Quantification des flux sédimentaires et de la subsidence du bassin ...

tel-00790852, version 1 - 21 Feb 2013
the slab of the African plate subducting beneath the European plate during an extensional phase.
This Corso–Sardinian micro-continent rotation resulted in the emplacement of an oceanic crust,
starting in the Late Aquitanian (23 Ma to 19 Ma) and ended at the Langhian (about 15 Ma).
Although rifting in back-arc basins might differ in some points from cratonic rifting, the mechanics
of thinning the continental crust should remain similar. Therefore the conjugate margins of the
Gulf of Lions and West Sardinia represent a unique natural laboratory to address fundamental
questions on rifting (e.g., on crustal thinning, on the nature of the continent–ocean transition zone
and on the style of rifting), because of their young age, complete sedimentary layers and accessibility.
Seven domains can be indentified in the Liguro-Provençal basin on the base of gravity, magnetic,
reflection and wide-angle seismic data. The figure 2 shows the Gulf of Lion side, with the four
western domains. Domain I represents a 20km thick continental crust, domain II, the necking zone,
domain III the intermediate crust and Domain IV the oceanic domain. Both ECORS-CROP and
Sardinia 1 reflection seismic profile show the existence of a prominent landward dipping reflector
located in the crust at the SE limit of the continental slope and called the T-reflector (Figure 3).
Both images show a wide zone of high velocities southeastward of this reflector. These high
velocities could be the expression of flowing lower continental crust underplated and intruded by
partial melt, or represent serpentinized peridotite material exhumed during the initial opening of
the basin. Based on these findings an opening along a lithospheric detachment fault (possibly
represented by the T-reflector) has been proposed for the basin with the Sardinia margin
representing the upper crustal plate, with exhumation of the mantle or lower crustal material
occurring on the Gulf of Lions side. But the lack of deep crustal seismic data from the Sardinia
margin has until now prevented to test this hypothesis and assess the asymmetry in depth.
Sardinia Experiment
Wide-angle seismic data can be used to quantify the continental crustal thickness, determine the
degree of symmetry of rift structures and hence address fundamental questions concerning the
mechanisms of rifting. During the SARDINIA experiment of the Ifremer French R/V L’Atalante,
six coincident wide-angle and reflection multi-channel seismic (MCS) profiles, as well as CHIRP and
bathymetry profiles, were acquired: three located in the Gulf of Lion area and three located on the
conjugate margin offshore Sardinia. The main aims of the Sardinia wide-angle seismic cruise were to
image continuously the deep crustal structure of the paired conjugate margins, to verify the
existence of a high-velocity zone on the Sardinia margin and to constrain the nature of the ocean–
continent transition zone.
First results based on tomographic modelling of the two main conjugate profiles of this experiment
showed a symmetrical distribution of seismic velocities on both sides (Figure 4 and ???) (no figure for
the other side).