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  • 1
    Description / Table of Contents: The world's mountain ranges are the clearest manifestations of long-term deformation of the continental crust. As such they have attracted geological investigations for centuries. Throughout this long history of research a few keynote publications stand out. One of the most important is the Geological Survey's 1907 Memoir on The Geological Structure of the North-West Highlands of Scotland. The Memoir summarized some of the Geological Survey's finest work, and outlined many of the principles of field-based structural and tectonic analysis that have subsequently guided generations of geologists working in other mountain belts, both ancient and modern. The thematic set of 32 papers in this Special Publication celebrate the 100th anniversary of the 1907 Memoir by placing the original findings in both historical and modern contexts, and juxtaposing them against present-day studies of deformation processes operating not only in the NW Highlands, but also in other mountain belts.
    Pages: Online-Ressource (VII, 872 Seiten)
    ISBN: 9781862393004
    Language: English
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  • 2
    Publication Date: 2021-09-08
    Description: We report new paleomagnetic and anisotropy of magnetic susceptibility (AMS) results from upper Tortonian to middle Pleistocene sediments which were deposited upon and adjacent to active thrust structures in southwestern Sicily. The data show that the Plio-Pleistocene sediments from the Belice and Menfi basins (covering the Saccense shelf limestones) underwent any internal shortening after the early Pleistocene (Santernian), as well as any net rotation. Sediments around this area (which overlie basinal Meso-Cenozoic successions) record systematic rotations: one upper Tortonian site to the west is ~30° counterclockwise rotated, while to the east, lower Pliocene to middle lower Pleistocene sites within the Gela Nappe domain show 25° to 56° clockwise (CW) rotations. These data show that the ductile basinal sediments were bent and rotated around the rigid Saccense carbonates during the thin-skinned southward propagation of the orogenic front. We document here that the coastal sediments from the southwestern Gela Nappe underwent both a post middle early Pleistocene ~30° CW rotation and a post middle Pleistocene E-W to ESE-WNW flattening (revealed by AMS). Our data then constrain to the late Pleistocene-Holocene the age of the last shortening episode occurring in the southwestern Gela Nappe front. Pleistocene rotations of similar amount also characterize the Sicanian domain, implying that it was incorporated in the Gela Nappe wedge during the recentmost episodes of deformation. This evidence allows us to better understand the very large (up to 114°) post Mesozoic rotations reported by Channell et al. [1980, 1990] for the Sicanian limestones, as related to both Miocene (or older?) deformational episodes and the Plio-Pleistocene evolution of the Gela Nappe.
    Description: Published
    Description: 1178-1197
    Description: JCR Journal
    Description: reserved
    Keywords: paleomagnetism ; tectonic rotations ; Sicily ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2011-11-17
    Description: For the past two decades geodetic measurements have quantified surface displacement fields for the continents, illustrating a general complexity. However, the linkage of geodetically defined displacements in the continents to mantle flow and plate tectonics demands understanding of ductile deformations in the middle and lower continental crust. Advances in seismic anisotropy studies are beginning to allow such work, especially in the Himalaya and Tibet, using passive seismological experiments (e.g. teleseismic receiver functions and records from local earthquakes). Although there is general agreement that measured seismic anisotropy in the middle and lower crust reflects bulk mineral alignment (i.e. crystallographic preferred orientation, CPO), there is a need to calibrate the seismic response to deformation structures and their kinematics. Here, we take on this challenge by deducing the seismic properties of typical mid- and lower-crustal rocks that have experienced ductile deformation through quantitative measures of CPO in samples from appropriate outcrops. The effective database of CPO and hence seismic properties can be expanded by a modelling approach that utilizes ‘rock recipes’ derived from the as-measured individual mineral CPOs combined in varying modal proportions. In addition, different deformation fabrics may be diagnostic of specific deformation kinematics that can serve to constrain interpretations of seismic anisotropy data from the continental crust. Thus, the use of ‘fabric recipes’ based on subsets of individual rock fabric CPO allows the effect of different fabrics (e.g. foliations) to be investigated and interpreted from their seismic response. A key issue is the possible discrimination between continental crustal deformation models with strongly localized simple-shear (ductile fault) fabrics from more distributed (‘pure-shear’) crustal flow. The results of our combined rock and fabric-recipe modelling suggest that the seismic properties of the middle and lower crust depend on deformation state and orientation as well as composition, while reliable interpretation of seismic survey data should incorporate as many seismic properties as possible.
