Synthesis, properties and stability of end member boromuscovite, KAl2[BSi3O10](OH)2

End member boromuscovite, with nearly the ideal composition, was synthesized as a single phase from mixtures of its own composition, or with excess boron and water, at high pressures of between 15 and 30 kbar at 700 °C. The mica synthesized consists of a mixture of 2M₁ and 1M polytypes with the cell dimensions of 2M₁: a=5.071(4), b=8.786(4), c=19.830(89) Å, #=95.84(12)°, V=878.5(1.4) ų; and 1M: a=5.059(5), b=8.819(6), c=10.025(17) Å, #=101.39(57)°, V=438.4(1.3) Å. The IR spectrum shows characteristic differences relative to that of muscovite. DTA registers an endothermic peak due to dehydration breakdown above 680 °C. Seeded experiments indicate that boromuscovite is a high-pressure phase requiring minimum pressures of 3 to 10 kbar at temperatures that concomitantly increase from 300 to 750 °C. At lower pressures, the anhydrous solid assemblage K-feldspar + Al-borate (probably Al₄B₂O₉) coexists with a vapor rich in boric acid. The conversion of this assemblage to boromuscovite is connected with increases in the coordination number of B from [3] to [4], and of Al from [4] to [6]. Above 10 kbar, the boromuscovite stability field is limited along its high-temperature side by congruent (or incongruent?) melting of the mica, starting near 750 °C and 10 kbar and increasing to about 900 °C at 50 kbar, although, at such very high pressures a supercritical fluid may be present. Because, even in the presence of excess-boron fluid, the synthetic mica shows invariable X-ray properties, it is concluded that one B atom per formula unit represents the maximum, and - contrary to olenitic tourmalines - no further substitution of Si by B linked with addition of hydrogen takes place. In contrast to muscovite, KAl₂[AlSi₃O₁₀](OH)₂, end member boromuscovite is not stable under normal P-T conditions of the Continental Crust along a 30 °C/km geotherm, and especially not during the intrusion of acidic igneous rocks including their pegmatites, which may explain its scarcity in nature. However, it may form in the waning hydrothermal stages of deep-seated (>10.5 km) pegmatites and - providing sufficient boron is available - in HP/LT subduction zone environments, where it may carry boron to considerable depths.     

Mondkraterformationen auf der Erde

Zusammenfassung Es wird gezeigt, dass wir einige irdische Vulkankrater kennen, deren morphologischer Aufbau nahezu identisch ist mit den typischen Formen der Mondkrater. Auf die Wichtigkeit dieses Befundes für das Problem der Entstehung der Mondkrater wird hingewiesen. Es ist zu vermuten, dass sich auf der Erde noch weitere Beispiele dieser Art werden finden lassen.

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Summary It is shown, that some terrestrial volcanic craters are known, the morphological structure of which is practically identical with the typical shapes of lunar craters. The importance of this relation for the problem of the origin of lunar craters is pointed out. It may be expected, that some more examples of this kind might be found.

     

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

In this article we discuss the importance of high‐resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi‐phase nature of the CGM in low‐redshift galaxies. High‐precision absorption‐line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi‐wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm‐hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ 6374.5 Å and [Fe XIV] λ 5302.9 Å absorption in optical QSO spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transformation of amplitudes and frequencies of precession and nutation of the earth’s rotation vector to amplitudes and frequencies of diurnal polar motion

The temporal change of the rotation vector of a rotating body is, in the first order, identical in a space-fixed system and in a body-fixed system. Therefore, if the motion of the rotation axis of the earth relative to a space-fixed system is given as a function of time, it should be possible to compute its motion relative to an earth-fixed system, and vice versa. This paper presents such a transformation. Two models of motion of the rotation axis in the space-fixed system are considered: one consisting only of a regular (i.e., strictly conical) precession and one extended by circular nutation components, which are superimposed upon the regular precession. The Euler angles describing the orientation of the earth-fixed system with respect to the space-fixed system are derived by an analytical solution of the kinematical Eulerian differential equations. In the first case (precession only), this is directly possible, and in the second case (precession and nutation), a solution is achieved by a perturbation approach, where the result of the first case serves as an approximation and nutation is regarded as a small perturbation, which is treated in a linearized form. The transformation by means of these Euler angles shows that the rotation axis performs in the earth-fixed system retrograde conical revolutions with small amplitudes, namely one revolution with a period of one sidereal day corresponding to precession and one revolution with a period which is slightly smaller or larger than one sidereal day corresponding to each (prograde or retrograde) circular nutation component. The peculiar feature of the derivation presented here is the analytical solution of the Eulerian differential equations.     

