Structure and evolution of the Gulf of Lions: The Sardinia seismic experiment and the GOLD (Gulf of Lions Drilling) project

T study of the deep structure and evolution of passive continental margins is important for the understanding of rifting processes and the formation of associated sedimentary basins. Since the classical models of McKenzie (1978) and Wernicke (1985), understanding how passive continental margins form, that is to say mainly the way that continental lithosphere is thinned leading to subsidence, remains one of the main challenges in the Earth sciences. Many recent observations and discoveries have modified our basic views of margin formation. The conservational models paradigm (i.e., simple shear, pure shear, or polyphase models), which exclude exchanges between lower continental crust and upper mantle and which are usually proposed to explain lithospheric stretching and consequent crustal thinning of passive continental margins, fail to completely explain all these observations. Furthermore, these models imply a large amount of horizontal movement, movements not observed in the field. In consequence, new concepts need to be built and tested. One of the main obstacles to our understanding of margin formation is the unknown nature of the transitional domain between the unthinned continental crust and the true oceanic crust. Using paleogeographic constraints, wide-angle refraction seismic and 2D reflection seismic profiles or modeling, some authors suggested that lower continental crust may have been removed from its original place and flowed toward the middle part of the system (allochthonous domain, part 2 in Figure 1) or/and toward both extremities of the conjugate margins system (Aslanian et al., 2009; Huismann and Beaumont, 2011; Aslanian and Moulin, 2012). Another challenge is to understand how margins evolve starting in a structurally elevated position during initial formation, with the presence of subaerial deposition of basalts, shallow-water evaporites, subaerial erosion, and/or construction of a carbonate platform, toward a basin affected by strong subsidence during the plate divergence phase. Passive margins seem to be close to sea level, even after the breakup as demonstrated by carbonates postdating the oceanic crust (e.g., on the central and the south Atlantic margins). We therefore need to be able to reconstruct the paleo-water depth at the time of the deposition of the syn-rift and post-rift sediments. D. ASLANIAN, M. MOULIN, P. SCHNURLE, F. KLINGELHOEFER, and E. LEROUX, Ifremer, Centre de Brest M. RABINEAU, IUEm A. GAILLER, CEAF F. BACHE, GNS Science C. GORINI, Paris VI University J. KURODA and N. EGUCHI, Japan Agency for Marine Earth Science and Technology A. DROXLER, Rice University K. ALAIN, LM2E F. ROURE, IFP Energies Nouvelles B. HAQ, National Science Foundation, USA