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  • 4
    Publication Date: 2011-11-17
    Description: The Nanga Parbat Massif (NPM), Pakistan Himalaya, is an exhumed tract of Indian continental crust and represents an area of active crustal thickening and exhumation. While the most effective way to study the NPM at depth is through seismic imaging, interpretation depends upon knowledge of the seismic properties of the rocks. Gneissic, ‘mylonitic’ and cataclastic rocks emplaced at the surface were sampled as proxies for lithologies and fabrics currently accommodating deformation at depth. Mineral crystallographic preferred orientations (CPO) were measured via scanning electron microscope (SEM)/electron backscatter diffraction (EBSD), from which three-dimensional (3D) elastic constants, seismic velocities and anisotropies were predicted. Micas make the main contribution to sample anisotropy. Background gneisses have highest anisotropy (up to 10.4% shear-wave splitting, AVs) compared with samples exhibiting localized deformations (e.g. ‘mylonite’, 4.7% AVs; cataclasite, 1% AVs). Thus, mylonitic shear zones may be characterized by regions of low anisotropy compared to their wall rocks. CPO-derived sample elastic constants were used to construct seismic models of NPM tectonics, through which P-, S- and converted waves were ray-traced. Foliation orientation has dramatic effects on these waves. The seismic models suggest dominantly pure-shear tectonics for the NPM involving horizontal compression and vertical stretching, modified by localized ductile and brittle (‘simple’) shear deformations.
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  • 5
    Publication Date: 2007-10-08
    Description: Understanding geological structure and structural evolution requires imagination, and the ability to see simple patterns in complex data and make the simplicity evident. It requires the transfer of insight and approach from one area of discipline (geographical or scientific) to another. To Mike Coward it was second nature to do these things, and he stood out as one of the most innovative structural geologists of recent years. He was a great exponent of what is currently referred to as up-scaling': understanding the significance of small-scale, local observations and datasets then using them to elucidate geological evolution on a crustal scale. This introductory paper is a brief review of some key themes in the study of the deformation of the continental crust, and how Coward influenced them. It focuses particularly on thinking in structural geology during the past 50 years or so, but does not cover such topics as seismicity, geodetic data or microstructural approaches in deformation studies. The emphasis is on the importance of understanding medium- to large-scale structural geometry. This was Mike Coward's forte, for it emphasizes the key role of field geology. The discipline of field mapping is a great aid in the interpretation of 3D relationships in seismic data volumes. It is no coincidence that this account begins in the field but leads into seismic data. It is a journey followed not only by Mike Coward but also by many of the authors contributing to this volume. Crustal-scale shear zone models Field geologists have long been aware ... This 250-word extract was created in the absence of an abstract.
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  • 6
    Publication Date: 2007-10-08
    Description: The Achnashellach Culmination is one of the major structures of the Moine Thrust Belt. As with other culminations in the belt, it is formed by a stack of imbricate thrusts. Up to 1 km of Torridon Group sediments, together with a further 200250 m of Cambrian strata, are repeated up to 10 times, but with ramp-on-ramp thrust geometries. Thus structural thickening was chiefly achieved by thick thrust sheets with individually and aggregated displacements that are substantially lower than elsewhere in the thrust belt. The culmination is limited on its flanks by lateral ramps that climb section out of Torridon Group and up into Cambrian strata. To the north the imbricate thrusts may be deduced to branch onto the major Kinlochewe Thrust. To the south the imbricates are represented only by stacked Durness Limestone. The northward-climbing lateral ramp coincides with a major Precambrian structure, the Loch Maree Fault, which controls the thickness of Torridonian strata preserved beneath the sub-Cambrian unconformity, a rare example of basement influence on thrust system geometry within the Moine Thrust Belt. The imbricates of the Achnashellach Culmination show back-steepening and have bulged up the overriding Kishorn and Kinlochewe thrust sheets. However, these structurally higher level tectonic units slice across imbricate structures in their footwalls. Elsewhere high-level thrusts are folded by some parts of underlying imbricates. Collectively these relationships are not compatible with classical duplex models. They are explained better by models of quasi-synchronous slip on imbricate thrusts. Discordant relationships beneath major thrust sheets, including those that cut down stratigraphic section in the transport direction, can be explained by such models without necessitating low-angle extensional faulting within the thrust belt.
