Evoluzione tettonica del cuneo di accrezione Ligure in Monferrato (NO-Italia): nuovi dati dall'analisi di melanges tettonici, sedimentari e diapirici.L'evoluzione tettonica del Monferrato e ben conosciuta a partire dagli episodi deformativi oligocenici. Al contrario, la sua evoluzione pre-oligocenica legata alle fasi di accrezione del Cretacico superiore-Eocene medio del cuneo di accrezione Ligure e ancora poco conosciuta.Le Unita Liguri Esterne che costituiscono il substrato della successione del Bacino Terziario Piemontese in Monferrato sono conosciute come un complesso caotico indifferenziato di eta Cretacico superiore-Eocene medio. Lo studio dettagliato di queste Unita ha permesso di distinguere al loro interno tre unita litostratigrafiche: le Argille varicolori (Santoniano-Campaniano), il Flysch di Monte Cassio (Campaniano superiore(?)-Maastrichtiano), e le Brecce argillose poligeniche (Oligocene superiore). Le Argille varicolori e le Brecce argillose poligeniche rappresentano il prodotto dell'interazione e sovrapposizione di processi tettonici, sedimentari e diapirici che hanno operato in momenti diversi dell'evoluzione del cuneo di accrezione Ligure formando melange poligenici. L'analisi della deformazione e la comprensione dei rapporti di sovrapposizione tra i diversi tipi di melanges poligenici individuati hanno permesso di: (i) distinguere piu fasi deformative (Cretacico superiore, Rupeliano e Oligocene superiore); (ii) comprendere i rapporti di interazione e sovrapposizione tra processi tettonici, sedimentari e diapirici che hanno portato alla formazione di diversi tipi di melanges poligenici; (iii) ridefinire piu in dettaglio, rispetto ai dati di letteratura, i tempi della deformazione dell'intervallo di tempo Chattiano–pre Burdigaliano.
The Late Jurassic Monviso ophiolite in the Western Alps is a multiply deformed, eclogite-facies metaophiolite that represents a remnant of the Alpine Tethyan oceanic lithosphere.The recent recognition of a pre-Alpine detachment fault in the Lower Tectonic Unit of this ophiolite has led to the discovery of an oceanic core complex, which developed during the initial stages of the tectonic evolution of the Alpine Tethys.The contains ductilely to cataclastically deformed blocks and clasts of Fe-Ti and Mg-Al metagabbros in a matrix made of mylonitic serpentinite and talc-chlorite schist with high Ni-Cr concentrations and high Cl contents.Intensely sheared ophicarbonate rocks and brecciated serpentinite within this shear zone are deformed by the Alpine-phase S1 foliation and D2 folds, providing a critical age constraint for the timing of its formation.Metabasaltic-metasedimentary rocks in the hanging wall increase in thickness away from the shear zone, characteristic of syn-extensional rock sequences in supradetachment basins.A Lower Cretaceous post-extensional sedimentary sequence unconformably cover the synextensional strata, the detachment shear zone, and the ophiolitic footwall, establishing a strong structural evidence for the intraoceanic, seafloor spreading origin of the tectonic fabric of the Monviso ophiolite, prior to the onset of subduction zone tectonics in the Alpine Tethys.The Monviso ophiolite and the Baracun Shear Zone represent a peridotite-localized oceanic core complex, which survived both the subduction and continental collision tectonic stages of the Alpine orogeny.Intraoceanic detachment faults and oceanic core complexes may play a significant role in subduction initiation, and hence their recognition in orogenic belts is an important step in reconstructing the record of ocean basin collapse and closure.
