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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Structural indicators of the direction and sense of shear from deformed rocks in convergent erogenic belts represent particle displacement paths, and have been used to infer past plate-motion directions6'7. In arcuate mountain chains such as the Alps, however, these indicators commonly show wide ...
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  • 2
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract A zone of mylonite is commonly developed beneath the Alpujarride nappe complex. The contact with the underlying Nevado-Filabride Complex is marked by a zone of calc mylonite, dolomitic breccia, iron-rich carbonate rocks, and marble. These lie on a thin zone of ultramylonite derived from Nevado-Filabride schist. Related ductile deformation decreases downwards, but may extend up to 400 m beneath the contact. This deformation produces a characteristic platy foliation, a strong elongation lineation, and a proto-mylonitic microstructure. Kinematic analysis of these rocks may help determine the direction of nappe transport. Mylonitic or protomylonitic microstructures are not developed in the Alpujarride rocks, although these are strongly deformed adjacent to the contact. Microstructural evidence suggests that deformation occurred by pressure-solution in these rocks, and not by the crystal-plastic processes that operated in the Nevado-Filabride protomylonitic schists.
    Abstract: Resumen Bajo el complejo de mantos de los Alpujárrides se observa comunmente el desarrollo de una zona milonitica. El contacto de dicho complejo con el de Nevado-Filabride está señalado por una zona de calcomilonitas, brechas dolomiticas, rocas carbonatadas ricas en hierro y mármoles. Estos se situan en una zona estrecha de ultramilonitas que se derivan de los esquistos del Nevado-Filabride, La deformación dúctil asociada decrece en sentido descendente, pero puedo extenderse hasta 400 m por debajo del contacto. Esta deformation produce una foliación planar characterística, una lineación de extensión muy pronunciada y una microestructura protomilonítica. Los análisis cinemáticos de éstas rocas pueden ayudar a determinar la dirección de transporte de los mantos. Las microestructuras miloníticas y protomyloníticas no se desarrollan en las rocas Alpujárrides, aunque dichas rocas están fuertemente deformadas junto al contacto. Las observaciones microestructurales sugieren que la deformación tuvo lugar por «pressure-solution» y no por procesos de plasticidad cristalina como los operantes en los esquistos protomiloníticos del Nevado-Filabride.
    Notes: Zusammenfassung Im Liegenden des Deckengebäudes der Alpujarriden findet sich an vielen Stellen eine Mylonitzone. Der Kontakt mit den unterlagernden nevado-filabriden Gesteinen ist durch Kalkmylonite, Dolomitbrekzien, eisenreiche Karbonate und Marmore markiert. Diese liegen auf einer dünnen Zone von Ultramylonit, der sich aus nevado-filabriden Glimmerschiefern entwickelt hat. Diese plastische Verformung nimmt zum Liegenden hin ab, kann aber bis zu 400 m unterhalb des Deckenkontaktes reichen. Sie erzeugt eine charakteristische, plattige Schieferung, eine stark ausgeprägte Streckungslineation und eine protomylonitische Mikrostruktur. Mit einer kinematischen Analyse dieser Gesteine kann die Transportrichtung der Deckeneinheiten bestimmt werden. Die Glimmerschiefer und Phyllite alpujarrider Zuordnung besitzen keine mylonitische Mikrostruktur, obwohl sie stark deformiert sind. Dies deutet darauf hin, daß, im Gegensatz zum intrakristallinen Gleiten in den nevado-filabriden Protomyloniten, vor allem Drucklösung als Deformationsmechanismus anzusehen ist.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 77 (1988), S. 577-589 
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The detachment and imbrication of thrust slices at the front of a thrust wedge is one of the principle modes by which such wedges grow. Collapse of the frontal ramp under longitudinal compressional stress cannot explain the regular formation of new slices of finite length, unless there are regularly spaced heterogeneities in the footwall layer or the underlying basement surface. Advance of the thrust wedge over the frontal ramp, however, increases both the vertical load on the ramp and the traction on the upper flat. This will in general produce a peak deviatoric stress in the footwall layer below the leading edge of the thrust wedge. Failure will occur at this point when the thrust wedge has advanced a distance L such that the deviatoric stress in the footwall layer exceeds its strength. L is a function of (a) rock density, (b) ramp angle, (c) the resistances to motion on the basal detachment, the ramp, and the upper flat, and (d) the strength and thickness of the footwall layer. These mechanical parameters can therefore control the formation of new thrust slices of regular length in the absence of footwall heterogeneities. Continued accretion of thrust slices at the front of the wedge progressively diminishes its overall taper until it becomes mechanically unstable. Reactivation of previously formed thrusts is a likely response, and will alternate with or occur concurrently with frontal imbrication. Thrust reactivation occurs at a diminishing rate back from the wedge front and is the main cause of back-rotation of older thrust slices. Further back in the wedge, reactivation is not possible, because the thrusts are too steep and have strongly curved trajectories. Thickening of the wedge in this area must occur by out-of-sequence thrusting, backthrusting, or ductile deformation.
