Seismic hazard of Egypt

Earthquake hazard parameters such as maximum expected magnitude,M _max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.     

Regional retrograde alteration of sub-greenschist facies chlorite to smectite

Dioctahedral smectite is present as a retrograde alteration product of chlorite in Permian-Triassic red slates of the Malaguide Complex in Sierra de Espuña (Betic Cordillera). Mineral assemblages and textures, illite crystallinity indices, and fluid inclusion data indicate sub-greenschist facies conditions that reached at least 180°C in the higher-grade tectonic unit of the Malaguide Complex, preceding formation of smectite. Smectite, having K as the dominant interlayer cation, occurs ubiquitously intercalated with trioctahedral chlorite as thin packets of layers and as individual layers that commonly change to chlorite along layers. Although some chlorite is typically homogeneous and trioctahedral, much chlorite shows signs of alteration and has compositions corresponding to different degrees of smectite contaimination. The incompatibility of metamorphic grade with the occurrence of smectite, the general association of chlorite and smectite, and the textural relations collectively show that dioctahedral smectite is derived through replacement of trioctahedral chlorite. Such replacement occurs on a regional basis and demonstrates that caution must be used in interpreting the occurrence of smectite in pelites as being due to prograde processes. Alteration of trioctahedral chlorite under oxidizing conditions due to introduction of phreatic water after uplift of the Betic Cordillera is proposed as the cause of formation of smectite.     

Once more on quasar periodicities

In an earlier paper Arp, Bi, Chu and Zhu investigated various quasar samples and recognized a periodicity of remarkable degree in them. Their conclusion was that the existence of such a periodicity is a counterevidence against the cosmological origin of quasar redshifts. Since this question is of great importance in a cosmological context, here we reanalyze some of the samples together with a galaxy sample of the pencil-beam survey of Broadhurstet al. Our result is that on the plane of cosmological parameters (₀, ₀) there is a non-negligible region where two quasar samples and the galaxy sample are simultaneously fairly periodic. Pure periodicity is still compatible with cosmological principles, at least on length scales much longer than the period length. So the regularities can fit into a cosmological context.     

Cosmic-ray modulation and long-duration solar flare events

The correlation between the long-term intensity variations of cosmic rays at neutron monitor energies and the LDE index measure of solar flares with long-lasting soft X-ray emissions is reported. Three subsequent solar cycles, 20–22, are taken into account and half-monthly data are analyzed. Possible explanation of this correlation is discussed in terms of the recent concepts of cosmic-ray modulation, in particular with merged interaction regions affecting the cosmic-ray intensity.     

Stratiform and vein U,Mo and Cu mineralization in the Novoveská Huta area,CSFR

U-Mo and Cu mineralization occurs in horizons as well as in veins in the Permian formations near Novoveská Huta. Ore mineralization is represented by uraninite, U-Ti oxides, coffinite, molybdenite, chalcopyrite, tennantite and pyrite. The isotopic composition of S and C displays a larger variability in the stratiform ores (³⁴S from –32.7 to +2.7 and ¹³C from –27.1 to — 0.5) These data suggest mixing of meteoric solutions with fluids of volcanic origin and a complex history. There is a narrower range of ³⁴S from –18.8 to –4.6 and ¹³C from –6.3 to –2.5% in quartz-carbonate veins with Cu mineralization suggesting a deep source of ore-bearing solutions. The Permian volcanics were a significant source of ore elements.Their contents of U, Mo, Cu and Y are from two to eight times higher than in sedimentary rocks. Accumulations of ore elements in the horizons were formed by the reduction and adsorption processes 240 ± 30 Ma ago according to U-Pb isotopic dating. Due to Alpine tectonism, these low-grade ores (U<0.1 wt%) were remobilized and higher-grade U-Mo ores (U>0.1 wt%) were formed 130 ± 20 Ma ago at temperatures ranging from 110 to 120° C, according to fluid inclusions. Younger veins with Cu mineralization were formed 115 ± 10 Ma according to the model age of Pb at temperatures ranging from 95 to 190°C.     

