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| Ligurian nappes | |
|---|---|
| Name | Ligurian nappes |
| Type | Thrust sheets |
| Period | Mesozoic–Cenozoic |
| Region | Western Alps, Apennines, Maritime Alps, Liguria |
| Country | Italy; France; Switzerland |
| Namedfor | Liguria |
| Lithology | Ophiolite, radiolarite, pelagic limestone, flysch |
Ligurian nappes are a suite of highly tectonized oceanic and continental margin thrust sheets emplaced during the Alpine orogeny in the Western Mediterranean domain. They comprise stacked ophiolitic and sedimentary sequences that record extension, ocean opening, subduction, and continental collision related to the Mesozoic Tethys and Cenozoic Alpine evolution. The nappes appear across the Western Alps, Apennine Mountains, Maritime Alps, and the coastal region of Liguria, and they have been studied by geologists from institutions such as the Italian Geological Survey, CNRS, and multiple universities.
The nappes are defined as large-scale tectonic slices derived from the former Ligurian Basin and associated passive margin, including ophiolite suites, Jurassic–Cretaceous pelagic successions, and Cenozoic flysch units. Classic mapping and synthesis were advanced by workers from the University of Turin, University of Genoa, University of Pisa, and École Normale Supérieure; key regional frameworks were developed in collaboration with the Società Geologica Italiana and the International Union of Geological Sciences. Field studies have focused on areas near Nice, Menton, Savona, Ventimiglia, Imperia, and the Cuneo sector.
The nappes occupy a stratigraphic package originating on the Mesozoic Ligurian Tethys seafloor, overlain locally by Maastrichtian–Paleogene pelagic carbonates and flysch of the Liguro-Piemontese domain. They include ophiolitic lithologies comparable to the Ligurian ophiolites and sequences analogous to the Corsica–Sardinia rifted margins and the Balearic Promontory realm. Stratigraphic correlations have been drawn with sections in the Briançonnais zone, Penninic nappes, and the Subalpine chains documented by field crews from the Ecole et Observatoire des Sciences de la Terre and the University of Montpellier.
Emplacement reflects a protracted history of seafloor spreading, transform motion, subduction rollback, and frontal accretion during convergence between the European and African plates, with modifications by microplate rotations involving Adria and interactions with the Iberian Plate and the Corsica–Sardinia block. Models invoking gravitational collapse, tectonic underplating, and large-scale thrusting have been proposed by groups at ETH Zurich, University of Basel, Imperial College London, and the US Geological Survey; numerical and analogue experiments were performed at facilities such as the GFZ German Research Centre for Geosciences and the Institut des Sciences de la Terre d'Orléans.
Lithological assemblages include ultramafic mantle peridotites, mafic cumulates, gabbros, pillow basalts, Mendelian ophicarbonates, radiolarites, cherts, pelagic limestones, marl, and turbiditic flysch. Petrological studies led by researchers at University of Florence, University of Bologna, University of Lausanne, and University of Barcelona document high degrees of serpentinization, metamorphic overprints including blueschist and greenschist facies, and melt-related geochemical signatures comparable to other Alpine ophiolites such as those studied on Elba Island and in the Sesia-Lanzo Zone.
Radiometric and biostratigraphic constraints from ammonite, foraminifera, and radiolarian assemblages tie parts of the sequences to Jurassic–Cretaceous ages, with emplacement events concentrated in the Paleogene–Neogene. Geochronological techniques—argon–argon, U–Pb zircon dating, and K–Ar—applied by groups at ETH Zurich, GFZ, Geological Survey of France, and the CNR provide temporal constraints that link ophiolite formation to Middle–Late Jurassic seafloor spreading and nappe emplacement to Eocene–Miocene tectonics contemporaneous with the Alpine orogeny and the Pyrenean orogeny.
Structures include tight to isoclinal recumbent folds, major thrust faults, extensional detachments, mylonitic shear zones, and mélange bodies. Fault kinematic analyses and microstructural studies from teams at University of Leeds, Max Planck Institute for Biogeochemistry, University of Oxford, and University of Paris reveal polyphase deformation associated with syn-orogenic extension, slab rollback, and late-stage wrenching tied to strike-slip systems such as the Liguro-Provençal Basin reorganization and the activity of regional lineaments recognized by the European Seismological Commission.
The nappes host mineral occurrences (chromite, magnetite, serpentine-related asbestos minerals, and localized sulfide mineralization) explored by entities including the Italian Ministry of Economic Development and mining firms with historical activity near Elba Island and parts of Liguria. Ground instability, landslides, and seismic hazard in alpine and coastal sectors have implications for infrastructure in cities like Genoa, Nice, and Marseille and for transport corridors such as the A10 motorway and the Aurelia road. Geological assessments by the Italian Civil Protection Department, BRGM, and regional planning authorities integrate nappe geometry into risk models and land-use planning.
Category:Geology of Italy Category:Geology of France Category:Ophiolites Category:Alpine orogeny