominant statistical mode of variability. The connection between both results is established by tracing the spatial and temporal expression of the multidecadal mode through the model hierarchy while monitoring changes in specific quantities (mechanistic indicators) associated with its physics. The proposed explanation of the properties of the AMO is eventually based on the changes in the spatial patterns of variability through the model hierarchy.Responsible Editor: Tal Ezer 相似文献
46.
Analysis and modeling of the seasonal South China Sea temperature cycle using remote sensing 总被引:1,自引:0,他引:1
Daniel J. Twigt Erik D. De Goede Ernst J. O. Schrama Herman Gerritsen 《Ocean Dynamics》2007,57(4-5):467-484
The present paper describes the analysis and modeling of the South China Sea (SCS) temperature cycle on a seasonal scale.
It investigates the possibility to model this cycle in a consistent way while not taking into account tidal forcing and associated
tidal mixing and exchange. This is motivated by the possibility to significantly increase the model’s computational efficiency
when neglecting tides. The goal is to develop a flexible and efficient tool for seasonal scenario analysis and to generate
transport boundary forcing for local models. Given the significant spatial extent of the SCS basin and the focus on seasonal
time scales, synoptic remote sensing is an ideal tool in this analysis. Remote sensing is used to assess the seasonal temperature
cycle to identify the relevant driving forces and is a valuable source of input data for modeling. Model simulations are performed
using a three-dimensional baroclinic-reduced depth model, driven by monthly mean sea surface anomaly boundary forcing, monthly
mean lateral temperature, and salinity forcing obtained from the World Ocean Atlas 2001 climatology, six hourly meteorological
forcing from the European Center for Medium range Weather Forecasting ERA-40 dataset, and remotely sensed sea surface temperature
(SST) data. A sensitivity analysis of model forcing and coefficients is performed. The model results are quantitatively assessed
against climatological temperature profiles using a goodness-of-fit norm. In the deep regions, the model results are in good
agreement with this validation data. In the shallow regions, discrepancies are found. To improve the agreement there, we apply
a SST nudging method at the free water surface. This considerably improves the model’s vertical temperature representation
in the shallow regions. Based on the model validation against climatological in situ and SST data, we conclude that the seasonal
temperature cycle for the deep SCS basin can be represented to a good degree. For shallow regions, the absence of tidal mixing
and exchange has a clear impact on the model’s temperature representation. This effect on the large-scale temperature cycle
can be compensated to a good degree by SST nudging for diagnostic applications. 相似文献
47.
Recent developments for estimating activity coefficients of electrolytes both in pure and multicomponent aqueous solutions are reviewed with good success generally attained up to saturation. Examples are presented to illustrate applications of these methods in calculating ion concentrations, vapor pressures, and solubility limits, for some problems encountered in hydrometallurgy. 相似文献
48.
49.
The computation of stresses within a finite element displacement method analysis of a shell of revolution is considered. The common procedure of applying the kinematic and constitutive laws to the displacement functions is examined and justified for models where the displacements are represented by high-order polynomial expansions. Also, two alternative computational formats within this technique are explored. The influence of the column-supported base condition on a hyperboloidal shell of revolution is studied with respect to the stresses calculated from a response spectrum analysis. These studies emphasize the importance of accurately modelling the base region of a column-supported shell such as a hyperbolic cooling tower. 相似文献
50.
Maurice Aubert 《Physics of the Earth and Planetary Interiors》1974,9(4):364-366
The pluri-annual variations of the earth's magnetic field in France increase their range of influence from East to West. This leads to presume a discontinuity of electric conductivities at the transition from the continental to the oceanic area. 相似文献