8,540 research outputs found
Physical constants of alpine rocks (density, porosity, specific heat, thermal diffusivity and conductivity)
No full textPhysical constans of 110 Alpine rocks are given. They include density, heat capacity, porosity, thermal diffusivity (with special regard to the anisotropy in different fabric directions). Most of the samples were collected in the Lepontine area which was subjected to a Tertiary metamorphism.An der Sitzung vom 18. Januar 1969 legte Herr Prof. E. Wenk ein Manuskript „Physical Coastants of Alpine Rocks (Density, Porosity, Specific Heat, Thermal Diffusivity and Conductivity)", verfasst von H.-R. Wenk und E. Wenk vor. Die Arbeit enthält die Ergebnisse von physikalischen Messungen an alpinen Gesteinen
Wenk, H.-R. Neutron scattering in the Earth Sciences.
No full textBook Review, Reviews in Mineralogy and Geochemistry, Vol. 63, 2006. This newvolume of the Reviews in Mineralogy
and Geochemistry Series, appropriately dedicated
to the late Jim Jorgensen, and carefully edited by
Hans-Rudolf Wenk, is a welcome and timely
additon to this renowned reference book series,
and it meets the high standards set by the previous
volumes
Analysis of P-1, I-1 and C-1 plagioclase structures
No full textThe paper reports the refinement of five plagioclase structures from different geological settings. Compositions and space groups of the samples are An0 (C-1), An66 (I-1), An91 (I-1), An94 (I-1), and An94 (P-1). Emphasis is on calcic plagioclases with highly significant results for 'a', 'b', 'c', and 'd' type reflections. The structural contribution to 'b', 'c', and 'd' type superstructure reflections is investigated with Fourier analysis. The resolution of the X-ray determination of the Al, Si tetrahedral site occupancies is explored. The Na, Ca positions are refined as split sites and found to be differently occupied by Na and Ca atoms, respectively. Individual tetrahedral bond lengths are shown to be highly correlated to their structural environment. Average tetrahedral bond lengths indicate that those four tetrahedra which represent an "albite-like" structural unit in a four-ring chain extending along z in I-1 anorthite maintain their identity also at intermediate compositions while the other four non-equivalent tetrahedra gradually change their Al content from an "anorthite-like" to an "albite-like" ordering pattern.Cette note est relative à l'affinement de la structure de cinq plagioclases de différents contextes géologiques. Les compositions et groupes spatiaux des échantillons sont An0 (C-1), An66 (I-1), An91 (I-1), An94 (I-1) et An94 (P-1). Une importance particulière est attachée aux plagioclases calciques pour lesquels des résultats significatifs sont donnés pour les réflexions de type V, 'b', 'c' et 'd'. La contribution structurale aux réflexions de surstructure de type 'b', 'c' et 'd' est étudiée par analyse de Fourier. On explore la résolution de la détermination par rayons X de l'occupation Al, Si des sites tétraédriques. L'affinement de la position des Na, Ca montre que les sites sont dédoublés, avec un taux d'occupation différent en atomes Na et Ca. Les longueurs de liaison individuelles dans les tétraèdres sont corrélées à l'environnement structural. Les longueurs de liaison moyennes dans les tétraèdres montrent que les quatre tétraèdres qui représentent une unité structurale de "type albite" dans une chaîne à quadruple cycle le long de z dans l'anorthite I-1, gardent leur identité même à des compositions intermédiaires tandis que les quatre tétraèdres non équivalents modifient progressivement leur contenu en Al depuis un arrangement de "type-anorthite" jusqu'à un arrangement de "type-albite".Wenk Hans-Rudolf, Kroll Herbert. Analysis of P-1, I-1 and C-1 plagioclase structures. In: Bulletin de Minéralogie, volume 107, 3-4, 1984. Feldspaths et Feldspathoïdes
Anisotropy in shale from Mont Terri
No full textAnisotropy of shales is the subject of this report, and we use an example of the Jurassic Opalinus Clay from Mont Terri (Switzerland) that is being investigated in the context of radioactive waste disposal. The study is targeted at the geomechanical characterization of shale by laboratory testing. The overall aim is to improve the constitutive material laws and their application in numerical models
Some roots of experimental rock deformation
