Geochemical Variation in the Greenstones of S.W. England     

FLOYD  P. A. 《Journal of Petrology》1976,17(4):522-545

The characteristic rocks of the Upper Palaeozoic greenstonesof S.W. England are intrusive dolerites and extrusive basicpillow lavas with minor intermediate volcanics and ultrabasics(picrites). Pyroclastics are represented by keratophyric andbasic tuffs. The intrusive greenstones show varying degrees of alteration(spilitization) from a primary ilmenite-plagioclase-clinopyroxene?olivineassemblage to a hydrous low-grade spilite (or meta-dolerite)assemblage composed of variable proportions of albite, chlorite,epidote, calcite, and amphibole. Based on the distribution of elements little affected by secondaryprocesses (Ti, P, Y, Nb, and Zn), the intrusive greenstonescontain representatives of both the alkali olivine basalt andtholeiitic basalt magma series. Magmatic differentiation isgenerally minimal with the Devonian alkali basalt greenstonesbeing principally basaltic, while some of the Carboniferousalkali basalt greenstones tend towards mugearitic compositions.No intrusive acid differentiates have yet been reported. Apart from differences of magma type and minor differentiation,low-grade alteration or ‘spilitization’ has alsogoverned the geochemical variation seen in the greenstones.Spilitization caused (a) local redistribution of principallyCa (forming epidote-rich and calcite-rich patches) and Mg (formingchlorite-rich patches), together with their respective coherenttrace elements, and (b) the variable, but often limited, lossof Ca, Sr, K, Rb, and Ba from many bodies, together with a gainin Na and H₂O. Progressive hydration, however, caused a decreasein the oxidation ratio—a feature found to be common inmany spilitic suites and mainly governed by the relative distributionof chlorite versus epidote.  相似文献   

Effects of suprathermal grains     

S. P. Tarafdar  N. C. Wickramasinghe 《Astrophysics and Space Science》1976,39(1):19-30

Grains ejected from stars at velocities of 10⁷ cm s^–1 and/or grains accelerated by the pressure of starlight in the intercloud medium to velocities in the range 2×10⁶–10⁷ cm s^–1 are slowed to velocities of about 2×10⁵ cm s^–1 in a typical interstellar cloud. The interaction of fast grains with gas atoms as they are slowed in clouds could provide (a) the dominant heat source for interstellar clouds; (b) sites for molecule formation; and (c) a mechanism of providing a pressure balance between clouds and the intercloud medium.Paper presented at the Symposium on Solid State Astrophysics, held at the University College, Cardiff, Wales, between 9–12 July, 1974.  相似文献   

THE MAKING OF THE SOUTH AUSTRALIAN LANDSCAPE: A STUDY IN THE HISTORICAL GEOGRAPHY OF AUSTRALIA. By Michael Williams     

P. J. Perry 《New Zealand geographer》1976,32(1):99-99

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LOCATIONAL TRENDS OF AN EXPERIMENTAL PUBLIC FACILITY: THE CASE OF NUCLEAR POWER PLANTS     

R. Keith Semple  Jeffrey P. Richetto 《The Professional geographer》1976,28(3):248-253

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Observation of temporal and spatial variations in the Fe/O charge composition of the solar particle event of 4 July, 1974     

T. P. Armstrong  S. M. Krimigis  D. Hovestadt  B. Klecker  G. Gloeckler 《Solar physics》1976,49(2):395-407

Comprehensive measurements of the temporal variations of the Z 6 charge composition in the 4 July 1974 solar event made with experiments aboard IMP-7 and 8 show that large variations in the charge composition occur in three-hour-averaged intensities. Hourly averaged fluxes show variations as large as factors of 3 to 4 from one hour to the next and 3 hour averages show nearly a factor of 10 peak to minimum over the event. The precision of the measurements are limited by counting statistics of the Fe-group channel. Iron to oxygen variations are established by both rate channel and pulse height analysis techniques. Comparison of measurements from IMP-7 and 8, separated by about 70 R _E shows that, while significant differences in composition and intensity exist for brief periods, the gross compositional variations are reproduced well at both spacecraft. These observations provide particularly stringent conditions for theories of the acceleration, release, and propagation of solar energetic particles.  相似文献   

Laser action in stellar envelopes     

Y. P. Varshni  C. S. Lam 《Astrophysics and Space Science》1976,45(1):87-97

It is shown that in high-temperature stars in which high speed mass loss is occurring, the rapidly recombining plasma in the stellar envelope can act as an amplifying medium. Model calculations for laser action in Heii 4686, using the collisional-radiative model, are presented. Menzel's hypothesis of laser action in distended stellar atmospheres is shown to be fully substantiated. The relevance of these results in resolving the problem of intensity anomalies in the spectra of Wolf-Rayet stars is pointed out.  相似文献   

