Heat production and seismic velocity of crustal rocks

Heat production of the continental crust can be determined from the seismic velocity structure. There is, however, a significant scatter in the determination, partly caused by the quality of geothermal data and partly by the fact that seismic velocity and radiogenic heat production are not uniquely related to each other by the chemical composition of rocks.     

Contiguous Laurentia and Baltica before the Grenvillian-Sveconorwegian orogeny?

Close geochronological correspondence of Mesoproterozoic extension-related magmatism and comparable tectonic and geochronological evolution of the Grenville and Svecononvegian orogens suggests that the Laurentian and Baltic Shields could have been joined during the Mesoproterozoic and did not separate until after the Grenvillian-Sveconorwegian orogeny. The combined Grenville-Svecononvegian orogen is here interpreted to have formed during the collision of coherent Laurentia-Baltica with an unknown craton, which is in contrast to earlier explanations that favour a late-Mesoproterozoic rotation between Laurentia and Baltica followed by collision of these two cratons with each other.     

X-ray spectroscopy of stellar coronae: History - present - future

Since in 1948 X-rays were detected from the solar corona, stellar coronae were among the first predicted non-solar X-ray sources. However, because of their relatively low X-ray luminosity, the first non-solar stellar corona was not detected in X-rays until 1974 - twelve years after the discovery of the first non-solar X-ray source. After the 1980s, with the advent of sensitive X-ray imaging instruments on board the EINSTEIN, EXOSAT, and later the ROSAT observatories, the study of stellar coronae has become a vastly growing field of research. These X-ray observations have demonstrated that X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. The instruments on board these satellites provided for the first time a taste of what can be achieved with X-ray spectroscopy and with the advent of the EUVE (1992) and ASCA (1993), detailed spectroscopy of stellar coronae in the EUV and X-ray regimes got off to a real start. The observations have permitted the identification of coronal material at different temperatures whose existence relates to a range of possible magnetic loop structures in the hot outer atmospheres of stars. The higher spectral resolution of the next generation of spectrometers on board NASA's AXAF (1998), ESA's XMM (1999), and the Japanese ASTRO-E (2000) will improve the determination of coronal temperature structure, abundances, and densities from which loop geometries can be derived and will enable velocity diagnostics. This paper reviews our present knowledge of observational stellar X-ray spectroscopy up to EUVE and ASCA and briefly discusses the perspectives for coronal diagnostics offered by AXAF, XMM, and ASTRO-E.Dedicated to Cornelis de Jager     

Late Holocene tephrochronology of the northern Antarctic Peninsula

Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct ¹⁴C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.     

Deterministic and stochastic parameters in inertial survey adjustment

In the adjustment of inertial position surveys the additional parameters describing the systematic errors of individual traverses can be considered as deterministic or stochastic. The paper deals with various aspects of the deterministic or stochastic approach by way of a standard functional model. If purely deterministic parameters are set up, the solvability of the least squares problem depends on redundant observations like coordinate discrepancies of forward and backward runs or coordinate differences at cross-over points of traverse networks. Inequalities are presented to handle the configuration problem for any net and for several ways of introducing parameter sets. Also condition equations being geometrically explainable are developed solving the datum problem in free adjustment applications. Based on the Ebersberger Forst campaigns with a large amount of Ferranti, Honeywell and Litton data, numerical investigations into the stochastic properties of the additional parameters and the observations follow. It turns out that additional parameters for Honeywell and Litton data can be considered as stochastic parameters while for Ferranti data significant azimuth and time dependent effects can be found. The investigations of true errors show that in case of the deterministic adjustment approach a diagonal covariance matrix can be introduced and in case of stochastic additional parameters a first order Gauss-Markov process serves as a good approximation for the stochastic behaviour of the observations.     

The changing geography of traditional medicine: Urban herbalism on the Witwatersrand,South Africa

While medical geographers have generally ignored medical pluralism in developing countries, a small but significant geographical literature on traditional medicine has emerged. Progress for research by geographers on traditional medicine lies through a broader contextualisation of medical pluralism sensitive to the socio-economic and political context of health and disease. In this paper, a brief overview of medical pluralism in South Africa is presented. Issues surrounding the changing geography of traditional medicine are illustrated with reference to urban herbalism on the Witwatersrand.     

