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961.
Michael A. Feierberg Harold P. Larson Uwe Fink Howard A. Smith 《Geochimica et cosmochimica acta》1980,44(3):513-524
A Fourier spectrometer was used to obtain IR spectra of asteroids 349 Dembowska and 4 Vesta (0.8–2.5μm; 25cm ?1 resolution). The spectrum of Dembowska shows olivine and pyroxene (Fs24 ± 8) with an olivine/pyroxene abundance ratio greater than 2, and possibly as high as 10. This is probably an unsampled achondritic composition, similar to the unique achondrite ALHA 77005. Similar olivine-rich compositions have also been proposed for the mantles of basaltic achondrite parent bodies. Dembowska's mineralogy therefore appears related in some way to the achondrites. but a direct link cannot as yet be made. Our IR observations of Vesta have more complete spectral coverage than those first obtained by Larson and Fink (1975b). Pyroxene (Fs50 ± 5) and plagioclase feldspar are both seen, with a pyroxene/feldspar abundance ratio between 1.5 and 2.0. Vesta's mineralogy is consistent with a mixture of eucrites and howardites on its surface. Time-resolved observations over one-half of the rotation period show no spectral variations at the 2% level, indicating compositional homogeneity. Both 349 Dembowska and 4 Vesta can be considered as candidates for the parent bodies of igneous meteorites. 相似文献
962.
An omphacite from the Nybø eclogite pod, Norway, has a chemical composition which plots within the gap, often regarded as a miscibility gap, which is evident in all previous compilations of natural jadeite-rich acmite-poor omphacite compositions. Its cation site populations determined by crystal structure refinement accord well with its chemical composition analysed by electron microprobe. Its disordered space group C2/c symmetry extends the known compositional range of C2/c pyroxene. The postulated miscibility gap is regarded as real and wide at low temperatures, but it appears to narrow with increasing temperature or ultimately with increasing acmite proportion. The adjacent primitive symmetry field appears to initially widen with increasing temperature or increasing acmite proportion, at the expense of the diminishing miscibility gap, before finally closing with further increase. 相似文献
963.
The effects of the variation of magnetic grain size on the magnetic properties of rocks have been studied throughout a reversely magnetized basaltic dyke with concentric cooling zones.Except in a few tachylites in which the magnetic mineral is a Ti-rich titanomagnetite, in the bulk of the dyke the magnetization is carried by almost pure magnetite grains. Although the percentage p of these magnetic oxides varies slightly, the large changes in the various magnetic parameters observed across the dyke are essentially attributable to large variations in the grain size of the magnetic particles.From the outer scoria region, where the magnetic grains are a mixture of single-domain (SD) and superparamagnetic (SP) grains, to the tachylite zone with finely crystallized basaltic glass containing interacting elongated SD particles, one observes an increase of both the ratio of the saturation remanent magnetization and the saturation induced magnetization Jrs/Jis, the bulk coercive force Hc, the median destructive field MDF, the intensity of the remanent magnetization Jr, and the Koenigsberger ratio Q. In the tachylites these parameters reach unusually high values, for subaerial basalts: These parameters decrease in the basalt toward the centre of the dyke where pseudo-single-domain (pseudo-SD) particles coexist together with multidomain (MD) grains. The susceptibility remains approximately constant from the inner basalt to the tachylite, but increases in the scoria up to values 10 times higher owing to the presence of SP particles. The magnetic viscosity increases also drastically toward the margin of the dyke due to an increase of the fraction of the SD particles just above the superparamagnetic threshold. 相似文献
964.
P. P. K. Smith 《Contributions to Mineralogy and Petrology》1977,59(3):317-322
Ion-thinned samples of augite from four plutonic igneous rocks have been examined in the electron microscope at 100 kV. Lamellae less than 0.08 m thick were observed parallel to (010) in all four samples. Electron diffraction shows that the lamellae consist of clino-amphibole, space group I2/m, with crystallographic axes parallel to those of the augite. Analytical electron microscopy of the lamellae in one specimen shows that they are a hornblende. The amphibole lamellae have nucleated at the interface between the augite host and exsolution lamellae of orthopyroxene parallel to (100) of the augite. The interface between the amphibole lamellae and the augite is coherent.It is thought that the amphibole lamellae have formed by exsolution from the augite, implying the existence of finite solid solution between members of the pyroxene and amphibole groups of minerals. 相似文献
965.
966.
Solid source mass spectrometry has been used to determine the relative cumulative fission yields of five elements in three samples of uranium ore from reactor zones in the Oklo mine site. Eighteen fission chains covering the mass range from105 ≤ A ≤ 130 have been measured for Pd, Ag, Cd, Sn and Te. These measurements have enabled a number of nuclear parameters to be calculated including the relative proportions of235U,238U and239Pu involved in the fission process.The concentration of the five elements in the Oklo samples have also been measured using the stable isotope dilution technique. These values have then been compared to the estimates of the amount of these elements produced by fission under the conditions that are appropriate to the three samples. This procedure enables the retentivity of the elements in the reactor zones to be evaluated. Our work confirms the fact that Pd and Te are retained almost in their entirety in the samples, whereas the other three elements have been partially lost from the reactor site. Almost all the Cd fission products have been lost, and more than 50% of the Ag and Sn fission-produced material has been removed. 相似文献
967.
968.
Sir Eric Smith 《Marine pollution bulletin》1982,13(2):71-72
969.
In a sample of seven red phalaropes (Phalaropus fulicarius: Aves) collected from a flock of 6000 late spring migrants, six stomachs contained plastic particles. A negative correlation between amount of plastic and fat condition suggests a detrimental effect of a widespread oceanic pollutant on a marine bird. 相似文献
970.