Remagnetizations used to unravel large-scale fold kinematics: A case study in the Cameros basin (Northern Spain)

Abstract

The occurrence of a generalized remagnetization at 100 Ma makes the Cameros Basin, an 8 km thick Cretaceous extensional trough inverted during the Cenozoic, a perfect natural frame to apply paleomagnetic vectors to geometrical reconstructions. The widespread remagnetization that occurred between the extensional and compressional episodes, linked to low-grade metamorphism, provides a tool to reconstruct the attitude of beds at the remagnetization time, thus giving a picture of basin geometry during the Cretaceous. This snapshot is compared with the present-day geometry to constrain the large-scale kinematic evolution of folds between these two stages. According to this methodology, a syncline, preinversion geometry of the sedimentary basin was determined and the position of its main axial surface was accurately located. Comparing with the present-day, postinversion geometry, a northward hinge migration of around 5 km is inferred. This migration is the result of the southward back thrusting in the southern basin border, favored by the detachment level at the base of the Mesozoic cover. Conversely, the main northward directed thrust, which involved both the Paleozoic basement and the Mesozoic cover, did not significantly affect the internal structure of the basin in spite of its overall displacement of more than 20 km. Plain Language Summary The Cameros basin (N Spain) developed during the Mesozoic and was inverted during the Alpine orogeny (Cenozoic). The generalized remagnetization undergone by its rocks and dated at 100 M.a. (between the extensional and the compressional stages) makes the basin a perfect natural frame to apply paleomagnetic vectors to geometrical reconstructions. By restoring the obtained remagnetized vectors to their position during the remagnetizing event together with the beds containing them, we were able to describe the geometry of the basin before the Cenozoic compression. According to the new data provided here, a syncline geometry of the sedimentary basin can be determined and the position of its main axial surface can be accurately located. In comparison with the present-day geometry (post-inversion attitude), a northwards hinge migration of around 5 km can be interpreted.