Volcanology and petrology of the Assab Range (Ethiopia)     

M. De Fino  L. La Volpe  L. Lirer 《Bulletin of Volcanology》1973,37(1):95-110

The results of petrological and volcanological investigations of the Assab area (Ethiopia) are reported. Fissure activity — which produced basaltic lava flows and several spatter cones — and central activity — represented by a cumulus dome and two explosive craters — have been recognized. The area is characterized by E-W and NE-SW tectonic trends, whereas the NNW-SSE « Eritrean trend » is absent. Transverse tectonics is limited to the blocks bordering the Danakil Depression, and never extends into the Depression itself. Mineralogical composition and chemical data point to an alkaline nature of the Assab lavas, which have been classified as: picritic basalts tending to ankaramites; alkali olivine basalts; hawaiites; and all the rock types ranging from mugearites to trachytes. Two rock groups have been identified which could be due to crystal fractionation processes controlled by different degree of oxidation. The petrological difference between the rocks from Afar proper and those from the Danakil block (unquestionably alkaline rock types in the Danakil block, and transitional rock types in Afar) is emphasized.  相似文献   

TheT e-T n difference in the lowerE region and radio-wave absorption     

Jan Laštovička  Reviewer J. Prokop 《Studia Geophysica et Geodaetica》1981,25(3):294-296

Summary The difference observed between the electron temperature, T _e , and the neutral atmosphere temperature, T _n , is shown to be able to contribute significantly to the observed variability of ionospheric radio-wave absorption (A1 andHF-A3 measurements).  相似文献   

Chloritoid stability in very iron-rich altered pillow lavas   总被引：2，自引：0，他引：2  

Timothy E. La Tour  R. Kerrich  R. W. Hodder  R. L. Barnett 《Contributions to Mineralogy and Petrology》1980,75(2):165-173

Conclusions Our major conclusions are that the strong correlation of P₂O₅ and light REE abundances in basalts does not (a) require residual apatite or whitlockite during partial melting, or (b) imply that P₂O₅ and REE-rich magmas are derived from more refractory sources than the source of magmas with lower P₂O₅ and REE contents.  相似文献   

Trace elements in tentacles from the jellyfish Pelagia noctiluca     

Giuseppe Cimino  Maria Alfa  Giuseppina La Spada 《Marine pollution bulletin》1983,14(5):197-198

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Nitric oxide concentration near the mesopause as deduced from ionospheric absorption measurements     

J. Laštovička 《Pure and Applied Geophysics》1982,120(4):607-614

Nitric oxide concentration in the upper D-region is estimated by comparing empirically derived ratios of Lyman- and X-ray contributions to the total radio-wave absorption (2775 kHz. A3 method) in medium latitudes with model ratios. Typical NO concentrations are about 8.5×10¹³ m^–3, at 90 km and 6.5×10¹³ m^–3 at 78 km. These values are higher than generally accepted model NO concentrations, but lie within the broad range of experimental values.  相似文献   

Diurnal asymmetry in the lower ionosphere — seasonal variability     

Jan Laštovička  Reviewer J. Prokop 《Studia Geophysica et Geodaetica》1978,22(3):309-313

Summary On the basis of long period measurements of ionospheric absorption in five A3 circuits in Central Europe, it is shown that the considerable seasonal variation of the diurnal asymmetry of absorption, found in[1], exhibits practically no year-to-year variability and is well-developed at equivalent frequencies f _eq 1 MHz, while it vanishes at F _eq 2 MHz. The limited data on the diurnal asymmetry of the D-region electron concentration are consistent with the seasonal pattern of the diurnal asymmetry in absorption. A tentative hypothesis of nitric oxide variability as the cause of the seasonal variation of the asymmetry is proposed.  相似文献   

A3 ionospheric absorption measurements at 1538 kHz — first results     

Jan Laštovička  Reviewer J. Prokop 《Studia Geophysica et Geodaetica》1978,22(4):390-401

Summary A series of absorption measurements covering more than two years, carried out by the A3 method (oblique incidence) on 1538 kHz at the Panská Ves Observatory, is studied. The measuring equipment is shortly described, as well as calibration and the measuring path. Both the diurnal variation of absorption, including its asymmetry, and the seasonal variation of absorption, including the winter anomaly, are observed in a predicted form. The computed height profile of absorption shows that nearly all the absorption is formed in the middle and upper D-region. The 1538 kHz absorption measurements could serve as a very good tool for studying the D-region, but there are still some difficulties attributed to the determination of the zero level of absorption. Suggestions are given how to remove this difficulty.  相似文献   

