Verfärbung von Steinsalz durch Röntgenstrahlen

Zusammenfassung Die Analyse der Verfärbungserscheinungen bei Bestrahlung von Steinsalz mit Röntgenstrahlen führt auf die Entstehung einer uneinheitlichen, optisch nicht trennbarenF-Bande mit einem ausgeprägten Absorptionsmaximum bei 465 m. Die unter den Bedingungen: unbehandeltes Kristallmaterial, Zimmertemperatur, schwaches diffuses Licht, durchgeführte Bestrahlung ergibt stabileF-,. metastabileF ^*- und instabileF-Zentren, die alle derF-Bande angehören. DieF ^*-Zentren sind während der Einstrahlung stabil, während sich dieF -Zentren proportional ihrer Anzahl umwandeln.Für die Umwandlung derF ^*-Zentren nach Aufhören der Einstrahlung nehmen wir den Übergang inF ₂-Zentren, die früher schon bei optischer Erregung durch Einstrahlung in die Hauptbande gefunden wurden, an. Die Entstehung dieser Zentren bei Erregung wird durch die Erweiterung des absteigenden Astes derF-Bande nach längeren Wellenlängen hin angezeigt.DieF-Zentren gehen während und nach der Bestrahlung inF ₃-Zentren über, die durch das Auftreten einer Nebenbande mit einem Absorptionsmaximum bei etwa 720 m gekennzeichnet ist. Dieser Vorgang wird besonders deutlich durch das Ansteigen derF ₃-Bande trotz Aufhörens der Einstrahlung. Die bei derF-Bande gefundene Aufteilung in unterschiedlich stabile Zentren ist auch auf die anderen Banden anzuwenden.Die hier entwickelten Vorstellungen über die Bildung und Umbildung der verschiedenen Zentrenarten stehen in Übereinstimmung mit den gemessenen Anklingungs- und Abklingungskurven.     

Das Hoch-Tief-Umwandlungsverhalten mikrokristalliner Quarze

The optical and x-ray investigation of 51 microcrystalline quartz samples show that they are built up of fibrous chalcedony (agates) or finest crystalline, isometric grained quartz (flints, cherts, jasper or Chrysoprase). These samples were examined by standardized d.t.a. — methods in order to get their inversion characteristics.

1. A third of the samples conteins low-temperature cristobalite in addition to quartz (in two samples even as main component); the high-low inversion of this mineral lies between 80 and 245° C according to its defect character. In five samples of jasper low- tridymite is occurring as minor component.
2. In contrary to macrocrystalline quartz crystals microcrystalline quartzes generally show no sharp inversion point. The inversion takes place over an interval of nearly 50° C, to be seen in the d.t.a. curve as a broad, only slightly endothermic effect with hardly visible peak or several small minima. In the curves of 15 samples no inversion could be detected. This broad inversion peak is caused by different defect characters of the crystals or even of parts of the crystals which invert at different temperatures (Flörke, 1955).
3. There is no dependance of t _i on the size of crystallites at least for crystals with diameter greater than 0.05 μ. The temperature of the most prominent inversion minimum allows a division of the microcrystalline quartz crystals analogous the macrocrystalline classification into samples with t _i below and above 570° C. The lowest (518±2° C) and the highest t _i (578,7+0,3° C) were measured at different parts of the same sample of a Chrysoprase.
4. The intensity of the brown and red coloured parts of agate and jasper grows with increasing Fe₂O₃-content, but there is no connection between t _i and chemical composition.
5. As in macrocrystalline quartzes of caverns and veins there are also some t _i -differences between the marginal and the central parts of agates or jaspers. The explanation lies in the mechanism of formation: higher t _i in the margin (e.g. in one globular jasper) points to a formation by silification, whereas higher t _i in the center indicates a formation by the filling up of cavities and veins.
6. The variation in t _i of microcrystalline quartzes and the comparison of these t _i ? with those of associated low-temperature cristobalite shows a connection between temperatures of formation and inversion: samples with low t _i (i.e. with a great number of defects) should be formed at low temperatures, that is by sedimentary or diagenetic processes, and samples with t _i above 570° C (i.e. nearly without defects in the structure) should have crystallized out of hydrothermal solutions. The weak inversion peaks below 570° which in d.t.a. curves often appear besides a main peak at 570° C represent the small amount of diagenetically formed microcrystalline quartz with a large degree of defect character.