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  • 7
    Publication Date: 2010-06-21
    Description: The world's mountain ranges are the clearest manifestations of long-term deformation of the continental crust. As such they have attracted geological investigations for centuries. Throughout this long history of research a few keynote publications stand out. One of the most important is the Geological Survey's 1907 memoir, The Geological Structure of the North-West Highlands of Scotland. The papers in this Special Publication celebrate the 100th anniversary of this remarkable book, placing the original findings in a present-day context by juxtaposing them against modern studies, not only from the NW Highlands, but also from elsewhere around the world. On first sight, the 1907 memoir by B. N. Peach and colleagues is simply a description of regional geology, albeit an exceptionally detailed one. However, the memoir outlines the Geological Survey's chief discoveries, and an abundance of minor ones, resulting from a decade of fieldwork in NW Scotland. At its height this activity occupied many of the most talented field geologists of Peach and Horne's generation and a significant number of the Scottish branch of the Survey. This team performed wondrous deeds, recognizing and interpreting many deformation structures on a variety of scales. The memoir describes these structures in a matter-of-fact manner, with occasional musings on their significance for broader tectonic processes. By focusing on the detail and establishing the supreme importance of getting the basic field relationships correct, the memoir's authors established the NW Highlands of Scotland as a prime location for training. Subsequent generations of geologists, from young students to...
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  • 8
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    In:  Geological Society Special Publication 335: 293-320.
    Publication Date: 2010-06-21
    Description: The NW Highlands of Scotland have been an important test-bed for concepts in thrust tectonics. Here, research following the breakthrough publication of the 1907 memoir is reviewed, especially that relating to structural evolution in the Moine Thrust Belt. This belt was WNW-directed, involving cover sediments and thin sheets of crystalline basement. Displacements total 50-100 km within a branching array of thrusts. There are significant lateral variations in imbricate thrust geometry and localization behaviour. Following the application of linked thrust tectonic models in the 1980s significant attention has been directed at deducing thrust sequences, patterns of strain localization, folding styles and the significance of extensional tectonics as part of the structural evolution. The key has lain in deducing the kinematic linkages between thrusts and other structures, tracing displacements and examining the consequences of structural interpretations through geometric restoration. Thrusting models have been up-scaled to the crust. However, these linked kinematic approaches have been applied only hesitantly to the ductile structures of the Moine Thrust Sheet where structural research has focused on outcrop-scale deformation, especially of folds. Consequently, the larger-scale significance for Caledonian tectonics of thrust systems in the NW Highlands of Scotland has yet to be developed fully.
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  • 9
    Publication Date: 2016-01-07
    Description: Turbidite sandstones and related deposits commonly contain deformation structures and remobilized sediment that might have resulted from post-depositional modification such as downslope creep (e.g. slumping) or density-driven loading by overlying deposits. However, we consider that deformation can occur during the passage of turbidity currents that exerted shear stress on their substrates (whether entirely pre-existing strata, sediment deposited by earlier parts of the flow itself or some combination of these). Criteria are outlined here, to avoid confusion with products of other mechanisms (e.g. slumping or later tectonics), which establish the synchronicity between the passage of overriding flows and deformation of their substrates. This underpins a new analytical framework for tracking the relationship between deformation, deposition and the transit of the causal turbidity current, through the concept of kinematic boundary layers. Case study examples are drawn from outcrop (Miocene of New Zealand, and Apennines of Italy) and subsurface examples (Britannia Sandstone, Cretaceous, UK Continental Shelf). Example structures include asymmetric flame structures, convolute lamination, some debritic units and injection complexes, together with slurry and mixed slurry facies. These structures may provide insight into the rheology and dynamics of submarine flows and their substrates, and have implications for the development of subsurface turbidite reservoirs.
    Print ISSN: 0016-7649
    Topics: Geosciences
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  • 10
    Publication Date: 2015-01-16
    Description: Three-dimensional seismic data are increasingly resolving original compositional heterogeneity and structural complexity in evaporitic successions within sedimentary basins. The relationship between basin structure, evaporite composition and its influence on subsequent deformation are investigated here using Messinian examples from the Maghrebian thrust system of Sicily and applied to the adjacent Ionian sea-bed. By integrating outcrop and onshore subsurface data, we demonstrate variations in evaporite stratigraphies deposited across thrust-top basins, and how these variations have controlled subsequent deformation of these basins. Gypsum and carbonate units develop broad single-layer buckle fold trains, with wavelengths reflecting layer thickness. The development of deformation appears limited by bending resistance at fold hinges, which can be overcome by syntectonic erosion. In contrast, the thick halite and K-salt accumulations in growth synclines have deformed with short-wavelength folds and distributed strain. These structures can display rapid lateral variations (on a scale of hundreds of metres). Similar structural styles, with buckle fold trains passing laterally into more homogeneously shortened, short-wavelength folding, are evident on seismic data from the buried Messinian interval beneath the Ionian Sea. Using the Sicilian outcrop as analogues, the structural styles for the Ionian may be used to infer evaporite type in these subsurface examples.
    Print ISSN: 0016-7649
    Topics: Geosciences
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