Weakening and strain localization produced by syn-deformational reaction of plagioclase   总被引：2，自引：0，他引：2  

Holger Stünitz  Jan Tullis 《International Journal of Earth Sciences》2001,90(1):136-148

There are many observations in naturally deformed rocks on the effects of mineral reactions on deformation, but few experimental data. In order to study the effects of chemical disequilibrium on deformation we have investigated the hydration reaction plagioclase + H₂OM more albitic plagioclase + zoisite + kyanite + quartz. We utilized fine-grained (2-6 µm) plagioclase aggregates of two compositions (An54 and An60), both dried and with 0.1-0.4 wt% H₂O present, in shear deformation experiments at two sets of conditions: 900 °C, 1.0 GPa (in the plagioclase stability field) and 750 °C, 1.5 GPa (in the zoisite stability field). Dry samples and those deformed in the plagioclase stability field underwent homogeneous shearing by dislocation creep, but samples with 0.1 to 0.4 wt% water deformed in the zoisite stability field showed extreme strain localization into very narrow (~1-3 µm) shear bands after low shear strain. In these samples the microstructures of reaction products in the matrix differ from those in the shear bands. In the matrix, large (up to 400 µm) zoisite crystals grew in the direction of finite extension, and relict plagioclase grains are surrounded by rims of recrystallized grains that are more albitic. In the shear bands, the reaction products albitic plagioclase, zoisite, white mica, and traces of kyanite form polyphase aggregates of very fine-grained (<0.1 µm) dislocation-free grains. Most of the sample strain after % ~2 has occurred within the shear bands, within which the dominant deformation mechanism is inferred to be diffusion-accommodated grain boundary sliding (DAGBS). The switch from dislocation creep in dry samples deformed without reaction to DAGBS in reacted samples is associated with a decrease in flow stress from ~800 to <200 MPa. These experiments demonstrate that heterogeneous nucleation driven in part by chemical disequilibrium can produce an extremely fine-grained polyphase assemblage, leading to a switch in deformation mechanism and significant weakening. Thus, localization of deformation in polyphase rocks may occur on any pressure (P),temperature (T)-path where the equilibrium composition of the constituent minerals changes.  相似文献   

Two counterrotating eddies in the Eastern North Atlantic: Lagrangian observations     

Holger Klein 《Ocean Dynamics》1990,43(1):19-26

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A note on momentum transfer in the bottom mixed layer of the West European Basin     

Holger Klein 《Ocean Dynamics》1988,41(2):45-56

Summary About 20 benthic storms, originated by deep reaching eddies, have been observed between September '83 and May '86 in the deep West European Basin. First results show, that these eddies influence the dispersion of tracers in the near-bottom layers significantly, e.g. due to deformation by shear. This paper is an attempt to estimate the eddy viscosity tensor in the bottom mixed layer. It will be examined as in to how far benthic storms and vortices result in changes of momentum transfer within this layer. The results indicate that the influence of these phenomena is mainly restricted on meso-scale processes.

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Über den Impulsaustausch in der durchmischten Bodenschicht des Westeuropäischen Beckens

Zusammenfassung Zwischen September 83 und Mai 86 wurden in der Tiefsee des Westeuropäischen Beckens 20 benthische Stürme beobachtet, die durch tiefreichende Wirbel verursacht wurden. Erste Ergebnisse zeigen, daß diese Wirbel die Ausbreitung von Stoffen in den bodennahen Schichten erheblich beeinflussen können, z. B. durch Deformation von Wasserkörpern infolge von Scherung. In dieser Arbeit wird versucht, den Impulsaustauschtensor in der durchmischten Bodenschicht abzuschätzen. Ferner wird untersucht, inwieweit benthische Stürme oder Wirbel den Impulsaustausch in dieser Schicht beeinflussen. Die Ergebnisse zeigen, daß sich ihr Einfluß im wesentlichen auf mesoskalige Prozesse beschränkt.

