In-situ Gesteinsspannungen und Mechanismen der Kluftöffnung

Zusammenfassung Die Orientierung von post-orogenen Klüften in proterozoischen Sedimentgesteinen des Elliot Lake-Gebietes, Canada, läßt sich mit der meßbaren Gesteinsentspannung in Bohrlöchern in Beziehung bringen. Steile lokale und regionale Kluftscharen ohne Bewegungsspuren streichen in Richtung der elastischen Hauptentformungsachse, also in Richtung der größten in-situ-Kompressionsspannung.Die Klüfte lassen sich deshalb wahrscheinlich als Extensionsfugen erklären, und zwar als Resultat der Wechselwirkung zwischen Oberflächenabtrag des Gesteins und remanenter tektonischer Gesteinsspannung. Der vorgeschlagene Mechanismus sollte auch zum Verständnis von spät-orogenen (ac)-Klüften in gefaltetem Deckgebirge und oberflächenparallelen Klüften in massigen Gesteinen beitragen.

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Orientation of post-orogenic joints in Proterozoic sedimentary rocks of the Elliot Lake area (Canada) seems to be directly related to elastic-strain-recovery as measured in boreholes. Steep local and regional joint sets without displacement are parallel with the axis of maximum elastic-strain-recovery (i. e. the direction of the major principal in situ stress component). Consequently these joints are interpreted as extension joints forming as a result of the interaction between natural (or artificial) erosion of the rock mass and its remanent tectonic stresses. The proposed mechanism should also help to understand late-orogenic (ac)-joints in folded cover rocks and exfoliation joints in otherwise unjointed rocks.

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Résumé L'orientation des diaclases post-tectoniques dans des roches sédimentaires protérozoïques de la région du Lac d'Elliot, Canada, peut être mise en relation avec les tensions élastiques des roches telles qu'on peut les mesurer dans les trous de forage. Les systèmes de diaclases redressées, locales et régionales, sans traces de mouvement, sont dirigés parallèlement aux axes principaux de la déformation élastique, c'est-à-dire à la direction de la plus grande compression in situ mesurée par le changement de forme d'un trou de sonde. Par conséquent, les diaclases s'expliquent vraisemblablement comme joints d'extension, et en fait comme le résultat de l'action réciproque entre des tensions tectoniques rémanentes et l'érosion en surface. Le mécanisme proposé explique aussi les diaclase (ac) tardives dans les couvertures plissées et l'exfoliation parallèle à la surface dans les roches massives.

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Orbital evolution studies of planet-crossing asteroids

Numerical integrations of 26 orbits of planet-crossing astetoids of Apollo-Amor type have been performed, in a solar system model including the perturbations by the planets from Venus to Neptune. The 15:th order RADAU integrator (Everhart, 1985) has been used. Orbits for the asteroids 433 Eros, 887 Alinda, 1036 Ganymed, 1221 Amor, 1580 Betulia, 1627 Ivar, 1685 Toro, 1862 Apollo, 1863 Antinous, 1864 Daedalus, 1865 Cerberus, 1915 Quetzalcoatl and 1916 Boreas have been integrated over 100 000 years forward in time and for 1866 Sisyphus, 2102 Tantalus, 2201 Oljato, 2329 Orthos, 3360 1981 VA, 3552 1983 SA, 1981 EJ30, 1985 PA, 1985 WA, 1986 DA 1986 JK and 1986 RA a period of about 33 000 years has been covered. The orbital evolutions of these asteroids are discussed. This work is part of a larger study of the long-term orbital evolution of planet-crossing asteroids and will be continued within the project SPACEGUARD (Milani et al., 1987).     

Effects of lava flows on lunar crater populations

It is shown that endogenic lava flow processes can be identified by their characteristic effects on lunar crater size distributions without necessarily being able to recognise individual flows on the photographs studied. The thickness of lava flows or a series of flows can be estimated from these crater size distribution characteristics. The lava flow histories of the Apollo landing sites 11, 12 and 15 are discussed in detail. The thicknesses of the most recent (3–3.4 × 10⁹ years ago) flows there and of the youngest flows in an area in south-west Mare Imbrium (3 × 10⁹ years) are found to range between 30 and 60 m. The subsequent flow episodes at the landing sites showing up in the crater size distributions can be related to differences in the radiometric ages of the respective lunar rocks.     

