Multiple Variscan nappes in Limousin, western Massif Central, France: geophysical constraints to the geological model and geodynamic implications

Abstract The upper crustal structure of Limousin, western Massif Central, France, results from tectonic superposition of major Variscan high-grade metamorphic crystalline nappes, one of them containing well preserved relicts of an early Paleozoic oceanic lithosphere. Three of these nappes outcrop in the studied area as evidenced by surface geological observations. Their overall present synclinorium structure is confirmed by the gravimetric data. Results from three short refraction seismic profiles recorded in this area are totally compatible either with the local tectonic model or with the global one recently proposed for Limousin. Although it would be an over-interpretation to derive a geological model from the only seismic profiles presented, this study shows that short seismic profiles are critical for 3-D extrapolation of the geological surface data in old orogenic regions. As ophiolites are located within a peculiar unit representing an early major thrust contact, the origin of the various nappes above and below may be defined in terms of plate tectonics.