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Contribution à l'étude des transports d'énergie dans la couche profonde du bassin ouest-européen de l'Atlantique Nord

Résumé Une vingtaine de tempêtes benthiques provoquées par des tourbillons à fort développement vertical ont été observées de septembre 1983 à mai 1986 dans les profondeurs du bassin ouest-européen de l'Atlantique Nord. Les premiers résultats montrent que ces tourbillons exercent une influence significative sur la dispersion des traceurs disposés dans les couches proches du fond, par suite des déformations dues au cisaillment. Une tentative d'estimation du tenseur de viscosité du tourbillon dans la couche de mélange profonde est proposée dans la présente contribution, qui étudie dans quelle mesure les tempêtes benthiques et les systèmes tourbillonnaires engendrent des modifications du transfert d'énergie cinétique au sein de cette couche. Les résultats semblent indiquer que l'influence de ces phénomènes n'est surtout sensible que pour les processus méso-échelle.

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Modelling the responses of mature forest trees to air pollution     

Heiner Schäfer Dr.  Hartmut Bossel  Holger Krieger  Norbert Trost 《GeoJournal》1988,17(2):279-287

Systems analysis of the responses of forest trees to air pollutants led to mathematical models which represent the essential life processes of mature trees (photosynthesis, respiration, growth etc.) under ‘normal’ conditions and — especially — under pollution strees. Computer simulations using these models have made it possible to test and analyse the consequences of — known or hypothetical — pollution effects. The simulation runs have led to the identification of three distinct behavioural modes (growth, stagnation, breakdown) and corresponding stable and unstable system states. The results have produced new insights and contributed to the understanding of the dieback process of spruce and beech trees. The presentation will concentrate on the most recent and most complex of the hitherto existing models, theBeech model.  相似文献   

Benthic storms,vortices, and particle dispersion in the deep West European basin     

Holger Klein 《Ocean Dynamics》1987,40(3):87-102

Summary During the NOAMP Experiment (September '83 to May '86), 20 benthic storms with velocities of up to 27 cm/s and a duration of between 3 and 25 days, have been observed in a region centered at 47° 20 N and 20° W. The calculation of streamfunction maps shows clearly, that all storms between September '83 and September '84 occur in connection with deep reaching synoptic vortices. These events are important mechanisms for the dispersion of tracers, which are released at the seabed. They enable the particles to pass the interface between the well-mixed bottom boundary layer and the stratified interior of the deep sea. The eddies, with lifetimes of up to several months, trap the particles and facilitate horizontal and vertical transports within the eddy. Each vortex, by means of its shear, deforms a parcel of contaminated water to thin sheets, respectively to thin filaments with regard to two dimensions. This makes small-scale mixing processes work effectively.

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Tiefseestürme, Wirbel und Teilchenausbreitung in der Tiefsee des Westeuropäischen Beckens

Zusammenfassung Während des NOAMP-Experiments wurden in einem Gebietbei 47° 20 N und 20° W 20 Tiefseestürme mit Geschwindigkeiten bis zu 27 cm/s und einer Dauer zwischen 3 und 25 Tagen gemessen. Stromfunktionskarten zeigen, daß, zumindest im Zeitraum von September '83 bis September '84, die Stürme stets im Zusammenhang mit tiefreichenden synoptischen Wirbeln auftreten. Diese Ereignisse sind von herausragender Bedeutung für die Ausbreitung am Tiefseeboden eingebrachter Stoffe. Sie ermöglichen den Austausch von Wasserkörpern durch die Sprungschicht zwischen der stark durchmischten Bodengrenzschicht und dem geschichteten Inneren der Tiefsee. Die Wirbel, mit Lebenszeiten bis zu mehreren Monaten, können Wasserkörper mit Eigenschaften, die ihn von der umgebenden Wassermasse unterscheiden, einfangen und transportieren sie vertikal und horizontal innerhalb des Wirbels. Jeder Wirbel deformiert solche Wasserkörper zu dünnen Scheiben, bzw. zu dünnen Filamenten im Zweidimensionalen, und schafft somit die notwendige Voraussetzung für das Wirken kleinskaliger Vermischungsprozesse.