Deep structure and kinematics of the Northern Calcareous Alps (TRANSALP Profile)

The Northern Calcareous Alps (NCA) of southern Bavaria and northern Tyrol constitute a carbonate-dominated polyphase fold-thrust wedge; together with its Grauwacken Zone Basement, it is the northernmost part of the far-travelled Upper Austroalpine thrust complex of the Eastern Alps. The present geometry developed in several kinematic stages. Jurassic extensional faults that affected large parts of the NCA and their basement originated when the main part of the NCA was still located southeast of the Central Alpine Ötztal-Silvretta complex. These faults and related facies transitions influenced the later style of detachment of the NCA thrust sheets. Mid to Late Cretaceous detachment, thrust-sheet stacking and motion over the Central Alpine complex are registered in clastic deposits of syntectonic basins. The latest Cretaceous to Cenozoic NNE- to N-directed motion of the NCA towards Europe in front of the Central Alpine complex created another set of significant contraction structures, which at depth overprinted all previous structures. During Cretaceous to Cenozoic deformation, the NCA experienced about 80 km of shortening, i.e., about 73% along the TRANSALP Profile. The European basement and autochthonous Mesozoic cover beneath the allochthonous NCA thrust sheets and flysch complexes seem to have remained relatively undeformed.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Progressive aqueous alteration of CM carbonaceous chondrites

CM chondrites are aqueously altered rocks that contain ∼9 wt% H₂O⁺ (i.e., indigenous water) bound in phyllosilicates; also present are clumps of serpentine-tochilinite intergrowths (previously called “poorly characterized phases” or PCP), pentlandite and Ni-bearing pyrrhotite. We studied 11 CM chondrites that span the known range from least altered to most altered. We used various petrologic properties (many previously identified) that provide information regarding the degree of aqueous alteration. There are no known unaltered or slightly altered CM chondrites (e.g., rocks containing numerous chondrules with primary igneous glass). Some CM properties result from processes associated with early and intermediate stages of the alteration sequence (i.e., hydration of matrix, alteration of chondrule glass, and production of large PCP clumps). Other petrologic properties reflect processes active throughout the alteration sequence; these include oxidation of metallic Fe-Ni, alteration of chondrule phenocrysts, changes in PCP composition (reflecting an increase in the phyllosilicate/sulfide ratio), and changes in carbonate mineralogy (reflecting the development of dolomite and complex carbonates at the expense of Ca carbonate).On the basis of these parameters, we propose a numerical alteration sequence for CM chondrites. Because there are no known CM samples that display only incipient alteration, the least altered sample was arbitrarily assigned to subtype 2.6. The most altered CM chondrites, currently classified CM1, are assigned to subtype 2.0. These highly altered rocks have essentially no mafic silicates; they contain chondrule pseudomorphs composed mainly of phyllosilicate. However, their bulk compositions are CM-like, and they are closer in texture to other C2 chondrites than to CI1 chondrites (which lack chondrule pseudomorphs). Using several diagnostic criteria, we assigned petrologic subtypes (±0.1) to every CM chondrite in our study: QUE 97990, CM2.6; Murchison, CM2.5; Kivesvaara, CM2.5; Murray, CM2.4/2.5; Y 791198, CM2.4; QUE 99355, CM2.3; Nogoya, CM2.2; Cold Bokkeveld, CM2.2; QUE 93005, CM2.1; LAP 02277, CM2.0; MET 01070, CM2.0.The proposed CM numerical alteration sequence improves upon the existing scheme of Browning et al. (1996) in that it does not require a complicated algorithm applied to electron-microprobe data to determine the average matrix phyllosilicate composition. The new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values.New neutron-activation analyses of QUE 97990, QUE 93005, MET 01070, Murchison and Crescent, together with literature data, confirm the compositional uniformity of the CM group; different degrees of alteration among CM chondrites do not lead to resolvable bulk compositional differences. This suggests that the textural differences among individual CM chondrites reflect progressive alteration of similar hypothetical CM3.0 starting materials in different regions of the same parent body, with minimal aqueous transport of materials over appreciable (e.g., meters) distances.     

A Discussion of IGS Solutions and Their Impact on Geodetic and Geophysical Applications

The International Association of Geodesy officially established the International GPS Service (IGS) on Janaury 1, 1994. Its prime objective is to provide support and a rerefence system for a wide variety of scientific and practical applications involving GPS. To fulfill its role the IGS also generates, in addition to its fundamental products (orbital/staion positions and consistent Earth orientation parameters), additional reference-system products providing the necessary infrastructure, standards, and means of calibrations for timing and various atmospheric applications of GPS. The generation and efficient application of IGS products and their impact on a number of positioning and atmospheric applications, including low earth orbit satellites, is reviewed and discussed. @ 1998 John Wiley & Sons, Inc.