Deep structure of the Armorican Basin (Bay of Biscay): a review of Norgasis seismic reflection and refraction data

• Published in: Journal of the Geological Society
• Main Authors: Thinon, Isabelle, Matias, Luis, Réhault, Jean-Pierre, Hirn, Alfred, Fidalgo-González, Luis, Avedik, Félix
• Other Authors: Bureau de Recherches Géologiques et Minières (BRGM), Faculdade de Ciencias, Universidade de Lisboa = University of Lisbon = Université de Lisbonne (ULISBOA), Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2003
• Subjects: Bay of Biscay; passive margins; transition zones; rifting; crustal thinning; OCEAN-CONTINENT BOUNDARY; CRUSTAL STRUCTURE; NORTH-ATLANTIC; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Long Ridge; North Atlantic
• Online Access: https://brgm.hal.science/hal-00647845; https://brgm.hal.science/hal-00647845/document; https://brgm.hal.science/hal-00647845/file/Thinon_SGL_2003_draft.pdf; https://doi.org/10.1144/0016-764901-103

International audience The Bay of Biscay is bounded to the North by the North Biscay margin, which comprises the Western Approaches and Armorican segments. In the 1970s and 1980s, most researchers considered this margin typical of a non-volcanic passive margin: It is characterized by a striking succession of tilted blocks beneath which occurs the S reflector and the continent/ocean boundary is abrupt. This paper examines the Armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data (NORGASIS cruise). An important result is the discovery of a 80-km wide Ocean-Continent Transition zone that coincides with the Armorican Basin (a deep sedimentary basin). It is characterized by a High-Velocity Layer-Crust (7.4-7.5 km/s) overlain by sediments. The other results are: i) the main crustal thinning occurs exclusively under the narrow continental slope. ii) The tilted blocks and the S-reflector are observed only at the base of the continental slope in the narrow domain called "neck area". iii) the North Biscay Ridge is a large oceanic plateau present only off the NW Armorican margin rather than a long ridge elongated off the whole North Biscay Margin.