Continental breakup and the dynamics of rifting in back-arc basins: The Gulf of Lion margin

Abstract

Deep seismic profiles and subsidence history of the Gulf of Lion margin reveal an intense stretching of the distal margin and strong postrift subsidence, despite weak extension of the onshore and shallow offshore portions of the margin. We revisit this evolution from the geological interpretation of an unpublished multichannel seismic profile and other published geophysical data. We show that an 80 km wide domain of thin lower continental crust, the "Gulf of Lion metamorphic core complex," is present in the ocean-continent transition zone and exhumed mantle makes the transition with oceanic crust. The exhumed lower continental crust is bounded upward and downward by shallow north dipping detachments. The presence of exhumed lower crust in the deep margin explains the discrepancy between the amount of extension deduced from normal faults in the upper crust and total extension. We discuss the mechanism responsible for exhumation and present two scenarios: the first one involving a simple coupling between mantle extension due to slab retreat and crustal extension and the second one involving extraction of the lower crust and mantle from below the margin by the southeastward flow of hot asthenosphere in the back-arc region during slab rollback. In both scenarios, the combination of Eocene crustal thickening related to the Pyrenees, the nearby volcanic arc, and a shallow lithosphere-asthenosphere boundary weakened the upper mantle and lower crust enough to make them flow southeastward. The overall hot geodynamic environment also explains the subaerial conditions during most of the rifting stage and the delayed subsidence after breakup.

Rifted margins: Ductile deformation, boudinage, continentward-dipping normal faults and the role of the weak lower crust

“…This further implies that, within the Ocean-Continent transition, lower crust and mantle have been exhumed by shearing during rifting, although the exact limits are difficult to position on the profiles. This behavior is similar in a first approach to the model recently proposed for the Gulf of Lion margin (Jolivet et al, 2015).…”

“…Once brought to shallow levels or even exhumed, a ductile lower crust is expected to behave in a brittle way and thus become undistinguishable in seismic reflection from an upper crust (e.g. Jolivet et al, 2015). This aspect should be kept in mind when attempting to restore conjugate margins (cf.…”

“…Some of them imply a ductile deformation of the lower crust Beaumont, 2011, 2014), with fluxes toward the ocean ( Fig. 1a; Driscoll and Karner, 1998;Jolivet et al, 2015) or…”

Extreme Mesozoic Crustal Thinning in the Eastern Iberia Margin: The Example of the Columbrets Basin (Valencia Trough)

“…This compressional deformation is also interpreted as the main phase of the Pyrenean orogeny (Muñoz, ; Vergés & García‐Senz, ; Vergés et al, ). It was followed by a late Oligocene to middle Miocene extensional event in relation with the complex interaction between the European Cenozoic rift system (Dèzes et al, ; Séranne, ; Vegas et al, ) and the Maghrebian‐Ligurian Tethys slab rollback (Auzende et al, ; Boccaletti & Guazzone, ; Etheve et al, ; Jolivet et al, ; Roca et al, ). This extension triggered the formation of the Liguro‐Provençal and Algerian basins as well as the Valencia Trough.…”

Pre-Pliocene tectonostratigraphic framework of the Provence continental shelf (eastern Gulf of Lion, SE France)

“…During the Late Oligocene a second extensional phase was initiated as a result of the opening of the Liguro-Provençal back-arc basin [Rehault et al, 1984;Hippolyte et al, 1993;Mauffret and Gorini, 1996;Mauffret et al, 2004;Gattacceca et al, 2007;Jolivet et al, 2015]. The opening of the Liguro-Provençal basin occurred in two steps: a syn-rift stage (Chattian to early Burdigalian: 30-20.5 Ma) and a post-rift stage (early Burdigalian-Langhian: 20.5-15 Ma) with oceanic crust accretion and associated anticlockwise rotation of the CorsicaSardinia continental block [e.g.…”