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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 72 (1983), S. 605-618 
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract A suite of marble specimens from the Sierra Alhamilla (Spain), deformed to large strains under natural conditions at about 300° C shows distinct variations in microstructure and fabrics. It can be demonstrated that the development of crystallographic preferred orientations and grain shape fabrics are strongly dependent on recrystallized grain size. This is interpreted to reflect the relative importance of various deformational mechanisms. Superplasticity seems to have a sharp upper grain size limit at 10–15 /smm. Within the power law creep regime, deformation in fine grained aggregates is probably dominated by diffusional, in coarser ones by dislocation mechanisms. The transition is a gradual one, and may span a grain size range of 30 /sm.
    Abstract: Résumé Une série d'échantillons de marbres de la Sierra Alhamilla (Espagne), fortement déformés sous des conditions naturelles de 300° C, montre des variations distinctes de microstructure et de texture. On peut démontrer que la formation des orientations préférentielles cristallographiques et de l'aplatissement des grains dépend clairement des dimensions des grains recristallisés. Ceci est interpreté a comme le reflet de l'importance relative de plusieurs mécanismes de déformation. Il apparaît, que le domaine de superplasticité a une limite bien definie a 10–15 /smm. Dans le domaine du fluage en σn, la déformation des aggrégats fins semble être dominée par des mécanismes de diffusion, et des aggregats de grande taille par des mećanismes de dislocation. La transition est graduelle, et peut comprendre un intervalle dimensionel des grains de 30 /smm.
    Notes: Zusammenfassung Eine Anzahl von Marmoren aus der Sierra Alhamilla (Spanien), intensiv deformiert unter natürlichen Bedingungen bei ca. 300° C, zeigt ausgeprägte Variationen in Mikrostruktur und Gefüge. Es kann gezeigt werden, daß die Entwicklung von bevorzugten Kristallorientierungen und Formanisotropien im Korngefüge erheblich von der rekristallisierten Korngröße abhängt. Dies wird als Ausdruck der relativen Aktivität verschiedener Deformationsmechanismen interpretiert. Superplastizität scheint eine relativ scharf definierte Obergrenze für Korngrößen von 10–15 /sm zu besitzen. Im Bereich des Potenzgesetz-Fließens wird die Verformung feinkörniger Aggregate wahrscheinlich von Diffusion, die von grobkörnigen von Dislokationsmechanismen bestimmt. Der Übergangsbereich zwischen beiden Mechanismen umfaßt einen Korngrößenunterschied von etwa 30 µ.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2013-12-21
    Print ISSN: 0276-0460
    Electronic ISSN: 1432-1157
    Topics: Geosciences
    Published by Springer
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  • 3
    Publication Date: 2015-10-27
    Print ISSN: 1437-3254
    Electronic ISSN: 1437-3262
    Topics: Geosciences
    Published by Springer
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  • 4
  • 5
    Publication Date: 1983-06-01
    Print ISSN: 0016-7835
    Electronic ISSN: 1432-1149
    Topics: Geosciences
    Published by Springer
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  • 6
    Publication Date: 2021-02-08
    Description: Pockmarks are variably sized crater-like structures that occur in young continental margin sediments. They are formed by gas eruptions and/or long-term release of fluid or gas. So far no pockmarks were known from the Pacific coast of South America between 51°S and 55°S. This article documents an extensive and previously unknown pockmark field in the Seno Otway (Otway Sound, 52°S) with multibeam bathymetry and parametric echosounding as well as sediment drill cores. Up to 31 pockmarks per square kilometer occur in water depths of 50 to 〉100 m in late glacial and Holocene sediments. They are up to 150 m wide and 10 m deep. Below and near the pockmarks, echosounder profiles image acoustic blanking as well as gas chimneys often crosscutting the 20 to 〉30 m thick glacial sediments above the acoustic basement, in particular along fault zones. Upward-migrating gas is trapped within the sediment strata, forming dome-like features. Two 5 m long piston cores from inside and outside a typical pockmark give no evidence for gas storage within the uppermost sediments. The inside core recovered poorly sorted glacial sediment, indicating reworking and re-deposition after several explosive events. The outside core documents an undisturbed stratigraphic sequence since ~15 ka. Many buried paleo-pockmarks occur directly below a prominent seismic reflector marking the mega-outflow event of the Seno Otway at 14.3 ka, lowering the proglacial lake level by about 80 m. This decompression would have led to frequent eruptions of gas trapped in reservoirs below the glacial sediments. However, the sediment fill of pockmarks formed after this event suggests recurrent events throughout the Holocene until today. Most pockmarks occur above folded hydrocarbon-bearing Upper Cretaceous and Paleogene rocks near the western margin of the Magallanes Basin, constraining them as likely source rocks for thermogenic gas.
