An interpretation model of semi-circular Bouguer anomalies found over the peripheral belt of the Ordenes complex (NW Spain)

Abstract

A gravity survey of the peripheral belt of the Ordenes comprex in Galicia (NW Spain) has been combined with a little used, although known, interpretation method. From the results of the survey and geological evidence, support was found for the hypothesis that the peripheral belt could be subdivided into separate units of shallow buried, but deep-reaching bodies of high-grade ultramafic material, which appear to have their-origin in diapiric movements of upper-mantle material into a crystalline lower crust of continental type. The depth of the western body, projected underneath the high-grade metamorphic complex of Santiago de Compostela, is computed at a depth of 780 metres, while the bodies of the complexes of Sobrado-Teijeiro and Mellid are computed at a depth of 550 metres and 150 metres, respectively. The semi-circular outline of all three Bouguer anomalies suggested diapiric structures comparative to salt-domes, which have been interpreted using a three-dimensional method.