Large Variscan overthrusts beneath the Paris Basin

Abstract

The ECORS project is devoted to the deep geophysical investigation of the continental and oceanic crust in France through the study of fundamental problems such as the formation of basins, mountain belts and continental margins. The first of the profiles completed is the ‘Nord de la France’, which is mainly devoted to the survey of the major units of the Northern Hercynian Belt and of the deep crust below the Mesozoic Paris basin. The deep geophysical investigations undertaken on this profile have led tothe acquisition of diverse information, such as vibroseismic, wide-angle reflection, refraction and magnetotelluric data. The main results presented here show evidence of large overthrusts in the Variscan chain which is currently buried beneath the thin Mesozoic cover of the Paris basin. They show a differentiation of structural units in the upper crust, their link with the lower crust, and the depth and geometry of the Moho. They also give rise to some speculations regarding the nature of various gravimetric and magnetic anomalies such as the large ‘anomalie magnetique du Bassin de Paris’ (AMBP).