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  • 1
    Description / Table of Contents: Palaeomagnetism is a technique used to understand complex deformation patterns in fold-and-thrust belts; it can be used to characterize the distribution, magnitude and timing of vertical axis rotations, an elusive variable using other methods. A combination of palaeomagnetic and structural geology analyses has helped to unravel the geometry and kinematics of fold-and-thrust belts around the world and of different geological ages for more than 50 years. This volume comprises three sections: the first shows thorough overviews of western Mediterranean arcs and the western Carpathians; the second depicts several examples from the Andes, the Alps, Anatolia, Pyrenees, Iberian Ranges and the Atlas; and the third shows the latest research on the use of palaeomagnetism to understand fold-and-thrust belts in 3D and 4D in a more quantitative way and it also includes some methodological proposals to avoid common errors. In the papers of the first two sections, the combination of palaeomagnetic analyses with structural data, AMS or magnetostratigraphic analyses demonstrate the usefulness of palaeomagnetism in deciphering complex deformation patterns in fold-and-thrust belts.
    Pages: Online-Ressource (282 Seiten)
    ISBN: 9781862397378
    Language: English
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  • 2
    Publication Date: 2015-08-23
    Description: The main objective of this work is to characterize the structures belonging to the Altomira Range and Loranca Basin (SW Iberian Chain, Central Spain) in terms of understanding their present-day orientation, highly oblique with respect to the NW–SE orientation of adjacent structures of the Iberian Chain. The Altomira and Loranca fold and thrust belts present a slightly curved geometry with a general north–south orientation at their central sector, and structures oriented NNE–SSW and north–south to NNW–SSE at their northern and southern sectors, respectively. Palaeomagnetic data from Middle Eocene–Lower Miocene rocks (including clays, fine sandstones and limestones) reveal the absence of vertical-axis rotations in the central sector of the studied area, where structures are oriented north–south, and up to 17° of clockwise and 21° of anticlockwise vertical-axis rotations in the northern and southern sectors, respectively. These data are supported by calculations of the theoretical vertical-axis rotations from shortening estimates and basement-cover structural relationships. This approach highlights the importance of integrating different datasets to characterize the obliquity of fold and thrust belts. Supplementary material: Complete information about the paleomagnetic sites and directions is available at http://www.geolsoc.org.uk/SUP18841
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 3
    Publication Date: 2015-08-05
    Description: New magnetostratigraphic results from a 3300 m-thick section across the syntectonic fluvial sediments of the Campodarbe Formation (Upper Eocene–Oligocene) in the Ebro foreland basin (NE Spain) are presented. The new data allow the top of the Campodarbe Formation to be correlated to Chron 7r (Chattian), younger than previously stated (C10r), therefore shifting the age of significant palaeogeographical changes in the foreland basin. The deformation in the southern front produces the cannibalization in the piggyback basin of 1300 m of sediments spanning c. 3.7 Myr. Average accumulation rates are lower in the Ebro foreland basin than in the piggyback basin and decrease from 35 to 27 cm kyr –1 by the time the San Felices thrust sheet activity decelerates (at c. 28 Myr). Shifts of accumulation rates result from accommodation space changes, which occur locally and are linked to the activity of the San Felices thrust, while the sediment supply occurs at orogenic scale (source of sediments is c. 200 km to the NE). Finally, sequence boundaries previously considered isochronous in the continental record of the Cenozoic Pyrenean basins are revealed to be 1.8–1 Myr older in the piggyback basin than in the Ebro foreland basin.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 4
    Publication Date: 2016-07-13
    Description: Extract Palaeomagnetism, that is, the study of the ancient magnetic field recorded in rocks, is the only vectorial indicator in the Earth sciences that is capable of associating geological bodies with their original location (primary vectors) or with intermediate locations (secondary vectors) during their geological history. For this reason, palaeomagnetism has played a key role in supporting continental drift theory. Beyond tectonic plate-scale applications, palaeomagnetism has become a fundamental tool for assessing the evolution of mountain ranges owing to its unique potential for quantifying vertical axis rotations (VAR). Since the pioneering applications of authors such as Norris & Black (1961) and Tarling (1969), palaeomagnetism has been applied to problems at a variety of scales in many orogenic systems (e.g. Elredge et al. 1985; Kissel & Laj 1989; Weil & Sussman 2004; Elmore et al. 2012). In particular, palaeomagnetic data have been increasingly used as key quantitative information for determining the timing, distribution and magnitude of vertical axis rotations (Van der Voo & Channell 1980; McCaig & McClelland 1992; Allerton 1998). ... This 250-word extract was created in the absence of an abstract.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 5
