Geophysical constraints on the deep structure along the Ecors Pyrenees Line

Abstract

The structure of the central part of the Pyrenean range, traversed by the ECORS vertical reflection seismic line, is further constrained by a joint interpretation of complementary and reprocessed data. Wide‐angle, low‐frequency profiling of Moho topography indicates an abrupt termination of the northern, European Moho at the North Pyrenean fault and a range of possible geometries of a deeper, Iberian Moho which does not seem to extend significantly to the north of this fault. When reprocessing vertical reflection data to 25 s two‐way travel time, strong clear straight reflections are discovered in the part of the section under the northern foreland, long after the Moho reflection. Their strong northward dip indicates that they originate in fact at reflectors at depth beneath the North Pyrenean fault, which may correspond to the connection between the two levels of Moho, the reflections then being from the northward inclined limit between the wedge of Iberian crust underlying the southern edge of the European mantle. A range of possible shapes is allowed by the conjunction of these seismic data, which is compatible with the results of a detailed gravity profile. This would indicate that the imbrication of European into Iberian lithosphere has been of limited extent with respect to the surface trace of the North Pyrenean fault, provided no strong density contrast in the mantle part of the section contributes significantly to the gravity anomaly.