A layered basic intrusion,deformed and metamorphosed in granulite faciès of the Sri Lanka basement

A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F₄-synform with an axis parallel to str₁ and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. Stretching continued along its axis. Late during formation of this fold a granite intruded, mainly following S₄ cleavage planes. The intrusion shows a homogeneous gabbroic series at the bottom, followed upwards by a differentiated and layered series. A thin sequence of ultramafic rocks occurs near the middle. This indicates multiple melt-injection. More homogeneous partly biotite-bearing amphibolites form the top of the succession. Magmatic layering is well preserved, but no magmatic minerals or grain fabrics have escaped deformation or metamorphism. Static annealing under granulite facies conditions outlasted all deformation and was accompanied and followed by the beginning of cooling. Hornblende-Plagioclase coronas formed round garnets at this stage. Geochemical work, carried out by STOSCH (1991) on our samples, confirms the cumulate nature of the rocks.

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Zusammenfassung Eine geschichtete Basische Intrusion wurde im Central Granulite Belt der tiefen, kontinentalen Kruste Sri Lankas entdeckt. Sie intrudierte parallel zur Schichtung in benachbarte Sedimente, vor aller oder sehr früh in deren Deformation. Die Deformation, die Sedimente und die Intrusion in gleicher Weise betraf, führte zu Plättung auf das ca. 1/20 der Ausgangsdicke und zu NNW-Streckung auf das ca. 20fache der Ausgangslänge. Heute ist die Intrusion 170–300 m dick. Der Hauptteil der Deformation wurde unter Granulit-Fazies-Bedingungen erworben. Noch bei hoher T wurde die Intrusion durch eine große F₄-Falte gefaltet. Deren Achse liegt parallel der Streckungsrichtung, stri, ihre Achsenebene ist steil. Eine steile, Achsenebenen-parallele S₄-Schieferung und kleinere Falten entstanden mit ihr. Während der Bildung dieser Falte hielt die Streckung parallel ihrer Achse an. Spät während ihrer Bildung intrudierte ein Granit. Er folgt im wesentlichen S₄. Die Intrusion beginnt unten mit einer homogenen, gabbroiden Serie. Nach oben folgt eine differenzierte, geschichtete. Ein dünnes Paket ultramafischer Lagen erscheint nahe der Mitte. Es weist auf multiple Schmelz-Zufuhr hin. Homogenere Amphibolite, teils mit Biotit, bilden den obersten Teil. Magmatischer Lagenbau ist gut erhalten, lokal mit Gradierung. Magmatische Minerale oder Korngefüge haben Deformation und Metamorphose nicht überlebt. Statische Temperung unter Granulit-Fazies-Bedingungen überdauerte alle Deformation. Sie beginnt und dauert an bei bereits sinkender T. Hornblende-Plagioklas-Koronas bilden sich in diesem statischen Endstadium. STOSCH (1991) untersuchte unsere Proben von der Intrusion geochemisch. Er bestätigte die Kumulatnatur der Gesteine.

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Résumé Une intrusion basique litée a été découverte dans la ceinture centrale granulitique du socle continental du Sri Lanka. L'intrusion s'est effectuée parallèlement à la stratification, avant la déformation des métasédiments encaissants ou tout au début de celleci. La déformation, qui affecte à la fois les métasédiments et l'intrusion, comporte un aplatissement jusqu'à ± 1/20 de l'épaisseur d'origine, et un allongement de ± 20 fois en direction NNW. L'intrusion présente actuellement une épaisseur de 170 à 300 m. La plus grande part de la déformation a été acquise dans les conditions du faciès des granulites. L'intrusion a ensuite été plissée, toujours à haute T, en un large synforme F₄ dont l'axe est parallèle à l'allongement stri et dont le plan axial est vertical. Ce grand pli est accompagné d'une schistosité S₄ plan-axiale redressée et de plis secondaires. L'allongement s'est poursuivi parallèlement à son axe. A la fin de la formation de ce pli, un granite s'est intrudé, qui suit en gros S₄. L'intrusion comporte à sa base une série gabbroïque homogène, suivie vers le haut par une série litée et différenciée. Elle contient, vers son milieu, une intercalation mince de roches ultramafiques. Ceci implique des injections répétées de magma. Le sommet est formé d'amphibolites homogènes partiellement biotitiques. Le litage magmatique est bien conservé, mais aucun minéral ou fabrique magmatique n'a échappé à la déformation et au métamorphisme. Un recuit statique dans les conditions granulitiques a suivi la déformation; il a été accompagné et suivi par le début du refroidissement. A ce stade, des couronnes à hornblende-plagioclase se sont formées autour des grenats. Une étude géochimique, effectuée en 1991 par Stosch sur nos échantillons confirme le caractère de cumulat des roches.

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- . , . , , 1/20 20- NNW . 170–300 . . F₄, str₁, . , S₄, . . . S₄. , , . . , , . coxpa . , .. . , . . . . STOSCH (1991) .