     

Canopy dieback in the upper montane rain forests of Sri Lanka

In 1978 a patch of dying upper montane rain forest had been observed on the slope of Thotupolakanda above Horton Plains. Patches in the upper montane rain forests of Sri Lanka were also recorded in 1980/81. All these sites were on windswept western slopes and ridges with stunted tree growth and shallow soil. From 1971 to 1983 Sri Lanka experienced some exceptionally dry years. The severe droughts of 1976 might have cause or “triggered” that dieback. After heavy rains between 1983 and 1986, these forests showed signs of recovery. Some trees had survived and sprouted again. Tree saplings were found, but regeneration was very low and further impeded by serious frost in February 1986. The influence of drought and frost clearly indicates the vulnerability of the stunted upper montane rain forest in the highest and wind-exposed regions of Sri Lanka.     

Predatory Promesostoma species (Plathelminthes, Rhabdocoela) in the Wadden Sea

Laboratory experiments were performed on the food ecology of four congeneric species of free-living plathelminths, Promesostoma caligulatum, P. marmoratum, P. rostratum, and P. meixneri, all inhabiting an intertidal sandflat near the island of Sylt (North Sea). Their prey spectrum is within the microcrustaceans: P. caligulatum preferred ostracods, while the other three species favoured copepods, with species-specific differences for copepod species and size classes. Daily consumption of prey species varied with the size of both the predator and the prey. On average, P. marmoratum consumed 0.76 Harpacticus flexus per day while this rate decreased to 0.06 in P. meixneri, the smallest predator. When these Promesostoma species were fed with Tachidius discipes, a smaller prey species, their predation rates were about 25% higher. While the larger predators preferred the larger harpacticoids as prey, the small P. meixneri preferred small cyclopoids over larger harpacticoids. In terms of biomass, P. marmoratum's mean consumption of T. discipes per day was about half the predator's own weight. This average varied with prey density and temperature. A comparison of these consumption rates with the field densities of the predators and their prey shows that the plathelminth predators may consume as much as 10% per day of their copepod prey populations, thus strongly influencing these prey populations on these sandflats. The predation pressure of P. caligulatum on ostracods was about 1% per day of the prey population. Since ostracods usually have fewer generations per year, the total effect on the population dynamics may be similar to that on copepods. Therefore, nocturnal swimming of copepods in the water column may be interpreted as an attempt to escape plathelminth predators.     

Magma evolution and the formation of porphyry Cu–Au ore fluids: evidence from silicate and sulfide melt inclusions

Silicate and sulfide melt inclusions from the andesitic Farallón Negro Volcanic Complex in NW Argentina were analyzed by laser ablation ICPMS to track the behavior of Cu and Au during magma evolution, and to identify the processes in the source of fluids responsible for porphyry-Cu-Au mineralization at the 600 Mt Bajo de la Alumbrera deposit. The combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle-derived mafic magma that contained approximately 6 wt.% H₂O and 200 ppm Cu. This magma and a rhyodacitic magma mixed in an upper-crustal magma chamber, feeding the volcanic systems and associated subvolcanic intrusions over 2.6 million years. Generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps: (1) Generation of a sulfide melt upon magma mixing in some parts of the magma chamber. (2) Partitioning of Cu and Au into the sulfide melt (enrichment factor of 10,000 for Cu) leading to Cu and Au concentrations of several wt.% or ppm, respectively. (3) A change in the tectonic regime from local extension to compression at the end of protracted volcanism. (4) Intrusion of a dacitic magma stock from the upper part of the layered magma chamber. (5) Volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber, generating a fluid with a Cu/Au ratio equal to that of the precursor sulfide. (6) Focused fluid transport and precipitation of the two metals in the porphyry, yielding an ore body containing Au and Cu in the proportions dictated by the magmatic fluid source. The Cu/S ratio in the sulfide melt inclusions requires that approximately 4,000 ppm sulfur is extracted from the andesitic magma upon mixing. This exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for S. The extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma. It appears, thus, that unusually sulfur-rich, not Cu-rich magmas are the key to the formation of porphyry-type ore deposits. Our observations imply that dacitic intrusions hosting the porphyry–Cu–Au mineralization are not representative of the magma from which the ore-fluid exsolved. The source of the ore fluid is the underlying more mafic magma, and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated. At Alumbrera, these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole. Sulfide inclusions in similar dykes of other, less explored magmatic complexes may be used to predict the Au/Cu ratio of potential ore-forming fluids and the expected metal ratio in any undiscovered porphyry deposit.Editorial handling: B. Lehmann     

Comparison of surface and borehole locations of induced seismicity

Monitoring of induced microseismic events has become an important tool in hydraulic fracture diagnostics and understanding fractured reservoirs in general. We compare microseismic event and their uncertainties using data sets obtained with surface and downhole arrays of receivers. We first model the uncertainties to understand the effect of different acquisition geometries on location accuracy. For a vertical array of receivers in a single monitoring borehole, we find that the largest part of the final location uncertainty is related to estimation of the backazimuth. This is followed by uncertainty in the vertical position and radial distance from the receivers. For surface monitoring, the largest uncertainty lies in the vertical position due to the use of only a single phase (usually P‐wave) in the estimation of the event location. In surface monitoring results, lateral positions are estimated robustly and are not sensitive to the velocity model. In this case study, we compare event location solutions from two catalogues of microseismic events; one from a downhole array and the second from a surface array of 1C geophone. Our results show that origin time can be reliably used to find matching events between the downhole and surface catalogues. The locations of the corresponding events display a systematic shift consistent with a poorly calibrated velocity model for downhole dataset. For this case study, locations derived from surface monitoring have less scatter in both vertical and horizontal directions.     

