Erratum notice

Abstract

Magnetic measurements were performed on sedimentary and volcanic rocks from the Itajaí basin. Rock magnetism analyses reveal that magnetite and hematite and paramagnetic minerals show different contributions to magnetic susceptibility. Magnetic fabrics were determined in 19 sites by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence magnetization (AARM). The analysis at the individual-site scale defines three AMS fabric types. The first type shows Kmin perpendicular to the bedding plane, while Kmax and Kint are scattered within the bedding plane itself. This fabric is usually interpreted as primary. The second type (77% of the sites) shows the three well-clustered AMS axes with Kmin still perpendicular to the bedding plane. The third type is characterized by well-clustered Kmax in the bedding plane, while Kmin and Kint are distributed along a girdle perpendicular to Kmax. The second and third fabric types are interpreted as combinations of sedimentary-compactional and tectonic contributions at the earliest, and at a slightly later stage of deformation, respectively. AMS represents the contribution of all the rock-forming minerals, while AARM isolates the contribution of remanence-bearing minerals with coercivity < 100 mT. For some sites, the AMS and AARM fabrics are non-coaxial, mainly with respect to the lineation orientations. The comparison of magnetic lineations and the regional structural data indicates that the rocks, with no mesoscopic or macroscopic deformation, were affected by the two deformation phases that occurred in the region. One of them results from compressional tectonics related to the collisional orogen (D1), and the other is extensional related to post-collisional orogen (D2). After the former tectonic event the volcanic rocks were emplaced at the top of the stratigraphic sequence and, after that the Itajaí basin as a whole was deformed by the extensional tectonic (D2) that occurred after 560 Ma which is the age of the intrusion.