High-pressure relics in meta-sediments intercalated with the Weissenstein eclogite,Münchberg gneiss complex,Bavaria

The mineral assemblages in the eclogites and meta-sediments of the Münchberg gneiss complex suggest minimum pressures of about 15 kbar, and temperatures of 600±30° C for the eclogite-facies metamorphism. Both rock types underwent a subsequent amphibolite-facies metamorphism at almost the same temperature range. In the Weissenstein borehole the eclogites and meta-sediments show an intimate interlayering on a centimetre scale. Contacts between the two rock types are often sharp and untectonized suggesting in-situ metamorphism of the eclogites. The following features indicate that the gneisses were subjected to eclogite-facies metamorphism:

1. Phengite relics and phengite inclusions in garnet contain up to 3.45 Si per formula unit while amphibolite facies phengites have considerably lower Si-contents (3.0–3.25 p.f.u.).
2. Omphacite relics occur in the form of Na-augite (6–9 mol% jadeite)-oligoclase symplectites.
3. Garnets with up to 40 mol% of the pyrope component occur.

The geological and mineral-chemical data indicate that large volumes of crustal material have been buried to depths possibly exceeding 70 km. The preservation of primary eclogitic textures as well as symplectitic textures in the presence of a fluid phase, are indicative of a rapid decompression. This would suggest a tectonic uplift (e.g. underthrusting) as is also indicated by the virtually constant temperature range during the uplift.     

A new view of martian evolution

Conventional evolutionary models for Mars adopt a dry mantle solidus. Taking into account the condensation conditions in the preplanetary nebula in the accretion zone of Mars, it can be concluded that large amounts of water or hydrated silicates have condensed in those regions. Therefore, water influences significantly the melting behaviour and the viscosity of the silicatic material. A model for the calculation of the thermal history of a planet is constructed. On this basis, and use of water — saturated solidus — it is possible to derive that the core is not liquid, as given in models employing a dry mantle solidus, but solid to a large extent, which prevents the operation of a large-scale dynamo and explains in that way the lack of a magnetic field. With these assumptions one can construct a possible evolutionary scheme that covers early crust differentiation, a hot thermal past and the missing magnetic field at present.     

Eine hochempfindliche Emanometer-Anordnung und ihre Anwendung zur Bestimmung des Radongehalts von Quellen und Seen in Oberbayern

Zusammenfassung Es wird eine Anordnung zur genauen und zuverlässigen Messung des Emanationsgehaltes von Luft und Wasser beschrieben. Die Entemanierung geschieht dabei ohne Benutzung einer mechanischen Pumpe; die Emanation kommt nur mit Glas und mit der zu untersuchenden Flüssigkeit in Berührung. Radonbestimmungen an See- und Quellwasser im oberbayrischen Raum lassen wichtige Gesetzmäßigkeiten geologischer und geophysikalischer Art für den Emanationsgehalt erkennen.

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Summary A device for exact and reliable measurements of the emanation content of air and water is described. The disemanation is effected without a mechanical pump; the emanation comes into contact only with glass and with the fluid to be investigated. Radon determinations of water from lakes and springs in the region of Upper Bavaria show important relations of the emanation content to geological and geophysical conditions.

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Résumé On décrit un procédé pour la mesure exacte et sûre de l'émanation dans l'air et dans l'eau. La séparation du gaz s'y fait sans intervention d'une pompe mécanique. L'émanation n'entre ainsi en contact qu'avec du verre et le liquide à analyser. Des déterminations de radon faites dans l'eau de lacs et de sources de Haute Bavière permettent d'établir des rapports étroits entre les quantités d'émanation recueillies et les conditions géologiques et géophysiques.

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Mit 3 Textabbildungen     

The transpressional connection between Dom Feliciano and Kaoko Belts at 580�C550?Ma

A new U?CPb SHRIMP age of 551?±?4?Ma on a mylonitic porphyry that intruded into the Sierra Ballena Shear Zone (Southernmost Dom Feliciano Belt, Uruguay) and a review of relevant published data make possible a more refined correlation and reconstruction of Brasiliano/Pan-African transpressional events. Paleogeographic reconstruction, kinematics and timing of events indicate a connection between the shear systems of the Dom Feliciano and Kaoko Belts at 580?C550?Ma. Sinistral transpression recorded in shear zones accommodates deformation subsequent to collision between the Congo and Río de la Plata Cratons. The correlation is strengthened by the similarity of magmatic and metamorphic ages in the Coastal Terrane of the Kaoko Belt and the Punta del Este Terrane of the Dom Feliciano Belt. This post-collisional sinistral transpression brought these units near to their final position in Gondwana and explains the different evolution at 550?C530?Ma. While in the Kaoko Belt, an extensional episode resulted in exhumation as a consequence of collision in the Damara Belt, in the Dom Feliciano Belt, sinistral transpression occurred associated with the closure of the southern Adamastor Ocean due to Kalahari-Río de la Plata collision.     

