1,721,012 research outputs found
Kinematic evolution of the outer zones of the Northern Apennines, Italy: the contribution of sequential cross-section balancing techniques
No full textA geological section across the southeastern zones of the Northern Apennines, from the Umbria-Marche Range to the Adriatic Foreland Folds (Spoleto Mizar 1 well), is described. These provinces are characterized by the widely outcropping deepest portions of the Umbria-Marche sedimentary cover which, due to a marked axial plunge, are largely buried under the Neogene deposits further to the North.
Restoration of the compressional structures allows for an evaluation of the shortening experienced by the Meso-Cenozoic sedimentary cover. The limited amount of contraction (about 20%) is broadly consistent with observation of thrust faults terminating both upwards and along-strike in asymmetrical fold pairs, an evidence supportive of tip-line folding processes.
This interpretation, in combination with with a hinterland-to-foreland thrust propagation inferred from structural overprinting relationships, provides a key for reconstructing the kinematic evolution of the outer zones of the Northern Apennines. A systematic use of sequential restoration methods can be halpful in the interpretation of coeval structures (such as those along the CROP 03 seismic profile) whose geometry is not accessible to direct investigation
Evidenze di tettonica distensiva sinsedimentaria nel bacino messiniano della Laga: implicazioni per l'evoluzione dell'Appennino Settentrionale
No full textL'Appennino umbro-marchigiano offre situazioni particolarmente favorevoli per lo studio dei rapporti fra tettonica e sedimentazione. All'interno della catena si riconoscono due importanti province fisiografico-strutturali, l'Appennino umbro-marchigiano s.s. e la fascia pedemontana marchigiana, che rappresentavano rispettivamente la catena e l'adiacente bacino di avanfossa durante il Messiniano. Nell'area compresa fra M. la Speluca e M. Prato, lungo un segmento della linea Olevano-Antrodoco-M. Sibillini, la Formazione della Lçaga, che costituisce il riempimento terrigeno dell'avanfossa messiniana, è interessata da faglie dirette il cui sviluppo ha preceduto la propagazione dei sovrascorrimenti. Il passaggio da distensione a compressione, estremamente rapido (meno di un milione di anni) si è realizzato durante l'intervallo Messiniano superiore-Pliocene inferiore. La presenza di strutture distensive all'interno della Formazione della Laga ha localmente controllato la geometria della superficie di sovrascorrimento di M. la Speluca-M. Prato. La distensione pre-orogenica rappresenta verosimilmente una risposta superficiale ai processi di flessurazione litosferica indotta dalla costruzione della catena e potrebbe aver condizionato la posizione del fronte messiniano del sistema catena-avanfossa-avampaese
Evidence for a double vergence in the Northern Apennines, Italy: Observations from the Arenarie di Poggio al Carpino Fm., Southern Tuscany, Italy [Evidenze di doppia vergenza nell'Appennino Settentrionale: osservazioni dalla Formazione delle Arenarie di Poggio al Carpino, Toscana Meridionale, Italia]
No full textL’analisi delle strutture mesoscopiche che caratteriz- zano la Formazione delle Arenarie di Poggio al Carpino (Permo-Triass) appartenente al Complesso Metamorfico Toscano, in località «I Canaloni» (Toscana meridionale), ha messo in evidenza la sovrapposizione di due fasi defor- mative principali a vergenza opposta. La prima fase è caratterizzata da trasporto tettonico top-to-the WSW. A questa fase è legato lo sviluppo di una foliazione attualmente preservata nei livelli più compe- tenti della Formazione. La seconda fase mostra senso di taglio top-to-the ENE ed è rappresentata da vene di estensione, pieghe asimmetriche, sovrascorrimenti con geometrie flat-ramp-flat e duplex.