    Publication Date: 2013-06-11
    Description: The timing of development of the magnetic fabric is a major issue in the application of anisotropy of magnetic susceptibility (AMS) as a strain marker. Analysis of AMS in unconcealed synsedimentary structures can be a sound approximation to this task. In this work, three types of early compactional structures (ECS) were studied by means of AMS, since they can help to understand the timing of development of the magnetic fabric. All three types of ECS are found in fine-grained detrital rocks (to avoid other influences such as palaeocurrents), claystones and marls of the Enciso Group within the Cameros Basin (NE Spain): dinosaur footprints, load structures due to differential compaction and dish-and-flame structures associated with fluid migration related to seismites. In addition, to determine possible influences of lithology on the magnetic fabric, different rock types (siltstones and limestones) were also sampled. In general, the influence of ECS results in scattering of the three magnetic axes, higher at the margins of the structure than at its centre. This fact suggests that ECS occurs during the development of the magnetic fabric, disturbing the incipient magnetic fabric stages, and strongly conditions its later evolution during diagenesis. The later homogeneous compaction process due to sedimentary load and physicochemical processes reorient the susceptibility carriers to some extent (i.e. the magnetic fabric is still under development), but not totally, since AMS still records the previous scattering due to ECS imprint. For the Enciso Group deposits, the magnetic fabric begins to develop at the earliest stages after deposition and it stops when diagenetic processes have finished.
    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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  • 6
    Publication Date: 2016-01-07
    Description: This work investigates how anisotropy of magnetic susceptibility (AMS) recorded the strain related to the Early Cretaceous extensional processes in synrift sediments of the Maestrat basin (eastern Spain). Forty-two sites, distributed throughout the Lower Cretaceous sequence with dominant gentle dips, were sampled. Minerals contributing to the AMS are mainly phyllosilicates. The parallelism between magnetic and sedimentary foliation seems to indicate that a primary (synsedimentary and early diagenetic) magnetic fabric was preserved at 84% of sites. Consequently, preferred orientations of magnetic lineations are interpreted to record the effect of extensional processes coeval with sedimentation and diagenesis during this period. At these 35 sites, two main magnetic lineation orientations are found, delimiting two large domains: a NE–SW orientation prevailing in the NW sector of the basin (parallel to the extension direction of the Iberian basin), and NW–SE to NNW–SSE orientations to the SE (parallel to the extension direction controlling the western Tethys margin). Directional variability demonstrates that the Maestrat basin is located at the boundary between two domains (Iberian and Tethyan) undergoing different plate-scale extensional processes. The subsequent Cenozoic tectonic inversion affected the synsedimentary magnetic fabrics at only a few sites at the borders of the basin, where compressive features are more developed.
    Print ISSN: 0016-7649
    Topics: Geosciences
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  • 7
    Publication Date: 2016-07-09
    Description: The application of palaeomagnetism in fold and thrust belts is a unique way to obtain kinematic information regarding the evolution of these systems. However, since many potential problems can affect the reliability of palaeomagnetic datasets and their interpretations, such data should be used with caution. In this paper, we thoroughly review the sources of error from palaeomagnetism with a particular focus on deciphering vertical-axis rotations and the assumptions behind the method. Recent investigations have demonstrated that the age of the magnetization and syn-folding results from the fold test must also be carefully examined: factors such as internal deformation, deficient isolation of components (i.e. overlapping) or incorrect restoration procedures may produce apparent syn-folding results. In fact, the restoration procedure used to return the palaeomagnetic signal to the palaeogeographic coordinate system may itself inhibit accurate estimations of vertical-axis rotations when complex deformation histories induce different, non-coaxial, deformation axes. We recommend the auxiliary use of the inclination v. dip diagram as an efficient tool for identifying many errors. Finally, to determine accurate vertical axis rotations, the reference direction should honour standard reliability criteria and would ideally be measured within the undeformed foreland of the thrust system. In this paper, we review five decades of palaeomagnetic research in fold and thrust belts by concentrating on maximizing standard reliability criteria procedures to reduce uncertainty and increase confidence when applying palaeomagnetic data to unravel the tectonic evolution of fold and thrust belts.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 8