Research Article| September 01, 2007 Interaction of tectonic, sedimentary, and diapiric processes in the origin of chaotic sediments: An example from the Messinian of Torino Hill (Tertiary Piedmont Basin, northwestern Italy) Francesco Dela Pierre; Francesco Dela Pierre 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso 35, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Andrea Festa; Andrea Festa 2Consiglio Nazionale delle Ricerche—Istituto di Geoscienze e Georisorse, Via Valperga Caluso 35, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Andrea Irace Andrea Irace 3Consiglio Nazionale delle Ricerche—Istituto di Geoscienze e Georisorse, Via Valperga Caluso 35, 10125 Torino, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Francesco Dela Pierre 1Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso 35, 10125 Torino, Italy Andrea Festa 2Consiglio Nazionale delle Ricerche—Istituto di Geoscienze e Georisorse, Via Valperga Caluso 35, 10125 Torino, Italy Andrea Irace 3Consiglio Nazionale delle Ricerche—Istituto di Geoscienze e Georisorse, Via Valperga Caluso 35, 10125 Torino, Italy Publisher: Geological Society of America Received: 12 Jul 2006 Revision Received: 01 Feb 2007 Accepted: 21 Feb 2007 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2007) 119 (9-10): 1107–1119. https://doi.org/10.1130/B26072.1 Article history Received: 12 Jul 2006 Revision Received: 01 Feb 2007 Accepted: 21 Feb 2007 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesco Dela Pierre, Andrea Festa, Andrea Irace; Interaction of tectonic, sedimentary, and diapiric processes in the origin of chaotic sediments: An example from the Messinian of Torino Hill (Tertiary Piedmont Basin, northwestern Italy). GSA Bulletin 2007;; 119 (9-10): 1107–1119. doi: https://doi.org/10.1130/B26072.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Geologic mapping and integrated stratigraphic and structural observations of a gypsum quarry from northwestern Italy allow evaluation of the relative contributions, the time relationships, and the causative links between tectonic, sedimentary, and diapiric processes in the genesis of chaotic sediments of Messinian age. Three chaotic units are exposed in the quarry: together, they make up a composite chaotic unit that is unconformably overlain by post-chaotic sediments. Unit 1 is composed of blocks of primary evaporites that are juxtaposed to marine marls by subvertical transpressive faults and are parallel to the fault surfaces. Unit 2 unconformably overlies Unit 1, and consists of a lenticular sedimentary body containing both angular and rounded blocks, randomly distributed in a fine-grained matrix. Unit 3 consists of a 10-m-wide body bounded by transpressive faults, and pierces both Units 1 and 2. It is composed of strongly deformed muddy deposits that envelop blocks of gypsum and carbonate rocks. Between the core and the margins, various zones have been defined based on the increasing amount of deformation toward the margins. The post-chaotic sediments unconformably overlie both Units 1 and 2, sealing the main fault systems.The composite chaotic unit is related to thrust propagation during a regional phase of deformation, and is the result of different evolutionary stages, in each of which a single genetic mechanism prevailed. Tectonic faulting prevailed during stage 1 and was responsible for the formation of a tectonically disrupted assemblage (Unit 1). During stage 2, gravity-driven sedimentary phenomena, related to slope oversteepening triggered by ongoing thrust propagation, resulted in the deposition of Unit 2. Gravity sliding was favored by the mechanical weakening of sediments caused by tectonic faulting. Over-pressure conditions resulting from the rapid deposition of Unit 2 triggered the rise of a diapir (Unit 3) that pierced Units 1 and 2. The involvement of methane-rich fluids in the formation of the diapir is suggested by the occurrence of blocks of methane-derived carbonates, found not in the quarry, but just outside it. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The External Ligurian Units in western Monferrato (NW-Italy) have been always described as an undifferentiated chaotic complex. This map, at 1:10,000 scale, describes in detail the tectono-stratigraphic setting of these Units in the sector of the Alps–Apennines junction. Here, the External Ligurian Units represent the northwestern prolongation of the Northern Apennines and consist of a Late Cretaceous chaotic succession represented by the Argille varicolori and the overlaying Monte Cassio Flysch. The late Eocene–Miocene episutural succession of the Tertiary Piedmont Basin rests unconformably on the External Ligurian Units. The mapped crosscutting relationships between stratigraphic unconformities and faults allow us to describe a complex tectono-stratigraphic setting that is the product of four tectonic stages. Layer-parallel extension related to Late Cretaceous–early Eocene deformation occurred in the internal sector of the Alpine accretionary wedge and is preserved within the External Ligurian Units which is sealed by the late Eocene deposits of the Tertiary Piedmont Basin. The unconformity at the base of the Oligocene succession records the drowning of shelf sediments controlled by NW-striking left-lateral transtensive faulting. A WNW-striking and NE-verging thrust superposes the External Ligurian Units onto the late Eocene–Oligocene deposits and it is sealed by the gravitational emplacement of late Oligocene Polygenetic argillaceous breccias. Both the WNW-striking thrust and the Polygenetic argillaceous breccias are cut by NW-striking right-lateral transpressive faults that are, in turn, sealed by the Tortonian unconformity.
