Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – II. Sardinia’s margin

Abstract

International audienceGeophysical data acquired on the conjugate margins system of the Gulf of Lion and West Sardinia (GLWS) is unique in its ability to address fundamental questions about rifting (i.e. crustal thinning, the nature of the continent-ocean transition zone, the style of rifting and subsequent evolution, and the connection between deep and surface processes).While the Gulf of Lion (GoL) was the site of several deep seismic experiments, which occurred before the SARDINIA Experiment (ESP and ECORS Experiments in 1981 and 1988 respectively), the crustal structure of the West Sardinia margin remains unknown. This paper describes the first modeling of wide-angle and near-vertical reflection multi-channel seismic (MCS) profiles crossing the West Sardinia margin, in the Mediterranean Sea. The profiles were acquired, together with the exact conjugate of the profiles crossing the GoL, during the SARDINIA experiment in December 2006 with the French R/V L’Atalante.Forward wide-angle modeling of both data sets (wide-angle and multi-channel seismic) confirms that the margin is characterized by three distinct domains following the onshore unthinned, 26 km-thick continental crust : Domain V, where the crust thins from ~26 to 6 km in a width of about 75 km; Domain IV where the basement is characterized by high velocity gradients and lower crustal seismic velocities from 6.8 to 7.25 km/s, which are atypical for either crustal or upper mantle material, and Domain III composed of “atypical” oceanic crust.The structure observed on the West Sardinian margin presents a distribution of seismic velocities that is symmetrical with those observed on the Gulf of Lion’s side, except for the dimension of each domain and with respect to the initiation of seafloor spreading. This result does not support the hypothesis of simple shear mechanism operating along a lithospheric detachment during the formation of the Liguro-Provencal basin

Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – I. Gulf of Lion’s margin

“…Finally, the refraction data confirm and precise the overall geometry obtained by tomography inversion: a clear symmetrical distribution of the velocity structures in the two conjugate margins [Gailler et al, 2009], but with some differences [see Afilhado et al, 2015]. This symmetrical distribution seems to exclude the hypothesis of simple shear mechanism along a lithospheric detachment fault.…”

“…Three profiles are located on the Gulf of Lion margin and three on the conjugate margin offshore Sardinia [see Afilhado et al, 2015]. The main objectives of the SARDINIA seismic experiment, conducted in December 2006 in the Provencal basin ( fig.…”

Seismic imaging of Late Miocene (Messinian) evaporites from Western Mediterranean back-arc basins

“…The formation of oceanic crust in the central Sardo-Provençal deep basin ( Fig. 1) has been demonstrated through the identification of magnetic anomalies (Rehault et al 1984), with magnetic and seismic reflection data (Fanucci & Morelli 2001) and with wide-angle and reflection seismic data (Afilhado et al 2015;Moulin et al 2015). The Sardo-Provençal basin is therefore considered a back-arc basin confined between the conjugated passive margins of the Corso-Sardinian micro-plate to the east and of the Gulf of Lions and Provence to the NW (Rehault et al 1984;Fanucci & Morelli 2001;Finetti et al 2005).…”

Sedimentary markers in the Provençal Basin (western Mediterranean): a window into deep geodynamic processes

“…The boundary between the necking and the transitional domains corresponds to the French‐side limit of the pre‐rift palaeogeography (Olivet, ). The base of the necking and transitional domains consists of a 4‐km thick layer with anomalous seismic velocities (6.8–7.5 km s −1 ) which are typical of neither continental crust nor oceanic crust (Pascal et al ., ; Gailler et al ., ; Afilhado et al ., ; Moulin et al ., in press). The nature of the transitional domain was a matter of debate (De Voogd et al ., ; Pascal et al ., ; Séranne, ; Gailler et al ., ; Bache et al ., ; Aslanian et al ., ) but the recent results of wide‐angle seismic analysis seem to favour exhumed lower continental crust (Afilhado et al ., ; Moulin et al ., in press).…”

“…In the Gulf of Lions, the sag basin is described as allochthonous, with exhumed lower crust near the necking domain and anomalous thinned oceanic crust in the middle of the basin (Aslanian et al ., ; Afilhado et al ., ; Moulin et al ., in press). This partitioning, with different magnetic and gravity patterns, fits the palaeogeographic reconstructions and is also observed in the salt geometry (connected/separated domes).…”