Foreign meteoritic material of howardites and polymict eucrites

Howardites and polymict eucrites are fragments of regolith breccias ejected from the surface of a differentiated (eucritic) parent body, perhaps, of the asteroid Vesta. The first data are presented demonstrating that howardites contain, along with foreign fragments of carbonaceous chondrites, also fragments of ordinary chondrites, enstatite meteorites, ureilites, and mesosiderites. The proportions of these types of foreign meteoritic fragments in howardites and polymict eucrites are the same as in the population of cosmic dust particles obtained from Antarctic and Greenland ice. The concentrations of siderophile elements in howardites and polymict eucrites are not correlated with the contents of foreign meteoritic particles. It is reasonable to believe that cosmogenic siderophile elements are concentrated in howardites and polymict eucrites mostly in submicrometer-sized particles that cannot be examined mineralogically. The analysis of the crater population of the asteroid Vesta indicates that the flux of chondritic material to the surface of this asteroid should have been three orders of magnitude higher than the modern meteoritic flux and have been comparable with the flux to the moon’s surface during its intense meteoritic bombardment. This provides support for the earlier idea about a higher meteoritic activity in the solar system as a whole at approximately 4 Ga. The lithification of the regolith (into regolith breccia) of the asteroid Vesta occurred then under the effect of thermal metamorphism in the blanket of crater ejecta. Thus, meteorite fragments included in howardites provide record of the qualitative composition of the ancient meteorite flux, which was analogous to that of the modern flux at the Earth surface.     

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Relations between metamorphism and orogeny in a typical section of the Indian Himalayas

Summary A comprehensive geological and petrological investigation has been undertaken in an area of about 10 000 km² in the Indian Himalaya (S-Lahul, Himachal Pradesh). The development of mineral assemblages in metamorphic rocks of medium grade is considered to be a dominant Alpine event, although almost exclusively Paleozoic and Precambrian rocks have been involved. The Barrowian type of this metamorphism, ranging from the anchi- to the sillimanite zone, took place under the elavated T-gradient of about 4°C/100 m. It is suggested that normal geothermal conditions prevailed only in the outermost zone of this orogenic belt. In the Late Tertiary this metamorphic series has been moved as a huge nappe upon the Lower Himalaya. During this process a unique feature of reverse metamorphism has been formed. It can be shown that this feature was caused by a combination of metamorphism and very rapid tectonic movements.

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Beziehungen zwischen Metamorphose und Orogenese in einem typischen Querschnitt des Indischen Himalaya

Zusammenfassung Ein etwa 10 000 km² großes Gebiet des Indischen Himalaya (S-Lahul, Himachal Pradesh) wurde einer umfassenden geologischen und petrographischen Bearbeitung unterzogen. Die Ausbildung der in den mittelgradig metamorphen Gesteinen vorliegenden Mineralparagenesen wird als ein dominant alpines Ereignis betrachtet, obwohl fast nur paläozoische und präkambrische Gesteine einbezogen wurden. Die Metamorphose selbst ist von Barrow-Typus und reicht von der Anchi- bis zur Sillimanitzone. Sie fand unter einem erhöhten Temperaturgradienten von etwa 4°C/100 m statt. Nur in der äußersten Zone des Orogens entsprach der Gradient etwa normalen geothermischen Verhältnissen. Im Spättertiär wurde diese alpin-metamorphe Serie in Form einer mächtigen Kristallindecke dem Niedrigen Himalaya aufgeschoben. Dabei wurde eine einzigartige Zone inverser Metamorphose ausgebildet. Es konnte gezeigt werden, daß diese inverse Metamorphose durch das Zusammenwirken von Metamorphose und sehr rasch ablaufender Tektonik entstand.

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With 13 Figures

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Dedicated to Prof. Dr. Dr. h. c.B. Sander on the occasion of his 90th birthday.     

