Of what is the centre of the Ibero-Armorican arc composed?

The Ibero-Armorican are is a large structural bend known between France and Iberia. A related structure may exist in the crust of the Grand Banks of N ewfoundland. European geological studies suggest that this now-segmented st ructure developed during the Carboniferous, but this deformation has not be en recognised in the easternmost mainland of Canada. In France, the centre of the are is occupied by an ancient craton that formed the southern Hercyn ian foreland. The northern part of this craton presently lies beneath the M esozoic and Cenozoic cover of the Aquitaine Basin (France). Interpretation of the new ECORS-Gascogne deep-seismic reflection lines and gravity modelli ng suggests that the old Aquitaine basement has thinned beneath the Mesozoi c Parentis basin. North of the basin, the deep Variscan structures dip nort heast. In the south, the centre of the Aquitaine basement corresponds with the Landes High. Analysis of the ECORS refraction seismic data shows the ab sence of any shallowing of the lower crust beneath this uplift. At the same level, a high-velocity, dense body, 'resting' on the lower crust, has been imaged. This body, which is probably a metamorphic block of Archaean basem ent at depth, lies in line with the Spanish Le Danois Bank in a reconstruct ion where the Biscay Bay is closed. It is postulated that this high-velocit y and high-density block is the only French remnant of the undeformed nucle us of the Ibero-Armorican are, now dismembered by the opening of the Biscay Bay. (C) 1999 Elsevier Science B.V. All rights reserved.