    Publication Date: 2014-10-15
    Description: The Castejón-Laspaúles basin is one of the South Pyrenean basins of Late Variscan age that were strongly inverted during the Alpine compression (Late Cretaceous–Tertiary). It is mainly composed by Stephanian pyroclastic and volcanic deposits that reach a maximum thickness of ~ 500 m, and are overlain by Permian and Triassic sedimentary units. A palaeomagnetic and magnetic fabrics (AMS) study was carried out in the Stephanian units, where the general absence of flow markers at the outcrop scale and the Alpine inversional structure prevent the straightforward reconstruction of the original volcanic and basinal configuration. Magnetic fabric data are not overprinted by Alpine internal deformation and can be interpreted in terms of primary volcanic and pyroclastic fabrics. The obtained directions coincide in the different sampled units, suggesting a constant source area during the development of the basin, and show the dominance of N–S-trending K 1 axes that are interpreted to be parallel to flow directions. Palaeomagnetic data indicate the presence of a pre-folding palaeomagnetic component that is rotated clockwise by an average of +37° (±32°) with regards to the Stephanian reference. This rotation probably took place during Alpine thrusting since it is also registered by the overlying Triassic deposits. The whole dataset is interpreted in terms of basin development under sinistral transtension with two main fault sets: deep-rooted E–W-striking faults, probably responsible for magmatic emissions, and shallow-rooted, listric faults of N–S orientation.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
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  • 9
    Publication Date: 2018
    Description: 〈span〉〈div〉Summary〈/div〉Of the several factors involved in the development of magnetic fabrics in fault zones at shallow crustal levels, lithology and deformation intensity have probably the most important consequences for the reconstruction of their kinematic history. The basement-involved Cenozoic thrusts in the Demanda Massif (N Spain) provide the opportunity for testing the applicability of Anisotropy of Magnetic Susceptibility (AMS) to the study of deformation in cataclastic fault rocks belonging to shallow fault zones. The Rastraculos thrust is a relatively minor basement thrust (dip-slip movement of 2 km defined from cross-sections and geological maps) of Cenozoic age. This thrust contains a re-activated fault zone involving different rock types both belonging to its hangingwall (Paleozoic) and its footwall (Triassic sandstones and dolostones and Jurassic limestones). AMS results show magnetic foliations parallel or slightly oblique to the fault zone, and both transport-parallel (projected onto the foliation plane) and transport-perpendicular (parallel to the observed intersection lineation) magnetic lineations. The two types of strain/magnetic fabric relationships can be related to deformational and mineralogical features inferred from the direct analysis of thin and polished sections under the microscope and the naked eye, respectively. Analysis of fault rocks in the Rastraculos fault zone indicates that in cataclasites, magnetic fabrics are particularly dependent on lithology and hence magnetic mineralogy. The results obtained prove the usefulness of AMS in fault zones where kinematic indicators are scarce and also give clues on the number of samples necessary to define magnetic susceptibility axes, depending on grain size, ellipsoid shapes and magnetic mineralogy.〈/span〉
    Print ISSN: 2051-1965
    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: 2015-09-04
    Description: The main objective of this work is to characterize the structures belonging to the Altomira Range and Loranca Basin (SW Iberian Chain, Central Spain) in terms of understanding their present-day orientation, highly oblique with respect to the NW–SE orientation of adjacent structures of the Iberian Chain. The Altomira and Loranca fold and thrust belts present a slightly curved geometry with a general north–south orientation at their central sector, and structures oriented NNE–SSW and north–south to NNW–SSE at their northern and southern sectors, respectively. Palaeomagnetic data from Middle Eocene–Lower Miocene rocks (including clays, fine sandstones and limestones) reveal the absence of vertical-axis rotations in the central sector of the studied area, where structures are oriented north–south, and up to 17° of clockwise and 21° of anticlockwise vertical-axis rotations in the northern and southern sectors, respectively. These data are supported by calculations of the theoretical vertical-axis rotations from shortening estimates and basement-cover structural relationships. This approach highlights the importance of integrating different datasets to characterize the obliquity of fold and thrust belts. Supplementary material: Complete information about the paleomagnetic sites and directions is available at http://www.geolsoc.org.uk/SUP18841
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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