1,721,071 research outputs found
Foreword of the special issue on Alps and Apennines: a natural laboratory for Structural Geology and Geodynamics
No full textCoalescence of fault-bend and fault-propagation folding in curved thrust systems: An insight from the Central Apennines, Italy
No full textThe coalescence and spatial variability of different thrust-related folding mechanisms involving the same mechanical multilayer along a curved thrust system are documented in this study. The field-based analysis of thrust-related folds spectacularly exposed in the Gran Sasso thrust system, Central Apennines of Italy, allowed us to reconstruct the interference fold pattern between fault-bend and fault-propagation folding. These two thrust-related folding mechanisms exhibit spatial variability along the differently oriented ramps of the curved Gran Sasso thrust system, passing from one style to the other. Their selective development is controlled by contrasting styles of compressional normal-fault reactivation related to positive tectonic inversion. Fault-bend and fault-propagation folding interact with a characteristic interference fold pattern in the salient apex zone of the curved thrust system due to their synchronous/in-sequence growth. This interference fold pattern might be helpful and predictive when reconstructing lateral variations in different thrust-related folds in similar subaerial or submarine thrust belts
Mesostructural analysis on the conglomerates of the outer marchean area (between M. Ascensione and S. Benedetto)
No full textA mesostructural analysis carried out on the conglomerates of the sedimentary sequence (Middle Pliocene-Early Pleistocene) of the coastward area of the Marche is presented.
These conglomerates are interbedded in epibathial to neritic clays. The sequence is about 2000 m thick and it constitutes a gentle NE dipping monocline.
An unconformity exists between this sequence and the underlying Messinian-Early Pliocene deposits which are involved in the thrusts affecting the Apennines during Miocene-Early Pliocene.
Deformational features, due to frictional pebble boundary sliding during deformation (slickolite striae and slickolites, mainly at microscopic scale) are analysed. This analysis suggests the presence of compression which postdates the Early Pleistocene, Late Pliocene and Middle Pliocene deposits from the E towards the W. The different shortening axes are subhorizontal, trending about N-S, NE-SW and NW-SE, and subvertical.
There is a good geometric analogy between the compressive fields, in these deposits, and the older ones suggested by the structural features of the Umbria-Marche chain (Miocene-Early Pliocene).
Nevertheless we think that is better to associate these findings to a context of downslope gliding and/or gravity spreading within the accretionary Umbria-Marche fold and thrust belt System
Analisi mesostrutturale dei depositi mio-pliocenici della zona marchigiana esterna.
No full textÈ stata condotta un'analisi mesostrutturale nei conglomerati tardo messiniani, rinvenuti alla base di una successione mio-pliocenica che si trova a contatto tettonico con le più occidentali unità paleogeniche della brachianticlinale di Cingoli (area marchigiana esterna). È risultato un campo di stress compressivo con asse principale massimo orientato N 50°, inquadrabile nel periodo compressivo che, nell'area marchigiana, ha avuto il suo acme alla fine del Pliocene inferiore.
L'elemento disgiuntivo, lungo il quale si realizza il suddetto contatto, ha un andamento complesso: N 10° ± 10 - N 150° e N 100° ± 10° da sud a nord, con immersione rispettivamente a ESE, NE e NNE.
Esso nel tratto appenninico è risultato essere un motivo inverso a vergenza sudoccidentale e può essere interpretato come un retro-scorrimento
The interaction of extensional and contractional deformations in orogenic belts: the example of the Central Apennines, Italy
No full textThe relationships among normal faults and thrusts in the Apennines of Italy are often unclear, and the local absence of syn-tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures. The activity of normal faults has been variously regarded as due to pre-, syn- or post-orogenic extension, and the contrasting evidence from different sites has produced an ongoing debate on the normal fault±thrust interaction. The results of a kinematic analysis on selected composite structures of the outer zones of the Central Apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations. Detailed mapping, outcrop-scale observations and structural overprinting relationships support a positive inversion tectonic history, where normal faults and fault-controlled escarpments formed ®rst, and were later deformed by thrusts and related folds. All normal faults control the distribution of foredeep deposits, thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the Apennine thrust belt. The systematic collection of structural data may help to unravel the evolution of adjacent sectors of the Apennine chain, as well as of other belt-foredeep±foreland systems whose extension±contraction relationships are poorly constrained
Shear zone fabrics and their significance in curved, inverted basin-derived thrust systems
No full textIn this study, we report how criteria inferred from structural and kinematic analysis of shear zone fabrics can be instrumental in deciphering events of positive or negative inversion tectonics. Mesoscopic structural and kinematic analyses are performed on well-exposed brittle-ductile thrust shear zones within curved thrust systems in the Central-Northern Apennines of Italy. The structural and kinematic features of thrust-related tectonites make it possible to outline a history of positive inversion. S/C- and S-tectonites/fabrics are distinctive of frontal or oblique thrust ramps, respectively. In particular, S-fabrics result from selective transpressional-reactivation of pre-thrusting normal faults. By contrast, more complex composite fabrics, characterized by folded cleavage, reveal a history of negative inversion tectonics. Mesocopic cleavage folding is ascribed to shear-sense reversal along the shear surfaces during extensional reactivation of pre-existing thrusts; or to synthetic reactivation by listric foreland-dipping normal faults, merging downwards on former thrust surfaces during protracted episodes of gravitational collapse. Shear zone fabrics identification criteria, here illustrated from thrusts of different size, if systematically used, may be diagnostic of different deformation paths, and hence provide useful tools to elucidate the tectonic history of curved thrust systems in orogens that have experienced multiple episodes of inversion
Along strike variation of inversion-related folds in foreland thrust belts: implications for tectonic style and petroleum prospectivity
No full textThe along-strike variation of different fault-related folds in a curved thrust system is documented in the Central Apennines of Italy. Fold profiles and kinematic mechanisms are reconstructed by integrating geological and structural data with restoration of key balanced cross-sections and description of panoramic natural transects. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor normal faults along the oblique and frontal ramps. Fault-bend reactivation and fault-propagation shortcut folding produce a characteristic fold interference pattern at the salient apex of the curved thrust system. The transition style depends on the pattern of the inherited normal fault template and on the amount of shortening achieved in the salient zone. The modest amount of shortening achieved by the inversion fault-related folds is consistent with a thick-skinned thrusting style. Inversion fold development modes and their diagnostic features are also important for petroleum prospectivity investigations
Considerazioni strutturali sull'area compresa tra la conca di Cascia e la valle del Tronto (Appennino umbro-marchigiano meridionale). Problemi di raccorciamento e neotettonica
No full textLo studio ha messo in evidenza un complesso assetto tettonico dell'area caratterizzato da due unità sovrascorse verso E. Il raccorciamento complessivo della copertira sedimentaria è stato valutato attorno al 55%
Short cut geometry along the N-S trending Gran Sasso and Morrone Thrust front (Central Apennines)
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