The South Moroccan margin and the first phases of Central Atlantic opening

• Main Author: Labails, Cinthia
• Other Authors: Domaines Océaniques (LDO), Centre National de la Recherche Scientifique (CNRS)-Institut d'écologie et environnement-Observatoire des Sciences de l'Univers-Université de Brest (UBO)-Institut national des sciences de l'Univers (INSU - CNRS), Université de Bretagne occidentale - Brest, Jean-Louis Olivet([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2007
• Subjects: non-volcanic continental passive margin; crustal structure; South Moroccan margin; combined wide-angle and deep reflection seismic; tectonic inheritance; marge continentale passive Sud Maroc; structure crustale; sismique réflexion et réfraction; héritage tectonique; [SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology; North Atlantic
• Online Access: https://tel.archives-ouvertes.fr/tel-00266944; https://tel.archives-ouvertes.fr/tel-00266944/document; https://tel.archives-ouvertes.fr/tel-00266944/file/figures-vol2.pdf; https://tel.archives-ouvertes.fr/tel-00266944/file/texte-vol1.pdf

We here propose a twofold approach to study the continental margins of the Central Atlantic Ocean, with special focus on the South Morocco Margin, in front of Reguibat bloc. This approach is based on plate kinematics reconstructions and geological field studies to map and constrain the geometry of the plate boundary though time and seismic sections (reflection and refraction) to decipher the tectonic and sedimentary history of the margin. Sahabi et al. (2004) recently showed that the opening of the central Atlantic Ocean started 195 my ago (Sinemurian basis) (i.e. 20 my later than what was generally proposed in earlier models). Based on this result and on the analysis of geophysical data (including new seismic lines, a new magnetic anomaly grid and satellite derived gravimetry), our kinematic study evidences several tectonic phases: oceanic accretion started at an extremely slow rate (~0.8 cm/y) during about 30 my (Lias-Dogger). At ~165 my ago (Callovian basis), a change in the relative plate motions occurred, that resulted in a change in basement topography and an acceleration of spreading rate, up to ~ 4.8 cm/y. The BSMA (Blake Spur Magnetic Anomaly) is related to this change. From Magnetic Chron M22 (150 my, Tithonian basis) onwards, the spreading rate slowed down to about 2.6 cm/y until Magnetic Chron M0 (125 my, Barremian-Aptian). On geodynamic side, the Atlantic domain divides into two major domains: whereas Europe and the future North Atlantic, at Permo-Triassic times, know period of distension, central Atlantic Ocean stay in compression during the end of Permian (Alleghanian phase) et seems to register distension only at Triassic times. Margin segment, localized between Moroccan Meseta and Nova Scotia, characterized by a huge Triassic province of evaporates, occupies an intermediate position between these two domains. Besides to this segment clearly inherited of Hercynian orogeny, meridional domain is also segmented with a segmentation wavelength of about 600 km. An analysis in several regions worldwide ...