Sizes, shapes, and albedos of the inner satellites of Neptune

Based on 87 resolved Voyager images of the five innermost satellites of Neptune, their shapes were measured and fit by tri-axial ellipsoids with the semi-axes of 48 × 30 × 26 km for Naiad, 54 × 50 × 26 km for Thalassa, 90 × 74 × 64 km for Despina, 102 × 92 × 72 km for Galatea, and 108 × 102 × 84 km for Larissa. Thomas and Veverka published a similar shape for Larissa (104 × 89 km, J. Geophys. Res. 96, 19261-19268, 1991). The other satellites had no published shapes. Using Voyager photometry of the six inner satellites by the same authors and the revised sizes, including the published size of Proteus, the reflectivity within this inner system was found to vary by about 30%. Geometric albedos in the visible are estimated between 0.07 for Naiad and 0.10 for Proteus. The rotational lightcurves of these satellites seem to be due to satellite shapes.     

Zur weiteren Kennzeichnung der Grüngesterne in der Bernsteiner Zone der Rechnitzer Serie

Ohne ZusammenfassungMit 10 TextabbildungenHerrn Prof. DDR.H. Wieseneder danke ich für die Aufnahme des größten Teiles der Mikrolichtbilder.     

New Apparatus and Experimental Setup for Long-Term Swelling Tests on Sulphatic Claystones

An apparatus and experimental setup were developed to carry out a series of extremely slow and long-lasting swelling, creep or chemo-mechanics tests simultaneously. The equipment was designed specifically for investigating the behaviour of sulphatic claystones. The tests will take at least 10–15 years to complete and will provide unprecedented information about the so-called swelling law, i.e. the relationship between swelling strain and swelling stress. The swelling law is very important for designing tunnels in swelling rock. Our knowledge of the swelling law, however, is only sufficiently reliable with respect to claystones without anhydrite (e.g. marls, opalinus clay). The swelling law for sulphatic claystones remains unknown, even in qualitative terms. This is due to the underlying physico-chemical mechanisms, which are fundamentally different from those of purely argillaceous rocks. Another reason is the extremely long duration of the swelling process of clay-sulphate rocks, which makes systematic field or laboratory investigations very difficult. In order to close this knowledge gap, a series of 25 long-term simultaneous swelling tests has been started.     

Die Ausbildung der Geologen muß ergänzt werden

Ohne Zusammenfassung     

Diapirism during regional compression: The structural pattern in the Chibougamau region of the archean Abitibi belt,Québec

The major fold pattern of the Chibougamau region in the Archean Abitibi Belt, Quebec, is the result of two fold phases. The principal F₁-synclines first formed as subsiding fault troughs, and were shortened in NS direction and molded around volcanic centers that had been consolidated by large synvolcanic plutons; they have a general easterly direction but curve locally to the NE or SE. N-trending F₁-folds are locally present in the anticlinoria and are thought to have been produced by the upwelling of basement gneiss and/or synvolcanic plutons. The F₂-folds have rather regular easterly trends; their axial plane schistosity S₂ is the predominant planar fabric element. Basin margin faults were transformed into east-trending thrust faults during the F₁- and F₂-folding.The superposed schistosities S₃ and S₄ are conjugate shear planes related to NS shortening. They and the kink bands produce only minor strain except at a few localities. Synkinematic and late kinematic diapiric plutons pierce the structural pattern. The F₁-folds, derived from the paleogeographic pattern during the uplift of volcanic islands and during the subsidence of fault basins, may also be interpreted as diapiric. Thus, diapirism took place during the whole period of NS compression.ENE trending left-lateral shear belts and their associated first and second order faults, displaced the Kenoran structures in late Archean and early Proterozoic time.

