Tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean: Example of the western Pyrenees

Abstract

In this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western Pyrenees. The Labourd‐Mauléon area situated in the western Pyrenees, at the termination of the V‐shaped Bay of Biscay, is an ideal natural laboratory to study how such complex basins evolve in time and space. Because of a mild inversion of the basin during Pyrenean compression, the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field. The basin shows a complex polyphase evolution that starts with left‐lateral dominated transtension in latest Jurassic–early Aptian time. This event is overprinted by a late Aptian–early Albian extension that is related to the counterclockwise rotation of Iberia away from Europe leading to the opening of the Bay of Biscay. During this stage, the Late Triassic to Jurassic carbonate platform was stretched, salt migrated, and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor. The final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by N40° to N60° transfer faults. The sedimentary architecture is characterized by late Aptian synrift sediments (e.g., Urgonian limestones) that were deposited in fault‐bounded basins and are overlain by thick latest Aptian to Albo‐Cenomanian sediments (e.g., Flysch noir) that define a sag sequence. The complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic/thermal event that postdates mantle exhumation.

Plate kinematics in the Cantabrian domain of the Pyrenean orogen

“…1a) (e.g. Choukroune et al, 1989;Roure et al, 1989;Muñoz, 1992;Pulgar et al, 1996;Teixell, 1998;Gallastegui, 2000;Vergés et al, 1995Vergés et al, , 2002Pedreira et al, 2007;Jammes et al, 2009). To the east, the Pyrenean arm of the Mesozoic Bay of Biscay-Pyrenean rift system has been sandwiched between the subducting Iberian Plate and the overriding Eurasian one (e.g.…”

“…With increasing the amount of data, incompatibilities have become increasingly evident. Jammes et al (2009) made explicit the difficulty of reconciling geology with models based on the interpretation of seafloor magnetic anomalies, and proposed a reconstruction where doubtful (i.e. probably not associated with newly formed oceanic crust) and geologically inconsistent magnetic anomalies are rejected.…”

“…probably not associated with newly formed oceanic crust) and geologically inconsistent magnetic anomalies are rejected. In essence, Jammes et al (2009) made the simple consideration that seafloor spreading was only part of the Mesozoic breakup and spreading process, as an important role in the Mesozoic motion of Iberia was played by the exhumed continental mantle, which is exposed in the Pyrenean Mountain Range (e.g. Lagabrielle et al, 2010), and surrounds the oceanic crust of the North Atlantic and of the Bay of Biscay (e.g.…”

High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the North Pyrenean passive paleomargin

“…At present, the Pyrenean domain is also considered as hosting relevant analogs of distal passive margins, and its pre-orogenic evolution is being intensely revisited (Lagabrielle and Bodinier, 2008;Jammes et al, 2009;Lagabrielle et al, 2010;Masini 2011;Clerc et al, 2012;Clerc et al, 2013;Masini et al, 2014;Tugend et al, 2014). Unlike the Alpine analog, the North Pyrenean domain did not undergo subduction, and the thermal pattern recorded in the pre-and syn-rift material has not been overprinted by major crustal overthrusts or subductions.…”

“…Triassic and Jurassic aborted rifting events predated the development of a major Cretaceous crustal thinning event, which culminated in the crustal separation between the Iberia and European plates (Puigdefabregas and Souquet, 1986;Vergés and Garcia-Senz, 2001). Continental rifting in the Pyrenean domain occurred in response to the counterclockwise rotation of Iberia relative to Europe, coeval with the onset of oceanic spreading in the Bay of Biscay between Chron M0 and A33o (approximately 125-83 Ma) (Le Pichon et al, 1970;Choukroune and Mattauer, 1978;Olivet, 1996;Gong et al, 2008;Jammes et al, 2009). After an early rifting episode during the late Aptian, narrow, non-connected Albian basins opened north of the basement of the Pyrenean Axial Zone, along a wide domain opened between Iberia and Europe (Choukroune and Mattauer, 1978;Olivet, 1996;Jammes et al, 2009).…”