A geological section across the Hesperian Massif in Western and central Galicia.

Abstract

A section across the axial zone of the northern Hesperian massif in Galicia is presented. It is extrapolated to a depth of 5 km on the basis of gravity data obtained over key areas near Mellid and Santiago de Compostela. Several lithotectonic units are distinguished in this part of the massif. Lower Palaeozoic supracrustals, closely associated with late Palaeozoic migmatites, granitic and metamorphic rocks constitute the regional tectonic framework. Infracrustal rock complexes occur in subcircular to elongate outcrops. Those representing the higher basement levels are of mesozonal metamorphic grade and contain abundant amphibolites and calcalkaline as well as peralkaline granite gneisses. Others, representing the lower basement levels, are predominantly catazonal and have prominent constituents of the continental upper mantle. Some of the latter are associated with dismembered metaophiolites of Palaeozoic age. For the evolution of the northern Hesperian Massif a mantle-plume/rift-system model is preferred. An outline of this model is provided.