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Zusammenfassung Der Faltenbau des Chibougamaugebietes im Archaischen Abitibi Belt, Quebec, ist das Resultat zweier Faltungsphasen. Die gro\en F₁-Synklinalen bildeten sich zuerst als absinkende Verwerfungströge, die später in NS-Richtung eingeengt wurden und gleichzeitig dabei an die verfestigten Vulkanzentren gepre\t wurden. Die gro\en synvulkanischen Plutone konsolidierten die vulkanischen Zentren. Die F₁-Falten streichen generell OW, biegen aber lokal in NO- und SO-Richtung um. Nord-streichende F₁-Falten finden sich lokal in den Antiklinorien und werden auf das Aufsteigen der basalen Gneisse und/oder der synvulkanischen Plutone zurückgeführt. Die F₂-Falten haben ein regelmä\iges Ost-Streichen; ihre der Faltenachsenfläche parallele Schieferung S₂ ist das deutlichste planare Strukturelement. Die Randbrüche der Verwerfungsbecken wurden während der F₁- und F₂-Faltungsphase in Oststreichende überschiebungen umgewandelt. Die S₃ und S₄-Schieferungen sind konjugierte Scherflächen in NS-Kompression. S₃ und S₄ und die Knickbänder verursachen nur lokal eine erhebliche Verformung. Synkinematische und spätkinematische Plutone durchbrechen diese Strukturen und die F₁-Falten, erzeugt durch den Aufstieg von Vulkaninseln und das Absinken von Verwerfungsbecken können ebenfalls als diapirische Strukturen gedeutet werden. Der Diapirismus überdauerte die ganze Periode der NS-Kompression.Linkshändig rotierte ONO-streichende Scherzonen und die dazugehörigen Verwerfungen erster und zweiter Ordnung versetzen die Kenorischen Strukturen während des späten Archaikums und des frühen Proterozoikums.

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Résumé Les plis majeurs de la région de Chibougamau dans la ceinture Archéenne de l'Abitibi au Québec sont le résultat de deux phases de plissement. Les synclinaux F₁ majeurs prenaient naissance comme bassins de faille subsidents et furent comprimés en direction NS. Ils furent moulés autour des centres volcaniques qui avaient été consolidés par des plutons synvolcaniques; leur direction générale est est-ouest mais ils s'incurvent localement vers le NE ou vers le SE. Des plis F₁ de direction N sont présents localement dans les anticlinoria et nous pensons qu'ils sont le résultat de l'ascension diapirique du gneiss du socle et des plutons synvolcaniques. Les plis F₂ ont une direction EO assez régulière; leur schistosité de plan axial (S₂) est l'élément structural planaire prédominant. Les failles en bordure des bassins de subsidence furent transformées en chevauchement lors des phases de plissement F₁ et F₂.Les schistosités superposées S₃ et S₄ sont des surfaces de cisaillement conjugées en compression NS. Ces schistosités et les plis en chevron ne sont pas responsables d'une déformation substantielle, sauf à quelques endroits. Des plutons diapiriques d'âge syn-cinématique à tardi-cinématique percent ce patron structural. Le patron des plis F₁, déterminé par le patron paléogéographique durant le soulèvement d'Îles volcaniques et la subsidence des bassins de faille peut aussi Être interprété comme une structure diapirique. Des ceintures de cisaillement senestre en direction ENE et leur cortège de failles de premier et deuxième ordre ont déplacé les structures Kénoréennes tard dans l'Archéen et tÔt dans le ProtérozoÏque.

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A comparison of Miocene and Archean rhyolite hyaloclastites: Evidence for a hot and fluid rhyolite lava

In this paper, we compare the geology and petrography of Miocene and Archean submarine rhyolite hyaloclastites. The hyaloclastites are sparsely (10% or less) plagioclase- (± quartz and pyroxene-) phyric. The hyaloclastites consist of a feeder dyke from which branch lava lobes and irregularly shaped lava pods. The lava bodies consist of a holocrystalline core with microlitic texture, grading outward into a flow-layered rim zone and, finally, into obsidian. The proportion of plagioclase and pyroxene microlites decreases outward. Some layers of the rim zone may be pumiceous (vesicularity up to 50%, vesicle size 1 mm or less), but most of the lava has less than 5% vesicles one or a few cm long. The obsidian shows perlitic fracture patterns. The lava bodies grade through an in-situ breccia into a hyaloclastite composed of angular obsidian granules and, in many cases, of fragments of lava lobes.Evidence for alteration at high temperature is as follows: in the Archean rhyolite hyaloclastites, plagioclase microlites are overgrown by quartz-albite spherulites. Furthermore, parts of the Miocene and Archean hyaloclastite have been cemented and granules have been marginally replaced by quartz and albite. Hyaloclastite cemented at high temperature locally shows columnar joints. At low temperatures, obsidian has been hydrated and/or has been replaced by clay minerals, zeolites, chlorite or prehnite. “Chess-board” albite and fibroradial prehnite in Archean hyaloclastite is possibly a pseudomorph after zeolites.The sparsely porphyritic nature of the lava and the absence of microlites from the quenched glass suggests that the thyolite hyaloclastites extruded at high (near liquidus) temperature. Furthermore pumice is present only locally, in the flow-layered rim zone and in fragments derived from that zone. These features suggest that vesiculation was inhibited by the weight of the water column. High temperature and possibly the volatile (H₂O) content explain the relatively low viscosity and shear strength of the lava, and resulted in the flow morphology particular to this type of hyaloclastic rhyolite flows.