Die Rolle des Wassers bei der Thermometamorphose von Salzlagerstätten

Zusammenfassung Experimente im System Na ₂ ²⁺ -Mg²⁺-Cl ₂ ^2– -SO ₄ ^2– -H₂O zeigen, daß bei der Thermometamorphose von Evaporiten die Metamorphoseprodukte eine Funktion Des primären Poren- und Hydratwassers sind. Der Deutschen Forschungsgemeinschaft danke ich für eine Sachbeihilfe.

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The influence of interstitial and hydrated water on thermometamorphism of evaporites

Experiments in the System Na ₂ ²⁺ -Mg²⁺-Cl ₂ ^2– -SO ₄ ^2– -H₂O show that the effect of thermometamorphism of evaporites is to produce new mineral assemblages different from primary assemblages due to redistribution of interstitial and hydrated water.

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Der Deutschen Forschungsgemeinschaft danke ich für eine Sachbeihilfe.     

Paläotemperaturen und Paläoklima in Obertrias und Lias der Alpen

Zusammenfassung Für 172 karbonatische Proben aus Nor bis Mittellias der Alpen wurden Paläotemperaturen nach dem¹⁸O/¹⁶O-Mischungsverhältnis bestimmt. Untersucht wurden vor allem Fossilien, und zwar bevorzugt solche, die primär vorwiegend oder gänzlich aus Calcit bestanden haben; daneben auch Ooide und Gesteine. Um diagenetischen Verschiebungen des¹⁸O/¹⁶O-Verhältnisses aus dem Wege zu gehen, wurde der Diagenese-Grad jeweils optisch und mit der röntgenographischen Phasen-Analyse geprüft; sichtbar rekristallisiertes Material wurde nicht verwertet.Die ermittelten Paläotemperaturen zeigen — nach Alter und Fazies-Gruppen getrennt dargestellt (Abb. 2) — meist deutliche Häufungen, die angesichts der relativ großen Probenzahlen und der unterschiedlichen diagenetischen Bedingungen für die einzelnen Proben den ursprünglichen Wasser-Temperaturen annähernd entsprechen dürften; diese Annahme wird durch Paläotemperaturen aus aragonitischem Material für das Rät bestätigt. Bei der Interpretation der Paläotemperaturen wurden paläogeographische Faktoren (Bathymetrie, Salzgehalt u. a.), soweit bekannt, berücksichtigt. Für die norischen Flachmeer-Proben ergeben sich Temperaturen um 25°C, für die rätischen etwas niedrigere Werte. Einem Temperatur-Minimum im Unterlias folgte im Mittellias eine Erwärmung um mehrere Grade. Demnach dürften die obertriassischen Korallen-Riffe in den Nördlichen Kalkalpen während während des Unterlias aus klimatischen Gründen abgestorben sein.

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172 carbonate samples from the Alps (mainly the Northern Calcareous Alps) ranging from Norian to Middle Liassic age, have been investigated for their¹⁸O/¹⁶O-content. Paleotemperatures have been determined. The analysed samples — fossils, mainly with primary calcitic shells, ooids and carbonatic sediments —were carefully selected by optical and x-ray methods.The results are given in fig. 2. Paleotemperatures are plotted in groups of the same age and equal or similar facies. The maximum of each group is assumed to represent the average water-temperature of that time. The interpretation of the paleotemperatures refers also to paleogeographic factors, e. g. bathymetry and salinity.The Noric shelf-sea paleotemperatures are in the range of about 25° C and show a systematic decrease to the Upper Rhaetian; a minimum temperature during the Lower Liassic (18° C) was followed by a warmer climatic period in the Middle Liassic. It is assumed that the Upper Triassic coral-reefs of the Northern Calcareous Alps died out because of the low temperature.

