Der Stabilitätsbereich des Pyrophyllits unter dem Einfluß von Säuren

Zusammenfassung Die in Teil I dargestellten Ergebnisse der experimentellen Untersuchungen über den Einfluß von Säuren auf den Stabilitätsbereich von Pyrophyllit werden in Teil II auf natürliche Paragenesen angewandt. In offenen Systemen ist im allgemeinen mit Assoziationen von zwei festen Phasen (z.B. Quarz + 1 Al-Silikat) zu rechnen, während in geschlossenen Systemen meistens Assoziationen von drei festen Phasen vorliegen werden (z.B. Quarz + 2 Al-Silikate). Mit wesentlich erhöhten Säurekonzentrationen in der fluiden Phase und starker Erniedrigung der Bildungstemperaturen von Pyrophyllit und Andalusit kann nur bei der Kontaktmetamorphose gerechnet werden, insbesondere dann, wenn gleichzeitig eine hydrothermale Tätigkeit stattfand. Bei der Regionalmetamorphose herrschten im allgemeinen wesentlich geringere Aciditäten; daher werden die Bildungstemperaturen von Pyrophyllit und Andalusit weniger stark herabgesetzt. Besondere Bedeutung haben die experimentellen Ergebnisse für die Genese von Pyrophyllit- und Andalusitlagerstätten; aus der Vielzahl der in der Literatur beschriebenen Vorkommen wurden drei ausgewählt und deren Genese mit Hilfe der Ergebnisse der Experimente diskutiert.

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The results of the experimental investigations of the influence of acids on the stability field of pyrophyllite, put forth in the first part of this paper, have been applied here on natural mineral assemblages. In general, assemblages with two solid phases (e.g. quartz and an aluminium silicate) are expected to occur in open systems, whereas in closed systems, usually three solid phases (quartz and two aluminium silicates) would be present. High acidity of the fluid phase, leading to a strong depression of the lower stability limits of pyrophyllite and andalusite, is liable to be encountered in contact metamorphism, especially when a notable hydrothermal activity was taking place simultaneously. In contradiction to that, the regional metamorphism is commonly characterized by an essentially lower acidity of the fluid phase, so that the temperatures of origin of pyrophyllite and andalusite were but slightly depressed. The results of the present experimental investigations are highly important in discussing the genesis of pyrophyllite and andalusite deposits. This has been demonstrated by applying them to three such cases chosen from the literature.

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Herrn Professor Dr. H. G. F. Winkler danke ich für sein Interesse and dieser Arbeit, für wertvolle Kritik und nützliche Ratschläge sowie für die Erlaubnis, die Experimente in Apparaturen durchzuführen, die ihm von der Deutschen Forschungsgemeinschaft zur Verfügung gestellt wurden.

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I. Mitteilung: Diese Zeitschrift 13, 31–50 (1966).     

Effects of water on strength and failure mode of coarse-grained granites at 300°C

Summary Deformation experiments have been performed in a triaxial compression cell at a temperature of 300°C and confining pressures up to 65 MPa using samples of homogeneous, fresh two-mica-granite (RM) and monzogranite (CM). The cylindrical specimens (d=70 mm, h=140 mm, V=540 cm³) were tested undrained under dry (105°C), as received, and water saturated conditions at deformation rates between and . The mechanical behaviour of the two types of coarse-grained, crystalloblastic granites is critically influenced by mineralogical composition, porosity, and the amount of intergranular water present in the samples. The failure stress of the CM granite is at about 65% of that of the RM granite; in both rocks strength decreases with increasing porosity and water content.The presence of interstitial water causes a failure mode of non-localized, homogeneously distributed microcracking in the central parts of the samples, whereas, in runs with dry granites, strain localization along a single shear fracture was observed. When aqueous fluids are present, the macroscopic style of deformation of granites appears to be ductile even at lowP andT conditions. Strength and angle of internal friction are reduced to very low values. The style of deformation, as well as the reduction of strength of the water-saturated rock samples, is due to mechanical and chemical effects of intergranular water at elevated temperatures.The maximum differential stresses measured for these coarse-grained granites are much lower than the strength commonly reported for other granites, e. g. Westerly and Charcoal granites. Our data suggest that the strength of the granitic crust under differential stress is lower than currently deduced from laboratory experiments.     

