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  • 1
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    Deformation Mechanisms, Rheology and Tectonics (1990)
    London : The Geological Society
    Details
    Keywords: Felsmechanik ; Deformation ; Gebirgsmechanik ; Gestein ; Rheologie ; Tektonik
    Description / Table of Contents: Role of Fluids in Rock Deformation --- N. L. Carter, A. K. Kronenberg, J. V. Ross, and D. V. Wiltschko: Control of fluids on deformation of rocks / Geological Society, London, Special Publications, 54:1-13, doi:10.1144/GSL.SP.1990.054.01.01 --- Richard H. Sibson: Conditions for fault-valve behaviour / Geological Society, London, Special Publications, 54:15-28, doi:10.1144/GSL.SP.1990.054.01.02 --- James P. Evans: Textures, deformation mechanisms, and the role of fluids in the cataclastic deformation of granitic rocks / Geological Society, London, Special Publications, 54:29-39, doi:10.1144/GSL.SP.1990.054.01.03 --- Fracture and Faulting --- Susan M. Agar: Fracture evolution in the upper ocean crust: evidence from DSDP hole 504B / Geological Society, London, Special Publications, 54:41-50, doi:10.1144/GSL.SP.1990.054.01.04 --- Martin Casey and Gilles Wust: The calculation of bulk rheologies of structured materials and its application to brittle failure in shear / Geological Society, London, Special Publications, 54:51-55, doi:10.1144/GSL.SP.1990.054.01.05 --- S. J. D. Cox and L. Paterson: Damage development during rupture of heterogeneous brittle materials: a numerical study / Geological Society, London, Special Publications, 54:57-62, doi:10.1144/GSL.SP.1990.054.01.06 --- S. J. D. Cox: Velocity-dependent friction in a large direct shear experiment on gabbro / Geological Society, London, Special Publications, 54:63-70, doi:10.1144/GSL.SP.1990.054.01.07 --- Susan J. Hippler and Robert J. Knipe: The evolution of cataclastic fault rocks from a pre-existing mylonite / Geological Society, London, Special Publications, 54:71-79, doi:10.1144/GSL.SP.1990.054.01.08 --- Ian G. Main, Philip G. Meredith, Peter R. Sammonds, and Colin Jones: Influence of fractal flaw distributions on rock deformation in the brittle field / Geological Society, London, Special Publications, 54:81-96, doi:10.1144/GSL.SP.1990.054.01.09 --- G. Zulauf, G. Kleinschmidt, and O. Oncken: Brittle deformation and graphitic cataclasites in the pilot research well KTB-VB (Oberpfalz, FRG) / Geological Society, London, Special Publications, 54:97-103, doi:10.1144/GSL.SP.1990.054.01.10 --- Iain S. Stewart and Paul L. Hancock: Brecciation and fracturing within neotectonic normal fault zones in the Aegean region / Geological Society, London, Special Publications, 54:105-110, doi:10.1144/GSL.SP.1990.054.01.11 --- Teng-Fong Wong: Mechanical compaction and the brittle—ductile transition in porous sandstones / Geological Society, London, Special Publications, 54:111-122, doi:10.1144/GSL.SP.1990.054.01.12 --- Instabilities and Localization --- Russell K. Davies and Raymond C. Fletcher: Shear bands in a plastic layer at yield under combined shortening and shear: a model for the fault array in a duplex / Geological Society, London, Special Publications, 54:123-131, doi:10.1144/GSL.SP.1990.054.01.13 --- H. W. Green II and P. C. Burnley: The failure mechanism for deep-focus earthquakes / Geological Society, London, Special Publications, 54:133-141, doi:10.1144/GSL.SP.1990.054.01.14 --- B. E. Hobbs, H.-B. Mühlhaus, and A. Ord: Instability, softening and localization of deformation / Geological Society, London, Special Publications, 54:143-165, doi:10.1144/GSL.SP.1990.054.01.15 --- Eva M. Klaper: Reaction-enhanced formation of eclogite-facies shear zones in granulite-facies anorthosites / Geological Society, London, Special Publications, 54:167-173, doi:10.1144/GSL.SP.1990.054.01.16 --- David L. Olgaard: The role of second phase in localizing deformation / Geological Society, London, Special Publications, 54:175-181, doi:10.1144/GSL.SP.1990.054.01.17 --- A. Ord: Mechanical controls on dilatant shear zones / Geological Society, London, Special Publications, 54:183-192, doi:10.1144/GSL.SP.1990.054.01.18 --- E. Carrio-Schaffhauser, S. Raynaud, H. J. Latière, and F. Mazerolle: Propagation and localization of stylolites