    Type: Article , PeerReviewed
    Format: text
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  • 7
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    Unknown
    Springer
    In:  In: Submarine Geomorphology. , ed. by Micallef, A. 〈https://orcid.org/0000-0002-9330-0648〉 Springer, Cham, pp. 409-424.
    Publication Date: 2021-05-11
    Description: Although only recognized in the middle of the last century, oceanic trenches are among the most spectacular structural and morphological features in the deep oceans. Caused by the collision and subduction of tectonic plates and shaped by the interplay of tectonic and sedimentary processes, the morphology of oceanic trenches can be manifold. In this chapter we discriminate between sediment starved trenches, partly sediment filled trenches, and sediment flooded trenches. In sediments starved trenches the tectonic signature is usually well preserved everywhere in the trench, including at the outer slope, the depression, and the inner slope. In contrast, in sediment flooded trenches the outer slope and the trench depression usually correspond to a flat seafloor that results from the deposition of thick sedimentary sequences that overprint all fault scarps. Here, a tectonic signature is only found at the trench inner slope where accretion of trench sediments results in thrust faulting. The remarkable differences in trench morphologies underline that for a comprehensive understanding of the structural evolution of a convergent margin, detailed knowledge on the sedimentary and tectonic history of the adjacent oceanic trench is necessary.
    Type: Book chapter , NonPeerReviewed
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  • 8
    facet.materialart.
    Unknown
    Springer
    In:  International Journal of Earth Sciences, 105 (7). pp. 2097-2110.
    Publication Date: 2019-09-23
    Description: We have analysed strain and flow kinematics in the footwall of the South Cyclades Shear Zone (SCSZ), an important tectonic boundary within the Attic-Cycladic Crystalline Complex exposed on Ios Island, Cyclades, Aegean Sea. Coarse-grained augen gneisses in the basement unit flooring the SCSZ and forming a metamorphic core complex are excellently suited to measure finite strain using the Fry method and estimate the vorticity number (Wk) of flow with the “blocked-object” method. The results show that Oligo-Miocene exhumation of the basement unit during extension brought approximately 70 % N–S crustal stretching and up to 40 % subvertical shortening in a plane strain environment (k = 0.99). Linear down-section strain decrease constrains a zone of contact deformation of the SCSZ of about 1.5 km thick. Kinematic vorticity number estimates suggest little deviation from pure shear (Wk = 0.26). Finite strain and Wk are not correlated, indicating that the Ios basement and the overlying cover units were stretched compatibly. While the SCSZ is a localized zone of high strain, net displacement, however, may be restricted to about ten kilometres. This has important repercussions on large-scale tectonic models for extension in the Aegean.
    Type: Article , PeerReviewed
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  • 9
    facet.materialart.
    Unknown
    Springer
    In:  Geologische Rundschau, 72 (2). pp. 605-618.
    Publication Date: 2018-01-17
    Description: A suite of marble specimens from the Sierra Alhamilla (Spain), deformed to large strains under natural conditions at about 300° C shows distinct variations in microstructure and fabrics. It can be demonstrated that the development of crystallographic preferred orientations and grain shape fabrics are strongly dependent on recrystallized grain size. This is interpreted to reflect the relative importance of various deformational mechanisms. Superplasticity seems to have a sharp upper grain size limit at 10–15 /smm. Within the power law creep regime, deformation in fine grained aggregates is probably dominated by diffusional, in coarser ones by dislocation mechanisms. The transition is a gradual one, and may span a grain size range of 30 /sm.
    Type: Article , PeerReviewed
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  • 10
    facet.materialart.
    Unknown
    Springer
    In:  In: Submarine mass movements and their consequences. , ed. by Yamada, Y., Kawamura, K., Ikehara, K., Ogawa, Y., Urgeles, R., Mosher, D., Chaytor, J. and Strasser, M. Springer, Dordrecht, pp. 463-474. ISBN 978-94-007-2161-6
    Publication Date: 2018-03-15
    Description: Ursa Basin on the Gulf of Mexico continental slope is a site of extremely fast sedimentation, building thick sequences of underconsolidated and overpressured muds and clays. Frequent sliding created mass transport deposits (MTD). In a study of strength, frictional behaviour, and fabrics of IODP Expedition 308 drillcores we find that mass transport is governed by very low friction coefficients and peak shear strengths of the sediments. The majority of the samples shows velocity weakening, enabling runaway instabilities in the sediment once deformation has started. While sediments at the bases of MTD seem to strengthen by the sliding, those below the bases remain weak, constraining a hazard for slide reactivation. Submarine sediment sliding leaves a strong and irreversible imprint, changing fabric geometries, and reducing the pore space. This is a transport phenomenon leading to expulsion of large amounts of pore fluids during sliding. MTD transport is probably as cohesive bodies, defining a considerable geohazard potential.
    Type: Book chapter , NonPeerReviewed
    Format: text
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