On the noon asymmetry of the diurnal variation of radio wave absorption     

Jan Laštovička  Reviewer J. Prokop 《Studia Geophysica et Geodaetica》1975,19(3):275-281

Summary The assymetry of the diurnal variation of radio-wave ionospheric absorption, measured by the A3 method on the 2775 kHz Kiel — Panská Ves circuit, is studied. Almost full symmetry of absorption is observed in winter and autumn. It is explained by electron concentration variations. A remarkable diurnal asymmetry of absorption is observed in spring and particularly in summer. The observed diurnal asymmetry of the electron concentration seems to be insufficient to account completely for the great absorption asymmetry observed.  相似文献   

The electrical conductivity of eclogites measured by two methods     

Marcela Laštovičková  Reviewer J. Buben 《Studia Geophysica et Geodaetica》1975,19(4):394-398

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Crystallization trends of pyroxenes from alkaline subvolcanites of Punta delle Pietre Nere (Gargano,Southern Italy)     

Maria De Fino  L. La Volpe  G. Piccarreta 《Mineralogy and Petrology》1982,29(3):177-192

Summary The results of microprobe analyses of clinopyroxenes from alkaline melasyenites and layered melagabbros, produced by intra-plate magmatism of Paleocene age at Punta delle Pietre Nere, are here given and discussed.The analysed pyroxenes range from diopsidic to acmite-rich compositions.The first crystallized pyroxenes (diopside) show Al^VI contents suggesting shallow depths of crystallization. In addition pyroxenes from melasyenite and those from melagabbro display different Cr contents, Al/Ti and Mg/(Mg+Fe²⁺+Fe³⁺) ratios confirming their crystallization from melts produced by different parental liquids.Diopsides and salites show an overall trend towards high Al, Ti and Fe³⁺, suggesting that the crystallization occurred under decreasing SiO₂/Al₂O₃ ratios and under relatively highpH₂O–pO₂ conditions.Pyroxenes from the Pietre Nere melasyenite show a progressive variation towards acmite rich compositions at Mg/(Mg+Fe²⁺+Fe³⁺) lower than 0.5; those from the layered melagabbro, instead, show a continuous enrichment in Ca Fe³⁺ AlSiO₆. This different behaviour is due to the co-crystallization, with the latest pyroxenes, of phases with different K/Na and Si/Al ratios.

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Kristallisations-Tendenzen der Pyroxene aus Alkali-Subvulkaniten auf Punta delle Pietre Nere (Gargano, Süditalien)

Zusammenfassung Es werden die Ergebnisse der Mikrosonden-Untersuchungen von Klinopyroxenen aus Alkali-Melasyeniten und schichtigen Alkali-Melagabbros, die durch Intra-plate-Magmatismus paläozenen Alters auf Punta delle Pietre Nere entstanden sind, beschrieben und erörtert.Die untersuchten Pyroxene reichen von diopsidischen bis zu Akmit-reichen Zusammensetzungen.Die zuerst kristallisierten Pyroxene (Diopsid) zeigen Al^VI-Gehalte, die auf geringe Tiefe des Kristallisationsvorganges hinweisen. Dazu zeigen die Pyroxene aus dem Melasyenit und aus dem Melagabbro unterschiedliche Cr-Gehalte; die Al/Ti- und Mg/(Mg+Fe²⁺+Fe³⁺)-Verhältnisse bestätigen deren Kristallisation aus Schmelzen, die aus unterschiedlichen Ursprungsmagmen stammen.Die Diopside und Salite zeigen eine einheitliche Tendenz zu hohem Al-, Ti- und Fe³⁺-Gehalt; dies deutet darauf hin, daß die Kristallisation unter abnehmenden SiO₂/Al₂O₃-Verhältnissen und unter relativ hohenpH₂O–pO₂-Bedingungen stattfand.Die Pyroxene aus dem Punta delle Pietre Nere-Melasyenit zeigen eine zunehmende Änderung zu Akmit-reichen Zusammensetzungen bei weniger als 0,5 Mg/(Mg+Fe²⁺+Fe³⁺); die Pyroxene aus dem schichtig differenzierten Melagabbro zeigen dagegen eine allmähliche Zunahme von CaFe³⁺AlSiO₆. Dieses unterschiedliche Verhalten rührt daher, daß Mineralphasen mit unterschiedlichen K/Na- und Si/Al-Verhältnissen zugleich mit den zuletzt gebildeten Pyroxenen kristallisierten.

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With 6 Figures  相似文献