    Abstract: Résumé Le décollement et l'imbrication des écailles au front d'un prisme de chevauchement constituent un des mécanismes principaux par lequel de tels prismes s'accroissent. La destruction de la rampe frontale par l'effet de contraintes compressives longitudinales ne peut expliquer la formation régulière de nouvelles tranches de longueur limitée, à moins que l'on n'admette l'existence d'hétérogénéités régulièrement espacées situées dans le mur ou à la surface du socle sousjacent. Cependant, l'avancée du prisme de chevauchement au-dessus de la rampe augmente la charge verticale supportée par celle-ci ainsi que la contrainte cisaillante dans la partie supérieure du substratum. Cette situation tend à produire un maximum de la contrainte déviatorique dans le substratum au-dessous du bord frontal du prisme de chevauchement. La rupture se produira à cet endroit lorsque le prisme se sera avencé d'une distance L telle que la contrainte déviatorique dans le substratum dépasse la résistance propre de celui-ci. La longueur L est fonction: (a) de la densité de la roche, (b) de l'angle de la rampe, (c) des résistances à l'avancement sur le décollement principal, la rampe et la surface supérieure de la partie sous-jacente. Ces paramètres mécaniques déterminent donc la géométrie de la nouvelle écaille. L'accrétion répétée d'écaillés à l'avant d'un prisme en coin diminue progressivement son angle frontal jusqu' à ce qu'il devienne mécaniquement instable. Il peut en résulter une réactivation des surfaces de chevauchement formés précédemment, soit alternativement, soit concurremment à l'imbrication frontale. Cette réactivation est de moins en moins active vers l'arrière du dispositif; elle constitue la cause principale de la rotation des écailles plus anciennes. Dans la partie du prisme située plus en arrière, cette réactivation n'est guère possible, car les chevauchements y sont trop pentés et ont des trajectoires fortement incurvées. Dans cette zone, l'épaississement du prisme peut se produire grâce à des chevauchements hors séquence (recoupant les surfaces antérieures), à des rétrochevauchements ou à une déformation ductile.
    Notes: Zusammenfassung Die Abscherung und Anstapelung von Schuppen an die Stirn eines Schuppenkeils stellt eine der wichtigsten Wachstumsarten von Schuppenkeilen dar. Der Verbrach einer frontalen Rampe wird durch die von ihr getragene longitudinale Normalspannung hervorgerufen. Die Entstehung neuer gleichförmiger Schuppen mit begrenzter Länge lä\t sich durch diesen Verbruch nicht erklären, ohne da\ man Heterogenitäten in gleichmä\igen Abständen in der liegenden Schicht oder dem Unterbau annimmt. Dennoch steigert der Vortrieb über die frontale Rampe eines Schuppenkeils sowohl die vertikale Last auf der Rampe als auch die Geschiebelast auf dem oberen der Schichtung parallelen Teil der überschiebung (upper flat). Infolgedessen ist es wahrscheinlich, da\ der Spannungsdeviator im Liegenden unter der Vorderkante des Schuppenkeils ein Maximum erreicht. Ein Bruch entsteht dann, wenn die Schubweite des Schuppenkeils einen WertL erreicht hat, von dem ab der Spannungsdeviator im Liegenden grö\er ist als dessen Bruchfestigkeit.L. ist von folgenden Variablen abhängig: (a) der Gesteinsdichte (b) dem Rampenwinkel (c) dem Geschiebewiderstand auf der basalen Abscherungsbahn, der Rampe und dem oberen der Schichtung parallelen Teil der überschiebung (d) der Bruchfestigkeit und Dicke der liegenden Schicht. Diese mechanischen Parameter haben also einen starken Einflu\ auf die Geometrie der neuen Schuppe. Durch fortlaufende Anstapelung von Schuppen an die Stirn des Schuppenkeils wird die Steigung des Keils progressiv reduziert, bis er mechanisch unstabil wird. Es ist wahrscheinlich, da\ dadurch frühere überschiebungsbahnen reaktiviert werden, und da\ dies entweder abwechselnd oder gleichzeitig mit der frontalen Anschuppung stattfindet. Die Wahrscheinlichkeit einer Reaktivierung von überschiebungsbahnen nimmt mit wachsender Entfernung von der Keilstirn ab. Das Reaktivieren ist die Hauptursache für die Rückrotation von älteren überschiebungen. Im hinteren Teil des Schuppenkeils ist das Reaktivieren nicht möglich, weil die überschiebungsbahnen zu steil und zu stark gekrümmt sind. Eine Verdickung des Keils in diesem Bereich mu\ durch eine — mehrere ältere überschiebungen durchschneidende — überschiebung (out of sequence thrust), durch eine Rücküberschiebung, oder durch eine duktile Verformung geschehen.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 361 (1993), S. 416-416 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN its broadest definition, structural geology encompasses everything concerned with rock deformation, from experimental and theoretical rock mechanics to large-scale tectonics, and overlaps with fields as diverse as basin analysis, seismology and metamorphic petrology. To many of its ...
