Modelling Compositional Change: The Example of Chemical Weathering of Granitoid Rocks

Perturbation on the simplex is an operation which can be used to numerically describe changes in the composition of, for example, soils, sediments, or rocks. The combination of perturbation and power transformation provides a strong tool for analyzing compositional linear processes in the simplex. When the process is constrained in the sense of a well-known starting (or final) composition, noncentred principal component analysis can be used to estimate the leading perturbation vector of the process. Applying these mathematical tools to chemical major element data from a weathering profile developed on granitoid rocks allows us to model the compositional changes associated with the process of chemical weathering. The comparison of these results with the compositional linear trend defined by erosional products of several of the world's major drainage systems yields close similarities. The latter observation allows for a mathematical formulation of a global mean weathering trend within the system Al₂O₃–CaO– Na₂O– K₂O. We further demonstrate the usefulness of the approach for validating processes behind individual trends and for combining the effects of different processes which modify the composition of soils, sediments, and rocks. Alternatives to the Chemical Index of Alteration (CIA) are discussed to obtain a translation-invariant scale for the process of chemical weathering.     

Active mud volcanoes on- and offshore eastern Makran, Pakistan

To study the activity, source and driving force of the venting of fluidized mud in the coastal Makran, we carried out reconnaissance surveys of two active onshore mud volcano fields (Chandragup and Jebel-u-Ghurab) and of a newly born (March 1999) offshore mud volcano (Malan Island). All studied on- and offshore mud volcanoes line up along one southwest/northeast-trending structural lineament, the axis of the Dhak Anticline. Isotopic data point to a bacterial origin of the gas (mainly methane). Mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub-surface depth of 2-3 km. Observed mud discharge varied between 0 and 1.4 m³ h^-1 and gas discharge rates between negligible amounts to 1 m³ s^-1. Mud temperatures in the crater lake of Chandragup I are near-ambient temperatures. They rise slightly (Б.5°C) during episodes of modest mud outflow. An area of 160,000 m³ of soft mud was vigorously extruded from the sea floor at a water depth of 10 m within days after 15 March 1999, forming Malan Island. The island was destroyed within a few months after its birth by deep-reaching wave action during the SW monsoon. This was possibly aided by local subsidence of the mud volcano structure due to the volume loss following rapid degassing and mud extrusion.     

Extraction replica and ion beam thinning techniques — New tools in manganese nodule research

In extension of earlier work by v. Heimendahl et al. (1976, 1977) two more electron microscopic techniques were applied for manganese nodule investigations. Both of them were successful to study the bulk, undisturbed nodule material, being prepared for transmission electron microscopic specimens — in contrast to the earlier reported powder results. Applications concern details of the so-called A- and B-nodules as described by Halbach et al. (1975, 1978).     

Zur stratigraphischen und morphologischen Altersbestimmung von Altflächen

Zusammenfassung Morphologische Altflächen können mit morphologischen und stratigraphischen Mitteln datiert werden. Die verschiedenen Ergebnisse solcher Datierungen an den gleichen Flächen beruhen darauf, daß verschiedenes bestimmt wird. Die Bestimmungen beziehen sich entweder auf die Anlage der Fläche oder auf ihr Endstadium. Dazwischen liegen Daten, die einen Weiteroder Fortbau der Fläche anzeigen; die meisten in der Literatur veröffentlichten Daten beziehen sich auf solche Zwischenstadien.An einigen Beispielen wird die Komplexität einer morphologischen Fläche gezeigt, die mehr ein dynamisches Lebewesen als eine statische Fläche wie eine Schichtfläche ist.

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Morphological paleoplains can be dated using morphological and stratigraphical means. The different results obtained from such kinds of dating of the same plains are due to the different aims of determination. They either refer to the origin of the plain or to its end phase. In-between-lying data indicate the progress and development in the formation of the plain. Most of the data published in literature refer to such intermediate stages.A number of examples shows the complexity of a morphological plain which is a dynamic organism rather than a static plain such as a bedding plane.

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Résumé Des surfaces anciennes morphologiques peuvent être soumises à une détermination d'âge à l'aide de méthodes morphologiques et stratigraphiques. Les résultats différents d'une telle détermination d'âge réalisée pour les mêmes surfaces se fondent sur le fait de ce que la détermination se réfère à des facteurs divers. Les déterminations se réfèrent ou à la formation de la surface ou à son stade final. Entre ces deux points d'extrémité il existe des données indiquant la formation continuée ou sous forme de différentiation de la surface. La plupart des données publiées dans la littérature se réfère à de tels états intermédiaires.A l'aide de plusieurs exemples l'auteur démontre la complexité d'une surface morphologique, laquelle donne plutôt l'aspect d'un être vivant dynamique que celui d'une surface statique tel que ce dernier cas se présente, par exemple, pour un plan de stratification.

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A gamma spectrometric study of Mont-Blanc granite samples

Summary Gamma-ray spectra of the samples were measured by standard laboratory multichannel spectrometry. The weighted least squares method was applied to the digital output data in order to determine the concentrations of U²³⁸, Th²³² and K⁴⁰ present. U and Th increase towards the rim of the massif (from 4 ppm U and 20 ppm Th in the coarse-grained central facies to 23 ppm U and 42 ppm Th in the fine-grained rim variety), whereas K remains fairly constant at 3.85%.On leave Eidgenössische Technische Hochschule, Zurich (Switzerland)     

Intergrowth and twinning in opal-CT lepispheres

Under conditions of unobstructed diagenetic growth, opal-CT usually forms spherical aggregates, so-called lepispheres. From a scanning electron microscope study of deep-sea porcelanites, the development of these structures is described, from isolated opal-CT platelets via complete lepispheres to large coalescent aggregates. The conspicuous symmetric ultrastructure of lepispheres—reflected by the constancy of angles between interpenetrating crystal blades—is crystallographically determined: The lepispheres consist of groups of opal-CT blades intergrown according to the (30–34) and (10–16) twinning laws of tridymite. The same rules of intergrowth can be applied to the morphology of hydrothermally synthesized opal-CT lepispheres.     

Neue methoden der sonnenbeobachtung

Ohne Zusammenfassung