GEOPHYSICAL INTERPRETATION OF THE GALLURA MAGNETIC ANOMALY (NORTHEASTSARDINIA, ITALY)

The metamorphic basement of northeastern Sardinia is mostly formed of migmatitic gneisses and exhibits Variscan granitic rocks characterized by a temporal differentiation evolving from a quite high content of F e-Mg to an Fe-Mg-poor member. This area is also characterized by the l argest magnetic anomaly in Sardinia, which has been interpreted by mea ns of Euler and Werner deconvolution techniques and modelled 2D and 2. 5D. In order to estimate the magnetic effect of the topographic irregu larities, samples of the most frequently outcropping rocks were collec ted and magnetic remanences and susceptibilities determined in the lab oratory. The effect of the topographic irregularities was computed in 2D. This effect is around twenty times smaller than the observed anoma ly and therefore the observed anomaly cannot be attributed to the topo graphic relief. The results of the deconvolutions were used to constra int the depth and horizontal locations of the magnetic sources for the 2D and 2.5D modelling. A purely geophysical model is presented, but s ome geological hypotheses that accord with the geophysical interpretat ion are proposed and briefly discussed.