1,721,114 research outputs found
Annual Conference of the Italian Group of Structural Geology: Udine, February 25-28, 2009. Summaries and short notes
No full textForeword of the special issue on Alps and Apennines: a natural laboratory for Structural Geology and Geodynamics
No full textMap analysis techniques and fold kinematics in the Umbrian Apennines, Italy
No full textThe structure of southeastern Umbria (Central Apennines. Italy), as obtained with the use of map analysis techniques, integrated with observations on mesoscopic structures, is described. The strike of major fold and thrust structures is remarkably parellel. both at frontal and lateral or oblique ramps, suggesting a common origin
for folding and thrusting. Folds at all scales strike parallel even when the minor structures are not consistent with the shearing sense expected for flexural-slip fold mechanisms: this indicates a multistage, progressive compressional deformation, resulting in a coaxial overprinting fold geometry. The complex structural evolution can be interpreted as due to simple breaching during the Neogene compression
Analisi geometrica e cinematica dei sovrascorrimenti compresi fra la Valnerina e la Conca di Rieti (Appennino iumbro-marchigiano-sabino)
No full textDetailed knowledge of thrust surface geometry and the topological links between different thrusts is important for relating kinematic analysis on the small scale to structural evolution across thrust belts. The thrust surfaces outcropping between the Nera River Valley and the Rieti Basin (Umbria-Marche-Sabina Apennines, Central Italy) are cherecterized by geometrical irregularities, such as dip and strike variations, either original or acquired during later deformation episodes. The use of map analysis techniques indicates the existence of a close relationship between the original dip variations of thrust surfaces and the competence contrasts within the stratigraphic template: these exert a strong control on development of stepped thrust surfaces, whose flats are localized within the less competent units and, such as the Late Trias evaporitic Burano Fm. and the Eocene-Oligocene marly Scaglia Cinerea Fm. The geometrical irregularities produced during later deformation episodes are mainly responsible for along-strike variations of the thrust surfaces orientation, which describe an arcuate feature convex towards the east, and for the present distribution of the thrusting direction vectors. The radial thrusting pattern could derive from development of new structures within the footwall to previous thrusts, suggesting that compressional deformation migrated towards the east in piggy-back fashion.
The application of map analysis techniques provides good information about the lithological control on thrust development and the thrusting sequence. These results provide, therefore, additional controls on constructing balancesd cross sections
Normal faults in thrust sheets: pre-orogenic extension, post-orogenic extension, or both?
No full textIn fold-and-thrust belts that experienced both pre-orogenic and post-orogenic extension, it may be dicult to establish whether observed normal faults pre-dated, post-dated, or were synchronous with thrusting. Geometrical structural patterns may be insucient to constrain the relative chronology of extensional and contractional deformations. The systematic use of kinematic criteria makes it possible to unequivocally de®ne the timing relationships of reverse and normal fault development, and hence to correctly unravel complex structural evolutions. Kinematic analysis in the southernmost Umbria±Marche Apennines of Italy, where both normal and thrust faults are present, revealed a history of repeated tectonic inversion, characterised by two distinct stages of extension separated by an episode of folding and thrusting. Structural overprinting relationships observed at thrust±normal fault intersections were useful for: (i) removing sequentially younger deformations; and hence (ii) separating and quantifying the eects of orogenic contraction from those of both pre-orogenic and post-orogenic extension
Structural evolution of a foreland fold-and-thrust belt: the Umbria-Marche Apennines, Italy
No full textOutcrop-scale structures that record a progressive sequence of deformation can be used to clarify the kinematic evolution of an entire fold-and-thrust belt. The temporal progression of the compressional deformation as reconstructed by means of a mesoscopic structural analysis provides a key for unraveling the kinematic history of the Umbria-Marche Apennines (central Italy). Overprinting relationships at outcrop-scale allow for the recognition of three distinct structural stages which are, in sequence: A- layer-parallel shortening; B- folding; C- thrusting. Individual stages are explained in the framework of a progressive deformation model, where shortening of the sedimentary cover was continuous and occurred during a single contractional episode as a consequence of a tip-line folding process. A comparison of this history with those reported from other fold-and-thrust belts shows that layer-parallel shortening, folding and thrusting are sequentially dominant processes in areas which have experienced compressional deformation
The character of Earth history
No full textThe patterns of human history can provide an original key to the interpretation and understanding of the much longer history of the earth. Some of the fundamental processes that regulate the evolution of the earth display a repetitive, cyclical behavior, whereas others are characterized by irreversible, unidirectional trends. Both processes, i.e. cycles and trends, may be seen as long-term patterns in earth history. These patterns may coexist, and may be modulated by occasional, but extremely important, chance events. It has been suggested that the interplay between chance events and long-term patterns is a feature in human history; in this paper we propose that the same character applies to earth history as well. This suggestion is illustrated with geological examples: we discuss the tectonic evolution of mountain belts that display components of both cyclical and unidirectional trends. We then provide an example of a dramatic, important chance event, namely the impact of a large meteorite on the earth’s surface that caused the Cretaceous–Tertiary boundary mass extinction 65 million years ago
The contribution of 3D restoration for the reconstruction of pre-thrusting basin geometry
No full textIn the Umbria-Marche fold-and-thrust belt, excellent examples of positive inversion tectonics are documented. They are explained as the effect of the structural heritage of the opening of the Mesozoic Tethis Ocean, on the geo- metry of the Neogene compressional structures, related to the Alpine Orogeny.
