Search

We investigated the kinematics of the coupled Helminthoid Flysch–Marguareis Unit outcropping in the High Tanaro Valley in order to constraint the tectonic evolution of the Western Ligurian Alps. Field mapping highlights a tectonic pile composed of, from top to bottom: the Marguareis Unit (Briançonnais Domain); the Helminthoid Flysch Unit (Ligurian Domain) and several continental-derived tectonic slices (Chambeuil Slices) showing affinity to the Briançonnais Domain. Each unit recorded different deformation histories represented by pre-, syn- and post-stacking structures. The syn-stacking structures are represented by thrusts and folds, both responsible for the coupling of the units and for their current structural relationships. In other sectors of the Alpine chain previous authors have highlighted similar structural architectures. We maintain that syn-stacking deformation events played a key role in the tectonic evolution of the Western Ligurian Alps.

The Internal Ligurian units (Northern Apennine) represent deformed and metamorphosed fragments of the oceanic lithosphere of the Ligure–Piemontese oceanic basin. Different tectonic models have been proposed for the geodynamic setting in which the deformation and metamorphism have been acquired. However, the lack of updated, clear, thermo‐barometric data has made it hard to unambiguously discriminate between these different proposed models. In this article, we provide evidence for the deformation of the Palombini Shale, i.e., pelagic deposits belonging to the Internal Ligurian units, under P and T peak conditions of 230–300°C. and 0.6–0.9 GPa, respectively. These data indicate that the Internal Ligurian units were affected by a blueschist facies metamorphism achieved during the underplating within the accretionary wedge developed during the Late Cretaceous—Early Tertiary Alpine subduction. These data support the hypothesis of a unique, pre‐Oligocene orogenic system for the Alpine belt and the westernmost sector of the Northern Apennines belt. [ABSTRACT FROM AUTHOR]

In Corsica Island (France), a belt of metamorphic continental units derived from the European margin is exposed at the western rim of the Alpine Corsica. This study provides a complete anatomy of one of these units (Tour de Valletto Unit) consisting of a Palaeozoic basement covered by an Early Jurassic – late Eocene sedimentary succession. This unit records a polyphase tectono-metamorphic history acquired during the late Eocene – lower early Miocene convergence processes involving the Adria and Europe continental plates. Using a multidisciplinary approach, we reconstructed in detail the P-T path of the Tour de Valletto Unit. The path shows a metamorphic climax at blueschist facies conditions suggesting that the unit was accreted at c. 40 km of depth. After its accretion, the Tour de Valletto Unit was exhumed up to the Earth surface following a path characterized by an increase of temperature and a decrease of pressure. The reconstructed tectono-metamorphic history of the Tour de Valletto Unit is compared with those of the other continental units located in western Alpine Corsica to discuss the exhumation processes active during continental subduction. [ABSTRACT FROM AUTHOR]

In the southern Central Pontides in northern Turkey the remnants of two Neotethyan oceanic basins, currently represented by the Intra-Pontide and the Izmir-Ankara-Erzincan sutures, and the interposing continental microplate (i.e., the Sakarya Composite Terrane) are completely dissected by the North Anatolian Shear Zone (NASZ). Within the resulting kilometre-scale, strike-slip fault-bounded blocks, several Late Cretaceous arc-type magmatic units have been detected. In this paper, we present new geochemical data from one of these magmatic units, the Yerkuyu Unit, that forms an ENE-WSW trending 30-km long and 10-km wide lens-shaped body surrounded by the splays of the NASZ. The studied igneous lithologies have a subduction-related magmatic geochemical signature matching with another lozenge-shaped magmatic block of the Tafano Unit. However, the tectono-magmatic characterization indicates that the Tafano Unit magmatism developed within a continental arc tectonic setting, while the volcanic rocks of the Yerkuyu Unit derived from oceanic arc magmatism. This finding indicates that the subducted oceanic lithosphere of the İzmir- Ankara-Erzincan branch of the Neotethys Ocean produced oceanic volcanic arcs close to the subduction zone (i.e., the Yerkuyu Unit) and beneath the Sakarya continental microplate (i.e., the Tafano Unit). [ABSTRACT FROM AUTHOR]

The occurrence of pervasive crystallization of antigorite associated to brittle tectonics is described for the first time in the External Ligurian peridotites of the Northern Apennine (Italy). Antigorite was found in a slide block of subcontinental peridotites included in the tectonized sedimentary mélange of the Leo Unit (western External Ligurian units). This mélange, as those from the External Ligurian units, originated in Santonian-early Campanian time span from a source area corresponding to the Ocean-Continent Transition Zone at the Adria plate margin. The antigorite was found within veins belonging to four systems, from V1 to V4, each characterized by different attitude and morphology. The morphology of the veins ranges from massive to fibrous, with the latter characterized by fibers both parallel and perpendicular to the vein walls. Rare occurrence of chrysotile and calcite were identified within the veins. The antigorite crystallization in the peridotites cannot be interpreted as related to an orogenic high-pressure metamorphism but most likely can be regarded as developed at shallow structural level in the late stage of the rifting phase when subcontinental mantle was progressively exposed at the surface, intruded by gabbro bodies, and cut by basaltic dykes. [ABSTRACT FROM AUTHOR]