Injection and arrest of dykes: implications for volcanic hazards

Dykes are the principal channels through which magma reaches the surface in volcanic eruptions. For this reason dykes observed in the field are commonly assumed to be feeders to lava flows. The actual proportion of dykes reaching the surface is, however, poorly known. In order to develop models for the purpose of estimating volcanic hazard, this proportion must be known. This follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes, but also the probability of the injected dykes being arrested. This paper presents field data on several thousand dykes from Iceland and Tenerife (Canary Islands) indicating that many, and probably most, dykes become arrested at various crustal levels and never reach the surface to feed eruptions. Using the results of analytical and numerical models, it is shown that, for common loading conditions, the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest. This means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested. The implication is that during periods of unrest in volcanoes, the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber.     

Correction for distortions of magnetotelluric fields: Limits of validity of the static approach

Subsurface inhomogeneities can be classified in three categories depending on the comparison of their sizes against the effective skin depth and “adjustment distance”. These categories are geological noise, local and regional inhomogeneities. Due to its random nature, geological noise leads to uncontrollable distortions of the magnetotelluric field. Such methods as curve shifting, distortion tensor techniques, decomposition and spatial filtering can effectively be used to correct for static shift caused by geological noise. It is shown that the effects of local and regional subsurface inhomogeneities reduce to static shifts of MT-curves when rather rigid conditions are satisfied. The methods used to suppress the effect of geological noise have limited applicability to local and regional inhomogeneities, which can be accurately accounted for only by modelling.     

Influence of food web structure on the biochemical composition of seston,zooplankton and recently deposited sediment in experimental freshwater mesocosms

The effects of food web structure on the quantity and biochemical composition of seston, zooplankton and recently deposited sediment in experimental freshwater mesocosms were examined. Food web structure was manipulated by addition of zooplanktivorous fish. Biochemical characterisations were carried out using lipid biomarkers (sterols, fatty acids, chlorophyll-derived compounds and long-chain alkanediols). Fish addition decreased zooplankton biomass and increased seston biomass and deposited sediment through a trophic cascade. Fish presence strongly influenced the biochemical characteristics of seston and sediment. In contrast, food web structure had a minor impact on the lipid biomarker composition of zooplankton. Although the relative abundance of sterols in the different compartments did not differ strongly between treatments, sterol profiles in seston and sediment depended on food web structure. The predominance of Δ⁷-sterols in seston and sediment in the fish treatment indicated a major contribution of Chlorophyceae. In contrast, the distribution of sterols in seston and sediment in the fishless treatment, dominated by cholesterol, indicated a major zooplanktonic input. The distribution of fatty acids and the relative abundance of chlorophyll-derived compounds and long-chain alkanediols agreed with the predominant contribution of phytoplankton or zooplankton to seston and sediment in the two treatments. The relative abundance of bacterial biomarkers suggested that the contribution of bacteria was rather low. The high relative abundance of polyunsaturated fatty acids (PUFAs) and the absence of stanols in sediments suggested low microbial reworking of organic matter in the recently accumulated sediments. The trophic cascade, generated by the addition of fish, increased the relative abundance of PUFAs in deposited organic matter, thus enhancing sediment quality and potential degradability.     

Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons

We have determined the production yields for radionuclides in Al₂O₃, SiO₂, S, Ar, K₂SO₄, CaCO₃, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides ¹⁰Be, ¹⁴C and ²⁶Al produced in quartz targets, ²⁶Al in Al₂O₃ and S targets, ³⁶Cl in K₂SO₄ and CaCO₃ targets, and ⁵³Mn in Fe₂O₃ targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ⁻ capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ⁻ capture, by fast muons and by neutron capture.     

Klüfte und Talrichtungen im Turon des südöstlichen Münsterlandes

Zusammenfassung Am Südostrand des Münsterländer Kreidebeckens fließen alle größeren Wasserläufe im Bereich der Turonkalke nach NNE oder NE, obwohl das allgemeine Gelände- und Schichtengefälle nach NNW gerichtet ist. Die Ursachen für diese Abweichung sind im Mechanismus der Felserosion zu suchen, der im wesentlichen durch die Eigentümlichkeiten der Karstgerinne und durch die Gesteinszerklüftung bestimmt wird. Bei den Detailuntersuchungen geben sich komplexe Beziehungen zwischen Fließrichtung und Kluftrichtungen zu erkennen.Besonders bedeutend für die Entstehung der NNE gerichteten Täler sind die 170°- und 30°-streichenden Klüfte.