Vegetation and hydraulic-morphological interactions at the individual plant, patch and channel scale

Interactions between vegetation, flow and sediment are a key ingredient for the development of vegetated islands in highly dynamic, fluvial alpine ecosystems such as the Tagliamento River, north-east Italy. There has been substantial research on factors influencing the establishment of vegetation and feedback mechanisms between vegetation, hydraulic, and geomorphological processes in such environments. This has yielded the development of conceptual models identifying different trajectories of vegetation and landform development from bare gravel to established floodplain forest. Nevertheless, some of the finer-scale processes underpinning such interactions are not well understood and parameterisation concepts that augment our knowledge from process understanding to quantified data and prediction models are not available until now. This paper identifies mechanisms and parameters of vegetation-flow interaction at the individual scale that are reflected at a patch or even at the channel scale. These mechanisms are reviewed from a multi-disciplinary perspective and concepts and analogies are proposed that provide ideas to progress research towards the development of predictive vegetation-flow models. Such models must incorporate both hydraulic and ecological components and this is demonstrated for a simplified force-bending model of Salicaceae seedlings. The development of such models demands advances in the individual disciplines of hydraulics, morphology, plant ecology and biomechanics, which offers many possibilities for multidisciplinary research between these disciplines.     

Fish and ostracod remains from the Santos Basin (Cretaceous to Recent), Brazil

For the first time, ichthyoliths are described from the Santos sedimentary basin, offshore southern Brazil. Isolated teeth, dermal scales and the first documented otoliths from Cretaceous (Albian) to Recent cuttings from five wells are described. The following groups are represented: Chondrichthyans: Triakidae, Carcharhinidae; Ginglymostomatidae: ?Ginglymostoma sp., Lamnidae indet., Scyliorhinidae; Osteichthyans: Teleostei; Myctophiidae: Diaphus aff. splendidus sp. complex, Diaphus spp., Diaphus cf. garmani, Ceratoscopelus aff. warmingii; Sternoptychidae: Valenciennellus tripunctulatus, teeth of indeterminate Teleostei. The majority of these ichthyofossils represent extant forms, known to occur in the Atlantic Ocean, and are of potential value for stratigraphical correlations between oil‐yielding basins in the region. Ostracods are not well preserved but can be identified to generic level indicating marine environments. The ostracod faunas offer potential for intrabasinal correlation in the Eocene and Oligocene. Copyright © 2002 John Wiley & Sons, Ltd.     

Tropical Atlantic biases and their relation to surface wind stress and terrestrial precipitation

Most coupled general circulation models (GCMs) perform poorly in the tropical Atlantic in terms of climatological seasonal cycle and interannual variability. The reasons for this poor performance are investigated in a suite of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled GCM. The experiments show that a significant portion of the equatorial SST biases in the model is due to weaker than observed equatorial easterlies during boreal spring. Due to these weak easterlies, the tilt of the equatorial thermocline is reduced, with shoaling in the west and deepening in the east. The erroneously deep thermocline in the east prevents cold tongue formation in the following season despite vigorous upwelling, thus inhibiting the Bjerknes feedback. It is further shown that the surface wind errors are due, in part, to deficient precipitation over equatorial South America and excessive precipitation over equatorial Africa, which already exist in the uncoupled atmospheric GCM. Additional tests indicate that the precipitation biases are highly sensitive to land surface conditions such as albedo and soil moisture. This suggests that improving the representation of land surface processes in GCMs offers a way of improving their performance in the tropical Atlantic. The weaker than observed equatorial easterlies also contribute remotely, via equatorial and coastal Kelvin waves, to the severe warm SST biases along the southwest African coast. However, the strength of the subtropical anticyclone and along-shore winds also play an important role.     

Greenhouse Gas Dynamics of an Increased Use of Wood in Buildings in Switzerland

Long-living wood products contribute to the mitigation of climate change in many ways. They act as a carbon pool during their service life, as they withdraw CO₂ from its natural cycle. After their service life, they can stitute for fossil fuels if they are incinerated in adequate furnaces. Furthermore, wood products can stitute for more energy-intense products made of ‘conventional’ materials. This paper quantifies the stitution and pool effects of an increased use of wood in the building sector in Switzerland for the years 2000–2130. Life cycle data on greenhouse gas (GHG) emissions of 12 wood products and their stitutes are used as proxies for relevant building products; this data is linked to the forecasted wood flows for each group of building products in a cohort-model. For the political assessment, GHG effects occurring abroad and in Switzerland are distinguished. The results show that the pool effect of an increased use of long-living wood products is of minor importance, whereas the energetic and material stitution effects are much more relevant, especially on a long-term. For construction products, the Swiss share of the GHG effect related to the material stitution is relatively high, as mainly nationally produced materials are stituted for. For interior products, the Swiss share of the GHG effect related to the material stitution is rather small because mainly imports are stituted for. The results must be considered as rough estimates. Nonetheless, these calculations show that an increased use of wood in the building sector is a valid and valuable option for the mitigation of greenhouse gas emissions and for reaching GHG emission targets in a mid- to long-term. Still, the pool and stitution capacity of an increased use of wood is relatively small compared to the overall GHG emissions of Switzerland.