Review of the dynamics in the Kirkwood gaps     

Michèle Moons 《Celestial Mechanics and Dynamical Astronomy》1996,65(1-2):175-204

The study of mean motion resonance dynamics was motivated by the search for an explanation for the puzzling problem of the Kirkwood gaps. The most important contributions in this field within the last 32 years are reviewed here. At the beginning of that period, which coincides with the first long-term numerical investigations of resonant motion, different hypotheses (collisional, gravitational, statistical and cosmological) to explain the origin of the gaps were still competing with each other. At present, a general theory, based on gravitational mechanisms only, is capable of explaining in a uniform way all the Kirkwood gaps except the 2/1 one. Indeed, in the 4/1, 3/1, 5/2 and 7/3 mean motion commensurabilities, the overlap of secular resonances leads to almost overall chaos where asteroids undergo large and wild variations in their orbital elements. Such asteroids, if not thrown directly into the Sun, are sooner or later subject to strong close encounters with the largest inner planets, the typical time scale of the whole process being of the order of a few million years. Unfortunately, this mechanism is not capable of explaining the 2/1 gap where the strong chaos produced by the overlapping secular resonances does not attain orbits with moderate eccentricity, of low inclination and with low to moderate amplitude of libration. In the light of the most recent studies, it appears that the 2/1 gap is the global consequence of slow diffusive processes. At present, the origin of these processes remains under study.  相似文献   

Marine pollution control regulation: Regional approaches     

Dominique Alhéritière 《Marine Policy》1982,6(3):162-174

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Mechanical twinning of plagioclase in a deformed meta-anorthosite — the production of M-twinning     

William L. Brown  Jean Macaudière 《Contributions to Mineralogy and Petrology》1986,92(1):44-56

Mechanical twins on both the Albite and Pericline laws are well developed on an optical scale in basic plagioclase from the Harris meta-anorthosite where the rock is affected by closely spaced shear fractures associated with pseudotachylite formation. In some cases the twinning is accompanied by kinking or intracrystalline fractures. The twins may be periodic and form a ladder structure and sometimes appear to intersect on an optical scale showing structures which very closely resemble those seen in microcline.Both Albite and Pericline twins are lenticular as observed by TEM, but isolated twin tips were rarely seen. No dislocations are associated with the twin tips. The twins in the optically observed ladder structure (when thicker than 2m), have themselves a very fine secondary ladder structure, consisting of periodic (200–600 nm) lenticular twins which impinge on the perpendicular twin wall. Intersecting twins were also observed and where two sets of equally thick twins intersect, M-twinning develops as shown by selected-area diffraction.The twin formation is analyzed in terms of the plagioclase structure and a coherent model for twin nucleation proposed. True twins can develop in plagioclase only if the Al/Si distribution is unchanged or nearly so after deformation. Mechanical twinning is quite easy in low plagio-clases between An₁₀₀ and about An₃₀ which have P¯1 or I¯1 lattices or domains with I¯1-type structures. Only one kind of nucleus can develop coherently in a single crystal, but it may grow to give either an Albite or a Pericline twin. Periodic nucleation and growth give complex textures. The qualitative variation of the twin energy as a function of the obliquity is given for different twin shapes and degrees of Al/Si order. M-twinning arises mechanically by coherent growth and interference of the strain fields.  相似文献   

The transition from alkali basalts to kimberlites: Isotope and trace element evidence from melilitites     

C. Alibert  A. Michard  F. Albarède 《Contributions to Mineralogy and Petrology》1983,82(2-3):176-186

Eighteen Cenozoic melilitite samples from Spain, France, West Germany and Czechoslovakia have been analyzed for major and trace elements (including REE) together with their Sr and Nd isotopic compositions. Leaching experiments produced significant shifts of their⁸⁷Sr/⁸⁶Sr ratio indicative of a contamination by a crustal component. Most samples fall within the Sr-Nd mantle array with ?_Nd values in the 1.5–6 range. These values are considered as minimum for the melilitite mantle source hence demonstrating its time integrated LRE depletion. The Ni and Cr contents of the samples are typical of primary magmas and exclude extensive crystallization of olivine and pyroxene in a closed system. However, the chemical relationships suggest that dilution of the liquids by mafic minerals of the conduits during their ascent has been important. The REE patterns show some variations which are interpreted by this dilution effect. Once normalized to Yb they are closely similar and perfectly distinguishable from those of alkali basalts and kimberlites. All of these rocks have Ce/Yb ratios which are high but distinctive for each rock type: 40 to 200 times the chondritic ratio for kimberlites, 20 to 30 for melilitites, 8 to 15 for alkali basalts. As contamination is likely to have modified somewhat the isotopic characteristics of most of these rocks, there is no overwhelming evidence that their source is chemically different. The Ba and Rb contents together with the REE patterns of the melilitites would constrain the degree of melting to be very small (<0.2%). The calculation of batch melting and steady zone refining models suggests that kimberlites, melilitites and alkali basalts may have been derived by equilibration of deep melts with different upper mantle levels characterized by decreasing garnet/clinopyroxene ratios. The strongly incompatible elements are enriched in the melt during its ascent by leaching of the wall rocks. For the steady zone refining model, the degree of melting concept loses its significance and the difficult requirement of extracting small liquid fractions from a molten source disappears. Within the frame of this model, the preenrichment of the kimberlite, melilitite and alkali basalts source in incompatible elements by metasomatic fluids is no longer necessary.  相似文献   

