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  • 1
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    Bureau de recherches géologiques et minières
    In:  Bulletin du Bureau de Recherches Géologiques et Minières / 1, 2 (3). pp. 149-178.
    Publication Date: 2020-06-26
    Description: Les données géologiques et géophysiques recueillies dans le golfe de Gascogne depuis 12 ans ont été partiellement réinterprétées d'après les forages IPOD du leg 48, et une nouvelle carte structurale en couleurs a été établie〈1〉. Cette carte montre la profondeur et l'extension du socle océanique et de la croûte continentale, amincie par les phases de distension mésozoïques et/ou épaissie par les phases de compression cénozoïques. Les structures sont classées d'après leur âge et leur nature: failles normales et décrochantes, témoins du « rifting » des marges armoricaine et aquitaine du Néocomien à l'Aptien; failles transformantes de la plaine abyssale, contemporaine de l'ouverture océanique de golfe à l' Albien et au Crétacé supérieur jusqu'au Santonien ; chevauchements, failles inverses, prismes d'accrétion tectonique, décrochements,failles normales et horsts créés par la subduction de la plaque européenne sous l'Ibérie du Maestrichtien (?) à l'Éocène moyen; enfin, structures tardives dues au rejeu à l'Oligocène ou au Miocène des accidents tectoniques antérieurs. Ces données structurales sont compatibles avec un modèle cinématique selon lequel l'Ibérie a subi, par rapport à l'Europe stable, au moins trois rotations successives depuis le Jurassique: déplacement en direction du sud-ouest au Crétacé inférieur jusqu'à l' Aptien supérieur; divergence et mouvement vers le sud-est de l' Aptien terminal au Santonien ; enfin, convergence et mouvement en direction du nord-ouest au Paléocène et à l'Éocène inférieur. IPOD drillings on the armorican margin allow to review geological and geophysical data collected in the Bay of Biscay for the past twelve years. They also allow to draw up a new structural sketch. The sketch displays the depth and extension of oceanic and continental basement. Structures fall into four catégories: 1) Neocomian-Aptian normal and associated probable strike-slip faults, related to the rifting of the armorican margin; 2) Albian-Santonian transform faults within the oceanic basement, resulting from the iberian rotation and correlative opening of the Bay of Biscay; 3) Maestrichtian(?)-middle Eocene thrusting, reverse faults, strike-slip faults, accretionary tectonic prism and normal faults linked to the subduction of the european plate beneath the north-spanish margin emphasised by a fossil marginal trench and a bulging of the deeping plate; and 4) Oligocene-Miocene reverse, normal and strike-slip faults. The structural data agree with a three phases kinematic model: a) Néocomian-Aptian NE-SW motion of the iberian plate with respect to the stable Europe (rifting); b) AlbianSantonian NW-SE drifting of lberia (and related oceanic accretion within the Bay); c) Paleocene-lower Eocene SE-NW converjence resulting in subduction of the european plate beneath the Iberian plate and subsequent shortening and thickening of the north-spanish margin.
    Type: Article , PeerReviewed
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  • 2
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    Geological Society
    In:  In: The tectonics, sedimentation and palaeoceanography of the North Atlantic region. , ed. by Scrutton, R. A. Geological Society London Special Publications, 90 . Geological Society, London, UK, pp. 71-91.
    Publication Date: 2018-03-21
    Description: The crustal structure of the Mesozoic deep Galicia margin and adjacent ocean-continent boundary (OCB) was investigated by seismic reflection (including pre-stack depth migration and attenuation of seismic waves with time). The seismic data were calibrated using numerous geological samples recovered by drilling and/or by diving with submersible. The N-S trending margin and OCB are divided in two distinct segments by NE-SW synrift transverse faults locally reactivated and inverted by Cenozoic tectonics. The transverse faulting and OCB segmentation result from crustal stretching probably in a NE-SW direction during the rifting stage of the margin in early Cretaceous times. The Cenozoic tectonics are related to Iberia-Eurasia convergence in Palaeogene times (Pyrenean event). In both segments of the deep margin, the seismic crust is made of four horizontal layers: (1) two sedimentary layers corresponding to post- and syn-rift sequences, where velocity ranges from 1.9 to 3.5 km s−1, and where the Q factor is low, the two sedimentary layers being separated by a strong reflector marking the break-up unconformity; (2) a faulted layer, where velocity ranges from 4.0 to 5.2 km s−1, and where the Q factor is high. This layer corresponds to the margin tilted blocks, where continental basement and lithified pre-rift sediments were sampled; (3) the lower seismic crust, where the velocity (7 km s−1 and more) and the Q factor are the highest. This layer, probably made of partly serpentinized peridotite, is roofed by a strong S-S’ seismic reflector, and resting on a scattering, poorly reflective Moho. A composite model, based both on analogue modelling of lithosphere stretching and on available structural data, accounts for the present structure of the margin and OCB. Stretching and thinning of the lithosphere are accommodated by boudinage of the brittle levels (upper crust and uppermost mantle) and by simple shear in the ductile levels (lower crust and upper lithospheric mantle). Two main conjugate shear zones may account for the observations and seismic data: one (SZ1), located in the lower ductile continental crust, is synthetic to the tilting sense of the margin crustal blocks; another (SZ2), located in the ductile mantle, accounts for the deformation of mantle terranes and their final unroofing and exposure at the continental rift axis (now the OCB). The S-S′ reflector is interpreted as the seismic signature of the tectonic contact between crustal terranes and mantle rocks partly transformed into serpentinite by syn-rift hydrothermal activity. It is probably related to both shear zones SZ1 and SZ2. The seismic Moho is lower within the lithosphere, at the fresh-serpentinized peridotite boundary.
    Type: Book chapter , NonPeerReviewed
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  • 3
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    Societe Geologique de France
    In:  Bulletin de la Societe Geologique de France, 8 (2). pp. 393-400.
    Publication Date: 2020-06-26
    Description: The west Galicia margin (Spain) is a typical passive margin. During the Mesozoic, the continental crust of the margin experienced several episodes of extension. The main stage was during the Berriasian-late Aptian interval (140-114 Ma). The stretching of the lithosphere resulted in (a) the thinning of the continental crust, testified by superficial extensional structures (normal faults, tilted fault blocks) and rapid subsidence, and (b) the emplacement of mantle rocks (peridotite) at the continental rift axis. The crustal thinning and the final emplacement of peridotite onto the seafloor are explained by asthenosphere diapirism succeeded by uniform, normal, simple shear of the thinned continental lithosphere.
    Type: Article , PeerReviewed
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  • 4
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    AGU (American Geophysical Union)
    In:  In: Deep Drilling Results in the Atlantic Ocean: Continental Margins and Paleoenvironment. , ed. by Talwani, M. AGU (American Geophysical Union), Washington, DC, pp. 138-153.
    Publication Date: 2016-07-28
    Description: The structural evolution of the northwestern Iberian margin has been reconstructed from the results of IPOD drill site 398, as well as from numerous dredgings and a dense network of seismic profiles. During the Mesozoíc the margin first underwent two consecutive extensional phases interpreted as the result of two episodes of rifting in the Atlantic. Then during Eocene, subsidence was interrupted by compression and related deformation caused by subduction of oceanic sea floor of the Bay of Biscay beneath the Iberian Peninsula. Present day marginal banks are interpreted as blocks of the older passive margin uplifted during early Tertiary as a result of that subduction. Fault escarpments provide opportunities to sample older sediments and basement by dredging.
    Type: Book chapter , NonPeerReviewed
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