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On the south-east border of the Cretaceous basin of Munster, Westfalia, the current directions of streams in the area of Turon-limestone go to NNE or NE, although the main dipping of land surface as well as bedding planes points towards NNW. This divergence is caused by the mechanism of rock erosion, which is determined by peculiarities of subterranean stream channels and joints in limestone. The investigations show complex relations between flow direction and direction of joints.The 170°- and 30°-striking joints are significant of the origin of the NNE direction of the valleys.

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Résumé Dans le Turonien au bord sud-est du bassin Crétacé de Münster (Westphalie) toutes les rivières coulent en direction nord-nord-est ou nord-est, quoique la surface morphologique générale et les couches soient penchées en direction nord-nord-ouest. Cette divergence est expliquée par le mécanisme de l'érosion qui dépend principalement des fentes et du caractère des ruisseaux karstiques. Pendant ces études on a pu observer des relations complexes entre la direction des courants et la direction des fentes.Les fentes en direction nord-nord-est (30°) et sud-sud-est (170°) ont considérablement influencé l'origine des vallées.

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- - , -. . . , NNE, , 170° 30°.

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Herrn Professor Dr.Roland Brinkmann zum 70. Geburtstag gewidmet.     

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log m_Au–m_NaCl–T frame fixed linear dependence between log m_Au and T at any studied iso‐pleth (m_NaCl) in the form of log m_Au = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log m_Au) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied f_O2/f_S2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower f_O2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H₂O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H₂O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 m_HCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log m_Pt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)₂ and Mn₂(OH)₃Cl). These phases are metastable and transfer to Mn₃O₄ with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn₃O₄, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn₂O₃–MnO₂ buffer. So at 400C, dissolved Au (log m_Au) increases from –4. 40 in water to –1. 00 in 0. 1 m_HCl, and ones of Pt (log m_Pt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.     

Na-rich carbonate inclusions in perovskite and calzirtite from the Guli intrusive Ca-carbonatite,polar Siberia

Carbonate phases, some rich in Na₂O and comparatively rich in SrO and BaO, occur as inclusions in perovskite and calzirtite (Ca₂Zr₅Ti₂O₁₆) in the carbonatite of the Guli complex, Siberia. This is the first record of alkali carbonates, akin to nyerereite [Na₂Ca(CO₃)₂], in plutonic igneous rocks. The inclusion populations suggest that the parental magma of the complex was Ca-rich but developed Na-rich differentiates during the latest stages. This points to the dominant calcic carbonatites of the complex not being derivatives of alkali-rich parental carbonatites. These alkali-rich carbonate inclusions (and rare inclusions of djerfisherite) have been preserved due to the resistance of perovskite and calzirtite to processes of leaching, hydrothermal alteration and weathering.     

Untersuchungen über die Mächtigkeit von Schlickschichten mit Hilfe des Echographen

Zusammenfassung Es wird über eine Methode zur Feststellung von Schlickmächtigkeiten, von Bodenschichtungen in weichem Boden und zur Ermittlung des Tiefenprofils des harten Untergrundes berichtet. An Hand von Echogrammen und im Vergleich mit Bodenproben wird die Methode diskutiert.

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Investigations into the thickness of mud layers with the aid of ultra sound records

Summary A method is discussed allowing to make investigations into the thickness of mud layers and to ascertain the stratification in soft ground as well as to reveal the relief of the solid substratum of the sea bottom. The method is explained by the aid of ultra sound records which are compared with bottom samples.

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Recherches sur l'épaisseur des couches vaseuses au moyen d'enregistrements d'ondes ultrasonores

Résumé Une méthode est exposée qui permet de déterminer qualitativement l'épaisseur de couches vaseuses, d'explorer la stratification dans des fonds meubles et de découvrir le relief du substratum solide du fond de la mer. Ensuite, cette méthode est illustrée à l'aide d'enregistrements d'ondes ultrasonores qui sont comparés avec des échantillons du fond de la mer.

     

Two notes on the modern theory of inverse problems in geophysics

On the basis of comparison of the approaches to the solution of inverse problems in information theory and geophysics, it is shown that results, obtained in information theory, are suitable to supplement the theory of geophysical inverse problems. The conditions of the existence and uniqueness of the solutions of inverse problems in their practical discrete statement are specified. The terms of ɛ-entropy H _ɛ and informational capacity C _ɛ, characterizing “volumes” of unknown and observed data, are introduced. It is shown, that the instability of the solution of the inverse problem decreases with increase in H _ɛ, (increase in the “complexity” of studied section), if the relation H _ɛ ≤ C _ɛ is maintained.