Continental margins are domains of interaction between oceans and continents, as well as between surface and deep processes. Thus, they represent key areas for understanding Earth dynamics and deformation mechanisms. Most of them are however too old to decipher all the complex mechanisms of their formation: erosion and sedimentation have removed part of information from the surface, relaxation of presumably perturbed temperature field, part of information from deep interior. Young margins only are able to provide the relevant observations on the early stages of their formation (from rifting to oceanic spreading). Among them, the Gulf of Aden conjugate margins are an archetypal example for continental margins, as they are both volcanic to the West (Yemen) and non volcanic to the East (Sultanate of Oman), and evolve from divergent to transform margins toward the East (Sultanate of Oman). Finally, our understanding of the Gulf of Aden opening is very important to the study of both lithosphere stretching mechanisms and interaction between plate boundaries. A comprehensive multi-disciplinary study of the eastern part of the Gulf of Aden has been undertaken recently in the framework of the French margins program, with the long-term objective to integrate in a consistent model of evolution field observations where the margin crops out, results of marine geophysical survey where the margins are submerged, seismological observations of deep interior structure and geodetic measurements. First results show the potentiality of such an approach in this area to understand the relationships between the dynamics of rifting and spreading, the observed structures and the vertical motions of a margin in its early stages. Among the main results, we evidence the structural and sedimentologic characteristics of the continental and oceanic domain of the margin, especially their segmentation, related to the opening obliquity, and their consequences on the oceanic spreading, the importance of the structural inheritance at both lithospheric and crustal scale. We also describe the presence of a ocean-continent transition zone with high heat flow values, of a deep thermal anomaly (170 km) and of a sub-active volcano in the deep margin, that relaunch debate on the importance of the volcanism in the margins formation. The results also emphasize that both the area of investigation and the methods should be extended to be able to describe and understand the variability and the evolution in space and time of the studied structures, notably related to the Afar hotspot. This project intends therefore to study the Gulf of Aden as a natural laboratory for the study of rifting and oceanic spreading onset processes. The numerous already acquired data mainly on the northern margin (field studies, marine surveys ENCENS-SHEBA, ENCENS and ENCENS-FLUX, seismologic Dhofar Seismic Experiment and ENCENS-UK and GPS networks) are a solid base for this self-working ANR proposal and give an international position of competitiveness. The extended further ongoing investigations onland in the eastern area (Oman) and its conjugate margins in the South (Socotra island) and in the volcanic margin in the West (Yemen) allow to reach the objectives concerning: - The deep structure and thermal regime (seismic tomography, OBS, heat-flow). - The crustal structure (tectonics-sedimentation relationships, MCS, Ocean Bottom Seismometer, receiver functions on land, gravity and magnetic anomalies, dredging on the ocean-continent transition, basalts geochemistry). - The vertical motions throughout the Cainozoic (topography-bathymetry analysis, sedimentology and stratigraphy field work, apatite fission tracks and U/Th/He thermochronology) and more recent deformation (concentrations of cosmogenic elements) - The present-day opening (GPS network monitoring and extension of the network) - The thermo-mechanical modelling (numerical and analogue models). The overall goal of this project is to build 3D images of the deep (mantle), intermediate (crust), and superficial (sediments) structures of the Gulf of Aden basin from its rifting to its present-day oceanic spreading in order to understand the mechanisms of continental margins formation. The project will be managed by the 'Lab. de Tectonique' from the UPMC with partner of IPG Paris, EOST Strasbourg, Bordeaux Univ. and will include the participation of several French (Géosciences Rennes, ENS Paris, Montpellier Univ. Brest Univ., obs. of Villefranche-sur-Mer, CEREGE Aix-Marseille…) and international labs (Leeds University, Bristol University, Rome 3 University, Barcelona University, Oxford University, Sultan Qabous Univ. at Muscat, Sanaa University).
Madame LEROY Sylvie (Université Paris VI)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CNRS-DR10 CNRS Délegation Régionale Alsace
U-BORD MONTAIGNE Université Bordeaux-Montaigne
U-Paris VI Université Paris VI
IPGP INSTITUT DE PHYSIQUE DU GLOBE DE PARIS
Help of the ANR 74,998 euros
Beginning and duration of the scientific project: December 2006 - 48 Months