Some maps of isanomalies in energy balance climatology

Summary A series of world maps of isanomalies of annual and seasonal global radiation, net radiation, latent heat flux, sensible heat flux, maps of residuals from regression, radiation efficiency, and the Bowen Ratio have been constructed on the data base ofBudyko's Atlas of the Heat Balance of the Earth, 1963. Among the major features observed was the dissimilarity in patterns of isanomalies for the eastern and western sectors of the world's semi-permanent subtropical highs and the great difference between oceanic and continental surfaces.

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Zusammenfassung Auf Grund der Werte vonBudykos Atlas der Wärmebilanz der Erde (1963) wurden eine Anzahl Weltkarten der Isanomalien der jährlichen und der jahreszeitlichen Werte für die Globalstrahlung, die totale Strahlungsbilanz, den latenten und den fühlbaren Wärmefluß sowie Karten für die Abweichungen von der Regressionsgeraden, für den Strahlungsgenuß und für den Bowen-Quotienten konstruiert. Als Hauptergebnisse sind die Unähnlichkeit im Verlauf der Isanomalien zwischen dem östlichen und dem westlichen Sektor der semipermanenten Hochdruckgebiete der Subtropen sowie die großen Unterschiede zwischen ozeanischen und kontinentalen Gebieten zu nennen.

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Résumé En partant des valeurs publiées parBudyko dans son Atlas du bilan thermique de la Terre (1963), on a établi un certain nombre de cartes du globe. Sur celles-ci, on a reporté les isanomalies des valeurs annuelles et saisonières de la radiation globale, du bilan total radiatif, du flux des chaleurs latente et sensible ainsi que l'écart à la droite de régression pour le rayonnement reçu et pour le rapport de Bowen. Le résultat principal en est l'appararition de dissemblances dans le cours des isanomalies entre les secteurs oriental et occidental des anticyclones semipermanents des zones subtropicales ainsi que de différences importantes entre les régions océaniques et continentales.

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With 28 Figures     

Problems resulting from misinterpretations of natural resources and natural hazards in tropical countries. The example of Peru

Natural resources in a tropical country like Peru are often overestimated. Peru is characterized by a wide range of regional differences, varied physical settings, and numerous natural hazards. Some climatical and hydrological conditions are examined and the factors causing instability in agricultural and nonagricultural production are discussed. Natural resources must be evaluated in the framework of internal political, social, and economic circumstances. Several points are recommended to foster economic development when considering the constraints of the physical environment.     

Monitoring volcanic hazard using eddy covariance at Solfatara volcano, Naples, Italy

An eddy covariance (EC) station was deployed at Solfatara crater, Italy, June 8–25, 2001 to assess if EC could reliably monitor CO₂ fluxes continuously at this site. Deployment at six different locations within the crater allowed areas of focused gas venting to be variably included in the measured flux. Turbulent (EC) fluxes calculated in 30-min averages varied between 950 and 4460 g CO₂ m⁻² d⁻¹; the highest measurements were made downwind of degassing pools. Comparing turbulent fluxes with chamber measurements of surface fluxes using footprint models in diffuse degassing regions yielded an average difference of 0% (±4%), indicating that EC measurements are representative of surface fluxes at this volcanic site. Similar comparisons made downwind of degassing pools yielded emission rates from 12 to 27 t CO₂ d⁻¹ for these features. Reliable EC measurements (i.e. measurements with sufficient and stationary turbulence) were obtained primarily during daytime hours (08:00 and 20:00 local time) when the wind speed exceeded 2 m s⁻¹. Daily average EC fluxes varied by ±50% and variations were likely correlated to changes in atmospheric pressure. Variations in CO₂ emissions due to volcanic processes at depth would have to be on the same order of magnitude as the measured diurnal variability in order to be useful in predicting volcanic hazard. First-order models of magma emplacement suggest that emissions could exceed this rate for reasonable assumptions of magma movement. EC therefore provides a useful method of monitoring volcanic hazard at Solfatara. Further, EC can monitor significantly larger areas than can be monitored by previous methods.