Synthesis and thermal stability of 2 \frac{1}{2}-octahedral sodium mica,NaMg2.5 (OH)2∫i4O10]

A new 2 \(\frac{1}{2}\) -octahedral sheet silicate, NaMg_2.5 Si₄O₁₀ (OH)₂, has been synthesized from oxide mixtures in the temperature range 500–600°C at pressures between 1 and 5 kb. The lattice parameters are a ₀ = 5.298 Å, b ₀ = 9.047 Å, c ₀ = 9.479 Å and ß=99.55°. X-ray data are given in the text. At temperatures above 605° C/1 kb and 630° C/5 kb, it decomposes to magnesiorichterite plus quartz.     

Noble gas tracers for characterisation of flow dynamics and origin of groundwater: A case study in Switzerland

The Grenchen aquifer system in the Swiss Plateau was extensively investigated in order to determine the extent of groundwater contamination and to assess the natural attenuation capacity. Environmental tracer data were applied to estimate groundwater travel times, mixing ratios, and evaluate groundwater origin. Recharge is basically possible in two distinct topographical areas, the immediate vicinity of the town of Grenchen and the elevated plateau of the first Jura Mountain ridge. Groundwater dating was performed with the ³H/³He dating method and supplemented by ⁸⁵Kr measurements. Stable isotope data (δ¹⁸O, δ²H) and dissolved noble gas concentrations allow the determination of the recharge temperature, which is correlated to the recharge elevation. Noble gas temperatures (NGT) decrease in the direction of groundwater flow and range from 10 to 13 °C in the upstream area of the town to 7–9 °C in the downstream river plain. This trend could suggest the admixture of water from the underlying limestone aquifer recharged under cooler infiltration conditions, e.g. at higher recharge elevations. However, it is shown in this study that the difference in NGT does not require such a recharge. Rather, increasing air temperatures over the last 40 years and the urban heat island effect could possibly explain most of the observed temperature shift. Furthermore, it is concluded that the downstream river plain is hydrologically disconnected from the upstream town area. Consequently most water from the town area is drained by the creek Witibach and recharge in the river plain is higher than previously assumed.     

The born-again (very late thermal pulse) scenario revisited: the mass of the remnants and implications for V4334 Sgr

We present 1D numerical simulations of the very late thermal pulse (VLTP) scenario for a wide range of remnant masses. We show that by taking into account the different possible remnant masses, the observed evolution of V4334 Sgr (a.k.a. Sakurai's object) can be reproduced within the standard 1D mixing length theory (MLT) stellar evolutionary models without the inclusion of any ad hoc reduced mixing efficiency. Our simulations hint at a consistent picture with present observations of V4334 Sgr. From energetics, and within the standard MLT approach, we show that low-mass remnants  ( M ≲ 0.6 M_⊙)  are expected to behave markedly differently from higher mass remnants  ( M ≳ 0.6 M_⊙)  in the sense that the latter remnants are not expected to expand significantly as a result of the violent H-burning that takes place during the VLTP. We also assess the discrepancy in the born-again times obtained by different authors by comparing the energy that can be liberated by H-burning during the VLTP event.     

High-resolution seabed imagery as a tool for biodiversity conservation planning on continental margins

Submarine canyons increase seascape diversity on continental margins and harbour diverse and abundant biota vulnerable to fishing. Because many canyons are fished, there is an increasing emphasis on including them in conservation areas on continental margins. Here we report on sponge diversity and bottom cover in three canyons of South-eastern Australia, test the performance of biological and abiotic surrogates, and evaluate how biological data from detailed seabed surveys can be used in conservation planning in these habitats. The biological data on sponge assemblage structure and species richness were obtained from 576 seafloor images taken between 148 and 472 m depth, yielding 65 morphospecies. Seafloor characteristics were similar within and between canyons, being almost exclusively composed of sediments with very few rocky substrates of higher relief. This environmental homogeneity did not, however, translate into biological uniformity of the megabenthos, and environmental factors were consequently poor predictors of biological features. By contrast, total bottom cover of sponges was highly correlated with species richness and served as a good proxy for species-level data in this situation. Design strategies that employ information on cover or richness of sponges provided a large dividend in conservation effort by dramatically reducing the number of spatial units required to achieve a specified conservation target of 50–90% of species to be included in reserves. This demonstrates that image-derived data are useful for the design of reserves in the deep sea, particularly where extractive sampling is not warranted. Using biological data on the sponge megabenthos to identify conservation units can also minimise socio-economic costs to fisheries because of a smaller geographic and bathymetric ambit of conservation areas.