in limestones / Geological Society, London, Special Publications, 54:193-199, doi:10.1144/GSL.SP.1990.054.01.19 --- Flow Mechanisms and Flow Laws --- R. C. M. W. Franssen and C. J. Spiers: Deformation of polycrystalline salt in compression and in shear at 250–350°C / Geological Society, London, Special Publications, 54:201-213, doi:10.1144/GSL.SP.1990.054.01.20 --- C. J. Spiers, P. M. T. M. Schutjens, R. H. Brzesowsky, C. J. Peach, J. L. Liezenberg, and H. J. Zwart: Experimental determination of constitutive parameters governing creep of rocksalt by pressure solution / Geological Society, London, Special Publications, 54:215-227, doi:10.1144/GSL.SP.1990.054.01.21 --- Jane A. Gilotti and Joseph M. Hull: Phenomenological superplasticity in rocks / Geological Society, London, Special Publications, 54:229-240, doi:10.1144/GSL.SP.1990.054.01.22 --- Martin Burkhard: Ductile deformation mechanisms in micritic limestones naturally deformed at low temperatures (150–350°C) / Geological Society, London, Special Publications, 54:241-257, doi:10.1144/GSL.SP.1990.054.01.23 --- A. N. Walker, E. H. Rutter, and K. H. Brodie: Experimental study of grain-size sensitive flow of synthetic, hot-pressed calcite rocks / Geological Society, London, Special Publications, 54:259-284, doi:10.1144/GSL.SP.1990.054.01.24 --- J. H. P. De Bresser and C. J. Spiers: High-temperature deformation of calcite single crystals by r+ and f+ slip / Geological Society, London, Special Publications, 54:285-298, doi:10.1144/GSL.SP.1990.054.01.25 --- M. S. Paterson and F. C. Luan: Quartzite rheology under geological conditions / Geological Society, London, Special Publications, 54:299-307, doi:10.1144/GSL.SP.1990.054.01.26 --- David J. Prior, Robert J. Knipe, and Mark R. Handy: Estimates of the rates of microstructural changes in mylonites / Geological Society, London, Special Publications, 54:309-319, doi:10.1144/GSL.SP.1990.054.01.27 --- Werner Skrotzki: Microstructure in hornblende of a mylonitic amphibolite / Geological Society, London, Special Publications, 54:321-325, doi:10.1144/GSL.SP.1990.054.01.28 --- Joseph Clancy White: Albite deformation within a basal ophiolite shear zone / Geological Society, London, Special Publications, 54:327-333, doi:10.1144/GSL.SP.1990.054.01.29 --- Rock Fabrics --- R.D. Law: Crystallographic fabrics: a selective review of their applications to research in structural geology / Geological Society, London, Special Publications, 54:335-352, doi:10.1144/GSL.SP.1990.054.01.30 --- M. W. Jessell and G. S. Lister: A simulation of the temperature dependence of quartz fabrics / Geological Society, London, Special Publications, 54:353-362, doi:10.1144/GSL.SP.1990.054.01.31 --- Jin-Han Ree: High temperature deformation of octachloropropane: dynamic grain growth and lattice reorientation / Geological Society, London, Special Publications, 54:363-368, doi:10.1144/GSL.SP.1990.054.01.32 --- Niels Ø. Olesen and Niels-Henrik Schmidt: The SEM/ECP technique applied on twinned quartz crystals / Geological Society, London, Special Publications, 54:369-373, doi:10.1144/GSL.SP.1990.054.01.33 --- H. Schaeben, H. Siemes, S. Höfler, and G. Will: Practical application of entropy optimization in quantitative texture analysis / Geological Society, London, Special Publications, 54:375-381, doi:10.1144/GSL.SP.1990.054.01.34 --- Deformation of Weak Sediments --- Daniel E. Karig: Experimental and observational constraints on the mechanical behaviour in the toes of accretionary prisms / Geological Society, London, Special Publications, 54:383-398, doi:10.1144/GSL.SP.1990.054.01.35 --- N. A. Yassir: The undrained shear behaviour of fine-grained sediments / Geological Society, London, Special Publications, 54:399-404, doi:10.1144/GSL.SP.1990.054.01.36 --- P.A.R. Nell: Deformation in an accretionary melange, Alexander Island, Antarctica / Geological Society, London, Special Publications, 54:405-416, doi:10.1144/GSL.SP.1990.054.01.37 --- Kevin T. Pickering, Susan M. Agar, and David J. Prior: Vein structure and the role of pore fluids in early wet-sediment deformation, Late Miocene volcaniclastic rocks, Miura Group, SE Japan / Geological Society, London, Special Publications, 54:417-430, doi:10.1144/GSL.SP.1990.054.01.38 --- Experimental Modelling