The concept of limiting magnitude and the performance of the Isaac Newton telescope for prime focus photography     

D. E. Blackwell  P. A. Ibbetson  C. A. Murray  N. M. Pratt 《Astrophysics and Space Science》1976,43(2):469-473

A quantitative definition of limiting magnitude for stellar photographs is proposed, together with a method of measurement employing a Racine prism. Limiting magnitudes inU, B andV for the Isaac Newton telescope at Herstmonceux derived from a total of 72 prime focus photographs are presented and the results correlated with the size of the photographed image. The limiting magnitude for an extrapolated value of the seeing of 1Prime" align="MIDDLE" BORDER="0"> isB=22^m.0, in good agreement with a value obtained by scaling the limiting magnitudes of the 200 inch telescope.  相似文献   

Martian glaciation and the flow of solid CO₂     

Bruce R. Clark  Rosemary P. Mullin 《Icarus》1976,27(2):215-228

The flow law determined experimentally for solid CO₂ establishes that a hypothesis of glacial flow of CO₂ at the Martian poles is not physically unrealistic. Compression experiments carried out under 1 atm pressure and constant strain rate demonstrate that the strength of CO₂ near its sublimation point is considerably less than the strength of water ice near its melting point. The data fit a power law “creep” equation of the form , where ? is compressive strain rate (sec^?1), σ is compressive stress (bars), R is the gas constant in calories per mole, and T is absolute temperature. The exponent of σ of 3.9 contrasts with a value near 3.1 for water ice, and indicates that the strain rate is somewhat more sensitive to stress for CO₂ than for water. Likewise, the low activation energy for creep, 12 200 cal mole^?1, illustrates that CO₂ is not highly sensitive to temperature and is thus likely to flow over a broad range of temperatures below its melting point. Strength values for CO₂ are of the order of one-tenth to one-third the strength of ice under equivalent conditions.A plausible glacial model for the Martian polar caps can be constructed and is helpful in explaining the unique character of the polar regions. CO₂-rich layers deposited near the pole would have flowed outward laterally to relieve high internal shear stresses. The topography of the polar caps, the uniform layering of the layered deposits, and the general extent of the polar “sediments” could all be explained using this model. Flow of CO₂ rather than water ice greatly reduces the problems with Martian glaciation. Nevertheless, problems do remain, in particular the large amounts of CO₂ necessary, the need to increase vapor pressure and temperature with depth in the polar deposits, and the lack of good observational evidence of flor features. Within the limits of the present knowledge of surface conditions of Mars, CO₂ glaciation appears to be a realistic alternate working hypothesis for the origin of the polar features.  相似文献   

The atmosphere of Io from Pioneer 10 radio occultation measurements     

A.J. Kliore  G. Fjeldbo  B.L. Seidel  D.N. Sweetnam  T.T. Sesplaukis  P.M. Woiceshyn  S.I. Rasool 《Icarus》1975,24(4):407-410

The occultation of the Pioneer 10 spacecraft by Io (JI) provided an opportunity to obtain two S-band radio occultation measurements of its atmosphere. The dayside entry measurements revealed an ionosphere having a peak density of about 6 × 10⁴ elcm^?3 at an altitude of about 100 km. The topside scale height indicates a plasma temperature of about 406 K if it is composed of Na⁺ and 495 K if N₂⁺ is principal ion. A thinner and less dense ionosphere was observed on the exit (night side), having a peak density of 9 × 10³ elcm^?3 at an altitude of 50 km. The topside plasma temperature is 160 K for N₂^? and 131 K for Na⁺. If the ionosphere is produced by photoionization in a manner analogous to the ionospheres of the terrestrial planets, the density of neutral particles at the surface of Io is less than 10¹¹?10¹² cm³, corresponding to a surface pressure of less than 10^?8 to 10^?9 bars. Two measurements of its radius were also obtained yielding a value of 1830 km for the entry and 192 km for the exit. The discrepancy between these values may indicate an ephemeris uncertainty of about 45 km. The two measurements yield an average radius of 1875 km, which is not in agreement with the results of the Beta Scorpii stellar occultation.  相似文献   

HENRY GEORGES FOURCADE     

L. P. Adams 《The Photogrammetric Record》1975,8(45):287-296

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