Correlación no lineal entre la susceptibilidad media, la contribución paramagnética a la susceptibilidad y la litología en el sector centro-occidental del Pirineo Central. Implicaciones para los estudios de ASM

Abstract

The magnetic susceptibility studies and its application to the fabric studies depend on the mineralogical susceptibility sources. The mineralogical characterization of ferromagnetic phases has been developed parallel to the paleomagnetism techniques. While the ferromagnetic or paramagnetic particles cannot change along a cross-section of an orogen, because they are related with the same source area, similar diagenetic processes and fluid compositions. The different weight of them to the susceptibility can change in a significant manner in the same lithological unit or even at outcrop scale. The general assumption that clay rich levels can represent a higher paramagnetic contribution to the susceptibility is true in some cases, while in others the expected paramagnetic contribution can differ significantly respect the expected values: high paramagnetic contribution in detrital continental deposits or low values in clay rich levels as the elevels of the Bouma sequence. With independence of the studied lithological unit, higher values of paramagnetic contribution to the susceptibility show more oblate fabrics or prolate fabrics and lower values of the degree of anisotropy in the most ferromagnetic samples. The relation between Km and the paramagnetic contribution to the susceptibility shows that only in a Km range this relation is direct. These results show that a special attention in the analysis of the paramagnetic contribution to the susceptibility must be made in the AMS studies. The utilization of magnetic parameters, as T or P´, as an indicator of intensity of deformation (clustering of particles) only can be used in sectors without changes in the paramagnetic contribution to the susceptibility, even when the external lithological aspect can be very similar and the samples comes from the same structural position