Abstract
Abstract. The Cantabrian domain represents the western portion of the Pyrenean orogen, in the area where the Iberian continental lithosphere was subducted toward the north underneath the transitional to oceanic lithosphere of the Bay of Biscay. There, the about 100 km of orogenic convergence have been mostly accommodated in the northern portion of the orogen (i.e. the retro wedge) developed in the Bay of Biscay abyssal plain, while only crustal-scale folding with limited internal deformation occurred in the Cantabrian southern wedge (pro-wedge). Integrated meso- and macrostructural analyses and a reappraisal of available information from the transitional area between the Pyrenean and Cantabrian domains are presented in this work, allowing to set geometric and kinematic constraints on the entire Meso-Cenozoic history of the northern portion of the Iberian Plate, including subduction initiation and evolution in the western portion of the Pyrenean orogen. The structural record of the Late Jurassic to Early Cretaceous deformation stage, which was associated with rifting and seafloor spreading in the Bay of Biscay, indicates a ridge perpendicular (NNE-SSW oriented) extension, with no evidence of relevant strike-slip components during rifting. A Cenozoic NNW-SSE oriented shortening stage followed, related to the limited (about 100 km) north-directed subduction of the Iberian continental lithosphere underneath the transitional to oceanic lithosphere of the Bay of Biscay. Subduction led to the formation of the poorly-developed Cantabrian pro-wedge, which is laterally juxtaposed to the well-developed Pyrenean pro-wedge to the east. During this convergence stage, the structural framework in the Cantabrian pro-wedge, and particularly along its transition with the Pyrenean wedge to the east, was severely complicated by the reactivation of Paleozoic and Mesozoic inherited structures. Data presented in this work fully support the development of the Cantabrian Mountains as related to indentation and consequent thickening of the Bay of Biscay transitional lower crust during north-directed subduction of Iberian continental lithosphere. In essence, the Cantabrian pro-wedge is a lithospheric south-verging fault-propagation anticline developing above the subduction plane. The structural record in the area indicates that a lithospheric fault-propagation folding stage was predated, during the very early stages of orogenic shortening, by the development of a lithospheric-scale open syncline overlying the nucleation point of lithosphere sinking. Such a syncline is today partially preserved and represents one of the few natural examples of subduction initiation.
Highlights
The E-W trending Pyrenean orogen represents the boundary between the Iberian and Eurasian plates and extends for more than 1000 km from the Mediterranean Sea to the Atlantic Ocean (Munoz, 2002)
It formed in Late Cretaceous to Cenozoic age due to the limited (i.e. 100–150 km) subduction of the Iberian Plate underneath the Eurasian one, which caused the inversion of a Mesozoic rift system to develop during the opening of the Bay of Biscay (Fig. 1a) (e.g. Choukroune et al, 1989; Roure et al, 1989; Munoz, 1992; Pulgar et al, 1996; Teixell, 1998; Gallastegui, 2000; Verges et al, 1995, 2002; Pedreira et al, 2007; Jammes et al, 2009)
To profile P5, the profile P6, running parallel to the strike of the Pyrenean orogen, shows a repetition of the lower crust below the Cantabrian Mountains. This repeated body matches with the indenting lower crust of profile P3, and its thickness along the profile P6 displays a strong correspondence with the topographic elevation, indicating that uplift of the Cantabrian Mountains was mostly determined by thickening of the lower crust. All these features indicate that the Cenozoic uplift of the western sector of the Pyrenean orogen related to indentation tectonics (e.g. Gallastegui, 2000; Pedreira et al, 2007), which can be extrapolated further to the west of profile P5, that caused coeval north-directed subduction of Iberian lithosphere and scraping of the Iberian crust above a north verging sole-thrust (Quintaand Tavani, 2012)
Summary
The E-W trending Pyrenean orogen represents the boundary between the Iberian and Eurasian plates and extends for more than 1000 km from the Mediterranean Sea to the Atlantic Ocean (Munoz, 2002). 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. Choukroune et al, 1989; Munoz, 1992; Teixell, 1998; Pedreira et al, 2007; Roca et al, 2011), which resulted in the development of a doubly vergent orogen.
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