Crustal types and Tertiary tectonic evolution of the Alborán sea, western Mediterranean

Multichannel seismic reflection images across the transition between the east Alborán and the Algero-Balearic basins show how crustal thickness decreases from about 5 s two-way traveltime (TWTT, ∼15 km thick) in the west (east Alborán basin) to ∼2 s TWTT typical of oceanic crust (∼6 km thick) in the east (Algero-Balearic basin). We have differentiated three different crustal domains in this transition, mainly on the basis of crustal thickness and seismic signature. Boundaries between the three crustal domains are transitional and lack evidence for major faults. Tilted blocks related to extension are very scarce and all sampled basement outcrops are volcanic, suggesting a strong relationship between magmatism and crustal structure. Stratigraphic correlation of lithoseismic units with sedimentary units of southeastern Betic basins indicates that sediments onlap igneous basement approximately at 12 Ma in the eastern area and at 8 Ma in the western area. Linking seismic crustal structure with magmatic geochemical evidence suggests that the three differentiated crustal domains may represent, from west to east, thin continental crust modified by arc magmatism, magmatic-arc crust, and oceanic crust. Middle to late Miocene arc and oceanic crust formation in the east Alborán and Algero-Balearic basins, respectively, occurred during westward migration of the Gibraltar accretionary wedge and shortening in the Betic-Rif foreland basins. Arc magmatism and associated backarc oceanic crust formation were related to early to middle Miocene subduction and rollback of the Flysch Trough oceanic basement. Subduction of this narrow slab beneath the Alborán basin was coeval with collision of the Alborán domain with the Iberian and African passive margins and subsequent subcontinental-lithosphere edge delamination along the Betic-Rif margins

Structural and geochemical data on the Rio Magno Unit: Evidences for a new "Apenninic" ophiolitic Unit in Alpine Corsica and its geodynamic implications

The Rio Magno Unit (RMU) tectonically overlies the Schistes Lustrés units in south-eastern Alpine Corsica. It is represented by an ophiolitic sequence, showing remarkable differences with respect to the commonly recognized Corsican ophiolites. This unit can be distinguished from the Schistes Lustrés by the lack of HP-LT metamorphism, reflecting different geodynamic setting, although both were involved early in the same tectonic events. Similarly, the RMU can be distinguished from the Balagne Unit by the presence of normal-MORB basalts and the scarcity of continent-derived sedimentary input, testifying a different oceanic paleo-geographic setting. Moreover, the petrochemical, and stratigraphic features of the RMU ophiolitic sequence show close analogies with the Internal Ligurides of Northern Apennine. The RMU represents the first record of a non-metamorphic “Apenninic”-type ophiolitic unit in Alpine Corsica, supporting the hypothesis that the Alpine Corsica - Northern Apennines system represent a double-vergent accretionary wedge

The Rio Magno Unit (Alpine Corsica): a review of its structural, stratigraphical and geochemical features and their geodynamic implications

The Rio Magno Unit (eastern Corsica) represents an Apenninic-type ophiolitic unit, quite similar to the Internal Ligurides; its ophiolitic sequence includes N-MORB basalts, Early Cretaceous Palombini-bearing limestones, and mid-Cretaceous flysch, and it is not affected by HP-LT alpine metamorphism. These features further support the hypothesis of close geodynamic relationships between the Corsican and Northern Apenninic ophiolites. We suggest that, in the Jurassic Piedmont-Ligurian oceanic basin, the Rio Magno and Internal Ligurides ophiolitic sequences represent a continuous, internal, oceanic paleo-domain. Subsequently, during the Late Cretaceous-Late Eocene, they underwent a similar orogenic evolution, escaping deep involvement during the subduction beneath the European continental margin

Did the “Autochthonous” European foreland of Corsica Island (France) experience Alpine subduction?

Despite the important role played by the Sardinia-Corsica block in the reconstruction of the Western Mediterranean geodynamics, the extent of involvement of the “Autochthonous” European margin exposed in Corsica (France) (i.e., Hercynian Corsica) in the Alpine orogeny remains uncertain. Stratigraphic and sedimentological studies in the post-Variscan deposits on the Hercynian Corsica are scarce and even scarcer are the structural and metamorphic constraints. To face these uncertainties, we present new stratigraphic, structural and metamorphic data from the area of Razzo Bianco, Central Corsica, where a complete sequence belonging to the Europeancontinental margin is exposed. Field and structural investigations demonstrate that the sequence represents the easternmost edge of the downgoing European plate. Metamorphic studies on the Eocene deposits indicate that the margin was buried at depth up to blueschist facies conditions and, subsequently, it was progressively exhumed mainly through the activation of oblique top-to the NW shear zones

La série saumâtre et continentale d'âge Miocène moyen et supérieur d'Eivissa (ex-Ibiza, Baléares)

At first, it is recalled that the main tectonics of Eivissa (Ibiza) involves white marls of upper Burdigalian- lower Langhian, with abundant planktonic microorganisms. But, near the south-west promontory of the island, in a site discovered a century ago by Vidai and Molina (1888), one find directly transgressive on the Senonian, polygenic conglomerates, then a sandy marly formation with Bivalvia (Cmssos- crea gryphoides, Mytilus aquitanicus, ...) and few benthic Foraminifera, finally coaly clays with brackish or estuary Gastropods. This "Formation of Cap Jueu" has also provided Langhian-like scarce paiynological assemblages. Strata of the same sedimentary cycle, also involved in the tangential tectonics, may be pointed out at the top of the imbrication of Roques Altes (ex- Rocas Altas), South West of la Talaia of Sant Josep (ex- San José) and near ant Rafael, maybe dating from the Tortonian (?) by microflora. It is possible to group here the "top conglomerates" from the center of the island, which lie up to Tnas, but usually ravining lower Langhian marls. So, an independent sedimentary cycle, prior to paroxysmal tectonics, dated as "middle" - ? upper Miocene (Langhian to ? Tortonian), may be defined, which goes before the deposit of marine "upper" Tortonian (Limestones of Portinatx), posterior to the main compressive phase. Clayey interstratifications in these limestones have provided poor paiynological assemblages corresponding to this Tortonian age. In short, the Miocene from Eivissa shows three independent sedimentary cycles which enable to date tectonic episodes concerning this eastern extension of Betic Cordilleras