Significance of AMS in multilayer systems in fold‐and‐thrust belts. A case study from the Eocene turbidites in the southern Pyrenees (Spain)

Abstract

The anisotropy of magnetic susceptibility (AMS), and other magnetic fabric techniques have been tested in a multilayer system of Eocene turbidites from the Southern Pyrenees. The identified magnetic fabrics can be grouped into (1) fabrics related to layer parallel shortening (LPS) acquired in pre-folding conditions, (2) fabrics related to cleavage development and (3) fabrics related to shear parallel to the thrust movement and intermediate cases. AMS depends on (i) the paramagnetic contribution to the susceptibility and (ii) on the position of sites in the fold-thrust belt. The study of sites in the southern Pyrenees shows that the processes underwent by rocks and recorded by the different magnetic fabrics are independent from their lithology. The most paramagnetic samples show fabrics related to LPS and cleavage, whereas shear parallel to the thrust movement is observed in the most ferromagnetic ones. Measurement of other magnetic fabrics shows the presence of more than one magnetic fabric at site scale with independence of the AMS ellipsoid aspect ratio. The intersection lineation fabrics are interpreted as composite magnetic fabrics, developing a progression between LPS, intersection fabrics (from magnetic foliation parallel to bedding, to magnetic foliation parallel to cleavage) and magnetic axes switching from K1 parallel to the intersection lineation, to K1 parallel to the dip direction of cleavage or amplification direction. This change can be inferred from the transition from the outer (farther from the Axial Zone) to inner domains of the studied zone, consistent with the intensity of cleavage at outcrop scale.

The carriers of AMS in remagnetized carbonates. Insights for remagnetization mechanism and basin evolution

“…100 Ma chemical remagnetization process, and aligning according to the general extension direction during this stage. Several works (Sagnotti et al, 1998;Parés, 2004;Pueyo-Anchuela et al, 2010;Dudzisz et al, 2018, among others) have indicated a relationship between phyllosilicate-related RT-AMS and compression in weakly deformed rocks, with the development of a RT-AMS defined by k max parallel to the strike of compressional structures and to the intersection lineation, keeping their k min perpendicular to bedding. The increase of flattening develops a transition to tectonic magnetic fabrics in which k min becomes perpendicular to cleavage planes.…”

Lithology-dependent reliability of AMS analysis: A case study of the Eocene turbidities in the southern Pyrenees (Aragón, Spain)

“…The general assumption that finer grain-size levels (e-level) can be more sensitive to strain is evident at outcrop scale, where penetrative cleavage is better developed in e-level with respect to sandstones. The comparison with other magnetic fabrics in these zones shows the coexistence of complex magnetic fabrics, with more paramagnetic fabrics (LTAMS, AGRM) linked to cleavage, intersection lineation or folding (Oliva-Urcia et al, 2009;Pueyo Anchuela, 2010).…”

“…Bulk susceptibility shows for the different Bouma analyzed levels values between 20 and 385 Â 10 À6 (SI Ferromagnetic particles are mainly related to magnetite and no significant high coercivity mineral phases are present in the studied rocks (Pueyo Anchuela et al, 2010). The comparison of the susceptibility at different fields (0, 1,…”

“…1f), consistently with an influence of cleavage in magnetic lineation. The detailed analysis of the magnetic fabrics throughout the western Central-Pyrenees has been carried out by Pueyo Anchuela et al (2010). In this work, the general trend, independent from the rock type, shows a change from magnetic foliation parallel to bedding and magnetic lineation parallel to structures to magnetic foliation parallel to cleavage, and magnetic lineation parallel to bedding strike, intersection lineation and dip direction of cleavage.…”

Anisotropy of magnetic susceptibility as an indicator for palaeocurrent analysis in folded turbidites (Outer Western Carpathians, Poland)

“…Pueyo Anchuela et al . , 2010). While samples from Nasiczne had a distinctly stronger magnetic remanence compared with other sites (Fig.…”