Experimental Na-K distribution between amphiboles and aqueous chloride solutions, and a mixing model along the richterite – K-richterite join

The cation exchange equilibrium has been investigated by hydrothermal experiments at 700 and 800°C at 200 MPa. To avoid equilibration problems of conventional exchange experiments, we synthesized amphiboles with an excess fluid allowing exchange between solid and fluid during the experiment. The exchangeable cations Na and K were provided as excess 1 to 2n chloridic solution. These exchange syntheses can be described by the reaction equation with ^(aq) for hydroxides and chlorides in aqueous solutions and _{( s )} and _{( p )}?=?start and product fluid. The amphiboles grew in presence of the exchange fluid and adjusted their stoichiometry in equilibrium with the fluid phase. The solid products consist of more than 99% amphibole (Na,K-richterite_ss) with traces of diopside and quartz. The amphiboles are up to 1?mm long and often ≈ 40 μm thick. Detailed EMP- and HRTEM-observations show that they are chemically homogeneous and structurally wellordered. The experimental results give consistent phase relations in the reciprocal ternary system Na-richterite–K-richterite–NaCl–KCl. We analysed the product fluid with AAS- and ICP-methods. The Na-K distribution coefficients between fluid and amphiboles of the richterite–K-richterite join are close to unity at 700°C and 800°C at 200 MPa. Small systematic deviations are explained by a symmetric solution model for the A-position of the amphiboles. Using ideal mixing for H₂O-NaCl-KCl fluids, a mixing model for the system richterite–K-richterite is presented. We suggest that the composition of richterite solid solutions can be used as a sensor for NaCl/KCl-ratios in metamorphic fluids.     

Faltung und Klüftung im Nordteil des Rheinischen Schiefergebirges

Zusammenfassung Die Ergebnisse von Untersuchungen der Kleintektonik in Grauwacken und Kalken im Nordteil des Rheinischen Schiefergebirges lassen darauf schließen, daß die Klüfte zu Beginn der Faltung aufrissen und ursprünglich senkrecht auf der Schichtfläche standen.Unter dieser Voraussetzung lassen die Klüfte als Vorzeichnung die Deformation der Bänke während der Faltung erkennen und ermöglichen eine zeitliche Einordnung der Vorgänge bei der Faltung. Es ergibt sich für die Faltung folgendes Bild:Mit der ersten leichten Verbiegung der Schichten bilden sich zwei Kluft-systeme aus, das eine symmetrisch zur Kraft, die die Faltung bewirkte, das zweite symmetrisch zum Biegungsfließen. Beide Systeme konnten sich entwickeln, ohne daß sie sich gegenseitig störten. Man muß also schließen, daß der Kluftabstand erst nach und nach verringert wurde und beide Systeme, im ganzen gesehen, gleichzeitig entstanden. Aus dem frühen Auftreten des Biegungsfließens, dessen Richtung dem heutigen Faltenbild entspricht, geht hervor, daß schon bei Beginn der Faltung das heutige Faltungsbild im großen und ganzen angelegt war und daß Faltung nicht nur Verbiegung der Schichten um die Faltenachse, sondern auch Verbiegung der Faltenachse bedeutet.Solange die Neigung der Schichten 20° bis 30° nicht überschritt, konnten die meisten auftretenden Spannungen durch das Biegungsfließen ausgeglichen werden. Bei der weiteren Faltung übernahm der Faltungsvorschub die Rolle des Biegungsfließens. Die Richtung des Faltungsvorschubes wurde durch Verwerfungen bestimmt, die also älter als der Faltungsvorschub sein müssen. Außerdem ließ sich feststellen, daß der Faltungsvorschub teilweise eine selbständige Bewegung ist, die aus dem Faltenmechanismus allein nicht erklärt werden kann.Das hier Aufgeführte ist das Ergebnis einer Anfangsstudie. Sie war Gegenstand einer Dissertation unter Leitung von Herrn Professor Dr.Hans Cloos. Ihm möchte ich dafür danken, daß er mich zur kleintektonischen Betrachtungsweise angeregt und mir in vielen Stadien der Arbeit geraten und geholfen hat. Den Herren Professor Dr.Bruno Sander, Professor Dr.Georg Knetsch, Dr.Sigismund Kienow, Dr.Gerhard Oertel und Dr.Herbert Karrenberg verdanke ich wertvolle Hinweise. Nicht zuletzt möchte ich an dieser Stelle meine Frau nennen, die sowohl bei den Geländemessungen als auch bei der Fertigstellung des Manuskriptes mich immer unterstützt hat.     

Predator-Prey Interaction between two Competing Sea Star Species of the Genus Astropecten

Abstract. The predator-prey interaction between two sea star species of the genus Astropecten known to be competitors was investigated at Costa Colostrai, Sardinia, Italy by means of SCUBA-Diving. It was estimated that predation of A. aranciacus would eliminate about 1 % of the prey population of A. bispinosus daily. Because densities of A. bispinosus were observed to be unaltered during the summer months, a considerable immigration of A. bispinosus into the area has to be postulated. A. bispinosus represents 40% of the dry organic matter consumed by A. aranciacus , and is one of the most important food items of this species.
A. aranciacus is not more efficient in preying upon A. bispinosus than in preying upon other food items; but efficiency is greater upon buried sea stars than upon walking ones.
Consequences for stability of the local ecosystem are discussed.