Iron in silicate glasses of granitic composition: a Mössbauer spectroscopic study

⁵⁷Fe Mössbauer spectra of natural glasses (pumices and obsidians) and of synthetic glasses of granitic composition have been analyzed. — Ferric iron is found in tetrahedral coordination if enough M⁺-cations are available to balance the charge of both M⁺Fe³⁺O₂ and M⁺AlO₂ complexes. In other compositions the ratio of tetrahedrally to octahedrally coordinated Fe³⁺ depends on the ratio of mono-to divalent cations. — Ferrous iron occurs in two distinctly different octahedral sites. The existence of these sites can be attributed to different anionic units adjacent to Fe²⁺. The degree of polymerization of these units is reflected in the quadrupole splitting. The anionic units adjacent to Fe²⁺ are depolymerized for increasing mean Z/r ² of the network modifiers, which do not stabilize M³⁺ in the tetrahedra by local charge balance. — Increasing pressure diminishes the geometric differences between these types of ferrous iron-oxygen-octahedra, which gives rise to a more even distribution of Fe²⁺ among these sites and thereby to an ordering in the network of melts.     

Ancient porosity preserved in ordinary chondrites: Examining shock and compaction on young asteroids

We use a combination of 2D and 3D petrographic examination and ⁴⁰Ar‐³⁹Ar analyses to examine the impact histories of a suite of seven ordinary chondrites (Baszkówka, Miller, NWA 2380, Mount Tazerzait, Sahara 98034, Tjerebon, and MIL 99301) that partially preserve their ancient, but postaccretionary, porosity ranging from 10 to 20%. We examine whether materials that seem to be only mildly processed (as their large intergranular pore spaces suggest) may have more complex shock histories. The ages determined for most of the seven OCs studied here indicate closure of the ⁴⁰Ar‐³⁹Ar system after primary accretion, but during (Baszkówka) or shortly after (others) thermal metamorphism, with little subsequent heating. Exceptions include Sahara 98034 and MIL 99301, which were heated to some degree at later stages, but retain some evidence for the timing of thermal metamorphism in the ⁴⁰Ar‐³⁹Ar system. Although each of these chondrites has olivine grains with sharp optical extinction (signaling an apparent shock stage of S1), normally indicative of an extremely mild impact history, all of the samples contain relict shock indicators. Given the high porosity and relatively low degree of compaction coupled with signs of shock and thermal annealing, it seems plausible that impacts into materials that were already hot may have produced the relict shock indicators. Initial heating could have resulted from prior collisions, the decay of ²⁶Al, or both processes.     

Ship-borne geochemical investigations of deep-sea manganese-nodule deposits in the Pacific using a radioisotope energy-dispersive X-ray system

A radioisotope energy-dispersive X-ray (EDX) system has been used on board the German research vessel “Valdivia” during an exploration expedition in the northern equatorial Pacific in 1973. The instrumentation used consisted of an X-ray detection system incorporating a 30 mm² effective-area Si (Li) detector with a measured energy resolution of 195 eV for Mn Kα X-rays, standard nuclear electronics, a 1024-channel analyser and a data read-out unit. The X-ray spectra in the manganese-nodule samples were excited by a 30-mCi ²³⁸Pu source.The six elements Mn, Fe, Co, Ni, Cu and Zn were analysed on board. Precision values for the analyses were less than 3% for Mn, Fe, Ni, Cu and Zn and about 5% for Co. A total amount of 350 analyses was carried out during a one-month cruise.Average contents of 190 analysed whole manganese-nodule samples from all the sampling sites of the covered area were 23.3% Mn, 6.7% Fe, 0.23% Co, 1.16% Ni, 0.94% Cu and 0.10% Zn. The average content of the base metals expressed as the sum of the Co, Ni, Cu and Zn contents was 2.48%. A linear relationship between Mn and Ni in all analysed samples, including whole manganese-nodule samples, zones of manganese nodules and manganese crusts, was observed. The Mn/Ni ratio calculated by regression analysis was 23.0. Zonal variations of the chemical contents of the six elements in the manganese nodules were found. A size classification of the manganese nodules has been suggested. Geochemical correlations of Cu and Ni versus Mn/Fe in the investigated samples are given.     