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Tempêtes de grands fonds, tourbillons, dispersion de particules dans les eaux profondes du Bassin de l'Europe de l'Ouest

Résumé Durant l'expérience NOAMP (septembre 1983 – Mai 1986), vingt tempêtes de grands fonds avec des vitesses supérieures à 27 cm/s et des durées comprises entre 3 et 25 jours, ont été observées dans un secteur centré sur le point 47° 20 nord et 20° ouest. Le calcul des cartes de courant montre clairement que les tempêtes sous-marines observées entre septembre 1983 et semtembre 1984 sont reliées à des tourbillons synoptiques atteignant de grandes profondeurs. Ces évènements sont des mécanismes importants pour la dispersion d'éléments — traces libérés sur le fond de l'océan. Ils permettent aux particules de franchir l'interface entre la couche limite de fond, homogène, et la partie stratifiée de la mer profonde. Les tourbillons qui ont des durées de vie de plusieurs mois, piègent les particules et facilitent leurs transports horizontaux et verticaux au sein même du tourbillon. Chaque tourbillon du fait du cisaillement, transforme un volume d'eau contaminée en minces couches, ou plutôt en minces filets d'eau, si l'on se place dans les deux dimensions. Cela génère en réalité un processus de mélange à petite échelle.

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Tree roots — Methodological review and new development in dating and quantifying erosive processes     

Holger Grtner 《Geomorphology》2007,86(3-4):243-251

Exposed roots have been used in Dendrogeomorphology since the 1960s to determine erosion rates. This was done by using the root axis as the relative position of the former soil layer and then relating this measure to the age of the root in order to quantify the amount of soil erosion over time. Recently, wood anatomical research revealed the possibility of determining the first year of exposure of roots due to specific anatomical changes within the respective annual ring. As a consequence, using exposed roots that are still in contact to the soil surface, it is possible to reconstruct the size and position of the root at the time of exposure. Consequently, a new equation is presented to calculate the thickness of the eroded soil layer allowing a detailed reconstruction of erosion rates. The technique also helps to determine if the root was exposed by erosional processes or just by its ongoing secondary growth without any erosion involved.  相似文献   

Vegetation and climate in the Early‐ and Pleni‐Weichselian in northern Central Europe     

Gerfried Caspers  Holger Freund 《第四纪科学杂志》2001,16(1):31-48

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Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter     

Nicole Kowalski  Olaf Dellwig  Melanie Beck  Maik Grunwald  Sibylle Fischer  Maike Piepho  Thomas Riedel  Holger Freund  Hans-Jürgen Brumsack  Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.  相似文献   

Seismo-engineering parameters for sites of interim storages for spent nuclear fuel at German nuclear power plants     

Günter Leydecker  Timo Schmitt  Holger Busche  Thomas Schaefer 《Soil Dynamics and Earthquake Engineering》2008,28(9):754-762

Within the scope of the licensing procedure for 12 interim storage facilities for spent nuclear fuel at nuclear power plants (NPP) and one for the dismantling of a NPP in Germany, site-specific expert reports were carried out to determine seismo-engineering design parameters. Our work was based on the German nuclear safety standard KTA 2201 part 1 “Design of Nuclear Power Plants against Seismic Events” which requires the derivation of the design earthquake in terms of (macroseismic) intensity. The intensity of the particular design earthquake was evaluated by the deterministic method stipulated in KTA 2201 part 1. According to the current state-of-the-art of science and technology supplementary to the deterministic approach, probabilistic evaluations were done setting a probability of exceedance for the occurrence of the design earthquake of 10⁻⁵ year⁻¹. Geological development and neotectonic conditions of the site surrounding areas were included in the evaluations. For 13 interim storage facility sites, soil-dependent design spectra and corresponding strong-motion duration values were determined.For sites with low seismic hazard site-specific design spectra from the literature were used. In the case of sites with higher seismic hazard (design earthquakeVII 1/2 MSK) strong-motion registrations representative for the site were selected from world wide data and subsequently evaluated to derive site-specific design spectra.  相似文献   

Anthropocene flooding: Challenges for science and society     

Saman Razavi  Patricia Gober  Holger R. Maier  Roy Brouwer  Howard Wheater 《水文研究》2020,34(8):1996-2000

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