Using Analogue Materials --- Shumin Liu and John M. Dixon: Centrifuge modelling of thrust faulting: strain partitioning and sequence of thrusting in duplex structures / Geological Society, London, Special Publications, 54:431-444, doi:10.1144/GSL.SP.1990.054.01.39 --- K. R. McClay: Deformation mechanics in analogue models of extensional fault systems / Geological Society, London, Special Publications, 54:445-453, doi:10.1144/GSL.SP.1990.054.01.40 --- C. J. L. Wilson and Thomas M. Will: Slickenside lineations due to ductile processes / Geological Society, London, Special Publications, 54:455-460, doi:10.1144/GSL.SP.1990.054.01.41 --- Deformation Mechanisms and Tectonics --- J. P. Gratier and J. F. Gamond: Transition between seismic and aseismic deformation in the upper crust / Geological Society, London, Special Publications, 54:461-473, doi:10.1144/GSL.SP.1990.054.01.42 --- Massimo Coli and Federico Sani: Vein distribution in a thrust zone: a case history from the Northern Apennines, Italy / Geological Society, London, Special Publications, 54:475-482, doi:10.1144/GSL.SP.1990.054.01.43 --- Federico Sani: Extensional veins and shear joint development in a thrust-fold zone (Northern Apennines, Italy) / Geological Society, London, Special Publications, 54:483-490, doi:10.1144/GSL.SP.1990.054.01.44 --- Robert E. Holdsworth and Colin J. Grant: Convergence-related ‘dynamic spreading’ in a mid-crustal ductile thrust zone: a possible orogenic wedge model / Geological Society, London, Special Publications, 54:491-500, doi:10.1144/GSL.SP.1990.054.01.45 --- J. E. Iliffe, I. Lerche, and K. Nakayama: Structural implications of compactional strain caused by fault block rotation: evidence from two-dimensional numerical analogues / Geological Society, London, Special Publications, 54:501-507, doi:10.1144/GSL.SP.1990.054.01.46 --- J. L. Urai, R. D. Schuiling, and J. B. H. Jansen: Alpine deformation on Naxos (Greece) / Geological Society, London, Special Publications, 54:509-522, doi:10.1144/GSL.SP.1990.054.01.47
    Pages: Online-Ressource (XV, 535 Seiten) , Illustrationen, Diagramme, Karten
    ISBN: 0903317583
    URL: http://sp.lyellcollection.org/content/54/1
    Language: English
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  • 2
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    Water Availability and Deformation Processes in Smectite‐Rich Gouges During Seismic Slip (2020)
    Wiley
    Details
    Publication Date: 2020-02-10
    Description: Smectite clays occur in subduction zone fault cores at shallow depth (approximately 1 km; e.g., Japan Trench) and landslide décollements (e.g., Vajont, Italy, 1963). The availability of pore fluids affects the likelihood that seismic slip propagates from deeper to shallow fault depths or that a landslide accelerates to its final collapse. To investigate the deformation processes active during seismic faulting we performed friction experiments with a rotary machine on 2‐mm‐thick smectite‐rich gouge layers (70/30 wt % Ca‐montmorillonite/opal) sheared at 5‐MPa normal stress, at slip rates of 0.001, 0.01, 0.1, and 1.3 m/s, and total displacement of 3 m. Experiments were performed on predried gouges under vacuum, under room humidity and under partly saturated conditions. The fault shear strength measured in the experiments was included in a one‐dimensional numerical model incorporating frictional heating, thermal, and thermochemical pressurization. Quantitative X‐ray powder diffraction and scanning electron microscopy investigations were performed on pristine and deformed smectite‐rich gouges. Under dry conditions, cataclasis and amorphization dominated at slip rates of 0.001–0.1 m/s, whereas grain size sensitive flow and, under vacuum, frictional melting occurred at fast slip rates (1.3 m/s). Under partly saturated conditions, frictional slip in a smectite foliation occurred in combination with pressurization of water by shear‐enhanced compaction and, for V = 0.01–1.3 m/s, with thermal pressurization. Pseudotachylytes, the only reliable microstructural markers for seismic slip, formed only with large frictional power (〉2 MW/m2), which could be achieved at shallow depth with high slip rates, or, at depth, with high shear stress in dehydrated smectites.
