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Oliva-Urcia, B.
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Oliva-Urcia, B.
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- PublicationOpen AccessRemagnetizations used to unravel large-scale fold kinematics: A case study in the Cameros Basin (Northern Spain)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.
206 23 - PublicationRestrictedMultidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)(2017)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (includ- ing structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and paleomagnetism, and paleo- thermometry) is used to define thrusting conditions, defor- mation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal dis- placement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analy- sis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside stria- tions) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direc- tion onto the kmax/kint plane in sites with strong shear defor- mation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong defor- mation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multi- disciplinary approach is useful when dealing with thrusts at shallow crustal levels.301 1