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101.
William S. Burgett Michael M. Vick David S. Davis Matthew Colless Roberto De Propris Ivan Baldry Carlton Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Nicholas Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654
102.
Large amounts of diorite—tonalite magma were intruded into the island-arc successions of the southern Arabian shield between ca. 900 and 700 Ma ago. Major oxide, trace element, rare earth (REE) and isotopic data are presented for two plutons exemplifying older and younger members of this plutonic phase. The Thurrat pluton, which was emplaced into virtually unmetamorphosed volcanics of sequence B, has yielded a 10-point Rb-Sr isochron indicating emplacement 744 ± 22 Ma ago and an initial ratio of 0.70281. It consists of gabbros, diorites, quartz diorites, tonalites and low-Al2O3 trondhjemites which are compositionally primitive, with depleted lithophile element contents and flat REE patterns with a negative Eu anomaly in the trondhjemites. The magma was most probably mantle-derived, and analogies with other trondhjemitic plutons suggest that it was probably emplaced in an island-arc setting. The Bidah pluton, which was emplaced into a compositionally very immature succession of metamorphosed volcanics and volcaniclastics of sequence C, has yielded a nine-point near-isochron (MSWD = 2.86) indicating an age of 901 ± 37Ma and an initial ratio of 0.70246. This date is accepted as the age of emplacement. The rocks are compositionally primitive gabbros, diorites, quartz diorites, tonalites and granodiorites with depleted lithophile element contents, and flat REE patterns with a negative Eu anomaly in the more siliceous components. The country-rock volcanics were formed in an immature island-arc environment, and the composition of the Bidah pluton is suggestive of a mainly mantle-derived magma emplaced into that arc. The data for these two plutons therefore provide further evidence that most of the rock material added to the Arabian shield between 900 and 700 Ma ago was derived from the mantle. 相似文献
103.
104.
105.
We consider the infrared brightness of a flattened comet belt beyond the orbit of Neptune using a disk-like model with a power-law density distribution of comets. We compare this spectrum with the emission from a model zodiacal dust cloud in the ecliptic and with published IRAS data and present some consequences of dust in the comet belt. 相似文献
106.
T. S. Jackson 《Planetary and Space Science》1974,22(12):1691-1701
The Moon is represented as an inhomogeneous spherical body in a steady thermal state. Radioactive heat sources are supposed distributed in a manner which is consistent both with the total measured heat flux near the surface and with the broad seismic evidence. Surface concentrations of uranium and thorium are those suggested by the study of Apollo 11 samples. The resultant internal temperature profile allows the details of Sonett's electrical conductivity profile to be understood if it is accepted that the Moon was not cold 4.5 × 109 yr ago. It would appear further that at least one of the maria was formed by the impact of planetesimals. 相似文献
107.
Peter Jackson 《The Professional geographer》1982,34(4):440-440
108.
Data are presented in this study from laboratory model experiments describing the behaviour of Cu, Pb, Zn and Ni at a simulated sediment-water boundary. The interactions involved are sorption by kaolin and by bentonite, organic complexing in solution by fulvic acid and by humic acid, carbonate reactions, hydrolysis, and desorption of the cations from a clay-bound phase and from their metal hydroxides by the organic acids. The organic acids increase the solubility of Cu, Zn and Ni in the presence of clay. The Pb solubility is variable and can even decrease, particularly at acidic pH, with organic complexing likely due to colloidal coagulation. Both Zn and Ni are influenced by hydrolysis at basic pH. When carbonate was added to the metal-organic acid-clay mixtures, a further decrease in solubility was observed for Ni and, to a lesser extent, for Zn. The organic acids prove capable of remobilizing Cu, Pb, Zn and Ni from the solid phases examined. However, there is a general kinetic hindrance to the desorption particularly at basic pH. Copper desorption appears to be the most kinetically hindered. Conclusions pertinent to the geochemical dispersion of these metals are drawn. 相似文献
109.
The positions and motions of solar bursts in the range 20 to 60 MHz have been measured by the means of a sweep-frequency grating interferometer with angular resolution of 5 arc at 60 MHz decreasing to 15 arc at 20 MHz. The positional characteristics of the decameter wavelength bursts are discussed in terms of the commonly accepted theories of the origin of radio bursts from plasma and synchrotron radiations. 相似文献
110.