    Description: Published
    Description: 10855-10876
    Description: 3T. Sorgente sismica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of water on stress relaxation of faulted and unfaulted sandstone (1978)
    Springer
    Pure and applied geophysics 116 (1978), S. 634-654 
    Details
    ISSN: 1420-9136
    Keywords: Strength of rocks ; Crack growth with water ; Rock mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A series of stress relaxation experiments have been carried out on faulted and intact Tennessee sandstone to explore the influence of pore water on strength at different strain rates. Temperatures employed were 20, 300 and 400°C, effective confining pressure was 1.5 kb and strain rates as low as 10−10 sec−1 were achieved. Most samples were prefaulted at 2.5 kb confining pressure and room temperature. This is thought to have secured a reproducible initial microstructure. The strength of the dry rock was almost totally insensitive to strain rate in the range 10−4 to 10−10 sec−1. In contrast, the strength of the wet rock decreased rapidly with strain rate at rates less than 10−6 sec−1. Brittle fracture of the quartz grains which constitute this rock is the most characteristic mode of failure under the test conditions used. The experimental data are discussed in terms of the possible deformation rate controlling processes, and it is suggested that in the wet experiments at intermediate to high strain rates (10−7 to 10−4 sec−1) the observed deformation rate is controlled by the kinetics of water assisted stress corrosion, whilst deformation at low strain rates (ca. 10−9 sec−1) is controlled by a pressure solution process. The results have implications for the rheology of fault rocks at depths of perhaps 10 to 15 km in sialic crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876530
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative microstructures of natural and experimentally produced clay-bearing fault gouges (1986)
    Springer
    Pure and applied geophysics 124 (1986), S. 3-30 
    Details
    ISSN: 1420-9136
    Keywords: Structural Geology ; faults ; S. E. Spain ; experimental rock mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Fault rocks formed in phyllosilicate-bearing rocks formed over a wide range of environmental conditions within the Earth's crust are characterised by similar structural and microstructural features. The most striking of these are (a) P foliation, defined by the preferred alignment of phyllosilicates in a plane oblique to the direction of shear and (b) small-scale shear zones either parallel to the shear direction (Y shears) or oblique to the direction of shear but with the opposite sense of obliquity relative to the P foliation (Riedel shears, R1). The minor shear zones have the same sense of displacement as the host shear zone. The occurrence of these and other structures in clay-rich fault gouges from exceptionally well-exposed fault zones in southeastern Spain is described. The pervasive development of these flow structures throughout large volumes of fault gouge permits fault-displacement vectors to be inferred. For the region studied the movement pictures is relatively simple and is superposed on a complex network of variably oriented fault zones. The naturally produced fault-gouge structures are compared with fault gouges produced experimentally by shearing kaolinite-quartz mixtures between intact blocks over a wide range of experimental conditions. Good correspondence between their respective microstructural features was observed. Finally, attention is drawn to the fact that natural clay-bearing fault gouges are the products of deformation accompanied by very low-grade retrogressive metamorphism, and that part of the micro-structure of these rocks may be ascribed to crystallization under stress. Microstructures are described that are from long-duration experimental runs, (5 months at high temperature and in the presence of water) which go some way towards simulating these effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00875717
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  • 5
    Electronic Resource
    Electronic Resource
    The low temperature brittle-ductile transition in a quartzite and the occurrence of cataclastic flow in nature (1983)
    Springer
    International journal of earth sciences 72 (1983), S. 493-509 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite (Oughtibridge Ganister), and compares its microstructural development with features of cataclastic deformation of rocks in nature. The brittle to ductile transition in dry ganister occurs at about 600 MPa at room temperature. At lower pressures shear oriented grain boundary cracks form both pre and post peak strength, loosening the microstructure to the point at which axial transgranular cracks develop. Fault zone localization then occurs. At high pressures fault localization is suppressed by friction, and cataclastic flow occurs by the formation of ultracataclasite shear zones around each grain boundary, Rhomb shaped, relatively intact grain cores survive to high (greater than 20%) strains. Hardening mechanisms responsible for the ductility are discussed. It is shown that natural zones of intense cataclasis (fault zones) often develop microstructures comparable with those seen in these experiments, but the less intense cataclastic flow often associated with folding of rocks at high crustal levels in the external zones of orogenic belts is not comparable inasmuch as grain-scale catalaclasis does not normally occur. It is emphasised that finite strain microstructural similarity does not necessarily point to comparable deformation paths and stress history.