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List of abbreviations ss sedimentary bedding - s₁ first cleavage, plane of first flattening - str₁ Direction of first stretching; although L is usually used for lineations of different kind, including stretching, we use this term to point out that extension is proved in each case - F₂ second folds = first folds folding s₁ - s₂ second cleavage or plane of flattening - F₃ third folds - s₃ third cleavage or plane of flattening - F₄ fourth folds, folding s_1,2,3 and F_1,2,3 - s₄ fourth cleavage or plane of flattening - str₄ direction of fourth stretching - F_5,6 fifth and sixth folds - gf(m) granulite facies (metamorphism) - af(m) amphibolite facies (metamorphism) - KNa-f KNa-feldspar - pg plagioclase - f feldspar - opx orthopyroxene - cpx clinopyroxene - px pyroxene - hb hornblende - bi biotite - cc calcite - do dolomite - qz quartz - mt magnetite     

On the systematic errors of the determinations of the absolute orientation of the meridian marks

The classical method of determination of the absolute azimuth (or Bessel's parameter n) can secure sufficiently precision for RA from observations of stars at high geographical latitudes during polar night only.     

Excitation class of nebulae—An evolution criterion?

A principally new, quantitative system of the classification of the spectra of planetary nebulae is proposed. Spectral class of excitation class of the nebulap is determined according to the relative intensities of emission lines (N ₁+N ₂) [OIII]/4686 HeII and (N ₁+N ₂) [OIII]/H (Table I, Figure 1). The excitation classes are obtained for 142 planetary nebulae of all classes—low (p=1–3), middle (p=4–8), and high (p=9–12⁺) (Tables II, III, and IV). An empirical relationship between excitation classp and mean radius of nebulae is discovered (Figure 2). This relationship as well as excitation classp, as an independend parameter, admit an evolutionary interpretation. It is shown that after reaching the highest class of excitationp=12⁺ the nebulae decrease their class of excitation with the further increases of sizes. The diagram of this relationship has two nearly-symmetric branches — rising and descending with the apogee onp=12⁺ (Figure 2).     

The far UV spectrum of the O4I(n)f star ζ Puppis

A detailed list of line identifications of the far UV spectrum of the O4I(n)f star Puppis (HD 66811) in the wavelength range 1168–1984 Å recorded on 16 April, 1981 with the International Ultraviolet Explorer (IUE) is presented. The detailed analysis of the radial velocities measured in the same wavelength range is also presented.     

Declination variations for zenith stars

The variations of the declinations of 36 Belgrade zenith stars from BZS1₇₀ Catalogue published in Astronomy and Astrophysics,177, 313–316 (1987) are examined by spectral analysis. The prospect is to evaluate multiples of the Chandler period of which the most prominent for all stars is the double one.     

Cosmological implications of BL Lac objects

It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F _obs = ^{3 +} F _intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem _v must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem _v ^corr and logZ have a good correlation.     

Double globular clusters in the Galaxy?

Four pairs of visual double star clusters with the lowest mass-to-luminosity ratio have been selected among globular clusters of our Galaxy. By taking into accounts the effects of dynamical friction and compressive gravitational shocks, we conclude that the probability for the pairs to be gravitationally bound is very low.     

Absolute and relative amplitudes of variations in radius of classical cepheids

On the basis of observational data for the absolute R and relative R/R amplitudes of variations in radius of galactic classical cepheids (55 stars from Balona and Stobie (1979) and 30 stars from Sollazzoet al. (1981)), four kinds of empirical linear relations are obtained: log(P V)–logR, logP–logR, log(P V)–log(R/R), and logP–log(R/R);P, R, and V are the pulsation periods, the mean stellar radii, and the amplitudes of light variations, respectively. Three groups of stars are considered: short-period cepheids (SPC)-with logP1.1; long-period cepheids (LPC)-with logP>1.1; and s-cepheids (sC). Both the R values and the R/R values increase withP andP V, for a given group of variables. A comparison is performed with our results obtained from data in other sources (Kurochkin, 1966; Gieren, 1982; etc.). The investigated relations can be applied for determining R and R/R of galactic classical cepheids, by using their observedP and V. All studied galactic classical cepheids have R/R<0.35, R<10R for SPC and 10R <R60R for LPC. The sC have smaller R and R/R values than other classical cepheids, at the same periods (the difference is about 2 times for R and 1.4–2.8 times for R/R); the studied sC have R/R in the range 0.025–0.075 and R in the range 1–3R (only Y Oph has R8R ).     

Photometric observations of CH Cygni in the period 1978–1987. Dust matter condensation in its circumstellar envelope during 1985–1987

We present the results of the photometric observations, in theUBVRJHKLMNQ system, of CH Cyg, made in the period 1978–1987. They have shown that from 1985 to 1987 dust condensed in its circumstellar envelope have taken place the condensation of the dust matter. In 1987 its mass and temperature were about 3×10^–8 M and 800 K, respectively.     

Population I pulsating stars

The radiiR and surface gravitiesg of Population I pulsating stars (89 Delta Scuti-variables and 155 classical cepheids) have been investigated. Semi-empirical period-radius (P-R) and period-gravity (P-g) relations are obtained for Delta Scuti-stars (for the four lowest modes of radial pulsations) and for classical cepheids. For Delta Scuti-stars, the uncertainties of radius and gravity estimations calculated from theP-R andP-g relations for different modes, are evaluated. There is a good agreement both between theP-R relations and between theP-g relations for Delta Scuti-stars and for classical cepheids, but a gap exists between the two types of variables. From models of Delta Scuti-stars, theoreticalP-R andP-g relations for the four lowest modes of radial pulsations are obtained, in a good agreement with the corresponding semi-empirical relations. There is an excellent agreement between the theoretical and semi-empirical period ratios of radial pulsations as derived from theP-R andP-g relations for Delta Scuti-stars. It is not necessary to take into account the colours (in addition to the periods), in order to estimate the radii and gravities of the variables under study.