Erzmikroskopische und mikroanalytische Untersuchungen an Manganerzkonkretionen aus dem pazifischen Ozean

Zusammenfassung Die Verteilung von Eisen, Mangan, Kupfer und Nickel in Manganerzkonkretionen wurde mit Hilfe der Elektronenstrahl-Mikroanalyse untersucht. Die einzelnen Manganknollen zeigen einen inhomogenen Aufbau aus Mn- und Fe-reichen Zonen, die sich erzmikroskopisch unterscheiden lassen. Auffallend sind die Korrelationen zwischen Mangan, Kupfer und Nickel auch im Mikronbereich. Die Zusammenhänge zwischen den spektralen Reflexionsfunktionen und der chemischen Zusammensetzung der Manganerzkonkretionen werden diskutiert.

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The distribution of iron, manganese, copper and nickel has been determinted in different zones of manganese nodules by electron probe analysis. A single nodule is characterized by the inhomogeneous distribution of these elements, and the correlation of Mn with Cu and Ni within certain zones. Concentrations of Mn, Cu and Ni of 41, 1.0 and 2.0 percent, respectively, have been found in layers containing 2.0 percent Fe only. On the other Land iron-rich layers are characterized by low contents of Mn, Cu and Ni. There is no considerable variation in the ratios of these elements with distance from the centre of an individual nodule. The correlation of reflectivity and chemical composition is emphasised.

     

Geoelektrische Untersuchung der Graphitlagerstätte Kropfmühle im Bayerischen Wald

Zusammenfassung Mittels Eigenpotentialmessungen werden genauere Angaben über die H?ffigkeit oberfl?chennaher Schichten im Bereich der Graphitlagerst?tte Kropfmühle m?glich. Widerstandsmessungen erlauben qualitative Schlüsse auf Graphitanreicherungen in Kombination mit den Eigenpotentialmessungen. Anhand typischer Beispiele für beide Methoden wird der geologische Aufbau des Untersuchungsgebietes diskutiert.

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Summary By means of the selfpotential method it is possible to state some details of the graphite deposit Kropfmühle (Bavaria). Resistivity- in connexion with selfpotential measurements allow qualitative conclusions on the occurrence of graphite. The general structure of this deposit is discussed by examples.

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Auszug aus der Dissertation ? Geoelektrische Untersuchungen zur Erschliessung von Graphitlagerst?tten unter besonderer Berücksichtigung der Eigenpotentialmethode ?; Diss. naturw. Fak. d. Univ. München, 1955.

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Dr.Friedrich Wilckens,Bonn, Argelanderstr. 9 (West-Deutschland).     

Evaluation of Modeled Spatially and Temporarily Highly Resolved Emission Inventories of Photosmog Precursors for the City of Augsburg: The Experiment EVA and Its Major Results

Emission inventories of NO_x, CO, and individual volatile organic compounds (VOC), highly resolved in space and time, belong to the most important input parameters for chemistry and transport models (CTM) used for ozone prediction. Because of the decisive influence of the input quality on the outcome of CTM simulations, the quality of emission inventories has to be assessed. This paper presents an experimental evaluation of the highly resolved emission inventories for the city of Augsburg. The emissions of the city, determined in March and October 1998 using mass balance and tracer techniques, and derived from the measured receptor concentration ratios, were compared with emissions modeled from an emission inventory. The modeled CO emissions were in agreement with the measured ones within the combined experimental and model uncertainties. More detailed CO emission model simulations suggest that the tendency of calculated CO emissions being smaller than the measured ones may be due to higher traffic activity in Augsburg. Modeled NO_x emissions were in agreement with the measured ones within the combined experimental and model uncertainties. Large deviations between modeled and measured values have been found for some individual NMHC compounds. The measured NMHC emission fingerprints were dominated by mobile sources. Substantial model predicted NMHC emissions from the solvent use could not be detected by measurements suggesting that they may not be correctly represented by the emission model.