Tectonic imprint in magnetic fabrics in foreland basins: A case study from the Ebro Basin, N Spain

Anisotropy of magnetic susceptibility (AMS) is analyzed in two cross-sections from the South Pyrenean frontal thrust to the central foreland Ebro Basin. The magnetic fabrics show magnetic foliation parallel to bedding and the magnetic lineation roughly parallel to the Pyrenean trend, with different degrees of clustering. From the frontal thrust to the foreland basin the magnetic lineation is progressively less defined (decrease of e12 angle, increase of the overlapping of parametric bootstrap eigenvalues and decrease of the magnetic lineation parameter). Reliability tests applied to the magnetic lineation show a zone of 30–40 km south of the frontal thrust with good definition of the WNW–ESE trending magnetic lineation, normal to the Pyrenean shortening. To the South, interchange between the long and intermediate susceptibility axes may appear. Farther South the magnetic lineation tests fail to discriminate efficiently the magnetic lineation, although the main orientation of the long susceptibility axes remains with a WNW–ESE trend at distances of more than 60 km and probable imprints even at distances of 80 km from the frontal thrust can be recognized. The fabric changes are mainly controlled by the distance to the frontal thrust and by the position within the series, observing poorer definition of the magnetic lineation at similar distances to the frontal thrust in younger materials. These results indicate that the tectonic imprint can be followed at distances beyond 60 km from the frontal thrust in sectors located in the central Ebro Basin without indicators of deformation at outcrop scale.

Research highlights
► Tectonic imprint in foreland basins inferred from magnetic fabrics.
► Factors affecting AMS fabrics in foreland basin settings: distance to the frontal thrust, position in the series (deposit age) and magnetic mineralogy.
► Progression of fabrics from magnetic lineation normal to shortening, interchange of axes and axes scattering within magnetic foliation.