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 576-576 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PLATT REPLIESá€"The evidence cited by Fry (unpublished when we wrote our paper1) for a late Eocene onset of deformation in the external zone of the southwest Alps is of considerable interest, as precise timing of the beginning of deformation in different parts of the Alps should ...
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  • 6
    Publication Date: 2015-01-16
    Description: Metamorphic core complexes are products of normal-fault displacements sufficient to exhume rocks from below the brittle–ductile transition. These faults (detachments) may initiate within the brittle crust at steep angles, but they sole into the ductile middle crust, and during displacement rotate to gentler dips due to hanging-wall extension. The exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment, and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping, low-friction shallow segments of the detachment. Metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress, strain localization and strain-rate with decreasing temperature, providing a window into physical conditions and deformational processes in the mid-crust. The metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault, in addition to those accompanying exhumation. These processes may include diapiric emplacement of gneiss domes, or exhumation in a subduction channel, and may not be directly related to formation of the core complex. Factors favouring core complex formation are high gravitational potential energy of the extending crust, weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence.
    Print ISSN: 0016-7649
    Topics: Geosciences
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  • 7
    Publication Date: 2016-10-08
    Description: Intersecting pairs of simultaneously active faults with opposing slip sense present geometrical and kinematic problems. Such faults rarely offset each other but usually merge into a single fault, even when they have displacements of many kilometers. The space problems involved are solved by lengthening the merged fault (zippering up the conjugate faults) or splitting it (unzippering). This process can operate in thrust, normal, and strike-slip fault settings. Examples of conjugate pairs of large-scale strike-slip faults that may have zippered up include the Garlock and San Andreas faults in California (USA), the North and East Anatolian faults (Turkey), the Karakoram and Altyn Tagh faults (Tibet), and the Tonale and Giudicarie faults (southern Alps). Intersecting conjugate ductile shear zones behave in the same way on outcrop and micro-scales. Zippering may produce complex and significant patterns of strain and rotation in the surrounding rocks, depending on the angle between the faults and the relative strength of the blocks they bound. A zippered fault will have a slip rate equal to the vector sum of the slip rates on the merging faults, unless that displacement is transferred into or out of the system by distributed strain in the surrounding rocks.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 8
    Publication Date: 2016-10-14
    Description: Intersecting pairs of simultaneously active faults with opposing slip sense present geometrical and kinematic problems. Such faults rarely offset each other but usually merge into a single fault, even when they have displacements of many kilometers. The space problems involved are solved by lengthening the merged fault (zippering up the conjugate faults) or splitting it (unzippering). This process can operate in thrust, normal, and strike-slip fault settings. Examples of conjugate pairs of large-scale strike-slip faults that may have zippered up include the Garlock and San Andreas faults in California (USA), the North and East Anatolian faults (Turkey), the Karakoram and Altyn Tagh faults (Tibet), and the Tonale and Giudicarie faults (southern Alps). Intersecting conjugate ductile shear zones behave in the same way on outcrop and micro-scales. Zippering may produce complex and significant patterns of strain and rotation in the surrounding rocks, depending on the angle between the faults and the relative strength of the blocks they bound. A zippered fault will have a slip rate equal to the vector sum of the slip rates on the merging faults, unless that displacement is transferred into or out of the system by distributed strain in the surrounding rocks.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 9
    Publication Date: 2013-08-13
    Description: Sets of E- to NE-trending sinistral and/or reverse faults occur within the San Andreas system, and are associated with palaeomagnetic evidence for clockwise vertical-axis rotations. These structures cut across the trend of active dextral faults, posing questions as to how displacement is transferred across them. Geodetic data show that they lie within an overall dextral shear field, but the data are commonly interpreted to indicate little or no slip, nor any significant rate of rotation. We model these structures as rotating by bookshelf slip in a dextral shear field, and show that a combination of sinistral slip and rotation can produce the observed velocity field. This allows prediction of rates of slip, rotation, fault-parallel extension and fault-normal shortening within the panel. We use this method to calculate the kinematics of the central segment of the Garlock Fault, which cuts across the eastern California shear zone at a high angle. We obtain a sinistral slip rate of 6.1 ± 1.1 mm yr –1 , comparable to geological evidence, but higher than most previous geodetic estimates, and a rotation rate of 4.0 ± 0.7° Myr –1 clockwise. The western Transverse Ranges transect a similar shear zone in coastal and offshore California, but at an angle of only 40°. As a result, the faults, which were sinistral when they were at a higher angle to the shear zone, have been reactivated in a dextral sense at a low rate, and the rate of rotation of the panel has decreased from its long-term rate of ~5° to 1.6° ± 0.2° Myr –1 clockwise. These results help to resolve some of the apparent discrepancies between geological and geodetic slip-rate estimates, and provide an enhanced understanding of the mechanics of intracontinental transform systems.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
    Publication Date: 1994-03-01
    Print ISSN: 0002-9599
    Electronic ISSN: 1945-452X
    Topics: Geosciences
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