Non lineal correlation between the mean susceptibility, the paramagnetic contribution to the susceptibility andthe lithology in the western Central-Pyrenees. Implications to the AMS studies

摘要

The magnetic susceptibility studies and its application to the fabric studies depend on the mineralogicalsusceptibility sources. The mineralogical characterization of ferromagnetic phases has been developedparallel to the paleomagnetism techniques. While the ferromagnetic or paramagnetic particles cannotchange along a cross-section of an orogen, because they are related with the same source area, similardiagenetic processes and fluid compositions. The different weight of them to the susceptibility can changein a significant manner in the same lithological unit or even at outcrop scale. The general assumption thatclay 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 elevelsof the Bouma sequence. With independence of the studied lithological unit, higher values ofparamagnetic contribution to the susceptibility show more oblate fabrics or prolate fabrics and lowervalues of the degree of anisotropy in the most ferromagnetic samples. The relation between Km and theparamagnetic contribution to the susceptibility shows that only in a Km range this relation is direct. Theseresults show that a special attention in the analysis of the paramagnetic contribution to the susceptibilitymust be made in the AMS studies. The utilization of magnetic parameters, as T or P´, as an indicator ofintensity of deformation (clustering of particles) only can be used in sectors without changes in theparamagnetic contribution to the susceptibility, even when the external lithological aspect can be verysimilar and the samples comes from the same structural position