Transformation of schoepite into the uranyl oxide hydrates: Becquerelite,billietite and wölsendorfite

Summary The transformation of schoepite into becquerelite, billietite and lead diuranate hydrate by direct reaction of Ca²⁺, Ba²⁺ and Pb²⁺ ions on solid schoepite at 60°C is demonstrated. The phases obtained in the experiments were identified by chemical and powder X-ray diffraction analyses.The solubilities of becquerelite and billietite were determined at 25° C as a function of pH. The distribution of the different uranyl hydroxyl complexes is computed and discussed. From the solubilities and uranyl hydroxyl distributions the K_sp's of becquerelite and billietite are calculated.

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Umwandlung von Schoepit in die Uranyl-Oxid-Hydrate Becquerelite, Billietit und Wölsendorfit

Zusammenfassung Die Umwandlung von Schoepit in Becquerelit, Billietit und Bleidiuranat-Hydrat durch die direkte Einwirkung von Ca²⁺, Ba²⁺ und Pb²⁺-Ionen auf festen Schoepit wird bei 60°C demonstriert. Die in den Experimenten erhaltenen Phasen wurden durch chemische Analyse und Röntgen-Pulvermethoden identifiziert.Die Löslichkeiten von Becquerelit und Billietit wurden bei 25° C als Funktion des pH bestimmt. Die Verteilung der verschiedenen Uranylhydroxyl-Komplexe wurde berechnet und wird diskutiert. Aus den Löslichkeiten `und den Uranylhydroxyl-Verteilungen werden die K_sp's von Becquerelit und Billietit berechnet.

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Kamchatka subduction zone,May 2013: the Mw 8.3 deep earthquake,preceding shallow swarm and numerous deep aftershocks

A sequence of 98 teleseismically recorded earthquakes occurred off the east coast of Kamchatka at depths between 10-90 km around latitude 52.5°N and longitude 160°E on May 16–23, 2013. The swarm occurred along the northern limit of the rupture area of the 1952 M_w 9.0 great Kamchatka earthquake, the fifth largest earthquake in the history of seismic observations. On May 24, 2013 the strongest deep earthquake ever recorded of M_w 8.3 occurred beneath the Sea of Okhotsk at a depth of 610 km in the Pacific slab of the Kamchatka subduction zone, becoming the northernmost deep earthquake in the region. The deep M_w 8.3 earthquake occurred down-dip of the shallow swarm in a transition zone between the southern deep and northern shallow segments of the Pacific slab. Several deep aftershocks followed, covering a large, laterally elongated part of the slab. We suppose that the two described earthquake sequences, the May 16–23 shallow earthquake swarm and the May 24–28 deep mainshock-aftershock series, represent a single tectonic event in the Pacific slab having distinct properties at different depth levels. A low-angle underthrusting of the shallow part of the slab recorded by the shallow earthquake swarm activated the deep part; this process induced the deep mainshock-aftershock series only three days after the swarm. The domain of the subducting slab activated by the May 2013 earthquake occurrence was extraordinarily large both down-dip and along-strike.     

The magnesium and calcium contents of sediments,especially pelites,as a function of age and degree of metamorphism

The silicate and carbonate fraction of 98 non-metamorphic shale samples from the Australian platform and of different geological age were analysed for calcium, magnesium, ferrous iron and carbonate. Cainozoic and Mesozoic shales prove to be essentially calcitic, Cambrian and Proterozoic shales are essentially dolomitic and sideritic. A similar trend of high MgO values can be demonstrated for the silicate fraction of the old shales. Extensive literature study confirms these trends for shales and carbonate rocks from all over the world. Slates, hornfelses and schists are Mg rich and Ca poor, whether young or old.Ronov's model of the evolution of the earth's crust ocean and atmosphere, explaining these trends, is critically reviewed but rejected because of impossible storage problems of calcium in the Proterozoic. The increased magnesium content of the old sediments is explained by calcium carbonate sweating out of the sedimentary column, magnesium introduction from altering volcanic rocks within the sedimentary pile and magnesium introduction from connate brines in sandstones. The increasing calcium content of all kinds of sediments with decreasing age is claimed to be related to preferential weathering of extrusive volcanic rocks and sweating out of calcium carbonate from the sedimentary column.     

First samples of acoustic basement recovered from the alpha ridge, Arctic ocean: New constraints for the origin of the ridge

The Alpha Ridge is one of three subparallel trending ridges that cut the Arctic Ocean. It is roughly Late Cretaceous to Eocene in age, and seismic refraction records suggest it comprises a thick sequence of oceanic crust. During the 1983 CESAR expedition 20 similar samples of acoustic basement were dredged from the walls of a major graben of the Alpha Ridge, at one site. These are the only basement samples ever recovered from the ridge and provide the first direct evidence for its nature, composition and possible origin.The basement samples are highly altered pyroclastic rocks composed almost entirely of basaltic volcanic clasts with little matrix. Although the rocks are highly altered, most primary textures and structures are preserved. Most clasts are highly amygdaloidal to scoriaceous, fine grained to glassy, and angular to subround with rare vesicle controlled boundaries. Little reworking is suggested because a single clast type predominates, many of the clasts are subangular, and any amount of reworking would result in destruction of the delicate scoriaceous clasts.Rare clinopyroxene phenocrysts comprise the only unaltered portion of the rocks. They are salitic in composition (Wo_49–53, En_32–41, Fs_11–15), with significant amounts of Ca, Al and Ti. Salitic clinopyroxenes are typical of alkalic basalts.Interpretation of the whole rock geochemistry based on relatively immobile elements, (Nb, Zr, Tio₂, and Y), and chondrite-normalized incompatible trace element and REE patterns indicates that the volcanic rock fragments are of alkalic basalt. Geochemical discriminators suggest a within-plate tectonic setting.Textural evidence suggests that the CESAR basement rocks were sampled from a rapidly emplaced submarine fallout deposit that was erupted at a depth at least less than 800 m and likely less than 200 m. High extrusive rates would have been required to build the ridge up to shallow depth prior to the cessation of volcanism. The alkalic affinity of the rocks strongly suggests that the Alpha ridge was not formed by volcanism at an island arc or a mature spreading centre. It is also unlikely that it formed as a “leaky” fracture zone. Alkalic basalts, however, are commonly associated with various types of oceanic aseismic ridges. It is suggested that the Alpha Ridge is an aseismic ridge that formed due to voluminous hotspot volcanism as spreading began in the Canada Basin. Such hotppot activity may have been responsible for initiating the rifting, breakup, and dispersal that eventually formed the Canada Basin.     