Magnetic properties,self-reversal remanence and thermal alteration products of smythite

Summary This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Kruné hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe³⁺ sulphate with a composition of Fe₂(SO₄)₃, oxidation of these sulphides gives rise to -Fe₂O₃. The result of the subsequent decomposition of the mentioned sulphate is the formation of -Fe₂O₃, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is -Fe₂O₃. In the smythite concentrate the conversion to Fe³⁺ sulphate and -Fe₂O₃ is about twice as intensive as in greigite. No direct conversion to -Fe₂O₃ was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10^–2 down to 10^–3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10^–4 down to 10^–6 in the temperature interval of Fe-oxides origin (above 400°C).Presented at the 3rd Conference on New Trends in Geomagnetism, Castle of Smolenice, Czechoslovakia, June 22–29, 1992     

Alkaline and ultramafic carbonate lamprophyres in Central Bohemian carboniferous basins,Czech Republic

Summary Dykes of alkaline and ultramafic carbonate lamprophyres (monchiquite-ouachitite and aillikite) intrude the Carboniferous sediments of Central Bohemia. Their characteristic feature is the presence of substantial amounts of a sodalite group mineral (presumably haüyne), carbonate and barite. Isotopic compositions of ¹³C (–3.4 to –6.2) and ¹⁸O ( + 13.5 to + 15.9) indicate that the carbonate is of primary magmatic origin and that fluids were formed at temperatures of 500 to 350°C. High contents of CO₂ (3.6 to 17.6 wt.%) and incompatible elements, high LREE/HREE ratios (30.0 to 57.7), and low Rb/Sr (0.025 to 0.078) and⁸⁷Sr/⁸⁶Sr (0.7038 to 0.7042) ratios suggest the ultramafic lamprophyres are related to deep-seated carbonated magmas of mantle origin. Low degree of partial melting ( < 1%) of the mantle peridotite is envisaged, with additional transport of fluids rich in incompatible elements into the crustal chamber. Alkaline lamprophyres are fractionated derivatives which originated from the same source. Magma intrusion from different levels of a magma chamber into fracture zones under horizontal tension without a central intrusion could result in variability in lamprophyre composition (cumulates or evolved derivatives).

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Alkalische und ultramafische Karbonat-Lamprophyre der zentralen böhmischen Karbonbecken, Tschische Republik

Zusammenfassung Alkalische und ultramafische Karbonat-Lamprophyrgänge (Monchiquit-Ouachitit und Aillikit) intrudieren in karbonische Sedimente Zentralböhmens. Sie sind charakterisiert durch das Auftreten von beträchtlichen Mengen an Mineralen der Sodalith-Gruppe (v.a. Haüyn), Karbonaten und Baryt. Ihre Isotopenzusammensetzung von ¹³C (–3.4 bis –6.2) und ¹⁸O (13.5 bis 15.9) zeigt, daß die Karbonate primär magmatischen Ursprungs sind und daß assoziierte Fluide in einem Temperaturbereich von 350 bis 500°C gebildet wurden. Hohe Gehalte an CO₂ (3.6 bis 17.6 Gew. %), inkompatiblen Elementen, hohe LREE/HREE-Verhältnisse (30.0 bis 57.7), sowie niedrige Rb/Sr—(0.025 bis 0.078) und⁸⁷Sr/⁸⁶Sr-(0.7038 bis 0.7042) Verhältnisse lassen vermuten, daß die ultramafischen Lamprophyre mit karbonatischen Magmen des Mantels in Beziehung stehen. Eine niedrige Aufschmelzungsrate ( < 1%) von Mantelperidotit mit zusätzlichem Transport von, an inkompatiblen Elementen angereicherten Fluiden, in die krustale Magmenkammer wird diskutiert. Alkalische Lamprophyre sind als stärker fraktionierte Magmen, die derselben Quelle entstammen, zu verstehen. Die Intrusion der aus verschiedenen Bereichen der Magmenkammer stammenden Magmen in durch horizontale Dehnung verursachte Störungszonen könnte das Fehlen eines zentralen Intrusionskörpers und die unterschiedliche Zusammensetzung der Lamprophyre (Kumulate oder entwickelte Derivate) erklären.