Âge des orthogneiss de la zone axiale de la Montagne Noire (France) par la méthode 87Rb-87Sr     

J. Hamet  C. J. Allègre 《Contributions to Mineralogy and Petrology》1972,34(3):251-257

The basement of Montagne Noire (South France), as represented by the orthogneisses of the axial zone, has been dated by means of whole rocks isochron at 530 m.y. This age is discussed with the assistance of petrographic observations and compared to similar results obtained by other authors in the Massif Armoricain and eastern Pyrénées ranges. The high initial ratio ⁸⁷Sr/⁸⁶Sr allows one to hypothesize that these igneous masses were originated from a segment of a preexisting crust.

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Contribution I.P.G.N.S. No 8.  相似文献   

Cyanophycées marines endolithes colonisant les surfaces rocheuses dénudées (Etages Supralittoral et Médiolittoral de la région de Marseille)     

Dr. Thérèse Le Campion-Alsumard 《Aquatic Sciences - Research Across Boundaries》1970,32(2):552-558

Résumé Etude des Cyanophycées endolithes, recolonisant les surfaces rocheuses dénudées, au niveau des Etages Supralittoral et Médiolittoral de la région de Marseille. Apparition de différentes formes évolutives de l’espèceEntophysalis deusta en fonction de l’intensité des facteurs du milieu. Niveau de l’Etage Supralittoral, humectation réduite, formes épilithes et peu pénétrantes; niveau de l’Etage Médiolittoral, humectation intense, formes endolithes filamenteuses. Il est à noter que ces formes se succèdent toujours dans le même ordre, seul le stade final est différent selon la condition du milieu envisagé. Ceci va donc à l’encontre d’une espèce unique avec divers stades évolutifs. La position extrême adoptée parF. Drouet etW.A. Daily au sujet de la systématique des Cyanophycées endolithes entra?ne de nombreuses réserves et seule une étude basée sur des cultures unialgales permettra de conna?tre avec précision la marge de variation des taxons.

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Summary The object of this study was the endolithic blue-green algae of the upper and middle litoral zone of the rocky coast near Marseille. Difficulties in determining these algae cropped up very soon because of their strong plasticity. To ascertain whether there were different species of algae or only different ecological types of the same species, two series of experiments were carried out in the region around Marseille: 1. small rock splinters from various places were cemented into place in the above-mentioned zones. 2. The regrowth of rock surfaces that were cleared of algae was observed. Moreover cultures of the individual species were made to find an unequivocal solution to the systematic and ecological problems of these algae. Only the results of the tests on recolonization of the rock surface by algae are dealt with in this paper. According to our observations, theEntophysalis deusta (Men.) Drouet and Daily developed in different patterns depending on the degree of moisture. In the upper litoral zone where the amount of moisture is less significant it takes on epilithic forms that do not penetrate into the rock. In the more humid middle zone they prevail in an endolithic stringy form. It is interesting to note that the various forms always appear in the same order; thus with increasing moisture one finds:Gloeocapsa, Entophysalis, Scopulonema (forms of the upper litoral zone) andHyella caespitosa, Hyella tenuior (forms of the middle zone). Other species such as theHormathonema that grow in the same biotope as theEntophysalis seem to react differently to outside stimuli. The conjectures concerning the plasticity of theEntophysalis deusta confirmDrouet andDaily’s theory. Yet this hypothesis needs to be confirmed through cultures of the forms observed.

