Interpretación en 2 1/2D de la anomalí magnética del País Vasco: implicaciones geodinámicas

Abstract

The Basque magnetic anomaly (BMA) follows aNW-SE trend over the Basque country with intensities up to 250 nT and displays a paired negative part to the north with intensities down to -60 nT. A model of the magnetic properties of the crust in the area has been carried out that takes into account previous geological and geophysical data. The models proposed indicate a mafic wedge ofmaterials with a magnetic susceptibility ofO.07 SI. This wedge is composed mainly ofUpper Cretaceous mafic intrusives with minor lower crustal rocks and reaches a minimum depth of5-7 km increasing to 12 km towards the northeast. Rocks on top ofthe anomalous wedge are deep marine facies rocks in transition to normal continental platform facies rocks to the southwest, and suggest that during the Upper Cretaceous this zone underwent crustal thinning due to rifting. Tectonic inversion during the Alpine deformation gave rise to displacement on a basal thrust and emplacement ofthe mafic wedge towards the northeast. The southeastern termination of the BMA may be produced by the lateral termination of the mafic rocks that constitute the anomalous wedge in a transform fauIt reIated to rifting processes.