A 2.5D INTERPRETATION OF THE EASTERN GALICIA MAGNETIC ANOMALY (NORTHWESTERN SPAIN) - GEODYNAMICAL IMPLICATIONS

The eastern Galicia magnetic anomaly (EGMA) shows intensities up to 190 nT and is one of the major features of the magnetic field in northwestern Spain. Taking into account the seismic refraction and surface geological data, a 2.5D model of the magnetic properties of the crust in the area of the EGMA has been carried out. Models show that the anomaly can be produced by a middle to lower crustal layer a few kilometers thick with magnetic susceptibility of approximately 0.045 SI emplaced with a ramp-flat-like geometry in higher crustal levels and giving rise to horizontal displacements of about 50 km on the basal eastern Galicia thrust. This structure is in close agreement with surface geology, since the culmination of the Lugo dome and the extensional Viveiro fault can be interpreted in relation with the displacement along the eastern Galicia thrust. The southern termination of the EGMA can be related to the termination of the anomalous layer on a lateral hanging-wall ramp of this thrust. Rocks in the magnetic layer are interpreted as mainly lower crust mafic and/or ultramafic rocks. In the northern sector, at least part of the anomaly must be attributed to ultramafic Hercynian intrusives cropping out in the vicinity of the Viveiro fault.