In the peri-Adriatic region, mélanges represent a significant component of the Apennine and Dinaride–Albanide–Hellenide orogenic belts as well as ancient and present-day accretionary wedges. Different mélange types in this broad region provide an excellent case study to investigate the mode and nature of main processes (tectonic, sedimentary, and diapiric) involved in mélange formation in contrasting geodynamic settings. We present a preliminary subdivision and classification of the peri-Adriatic mélanges based on several years of field studies on chaotic rock bodies, including detailed structural and stratigraphic analyses. Six main categories of mélanges are distinguished on the basis of the processes and geodynamic settings of their formation. These mélange types are spatially and temporally associated with extensional tectonics, passive margin evolution, strike-slip tectonics, oceanic crust subduction, continental collision, and deformation. There appears to have been a strong interplay and some overlap between tectonic, sedimentary, and diapiric processes during mélange formation; however, in highly deformed regions, it is still possible to distinguish those mélanges that formed in different geodynamic environments and their main processes of formation. This study shows that a strong relationship exists between mélange-forming processes and the palaeogeographic settings and conditions of mélange formation. Given the differences in age, geographic location, and evolutionary patterns, we document the relative importance of mélanges and broken formations in the tectonic evolution of the peri-Adriatic mountain belts.
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The Ligurian-Piedmont Ocean (LPO) is inferred as a relatively narrow oceanic basin in palaeogeographic restorations, but the actual amount of oceanic lithosphere generated and the timing of magmatic accretion are still debated. Magmatic ages obtained from LPO intrusive rocks predominantly range between 165 and 160 Ma, supporting the interpretation of the LPO as a magma-poor ocean. However, this relatively short timespan of magmatic accretion may also suggest that the orogen sampled older sectors of the oceanic lithosphere, while younger (and more oceanward?) sectors could have been deeply subducted without returning.We therefore focus on studying a poorly-known stack of oceanic lithosphere (i.e., the Susa and Lanzo Valley Ophiolites; SLVO), which is exposed in the inner-central sector of the Western Alps and tectonically juxtaposed with the Gran Paradiso and Dora-Maira massifs. The SLVO were metamorphosed under eclogite-facies peak conditions and consist of large volumes of serpentinite hosting up to kilometer-sized metagabbro bodies, with Fe-Ti-rich differentiated masses and rare metaplagiogranite dykes. The metaophiolite sequence also includes widespread metabasaltic rocks and a metasedimentary cover consisting of minor quartzite and marble levels overlain by calcschist.Two pairs of Fe-Ti metagabbro and metaplagiogranite s.l. sampled close to the Avigliana (lower Susa Valley) and Mondrone (middle Ala Valley) localities have been selected for zircon U-Pb dating. In each sample, the dated zircons yield magmatic ages falling within the uppermost Jurassic Period (~150 Ma). The common age, along with similar major and trace element compositions, suggests a cogenetic origin within differentiation trends for the two pairs of metagabbro-metaplagiogranite (De Togni et al., 2024). Consequently, the SLVO were sampled from a sector of the LPO characterized by magmatic activity at ~150 Ma, significantly younger than most of previously reported ages for the LPO magmatism. We argue that the SLVO represent the youngest oceanic lithosphere accreted in the Western Alps and they may provide new constraints on the structural architecture of the LPO. De Togni, M., Balestro, G., Rubatto, D., Castelli, D., Gattiglio, M., & Festa, A. (2024). Late Jurassic magmatism in the Ligurian-Piedmont Ocean constrained by zircon ages of mafic and felsic meta-intrusives. Terra Nova, 00, 1–11. doi.org/10.1111/ter.12723
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