Le strutture della prima fase sono probabilmente collegate alle fasi Cretaceo-Paleogeniche alpine, caratterizzate in generale da condizioni di HP-LT, e potrebbero essersi sviluppate in seguito ad un processo precoce di subduzione con polarità orientale. Rocce metamorfiche di HP-LT sono attualmente esposte in altri settori dell’Appennino settentrionale (metaofioliti del Monte Argentario e rocce a Mg-carfolite).In locality «I Canaloni» (Southern Tuscany), the analysis of mesoscopic structures within the Arenarie di Poggio al Carpino sandstones Fm. (Permian-Triassic), belonging to the Tuscan Metamorphic Complex, highlighted the occurrence of two main deformational episodes with opposite sense of shear. The first episode is characterized by top-to-the WSW sense of shear and it is responsible for the development of a foliation preserved within the stiff layers of the Formation. The second episode shows top-to-the ENE shear sense and it is represented by extensional veins, asymmetric folds, thrusts showing flat-ramp-flat geometries and duplexes. The structures of the first deformational episode probably developed during Cretaceous-Paleogene alpine phases, generally characterised by HF-LT metamorphic conditions, and they may represent the evidence of an initial east-dipping subduction process. HP-LT metamorphic rocks are exposed in other locations along the inner zones of the Northern Apennines (Argentario Mt. meta-ophiolite and Mg-carpholite-bearing rocks)
A mesoscopic inversion duplex in SW Tuscany, Italy: implications for inferring the deep geometry of collision orogens
No full textThe advances in the field of inversion tectonics illustrate that pre-orogenic extensional deformations largely control the geometry and evolution of thrust systems. While the relationships between extensional and con- tractional structures are widely documented from restoration of thrust fans, they are significantly less documented in duplex structures. In this contribution we briefly describe a mesoscopic scale duplex developed, within the Arenarie di Poggio al Carpino Fm, across a precursor boudinage structure inherited from an episode of Mesozoic age extension. The structure crops out at «I Canaloni» localty (Farma River) along the Mid Tuscan Ridge, SW Tuscany (northern Apennines of Italy)
Modes of propagation of the compressional deformation in the Umbria-Marche Apennines
No full textOverprinting relationships among major and minor structures in the sedimentary cover of south-eastern Umbria and northern Latium (Central Italy) provide significant information on the modes of compressional deformation propagation in the Umbria-Marche Apennines during the Neogene. The innermost thrust sheets are deformed by outer, younger thrust-related folds: this indicates a progressive migration of compressional fronts towards the east, in a piggy-back thrusting sequence. Jurassic, Cretaceous-Paleogene and Messinian age normal faults within the pre-thrusting template effectively controlled the geometry of the evolving Late Miocene-Early Pliocene compressional features. Locally anomalous younger-over-older relationships along upward-propagating thrust faults are interpreted in the framework of a progressive, rather than multistage, compressional deformation. Structural evidence is effective in reconstructing the kinematic evolution of the fold-and-thrust belt through sequential cross-section restoration
Pre-orogenic extensional deformations within Permian-Triassic rocks of Southern Tuscany: structural record of an episode of Early Mesozoic continental rifting?
No full textThe advances in the field of inversion tectonics have shown that many thrust belts were originated at the expenses of pre-orogenic rift basins with complex extensional architectures. Pre-orogenic extensional deformations have been widely documented across the northern Apennines of southern Tuscany by the recognition of syn- sedimentary normal faults within the Mesozoic carbonate sequences of both metamorphic and non-metamorphic tectonic units. In local- ity «I Canaloni», in the heart of southern Tuscany, a detailed struc- tural analysis of the shallow marine deposits belonging to the Arenarie di Poggio al Carpino Formation reveals that inherited extensional structures also occur within Permian-Triassic meta-sedi- mentary deposits. The extensional structures recognized in this locality played a key role on nucleation and development of Tertiary contractional structures. Thrusts splays of a composite duplex, that we indicate as Canaloni Duplex, constantly located at boudin necks which represent mechanical perturbations within the sequence. The restoration of contractional structures highlights the nature and extent of the extensional deformation within the Permian-Triassic sequence. The observation of pre-orogenic extensional structures within the Arenarie di Poggio al Carpino Formation together with syn-sedimentary normal faults within the overlying Upper Triassic strata of the Verrucano Group, may be interpreted as evidence for an episode of Early Mesozoic continental rifting
Deformation of S-C tectonites in the Scaglia cinerea Formation in the Spoleto area (south-est Umbria).
No full textAnalysis of a mesoscopic duplex in SW Tuscany, Italy: implications for thrust system development during positive tectonic inversion
No full textThe advances in the field of inversion tectonics, pioneered by Mike Coward and co-workers, have shown that many thrust belts originated at the expense of pre-orogenic rift basins that originally had complex extensional architectures. These architectures are reflected by significant lateral thickness and facies changes within the deformed stratigraphic sequences. Although these changes are widely documented from the restoration of balanced sections across thrust fans, they are significantly less well documented from restoration of duplex structures. As a consequence, most available duplex models assume layer-cake stratigraphic sequences. In this contribution a peculiar mesoscopic duplex is described. This structure developed across a single irregular, previously extended quartzite layer of the Arenarie di Poggio al Carpino Formation (Upper Permian-Lower Triassic), during the Late Tertiary orogenic event that led to development of the Apennine chain. Through comparison of the analysed duplex with macroscopic analogues, it is proposed that similar structures may occur on a wide variety of scales, in the Apennines as well as in other orogenic belts. © The Geological Society of London 2007
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