The tectonic significance of K/Ar illite fine-fraction ages from the San Luis Formation (Eastern Sierras Pampeanas, Argentina)

The Sierra de San Luis forms the southern tip of the Eastern Sierras Pampeanas in central Argentina. Two narrow belts of low-grade phyllites and quartz arenites, i.e. the San Luis Formation, have accommodated part of the strain-related differential exhumation of the medium- to high-grade metamorphic domains that constitute to the basement complex of the sierra. Eleven phyllite samples were subjected to the K/Ar fine-fraction dating technique. Results are interpreted in relation to the Kübler index of the illites, which indicate epimetamorphic conditions for the majority of the samples. Obtained ages between 330 and 290 Ma cover a period of compressional tectonics in the late Mississippian (Visean/Serpukhovian boundary) followed by the subsidence during the formation of the Paganzo Basin in the provinces of La Rioja and San Luis. These tectonic movements are coincident with the Toco orogeny in northern Chile and southern Bolivia. This suggests that the older K/Ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement.     

Influence of shape fabric and crystal texture on marble degradation phenomena: simulations

Microstructure-based finite element simulations were used to study the influence of grain shape fabric and crystal texture on thermoelastic responses related to marble degradation phenomena. Calcite was used as an illustrative example for studying extremes of shape preferred orientation (SPO) in shape fabric and lattice preferred orientation (LPO) in crystal texture. Three SPOs were analyzed: equiaxed grains, elongated grains, and a mixture of equiaxed and elongated grains. Three LPOs were considered: a random orientation distribution function and two degrees of strong directional crystal texture. Finally, the correlation between the direction of the LPO with respect to that of the SPO was examined. Results show that certain combinations of SPO, LPO, and their directional relationship have significant influence on the thermomechanical behavior of marble. For instance, while there is no major dependence of the elastic strain energy density and the maximum principal stress on SPO for randomly textured microstructures, there is a strong synergy between LPO and its directional relationship with respect to the SPO direction. Microcracking precursors, elastic strain energy density, and maximum principal stress, decrease when the crystalline c-axes have fiber texture perpendicular to the SPO direction, but increase significantly when the c-axes have fiber texture parallel to the SPO direction. Moreover, the microstructural variability increases dramatically for these latter configurations. In general, the influence of LPO was as expected, namely, the strain energy density and the maximum principal stress decreased with more crystal texture, apart from for the exception noted above. Spatial variations of these precursors indicated regions in the microstructure with a propensity for microcracking. Unexpectedly, important variables were the microstructural standard deviations of the spatial distributions of the microcracking indicators. These microstructural standard deviations were as large as or larger than the variables themselves. The elastic misfit-strain contributions to the coefficients of thermal expansion were also calculated, but their dependence was as expected.     

Natural building stones of Mexico–Tenochtitlán: their use, weathering and rock properties at the Templo Mayor, Palace Heras Soto and the Metropolitan Cathedral

In the Aztec period and in colonial times different natural stones originating in the Valley of Mexico were used for building construction. Stone weathering was investigated onsite at various historical buildings within the old quarter of Mexico City. In this study, different aspects of weathering and deterioration at three significant historical buildings will be presented, the Aztec excavation site Templo Mayor, the Metropolitan Cathedral, and the colonial palace of the dukes of Heras Soto. Petrophysical properties of the main building stones of these structures were investigated like density, porosity, pore radii distribution, water uptake rate and coefficient, thermal and hygric expansion, and the mechanical properties of uniaxial compressive strength. A relationship between single critical property values, according to anisotropy fabric characteristics, and specific weathering forms could be deduced.     

Dolomitic slates from Uruguay: petrophysical and petromechanical characterization and deposit evaluation

Slates are internationally known as roof and façade-cladding material since prehistoric times. The methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones. This has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes. In Uruguay several slates are mined and used in architecture, especially as façade cladding and floor slabs. The most important slates regarding their production and utilization are the dolomitic slates. These dolomitic slates are associated with the Neoproterozoic thrust and fold belt of the Dom Feliciano belt. Representative samples have been geochemically and petrographically characterized, as well as petrophysically and petromechanically analyzed. The petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new European standards, showing values comparable to those registered for internationally known slates. Detailed structural and deposit analysis were carried out in Uruguay in order to evaluate the dolomitic slate deposits. The slates are linked to calc-silicate strata in a greenschist facies volcano-sedimentary sequence and the deposits are located in the limb of a regional fold, where bedding and cleavage are parallel. The main lithotype is a layered and fine-grained dolomitic slate with a quite diverse palette of colors: light and dark green, gray, dark gray, reddish and black. The mined slate is split into slabs 0.5–2 cm thick. In the past, the average production in Uruguay was around 4,000 tons/year and a historical maximum of 13,000 tons was reached in 1993 (Oyhantçabal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity, but our investigation shows a considerable volume of indicated resources and therefore a very good potential.