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Zusammenfassung Die endolithischen Blaualgen der supralitoralen und mediolitoralen Zone an der felsigen Küste in der Region von Marseille wurden untersucht. Schon zu Beginn der Arbeit zeigten sich Schwierigkeiten bei der Bestimmung dieser Algen, da sie zum Teil eine starke Plastizit?t aufzuweisen scheinen. Um abzukl?ren, ob verschiedene Arten oder nur unterschiedliche ?kotypen ein, und derselben Art vorliegen, wurden zwei Untersuchungsserien in der Region von Marseille durchgeführt: 1. Kleine Felssplitter verschiedener Herkunft wurden in den genannten Zonen festzementiert. 2. Es wurde beobachtet, wie Stellen, die man von Algen entbl?sste, wieder besiedelt wurden. Ferner begann man Kulturen der einzelnen Typen herzustellen, um die systematisch-?kologischen Probleme dieser, Blaualgen eindeutiger zu l?sen. In dieser Mitteilung sind nur die Resultate derWiederbesiedlungsversuche dargestellt. Die Beobachtungen ergaben im wesentlichen, dass die ArtEntophysalis deusta (Men.) Drouet et Daily sich je nach Intensit?t der Benetzung in verschiedenen Formen entwickelt. So tritt sie in der supralitoralen Zone, die einen reduzierten Feuchtigkeitsgrad aufweist, in epilithischen Formen auf, die wenig in den Fels eindringen. In der mediolitoralen Zone mit grosser Feuchtigkeit findet man sie als endolithische f?dige Formen. Interessant ist, dass diese verschiedenen Erscheinungsformen stets in gleicher Reihenfolge auftreten, und zwar begegnet man mit zunehmender Feuchtigkeit folgenden Formen:Gloeocapsa, Entophysalis, Scopulonema (= Formen der supralitoralen Zone),Hyella caespitosa, Hyella tenuior (= Formen der mediolitoralen Zone). Andere Gattungen, wie z. B.Hormathonema, die im gleichen Biotop wieEntophysalis auftreten, scheinen anders auf die Umweltfaktoren zu reagieren. Die Vermutungen über die Plastizit?t vonEntophysalis deusta best?tigen eigentlich die Auffassung vonDrouet undDaily. Doch diese Hypothese verlangt eine Best?tigung mittels Kulturen der beobachteten Erscheinungsformen.

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Contribution à l’étude des Cyanophycées lithophytes des Etages Supralittoral et Médiolittoral (région de Marseille), Tethys1 (1), 119–172 (1969).  相似文献   

Cenozoic volcanics of the Erzurum area (Turkish Armenia)     

Prof. G. Pasquarè 《International Journal of Earth Sciences》1971,60(3):900-911

The outlines of the Cenozoic volcanism developed between the Pontian and Taurian orogenic belts in the Erzurum area, are described. The following volcanic units are recognized, from the oldest ones: andesiticbasaltic fissurai strato-volcanoes; rhyodacitic and dacitic domes; andesitic domes followed by strong ejective activity; basaltic domes and flow-domes; basaltic fissure volcanoes. The relationships between these units and the main tectonic phases, which developed in this region during the latest periods of the Alpine orogenesis, are discussed.  相似文献   

Corrosions causées par l'incinération des résidus urbains     

J. Defèche 《Aquatic Sciences - Research Across Boundaries》1969,31(2):476-487

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Le volcanisme des Causses et du Bas-Languedoc (France)     

Bernard Gèze 《Bulletin of Volcanology》1955,17(1):73-89

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The growth of the continent through geological time studied by Nd isotope analysis of shales   总被引：2，自引：0，他引：2  

Claude J. Allègre  Dominique Rousseau 《Earth and Planetary Science Letters》1984,67(1):19-34

We determined the Nd isotopic composition and the Sm/Nd ratios in a series of Australian shales ranging from 0.2 Gy to 3.3 Gy. The first result of this study is the constancy of the Sm/Nd ratio in these shales, as in granitoids. Secondly, the initial (¹⁴³Nd/¹⁴⁴Nd) ratio gives a regular curve decreasing through geological time. Both results confirm that shales are representative samples of the continental crust, when insoluble elements, like REE, are studied.We calculated their Nd model ages of crustal differentiation. The model ages regularly decrease with the stratigraphic ages and after 2 Gy, the curve flattens and tends to an asymptotic value at around 1.8 Gy. The significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin.From these results, we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas. We propose that the results obtained here are representative of the whole Gondwana continent.Having studied the case of the Australian shales, we try to extend our study. First we applied our quantitative approach to the recent results obtained by O'Nions et al. on North Atlantic provinces. The continental growth curves obtained by our inversion procedure are quite distinct from the Australian shales showing the regional character of shales.With these two cases studied we try to compare our results with the already developed model for continental growth. The consideration of the surface conservative versus surface non-conservative models clearly show the non-uniqueness of the geological interpretation of the growth curve. On the other hand, we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the Hurley-Rand province age curve. Such recycling increases with time in agreement with the data obtained on Nd and Sr initial ratios on granitoids.  相似文献