    Abstract: Résumé L'article décrit les caractéristiques mécaniques et microstructurales associées à la transition écoulement par voie cassante à cataclastique dans un orthoquartzite (le ganister de Oughtibridge), et compare son développement microstructural aux manifestations de la déformation cataclastique des roches dans la nature. La transition cassant-ductile dans le ganister à l'état sec a lieu à environ 600 Mpa à température ambiante. Aux basses pressions il se forme, à la fois avant et après le pic de la force, des craquelures en bordure des grains et orientées par la tension, qui ont pour effet de relâcher la microstructure jusqu'à développer des fissures axiales au travers du grain; à ce moment une zone cassante prend place. Aux hautes pressions, la localisation de cette zone est supprimée par la friction, et un flux cataclastique se produit par la formation de zones tensionelles ultracataclastiques autour de chaque bordure de grain. Des noyaux de grains de forme rhombique peuvent survivre à l'état relativement intact jusqu'à des tensions fortes (supérieures à 20%). Les mécanismes de durcissement responsables de la ductilité sont discutés. On montre que les zones naturelles de cataclase intense (zones failleuses) développent souvent des microstructures comparables à celles observées dans les expériences; mais le flux cataclastique moins intense souvent associé avec le plissement des roches aux hauts niveaux crustaux dans les zones externes des ceintures orogéniques n'est pas comparable, pour autant que la cataclase à l'échelle du grain ne se produise pas normalement. On souligne que la similitude microstructurale sous déformation finie n'implique pas nécessairement des voies de la déformation et de l'histoire des tensions qui soient compables.
    Notes: Zusammenfassung Die Arbeit befaßt sich mit den mechanischen und mikrotexturellen Charaktereigenschaften des spröden bis kataklastischen Fließüberganges eines Orthoquarzits (Oughtibridge Ganister). Sie vergleicht die Entwicklung der Mikrostrukturen mit Merkmalen der kataklastischen Deformation natürlicher Gesteine. Der Übergang von sprödem in plastischen Zustand des trockenen Orthoquarzits setzt bei etwa 600 MPa bei Zimmertemperatur ein. Bei niedrigerem Druck bilden sich spannungsorientierte Korngrenzenrisse sowohl vor als auch nach der Belastungsspitze. Diese lockern die Mikrostruktur so, daß axiale, quer durch das Korn verlaufende Risse entstehen. Danach setzt die Lokalisierung einer Störungszone ein. Bei hohem Druck wird die Lokalisierung von Störungen durch die Reibung unterdrückt und es entwickeln sich ultrakataklastische Scherzonen um jede Korngrenze. Rautenförmige, relativ intakte Kerne von Körnern überleben bis zu hohen Spannungen (über 20%). Härtungsmechanismen werden als mögliche Ursache für die Formbarkeit diskutiert. Es kann gezeigt werden, daß natürliche Zonen mit intensiver Kataklase (Störungszonen) vielfach Mikrostrukturen entwickeln, die mit denen dieser Experimente vergleichbar sind. Das weniger starke kataklastische Fliesen jedoch, das häufig mit der Faltung von Gesteinen in höheren Krusten-Stockwerken der externen Zonen von Orogenzonen verbunden auftritt, ist nicht vergleichbar insofern, als Kataklase im Korngrößen-Maßstab normalerweise nicht auftritt. Es muß betont werden, daß mikrostrukturelle Ähnlichkeit im Bereich begrenzter Verformung nicht notwendigerweise auf vergleichbare Wege der Deformation und Geschichte der Belastung hinweist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01822079
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  • 6
    Electronic Resource
    Electronic Resource
    The role of tectonic grain size reduction in the rheological stratification of the lithosphere (1988)
    Springer
