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

The eastern Galicia magnetic anomaly (EGMA) shows intensities up to 19 0 nT and is one of the major features of the magnetic field in northwe stern Spain. Taking into account the seismic refraction and surface ge ological 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 anoma ly 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 ri se to horizontal displacements of about 50 km on the basal eastern Gal icia thrust. This structure is in close agreement with surface geology , since the culmination of the Lugo dome and the extensional Viveiro f ault can be interpreted in relation with the displacement along the ea stern Galicia thrust. The southern termination of the EGMA can be rela ted to the termination of the anomalous layer on a lateral hanging-wal l ramp of this thrust. Rocks in the magnetic layer are interpreted as mainly lower crust mafic and/or ultramafic rocks. In the northern sect or, at least part of the anomaly must be attributed to ultramafic Herc ynian intrusives cropping out in the vicinity of the Viveiro fault.