Wolkenklassifikation auf Morphologischer Grundlage

Zusammenfassung Es wird eine Wolkensystematik vorgeschlagen auf Grund der Wolkenform, der struktur — Verband — des Wolkenhimmels und auf Grund der räumlichen Verteilung der Wolken. Jede an einer Einzelwolke selbständig auftretende Form wird als Hauptform bezeichnet und folgende Typen werden genannt: Schicht, Scheier, Faser, Welle, Linse, Balle, Flocke, Haufen (Cumulus) und Dorn. Andere, dem Verfasser bisher unbekannte Formen könnten dazugefügt werden. Zwischen den Hauptformen treten alle möglichen Uebergänge auf, die noch mit der nicht dominierenden Hauptform, Nebenform genannt, charakterisiert werden. Zusätzliche Formen-elemente, die aber nicht selbständig auftreten können, werden Spielformen genannt (Mammatus etc.).Auf die Bedeutung der Verbandsverhältnisse und der räumlichen Anordnung wurde in Beispielen hingewiesen. Die klare Unterscheidung zwischen Form, Verband und Anordnung gestattet, Wolkenbestimmungstabellen zu erstellen.

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Summary The author proposes a systematical cloud classification according to their form (shape), their association (structure) and their repartition on the sky. Every form of a single cloud which appears independent of other forms is called main form or main shape. The following forms can be distinguished: layer, wave, lens, veil, thred, bale, flake, cumulus, thorn. Other forms may be added if necessary. All possible combinations of forms are to be found inbetween the main forms, so that there will be a secondary form next to the mainform (e. g. wave-lens). Additional forms which exist only together with main or secondary forms are details (e. g. mammatus). Some examples given in this study show the importance of combination's assembly and their repartitition in space. A clear difference made between the form, association and repartition allows to establish a convenient way of determining the clouds.

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Résumé L'auteur propose une classification des nuages d'après leur forme, leur structure (assemblage) et aussi d'après leur répartition dans l'espace. L'allure d'un nuage indépendant donne sa forme principale définie comme suit: couche, voile, veine, vague, lentille, balle, flocon, cumulus et pointe. D'autres formes peuvent être ajoutées. Entre les formes principales se trouvent toutes les combinaisons possibles qui ne sont pas dominantes, elles sont nommées les formes secondaires. Des états supplémentaires qui ne sont pas indépendants, constituent le jeu des formes.

     

Gedenktage

Ohne Zusammenfassung     

Temperature of cometary dust

The variation of the dust temperature with heliocentric distance for a comet is calculated using the optical constants of an astronomically important silicate.     

Behavior of Titan's atmosphere during a total eclipse

The edge-on presentation of Saturn's rings and satellites system has provided a rare opportunity to observe total eclipses of Titan. During its emersion from the Saturnian shadow (1980, June 28), Titan has been observed simultaneously in the visible and the infrared ranges (6000–9000 Å, 11.8 μm and 20 μm). No change has been recorded in these three spectral ranges. Our observations tend to support the thick-atmosphere model, which has been shown to be valid by Voyager a few months later.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Depleted lithosphere from the mantle wedge beneath Tres Lagos, southern Patagonia, Argentina

Anhydrous spinel lherzolite and harzburgite xenoliths from Tres Lagos, situated inboard of the Volcanic Arc Gap (VAG) in southernmost Patagonia, are samples of a depleted lithospheric mantle and can be divided into two major groups: metasomatized and non-metasomatized. Metasomatized samples, which are the minority, are partly mylonitized and their metasomatism is related to this tectonic process. A group of non-metasomatized samples have enriched whole rock LREE-abundances that are not consistent with the depleted LREE-abundances in their clinopyroxenes. Intergranular host basalt infiltration could be responsible for the whole rock LREE enrichments. Their Sr- and Nd-isotopic ratios have also been affected by host basalt infiltration, whereas their high Sr-isotopic ratios point to subsequent contamination by ground-water and/or Ca-rich surface solutions. Similar contamination is thought to cause the decoupling of Sr- and Nd-isotopes (high Sr- and Nd-isotopic ratios) observed in the non-metasomatized samples with depleted whole rock LREE. A two-stage partial melting process could be responsible for the origin of the Tres Lagos xenoliths. Model calculations have shown that in the first stage, 2% of batch melting took place in the garnet peridotite field and subsequently the residue experienced 2–8% batch melting in the spinel peridotite field. The Tres Lagos peridotites have not been affected by subduction-related metasomatic processes and they could represent an old lithospheric mantle.