No full textThe paper reviews the early history of experimental rock deformation in the United States, illustrating how a new branch of science develops around some extraordinary people. Most crucial influence was that of E. Knopf, D. T. Griggs and F. J. Turner. Through their students and associates, experimental rock deformation became what it is today.Cette revue sur l'histoire de la déformation expérimentale des roches aux États-Unis retrace les origines de cette nouvelle branche de la science qui a vu le jour grâce à des personnages extraordinaires. Des rôles importants ont été joués par E. Knopf, D. T. Griggs et F. J. Turner qui, avec leurs élèves, ont mis au point des méthodes et obtenu des résultats qui constituent actuellement les bases de cette science si importante dans le domaine des sciences de la terre.Wenk Hans-Rudolf. Some roots of experimental rock deformation. In: Bulletin de Minéralogie, volume 102, 2-3, 1979. Mécanismes de déformation des minéraux et des roches
Predigt über Lucä XII. 42-44 : gehalten in der Kirche zu Riehen Sonntags den 16 Heumonat 1797. bey der feyerlichen Uebergabe des richterlichen Stabes durch T. Herrn Joh. Lucas Legrand des Raths und Obervogt in Riehen an den neuerwählten Untervogt Johannes Wenk im Meyerhof
No full textAnrede gehalten von T. Herrn Joh. Lucas Legrand des Raths und Obervogt in Riehen an den neuerwählten Untervogt Johannes Wenk im Meyerhof den 16 Heumonat 1797von Joh. Rudolf Huber, Pfarrer zu RiehenAnhang mit eigenem Titelblatt, aber durchlaufender Paginierun
Distribution of plagioclase in Carbonate rocks from the Tertiary metamorphic belt of the Central Alps
No full textA new map is presented which shows the variation of plagioclase composition and the distribution of microscopic crystallographic intergrowths of two or three plagioclases in calcite-bearing rocks from the Tertiary metamorphic belt of the Central Alps. Microprobe and U-stage determinations of An content, performed on well over 600 rocks, demonstrate a regular distribution pattern with a marginal albite-zone and a central core where anorthite occurs. In this central part bytownite-anorthite An80-100 is present in rocks of high normative. An-content, whereas labradorite An60-70 and andesine An30-40 occur in rocks of lower An-content. Rational intergrowths of these phases, spanning over discontinuities in the series, are common. This empirical result confirms that, depending on rock composition, plagioclases An30-40, 60-70 and 80-100 coexist over a broad range of P-T conditions. But the central region An > 80 is surrounded by zones of lower anorthite content, and isograds An40, 30 and 17 can be drawn. We conclude that intermediate feldspars form also at lower temperature than anorthite. Our results refer to long range ordered superstructures of low plagioclases, not to disordered high plagioclases. They concern systems with high CO₂-pressure, but compare favourably with experimental results of Goldsmith (1982).
Anorthite-isograds are compared with the distribution of Al₂SiO₅ polymorphs. The isograds "staurolite and kyanite in" closely coincide with the line An30 calcite. The boundaries An 17 for calcite- and calcic amphibole-assemblages are almost identical.On présente sur une carte les variations de la composition des plagioclases et la distribution d'intercroissances cristallographiques microscopiques de deux ou trois plagioclases dans des roches calcaires de la ceinture métamorphique tertiaire des Alpes centrales. La détermination du contenu en An par microsonde et à la platine universelle sur plus de 600 roches montre un diagramme de distribution régulier avec une zone d'albite marginale et une partie centrale ou apparaît l'anorthite. On trouve dans cette partie centrale des bytownites-anorthites An80-100 dans des roches de forte teneur en An normative, tandis que la labradorite An60-70 et l'andésine An30-40 apparaissent dans des roches de plus faible teneur en An. Des intercroissances rationnelles de ces phases sont communes, s 'étendant par dessus les discontinuités dans les séries. Ce résultat empirique confirme que, selon la composition de la roche, les plagioclases An30-40, 60-70 et 80-100 coexistent sur un large domaine de conditions P/T. Mais la région centrale avec An > 80 est entourée de zones de plus faible teneur en An, et l'on peut tracer des isogrades An40, 30 et 17. On en déduit que les feldspaths intermédiaires se forment aussi à plus basse température que l'anorthite. Nos résultats s'appliquent aux structures ordonnées à longue distance des plagioclases BT et non aux plagioclases HT désordonnés. Ils concernent les systèmes à haute pression de CO₂ et sont en bon accord avec les résultats expérimentaux de Goldsmith (1982).