    International journal of earth sciences 77 (1988), S. 295-307 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract With the aid of published constitutive flow laws for common crustal and upper mantle rock types, it is possible to construct curves showing variation of rock strength with depth in the continental lithosphere, assuming a particular crustal stratification of rock types and a particular geothermal gradient. Such exercises lead to the conclusion that marked changes in strength can occur at major petrological interfaces, such as the Moho discontinuity, which are therefore likely to be associated with a tendency for major, sub-horizontal detachments to form. Constitutive flow laws used for such purposes are usually assumed to represent steady-state flow, at constant rock microstructure. We argue that perhaps the most significant tectonic displacements of rock masses occur across major, localized shear zones, characterized by intense grain-size reduction, and illustrate this by reference to deformation in the metabasic and ultrabasic rocks of the lower part of the Ivrea Zone of northern Italy, which is believed to provide a section through what was once part of the deep continental crust. Calculations of the variation of the flow strength with depth of rocks should therefore use flow laws which include provision for strain dependent variations of strength, arising from strain dependent microstructural changes. We use the results of recent studies of grain-size dependent flow of olivine to estimate strain dependent variations in the flow strength of the sub-continental upper mantle, arising from dynamic recrystallization. From this we argue that after an initial period of flow at high stress, parts of the upper mantle can become very weak, if grain size is sufficiently reduced. Under favourable circumstances, flow can be concentrated immediately below the Moho, or in a band below the Moho. Such behaviour is consistent with our observations of the behaviour of dunites in the Ivrea Zone, and with some interpretations of upper mantle seismic reflectors.
    Abstract: Résumé En utilisant les lois de fluage fournies par la littérature à propos des roches courantes de la croûte et du manteau supérieur, il est possible de construire des courbes montrant la variation de la rigidité des roches en fonction de la profondeur dans la lithosphére continentale, ceci pour un gradient géothermique déterminé et pour une superposition déterminée des divers types de roches dans la croûte. De telles recherches conduisent à la conclusion que des changements brusques de rigidité peuvent se produire aux interfaces pétrologiques majeures, telle la discontinuité Moho; ces interfaces apparaissent de la sorte comme des endroits favorables à la production de décollements subhorizontaux importants. Les lois de fluage utilisées sont généralement supposées s'appliquer à la déformation plastique d'une roche à microstructure constante. Les auteurs pensent que les déplacements tectoniques les plus significatifs des masses rocheuses s'opèrent le long de shear zones localisées, caractérisées par une forte réduction de la taille des grains. Cette conception est illustrée par la déformation des roches basiques et ultrabasiques de la partie inférieure de la zone d'Ivrée (Italie du Nord), considérée comme une coupe à travers une partie d'une ancienne croûte continentale profonde. Les calculs de la variation de la ductilité des roches en fonction de la profondeur devraient donc utiliser des lois de fluage qui tiennent compte des variations de rigidité résultant des modifications microstructurales induites par la déformation. Les auteurs ont utilisé les résultats d'études récentes relatives aux relations entre le fluage de l'olivine et sa granularité; ils ont appliqué ces données à l'estimation de la manière dont varie la ductilité en fonction de la déformation dans le manteau supérieur sub-continental, dont les roches résultent de la recristallisation dynamique. Il en concluent qu'après une période initiale de flux sous haute contrainte, certaines parties du manteau supérieur peuvent devenir très déformables si leur grain a été suffisamment réduit. Dans des circonstances favorables, le flux peut se concentrer immédiatement sous Moho, ou se répartir dans une zone située sous Moho. Un tel comportement est en accord avec celui des dunites de la zone d'Ivrée, ainsi qu'avec l'interprétation des réflecteurs sismiques du manteau supérieur.