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With 8 Figures     

On the tidal variation of the geopotential

In this paper analytical expressions are derived for the temporal variations ofJ ₂ andJ ₂₂ due to the tides of the solid Earth, taking into account only the deformation of the mantle, and employing a procedure already used by the authors in their Hamiltonian theory of the Earth's rotation, which obtain the necessary parameters in a direct way by integration of those provided by a selected model of Earth interior.Numerical tables giving the periodic variation of coefficients are given, as well as a new prediction for UT1. For J ₂ and J ₂₂ the amplitudes reach such a magnitude that both two variations should not be ignored in studies involving the analysis of highly precise satellite tracking data. Moreover, the possibility of improving our knowledge of the value of those harmonic coefficients in only a more exact digit appears as to be strongly dependent on the limitations in the theoretical modeling of the variations of the inertia tensor due to solid tides.     

Dust particle and solar radiation

Influence of the solar radiation (electromagnetic and corpuscular - solar wind) on the motion of the interplanetary dust particle is investigated. The ratio time of inspiralling toward the Sun: time of inspiralling neglecting the change of mass of the particle is presented as a function of initial eccentricities.     

Pristine vs. contaminated trends in Nb,Ta-oxide minerals of the Jihlava Pegmatite District,Czech Republic

Summary Columbite-tantalite is widespread in the lepidolite-subtype rare-element pegmatites of the Jihlava pegmatite district, western Moravia, Czechoslovakia. In most pegmatites, fractionation of columbite-tantalite shows initial enrichment in Mn followed by increasing Ta, in accordance with the usual trend from ferrocolumbite through mangano-columbite to manganotantalite, typical of the lepidolite pegmatites. Many dikes, however, show local deviations toward Fe- and Ti-rich compositions. In extreme cases, all columbite-tantalite is strongly enriched in Fe and Ti, and is associated with ixiolite and tantalian rutile. The degree of enrichment of the Nb,Ta oxide-mineral assemblage in Fe and Ti is proportional to tectonic introduction of wallrock xenoliths of mafic pyroxene-biotite syenite into the pegmatites during late stages of their consolidation. Extensive reaction of the residual pegmatite melt with the xenoliths contaminated the near-by melt, and generated Nb,Ta oxide minerals and tourmaline of non-typical chemistries. Late fersmite probably formed after thermal equilibration of the pegmatites with their syenitic country rocks, from Ca-bearing regional interstitial fluids pervading through the solidified pegmatites.

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Zusammenfassung In Selten-Element Pegmatiten (Lepidolith-Subtyp) des Jihlava Pegmatit Distriktes, West-Mähren, Tschechien, ist Columbit-Tantalit weitverbreitet. In den meisten Pegmatiten führte die Fraktionierung von Columbit-Tantalit zur einer anflinglichen Anreicherung von Mn gefolgt von einer Zunahme in Ta, vergleichbar mit dem für Lepidolith-Pegmatit bekannten Trend Ferrocolumbit-Manganocolumbit-Manganotantalit. Viele Gänge zeigen jedoch lokale Abweichungen zu Fe- und Ti-reichen Zusammensetzungen. In extremen Fällen ist Columbit-Tantalit stark an Fe und Ti angereichert und mit Ixiolith und Tantalo-Rutil vergesellschaftet. Das Ausmaß der Fe und Ti Anreicherung in (Nb,Ta)-Oxid-Assoziationen ist proportional dem tektonisch bedingten Eindringen von maischen Pyroxen-Biotit-reichen Syenit-Nebengesteinsxenolithen in die Pegmatite gegen Ende ihrer Verfestigung. Tiefgreifende Reaktion der Pegmatit-Restschmelze mit den Xenolithen kontaminierte die Schmelze und führte zur Bildung von (Nb,Ta)-Oxid-Mineralen und Turmalin ungewöhnlicher Zusammensetzung. Möglicherweise nach der thermischen Gleichgewichtseinstellung der Pegmatite mit ihren syenitischen Nebengesteinen bildete sich Fersmit unter Beteiligung von Ca-führenden regionalen Porenlösungen, welche die verfestigten Pegmatite durchdrangen.

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With 6 Figures