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Résumé Pour 172 échantillons carbonates allant du Norien jusqu'au Lias moyen des Alpes on a déterminé les paleotemperatures d'après le rapport¹⁸O/¹⁶O. Étudiant surtout des fossiles, nous avons préféré ceux qui, dès l'origine, consistaient en grande partie ou totalement en calcite; en outre nous avons utilisé des ooides et des roches. Pour éviter l'altération diagénétique du rapport¹⁸O/¹⁶O, on a examiné le degré de la diagnèse sous le microscope et à l'aide des rayons X; le matériel visiblement récristallisé a été exclu de l'étude.Les températures déterminées — groupées selon l'âge et le faciès (fig. 2) —s'accumulent pour la plupart clairement autour de valeurs qui, vraisemblablement, représentent les températures originales de l'eau de mer — vu le nombre élevé des échantillons et les conditions variées de diagenèse qu'ils ont subi. Cette supposition a été vérifiée par des températures determinées sur de l'aragonite pour le Rhétien (Kaltenegger 1967). En interprétant les paléotempératures on a tenu compte des facteurs de paléogéographie (bathymétrie, salinité etc.).Les échantillons noriens provenant d'une mer peu profonde ont donné des températures d'environ 25° C, les échantillons rhétiens des valeurs un peu plus basses. Un minimum pendant le Lias inférieur a été suivi, pendant le Lias moyen, par un réchauffement de plusieurs degrés. On peut donc penser que les récifs coralliens du Trias supérieur dans les Alpes calcaires septentrionales se sont retirés pour des raisons climatiques au cours du Lias inférieur.

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Submicroscopical twinning in lunar and experimentally deformed pyroxenes

During deformation experiments at high pressures (10 kb) and medium temperatures (500–650°) diopside became twinned on {100} in small optically invisible domains. If host and twin occur with equal frequency, the X-ray single-crystal photograph would show orthorhombic symmetry due to the special geometry of the diopside lattice. A crystal of pyroxene from Mare Tranquillitatis has been found to give just such an X-ray photograph with orthorhombic symmetry; this is explained as a possible deformation product.     

Mineralogy of Erromango lavas (New Hebrides): Evidence of an early stage of fractionation in island arc basalts

The orogenic volcanic rocks of Erromango island are divided into a Quaternary theoleiitic group and an older Pliocene one showing calc-alkalic affinity. The microprobe mineralogy of these lavas agrees with this geochemical distinction and indicates a marked iron enrichment trend in the recent tholeiitic lavas, whereas titanomagnetite occurs as early formed phenocrysts (Al, Cr, Mg-rich) only in Pliocene basalts. Some Ni and Mg-rich olivine phenocrysts (Fo88) and unusual chemically zoned clinopyroxene megacrysts are described from Pliocene basic lavas and interpreted as deep-fractionated minerals. The large compositional range of these latter (diopside core to augite rim, through salite intermediate zone) leads us to discuss the physical conditions and the corresponding cation substitutions prevailing during their formation. Diopside cores crystallized at depths of about 20 km from a relatively ‘primitive’ melt. The formation of salite is considered to be the result of concomitant fractionation of Mg-rich phases and increase of f_O2. An early stage of fractionation of Cr-bearing diopside + Ni-bearing olivine would account for the typical Cr and Ni depletion of Erromango lavas.     

Isotopic dating of pre-Alpidic rocks from the island of Ios (Cyclades,Greece)

The lower tectonic unit of Ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal Pelagonian.Metamorphic country rocks of unknown age were intruded about 500 Ma ago, as concluded from a Rb-Sr whole rock (WR) isochron on relic tonalites to granodiorites which largely escaped the polyphase postmagmatic overprints.A Hercynian amphibolite facies metamorphism, during which the igneous rocks were partly recrystallized to orthogneisses, is dated by a lower intercept age of 300–305 Ma of U-Pb determinations on zircons and by three almost concordant Rb-Sr muscovite-WR ages of 295 to 288 Ma.K-Ar analyses on these muscovites and on biotites, and Rb-Sr tie lines WR-biotite and WR with other relic magmatic minerals yielded various apparent ages between 260 and 60 Ma. They are interpreted as mixed ages between a Hercynian cooling age and the two stage Alpidic overprints.White micas formed during the Eocene high P/T and/or Oligocene/Miocene Barrovian-type overprints yielded K-Ar dates ranging from 82 to 26 Ma, as well as a single Rb-Sr date of 13 Ma. These Alpidic dates resemble the more detailed age patterns of other Cycladic islands. But they are not sufficient for an independent dating of the Tertiary evolution on Ios island.     