    Notes: Zusammenfassung Mit Hilfe von veröffentlichten wesentlichen Fließgesetzen für die meisten Krusten- und oberen Mantelgesteinstypen ist es möglich Kurven zu konstruieren, die Variationen in der Gesteinsfestigkeit in Abhängigkeit von der Tiefe innerhalb der kontinentalen Kruste zeigen. Dies unter der Annahme einer bestimmten krustalen Schichtung der Gesteinstypen sowie einem bestimmten geothermischen Gradienten. Derartige Untersuchungen führen zu dem Schluß, daß deutliche Unterschiede in der Gesteinsfestigkeit an markanten petrologischen Grenzflächen auftreten können, wie z. B an der Moho-Diskontinuität. Derartige Grenzflächen haben somit wahrscheinlich die Tendenz subhorizontale Ablösungsflächen auszubilden. Die allgemeinen Fließgesetze, die für diese Berechnungen angewandt wurden, repräsentieren gewöhnlich bei unverändertem Gesteinsmikrogefüge den »steady-state«Zustand. Es ist anzunehmen, daß die bedeutendsten tektonischen Verschiebungen in den Gesteinsmassen entlang großer, definierter Scherzonen stattfinden, die durch intensive Korngrößenreduktion charakterisiert werden. Belegt wird dies anhand der Deformation in den metabasischen und ultrabasischen Gesteinen des tieferen Teiles der Ivrea-Zone in Norditalien, von der angenommen wird, daß sie einen Schnitt durch denjenigen Teil darstellt, der ehemals dem tieferen Abschnitt der kontinentalen Kruste angehörte. Berechnungen der Variation der Fließfähigkeit von Gesteinen in Abhängigkeit von der Tiefe sollten daher Fließgesetze verwenden, die deformationsabhängige Variationen im Festigkeitsverhalten, das sich aus dem deformationsabhängigen Gefügewechsel ergibt, berücksichtigen. Wir benutzen die Ergebnisse neuerer Untersuchungen über korngrößenabhängiges Fließen von Olivin, um die Deformationsabhängigen Variationen im Fließverhalten des subkontinentalen oberen Mantels, das aus der dynamischen Rekristallisation entsteht, abzuschätzen. Hieraus läßt sich schließen, daß nach einer anfänglichen Periode des Fließens bei hohem Streß Teile des oberen Mantels sehr weich werden können, sofern nur die Korngröße genügend reduziert wird. Unter günstigen Bedingungen kann sich das Fließen direkt unter, zumindest aber in einem Bereich unter der Moho konzentrieren. Ein derartiges Verhalten steht in Übereinstimmung mit den Beobachtungen des Verhaltens der Dunite in der Ivrea-Zone sowie mit Interpretationen von seismischen Reflektoren des oberen Mantels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01848691
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  • 7
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    Electronic Resource
    Thermally-induced grain growth of calcite marbles on Naxos Island, Greece (1989)
    Springer
    Contributions to mineralogy and petrology 101 (1989), S. 69-86 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The island of Naxos is composed of an elliptically shaped structural and thermal dome of Miocene age. Peak metamorphic temperatures within the central migmatite complex exceeded 700° C, decreasing to about 300° C at the most distant exposures on the island. Equigranular calcite marbles which outcrop together with metapelites and metabasites over the whole island show a systematic pattern of increasing grain-size towards the central migmatite complex, with a significant discontinuity in the pattern corresponding approximately with the 500° C isotherm. The microstructures and grain-size distributions in the marbles are consistent with normal grain-growth. The variation of grain-size with peak temperature attained can be explained equally well by the assumptions that (a) a maximum grainsize had developed, particularly at higher temperatures, or that (b) the grain-size had been frozen-in by a combination of cooling and coarsening, both of which combine to reduce the rate of grain-growth. The grain-size data do not impose strong constraints on the mechanism of transport of heat responsible for the metamorphism, whether by conduction or by advection, but the 500° C discontinuity indicates that the tectonothermal history of the migmatitic core and its envelope of metasediments were different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387202
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  • 8
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    High-strain deformation tests on natural gypsum aggregates in torsion (2007)
    In:  Geological Society Special Publication 245: 277-290.