Massive stars

We describe the present state of massive star research seen from the viewpoint of stellar evolution, with special emphasis on close binaries. Statistics of massive close binaries are reasonably complete for the Solar neighbourhood. We defend the thesis that within our knowledge, many scientific results where the effects of binaries are not included, have an academic value, but may be far from reality. In chapter I, we summarize general observations of massive stars where we focus on the HR diagram, stellar wind mass loss rates, the stellar surface chemistry, rotation, circumstellar environments, supernovae. Close binaries can not be studied separately from single stars and vice versa. First, the evolution of single stars is discussed (chapter I). We refer to new calculations with updated stellar wind mass loss rate formalisms and conclusions are proposed resulting from a comparison with representative observations. Massive binaries are considered in chapter II. Basic processes are briefly described, i.e. the Roche lobe overflow and mass transfer, the common envelope process, the spiral-in process in binaries with extreme mass ratio, the effects of mass accretion and the merging process, the implications of the (asymmetric) supernova explosion of one of the components on the orbital parameters of the binary. Evolutionary computations of interacting close binaries are discussed and general conclusions are drawn. The enormous amount of observational data of massive binaries is summarized. We separately consider the non-evolved and evolved systems. The latter class includes the semi-detached and contact binaries, the WR binaries, the X-ray binaries, the runaways, the single and binary pulsars. A general comparison between theoretical evolution and observations is combined with a discussion of specially interesting binaries: the evolved binaries HD 163181, HD 12323, HD 14633, HD 193516, HD 25638, HD 209481, Per and Sgr; the WR+OB binary V444 Cyg; the high mass X-ray binaries Vela X-1, Wray 977, Cyg X-1; the low mass X-ray binaries Her X-1 and those with a black hole candidate; the runaway Pup, the WR+compact companion candidates Cyg X-3, HD 50896 and HD 197406. We finally propose an overall evolutionary model of massive close binaries as a function of primary mass, mass ratio and orbital period. Chapter III deals with massive star population synthesis with a realistic population of binaries. We discuss the massive close binary frequency, mass ratio and period distribution, the observations that allow to constrain possible asymmetries during the supernova explosion of a massive star. We focuss on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given to the O-type star/WR star/red supergiant star population, the pulsar and binary pulsar population, the supernova rates. Received 17 July 1998     

Comment on “Parent body depth‐pressure‐temperature relationships and the style of the ureilite anatexis” by P. H. Warren (MAPS 47:209–227)

Ureilites are carbon‐rich ultramafic (olivine + dominantly low‐Ca pyroxene) achondrites with poorly understood petrogenesis. One major problem concerns the origin of extensive variation in FeO content (olivine core Fo values ranging from approximately 75 to 95) among the individual ureilites. The two main competing hypotheses to explain this variation are: (1) equilibrium smelting, in which ureilite Fo values were established by pressure‐dependent (depth‐linked) carbon redox reactions on the ureilite parent body during partial melting; or (2) nebular inheritance, in which the variation in FeO contents was derived from ureilite precursors and was preserved during partial melting. The paper “Parent body depth‐pressure‐temperature relationships and the style of the ureilite anatexis” by Warren (2012) discusses a series of topics related to ureilite petrogenesis. In each case, an argument is presented within the context of smelting versus nonsmelting models. Collectively, these arguments create the impression that there are many valid arguments against smelting. The purpose of this comment is to point out flaws in some of these arguments, and/or to show that the issues they address are independent of smelting versus nonsmelting models. Both equilibrium smelting and nebular inheritance (simple anatexis) models face challenges in explaining all the properties of ureilites, but both remain viable.     

Radio,X-ray,and optical observations of the flare of June 13, 1980, at 6h22m UT

A subflare of importance Sf was observed on June 13, 1980 simultaneously by instruments aboard the Solar Maximum Mission (SMM) and various ground based observatories. We describe and compare different kinds of observations, with emphasis on the Hard X-Ray Imaging Spectrometer (HXIS) images and spectra, and on the one-dimensional microwave images with high time and spatial resolution, obtained with the Westerbork Synthesis Radio Telescope (WSRT). The fast electrons causing the X-ray and microwave impulsive bursts had a common acceleration source, but the burst were produced at the opposite footpoints of the loops involved, with microwaves emitted near to a sunspot penumbra. The flare (of a ‘compact’ type) was probably triggered by an emerging flux, and two possible interpretations of this process are briefly discussed.