Regional policy in Switzerland: an analysis of its effectiveness and an outline of a strategic reorientation

First, regional policy in Switzerland is examined theoretically. This is followed by a short review of those partial effects of this policy which, according to current empirical findings, can be regarded as proved. Finally, with the failings of present policy in mind, the basis for a strategically new concept is drawn up. Swiss regional policy is unlike that of other countries, in that it is not influenced by any one particular theory of regional economics. On the contrary, there is a combination of widely varying forms, especially a mixture of theoretical elements based on both neoclassicism and polarization. Viewed as a whole, this concept can be considered well-balanced, despite the criticisms brought forward here. A radical departure from the present concept appears neither necessary nor sensible, although the individual points of criticism show that to be really effective, present policy requires a few additions or shifts of emphasis. Thus regional policy should increasingly build on the region's existing potential, aiming for the broadest possible development and mobilization of local resources. This should enhance regional self-reliance, simultaneously, in economic, social-cultural, and political terms. In addition, appropriate measures should be taken to improve the innovative strength of peripheral regions. Finally, an essential aspect of strategic reorientation is increased attention to the problems of settlement structure in peripheral parts of the country. In this respect the promotion of small and medium-sized development centres deserves special attention.     

An experimental investigation of hydroxyl solubility in jadeite and Na-rich clinopyroxenes

The solubility and incorporation mechanisms of water in synthetic, water-saturated jadeite and Na-rich clinopyroxenes have been experimentally investigated. Infrared spectra for water-saturated jadeite synthesised from 2.0 to 10 GPa show two prominent sharp peaks at 3,373 and 3,613 cm^–1 together with several weaker features in the OH-stretching region, indicating that there are at least 5 distinct modes of hydrogen incorporation in the structure. Water solubility in pure jadeite reaches a maximum of about 450 ppm by weight at 2 GPa and slowly decreases with increasing pressure to about 100 ppm at 10 GPa. Solubility can be described by the function c_OH=A f_H2O^0.5 exp (–PV_Solid/RT), where c_OH is water solubility in ppm H₂O by weight, A is 7.144 ppm/bar^0.5, f_H2O is water fugacity, and V_Solid=8.019 cm³/mol is the volume change of the clinopyroxene upon incorporation of OH. Jadeite provides a good model for understanding hydrogen incorporation mechanisms in more complex omphacite compositions. Assignment of absorption bands in IR spectra verifies the importance of cation vacancies on the M2 site in providing mechanisms for hydrogen incorporation. However, results also suggest that substitution of lower valency cations onto the M1 site may also be important. Solid solution of jadeite with diopside and in particular, with Ca-Eskola component leads to a drastic increase of water solubility, and the bulk composition has a more important effect on the capacity of omphacite to store water than pressure and temperature. Omphacite is expected to be the major carrier of water in a subducted eclogite after the breakdown of hydrous minerals.Editorial responsibility: W. Schreyer     

Evidence of chromosomal damage in common eiders (Somateria mollissima) from the Baltic Sea

Common eiders nesting in the Baltic Sea are exposed to generally high levels of contaminants including potentially genotoxic polycyclic aromatic hydrocarbons and organochlorines. Blood samples were collected from eiders at eight sites in the Baltic Sea and two sites in the Beaufort Sea. DNA content variation was estimated using the flow cytometric method, and subsequently utilized as a biomarker of genetic damage. We observed no significant differences in genetic damage among populations within either the Baltic or Beaufort Seas. However, eider populations from the Baltic Sea had significantly elevated estimates of genetic damage compared to populations from the Beaufort Sea.