    Details
    Publication Date: 2007-10-08
    Description: Evaporitic minerals, such as gypsum, within sedimentary sequences play an important role in localizing deformation, especially in thrust tectonics, implying that their strength is generally lower than that of other rocks. To study the rheological and microstructural evolution of gypsum with strain, a set of experiments was performed on natural gypsum samples from Volterra (Italy). To reach high shear strain (up to {gamma} = 5), deformation tests were performed in torsion at 300 MPa confining pressure, at temperatures up to 127 {degrees}C, and at shear strain rates between 10-3 and 10-5 s-1. All samples were studied by optical microscopy, to investigate the evolution of the microstructure with strain, and by X-ray diffraction (XRD) analyses, to determine whether and to what extent gypsum dehydrated during deformation. The shear stress increased with shear strain rate and decreased with temperature. A peak stress was usually reached at {gamma} between 0.5 and 1.5. After the peak, 30-40% of weakening occurred but mechanical steady-state conditions were never reached. The microstructure evolved from a plastic deformation microstructure, where grains changed shape according to the bulk strain imposed, into a recrystallization-dominated microstructure, where grains were more equant. The shear stress sensitivity to strain rate increases with progressive strain, thus a meaningful constitutive flow law can only be determined from experiments in which steady-state flow is eventually reached. These results imply that gypsum in nature will flow plastically at shear stress levels lower than those expected from previous experimental studies due to the strain weakening associated with dynamic recrystallization, which can occur at temperatures even lower than gypsum dehydration.
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    On the structure and mechanical properties of large strike-slip faults (2008)
    In:  Geological Society Special Publication 299: 139-150.
    Details
    Publication Date: 2008-07-02
    Description: Elucidation of the internal structure of fault zones is paramount for understanding their mechanical, seismological and hydraulic properties. In order to observe representative brittle fault zone structures, it is preferable that the fault be passively exhumed from seismogenic depths and the exposure must be in arid or semi-arid environments where the fragile rocks are not subject to extensive weathering. Field observations of two such faults are used to constrain their likely mechanical properties. One fault is the Carboneras fault in southeastern Spain, where the predominant country rocks are phyllosilicate-rich lithologies, and the other is part of the Atacama fault system in northern Chile, where faults pass through crystalline rocks of acidic to intermediate composition. The Carboneras fault is a left lateral fault with several tens of kilometres offset exhumed from approximately 4 km depth, and displays multiple strands of clay-bearing fault gouge, each several metres wide, that contain variably fractured lenses of protolithic mica schists. The strain is evenly distributed across the gouge layers, in accordance with the measured laboratory mechanical behaviour which shows predominantly strain hardening characteristics. The overall width of the fault zone is several hundred metres. Additionally, there are blocks of dolomitic material that are contained within the fault zones that show extremely localized deformation in the form of faults several centimetres wide. These are typically arranged at an angle of c. 20{degrees} to the overall fault plane. These differing types of fault rock products allow for the possibility of mixed mode' seismicity, with fault creep occurring along the strands of velocity strengthening clay-rich gouge, punctuated by small seismic events that nucleate on the velocity weakening localized faults within the dolomite blocks. The Caleta Coloso fault in northern Chile has a left-lateral offset of at least 5 km and was exhumed from 5-10 km depth. The fault core is represented by a 200-300 m wide zone of hydrothermally altered protocataclasite and ultracataclasite. This is surrounded by a zone of micro and macro-fractures on the order of 150 m thick. The fault core shows a heterogeneous distribution of strain, with alternate layers of ultracataclasite and lower strain material. The strain-weakening behaviour of crystalline rocks might be expected to produce highly localized zones of deformation, and thus the wide core zone must be a result of additional process such as precipitation strengthening or geometric irregularities along the fault plane.
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    Rock mechanics constraints on mid-crustal low-viscosity flow beneath Tibet (2011)
    In:  Geological Society Special Publication 360: 329-336.
    Details
    Publication Date: 2011-11-17
    Description: It has been inferred from various types of geophysical data that the Tibetan middle and upper crust is detached from the underlying lower crust and mantle by a weak, mid-crustal zone involving partial melting at about 30–35 km depth. Previous modelling of the flow has used an arbitrary mid-crustal rheology to match the constraints imposed by the overall flow regime. Here we show that extrapolation of experimental rock mechanics data for solid-state flow of a quartz-dominated Tibetan middle and upper crust, plus flow of partially molten synthetic ‘granitoid’, are consistent with the geophysical constraints and provide an experimentally constrained basis for the modelling of crustal rheology involving partially molten rocks.
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