Rotational basement kinematics deduced from remagnetized cover rocks (Internal Sierras, southwestern Pyrenees)

[1] Paleomagnetic data from the Internal Sierras unravel the kinematic relationship between basement (Guarga, Gavarnie, Bielsa) and cover thrusts (Larra-Monte Perdido). The new data come from an area of 100 km along strike and 5–15 km across strike of the southwestern Pyrenees. The area covers a variety of structural positions that range from cover to basement thrusts. From 84 sites located in Upper Cretaceous, two meaningful magnetic components are found: (1) the higher-temperature C component (unblocks at 575°C) presents two polarities, is prefolding, has a mean declination and inclination (D/I) of 010/44 (α95 = 8, k = 15), and is considered primary; and (2) the intermediate B component (unblocks between 250°C and 450°C) has a mean D/I of 198/–43 (α95 = 4, k = 18) and has always reverse polarity and postfolding. The nine sites located in the Eocene flysch, south of the Upper Cretaceous, show the same postfolding component (B). The acquisition of this intermediate component alludes to a widespread, tectonic-related remagnetization event affecting the Internal Sierras. This event must be younger than the folding of the flysch deposits (middle-upper Eocene). The tilting induced by the basement thrust (Gavarnie, Bielsa) in the axial zone does not alter the inclination of the B, so that the sediments acquire the B component later than Priabonian (emplacement age of the Gavarnie thrust). The B component is rotated clockwise with respect to the Tertiary reference. This means that the rotation takes place after the remagnetization event. The position of the C component before the rotation of the B component is negligibly rotated (D/I of 002/44; α95 = 7, k = 94) with respect to the Cretaceous reference; therefore the B component records the last and only rotational event in the region. The rotation is related to the latest basement deformation (Guarga thrust) during upper Oligocene times, and it reflects the regional shortening gradient in the southwestern Pyrenees. The emplacement of the Larra-Monte Perdido cover thrust system that took place prior to basement thrusts mentioned above did not undergo any significant rotation.