ALBERT

Description: Abstract Contractional deformation in the transition between the Iberian and Catalan Coastal Ranges (Linking Zone) generated both thin‐skinned structures detached in low‐strength Triassic units, and basement‐involved structures. To evaluate their extent and relative contribution to the overall structure, we carried out a study combining structural geology and gravimetry. New gravity data (938 stations) and density determinations (827 samples) were acquired and combined with previous existing databases to obtain Bouguer anomaly and residual Bouguer anomaly maps of the study area. Seven serial and balanced cross sections were constructed, their depth geometries being constrained through the 2.5D gravity modelling and the 3D gravity inversion that we accomplished. The residual Bouguer anomaly map shows a good correlation between basement antiforms and gravity highs whereas negative anomalies mostly correspond to (i) Meso‐Cenozoic synclines and (ii) Neogene‐Quaternary basins. Cross sections depict a southern, thick‐skinned domain where extensional, basement faults inherited from Late Jurassic‐Early Cretaceous times were inverted during the Cenozoic. To the North, we interpret the existence of both Triassic‐detached and basement‐involved deformation domains. The two deformation styles are vertically overlapped in the southernmost part of the Catalan Coastal Ranges but relay both across and along strike in the Eastern Iberian Range. These basement and cover relationships and their along‐strike variations are analyzed in terms of the interplay between structural inheritance, its obliquity to the shortening direction and the continuity and effectiveness of Triassic décollements in the study area.

Description: SUMMARY The anisotropy of magnetic susceptibility (AMS) at room temperature has been used for decades to obtain the petrofabric orientation in granites as a kinematic marker to establish models explaining the emplacement of plutons. To assess the significance of AMS in terms of mineral orientation, we have performed a multidisciplinary study at five sites of an ilmenite-type pluton (Marimanha, central Pyrenees) with significant facies changes. To test the reliability of AMS measurements at room temperature, the following methods were applied: low temperature AMS; image analyses and X-ray texture goniometry (XTG) of biotites; and electron backscatter diffraction (EBSD) to obtain c -axes directions of quartz. The total (para-, ferro- and dia-)magnetic fabric analysed by AMS is compared with the paramagnetic fabric (low-T AMS), mica orientation (with image analyses and XTG) and the diamagnetic fabric (EBSD). Results indicate that weakly oriented paramagnetic minerals can give well-defined magnetic fabrics (AMS at room and low temperatures). Furthermore, the AMS ellipsoid is the result of composite biotite fabrics resulting from both orientation and spatial distribution of crystals, as demonstrated by 2-D mathematical models presented in this study. AMS is the most effective technique for quickly measuring composite fabrics. In addition, the advantage of using AMS analyses is twofold: (1) it is a fast way of analysing standard samples that can give clues for subsequent image/mineral orientation analysis and (2) it is a volume-related method that gives a picture of the rock fabric as a whole.

Description: The occurrence of a generalized remagnetization at 100 Ma makes the Cameros basin, a 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 the 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, pre-inversion geometry of the sedimentary basin was determined and the position of its main axial surface was accurately located. Comparing with the present-day, post-inversion geometry, a northwards hinge migration of around 5 km is inferred. This migration is the result of the southwards backthrusting in the southern basin border, favored by the detachment level at the base of the Mesozoic cover. Conversely, the main northwards-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.