A portion of the southernmost belt, between the Nera river and the Rieti Basin, is used as natural example to test the kinematic consistency of linked fold-and-thrust systems, and infer the pre-thrusting geometry of the origi- nal extensional basin. The dominant thrust systems and related folds affec- ted a Triassic-Neogene marine sequence during the Late Miocene-Early Pliocene time. The overprinting structural relationships, both at the mesoscopic and macroscopic scales, provided keys for remove the effects of progressi- vely older deformation; in doing so, the sequential cross- section restoration technique was applied in conjunction with 3D monitoring of the resulting geometry, by using specific computer software (2DMove and Gocad). This approach allows for the definition of the thrust segment nucleation and linkage, and for infer the geometrical pat- tern of the pre-existing normal faults, hence the 3D archi- tecture of the pre-thrusting extensional basin. The close coincidence between extensional structures and the Neogene thrust ramps support the interpretation that the geometry of the latter was controlled by the map distribution of the former
The complete Apennines orogenic cycle preserved in a transient single outcrop near San Fele, Lucania, southern Italy
No full textOrogenic cycles may be viewed as comprising two extensional stages that are separated by a stage of contraction. This sequence has characterized the evolution of most mountain belts resulting from continental collision, and the structural signature of individual stages is recognized on a wide variety of scales, i.e. from microscopic to regional. Whereas the history of mountain belts is generally inferred from observations carried out at different sites, the entire sequence of deformation is very rarely recorded in single exposures. The double switch in tectonic regime that led to the development of the Lucanian Apennines in southern Italy, from pre-orogenic drifting through synorogenic thrusting to post-orogenic extension, is preserved in a superb metre-scale outcrop at Serra Manarella, in the vicinity of San Fele. A Late Jurassic, synsedimentary normal fault is sealed by strata affected by a Mid-Pliocene thrust-related fold. This composite structure, in turn, is truncated by a Mid-Pleistocene normal fault. Observation of these relationships represents a unique opportunity to unequivocally establish the relative chronology of deformations in the Lucanian Apennines, and may provide useful constraints for regional cross-section restoration
Post-orogenic extension in southern Tuscany: distinct extensional episodes or progressive exhumation?
No full textA detailed structural analysis of the Pseudoverrucano Unit at Punta delle Rocchette, southwestern Tuscany, Italy, reveals a complex kinematic evolution for well-ex- posed marly limestones and shales of the the Punta delle Rocchette Fm. of Middle Liassic age. These rocks, defor- med under very-low metamorphic conditions, are affected by W-verging, asymmetrical chevron folds that were first recognized in the '60s. The folds are characterized by horizontal to moderately ESE-dipping axial surfaces and sub-horizontal, NNE trending axes. These structures are intimately associated to W-dipping, low-angle normal faults cutting across the Punta delle Rocchette Fm. and small stepped faults cutting across the fold reverse limbs. The latter are mainly isolated, but occasionally they are linked to form extensional duplex structures with an overall top-to-the- west sense of shear. Low-angle normal faults trend parallel to fold axes, and are cut by a set of high-angle normal faults. Both normal fault sets are parallel in trend and dip, and are kinematically consistent to all previously de- scribed structures. The NNE trending high-angle normal faults separate the Punta delle Rocchette Fm. from the conformably underlying Upper Triassic Clastic basal Fm. (Pseudoverrucano s.s.) to the east, and from Upper Oligo- cene Macigno costiero Fm. and other terrains of the un- metamorphosed Falda Toscana Unit, to the west. Because of the close geometric and kinematic consistency between folds, low-angle and high-angle normal faults, it seems reasonable that folding of the Punta delle Rocchette Fm. was due to vertical shortening (i.e. flattening) accompanied by top-to-the-west shear. Detailed examination of the deformation fabrics associated with each recognised class of structures reveals that folding was dominantly ductile, whereas low-angle and high-angle normal faults were developed under brittle-ductile and brittle deformation conditions, respectively. Folds and normal faults postdate the development of top-to-the east duplexes hence an episode of horizontal shortening
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