On compare les isogrades de l'anorthite avec la distribution des polymorphes Al₂SiO₅. Les isogrades "staurolite et disthène" coïncident avec la ligne An30 calcite. Les limites An 17 pour la calcite et l'amphibole calcique sont presque identiques.Wenk Eduard, Wenk Hans-Rudolf. Distribution of plagioclase in Carbonate rocks from the Tertiary metamorphic belt of the Central Alps. In: Bulletin de Minéralogie, volume 107, 3-4, 1984. Feldspaths et Feldspathoïdes
Preferred orientation of phyllosilicates: Comparison of fault gouge, shale and schist
No full textSamples of fault gouge from the San Andreas Fault drill hole (SAFOD), a shale from the North Sea sedimentary basin and schists from metamorphic rocks in the Alps have been analyzed with high energy synchrotron X-rays to determine preferred orientation of mica and clay minerals. The method relies on obtaining 20 diffraction images which are then processed with the crystallographic Rietveld method, implemented in the software MAUD, allowing for deconvolution of phases and extraction of their orientation distributions It is possible to distinguish between detrital like/muscovite and authigenic illite/smectite, kaolinite and chlorite, and muscovite and biotite, with strongly overlapping peaks in the diffraction pattern The results demonstrate that phyllosilicates show large texture variations in various environments, where different mechanisms produce the rock microfabrics. fault gouge fabrics are quite weak and asymmetric with maxima for (001) in the range of 15-25 multiples of random distribution (m.rd.). This is attributed to heterogeneous deformation with randomization, as well as dissolution precipitation reactions. Shale fabrics have maxima ranging from 3 to 9 m.r.d and this is due to sedimentation and compaction. The strongest fabrics were observed in metamorphic schists (10-14 m.r.d) and developed by deformation as well as recrystallization in a stress field. In the analyzed samples, fabrics of co-existing quartz are weak. All phyllosilicate textures can be explained by orientation of (001) platelets, with no additional constraints on a-axes (C) 2010 Elsevier Ltd. All rights reserve
Microlite orientation in obsidian flow measured by synchrotron X-ray diffraction
Get PDFClinopyroxene and plagioclase (andesine) microlites in an obsidian flow from Glass Mountain (NE California, USA) display strong alignment. Synchrotron X-ray diffraction, coupled with Rietveld analysis, was used to quantify crystallographic-preferred orientation (CPO). Clinopyroxene, with a rod-shaped morphology, shows a strong alignment of [001] in the flow direction and (010) aligned parallel to the inferred flow plane. Andesine, with a platy morphology, displays an alignment of (010) platelets in the flow plane. Some pole densities exceed 90 multiples of random distribution. Applying a model of rigid ellipsoidal inclusions in a viscous matrix, the local pure shear strains are between 2 and 3
Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete
Get PDFPozzolanic reaction of volcanic ash with hydrated lime is thought to dominate the cementing fabric
and durability of 2000-year-old Roman harbor concrete. Pliny the Elder, however, in first century CE
emphasized rock-like cementitious processes involving volcanic ash (pulvis) “that as soon as it comes
into contact with the waves of the sea and is submerged becomes a single stone mass (fierem unum
lapidem), impregnable to the waves and every day stronger” (Naturalis Historia 35.166). Pozzolanic
crystallization of Al-tobermorite, a rare, hydrothermal, calcium-silicate-hydrate mineral with cation
exchange capabilities, has been previously recognized in relict lime clasts of the concrete. Synchrotron-based
X-ray microdiffraction maps of cementitious microstructures in Baianus Sinus and Portus
Neronis submarine breakwaters and a Portus Cosanus subaerial pier now reveal that Al-tobermorite
also occurs in the leached perimeters of feldspar fragments, zeolitized pumice vesicles, and in situ
phillipsite fabrics in relict pores. Production of alkaline pore fluids through dissolution-precipitation,
cation-exchange and/or carbonation reactions with Campi Flegrei ash components, similar to processes
in altered trachytic and basaltic tuffs, created multiple pathways to post-pozzolanic phillipsite and
Al-tobermorite crystallization at ambient seawater and surface temperatures. Long-term chemical
resilience of the concrete evidently relied on water-rock interactions, as Pliny the Elder inferred. Raman
spectroscopic analyses of Baianus Sinus Al-tobermorite in diverse microstructural environments
indicate a cross-linked structure with Al3+ substitution for Si4+ in Q3
tetrahedral sites, and suggest
coupled [Al3++Na+
] substitution and potential for cation exchange. The mineral fabrics provide a geoarchaeological
prototype for developing cementitious processes through low-temperature rock-fluid
interactions, subsequent to an initial phase of reaction with lime that defines the activity of natural
pozzolans. These processes have relevance to carbonation reactions in storage reservoirs for CO2 in
pyroclastic rocks, production of alkali-activated mineral cements in maritime concretes, and regenerative
cementitious resilience in waste encapsulations using natural volcanic pozzolans
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