CRUSTAL STRUCTURE OF THE CADOMIAN BLOCK IN THE NORTH BRITTANY (FRANCE) - SEISMIC-REFLECTION AND MAGNETOTELLURIC SOUNDING (GEOFRANCE 3D ARMOR PROJECT)

A new deep seismic profile has investigated the Upper Proterozoic terr ains assembled during the Cadomian orogeny in the Northern Armorican M assif. This 60 km land profile prolongs the marine Swat10 profile of t he ECORS-BIRPS programme. Although the upper crust is poorly reflectiv e on the stack section, several NW dipping reflectors have been observ ed and modelled from single shot records. They can be correlated with outcropping strike-slip and overthrusting major contracts. The reflect ivity of the lower crust, below 5 s, varies from one domain to another but it is relatively high and characterized by subhorizontal reflecto rs. The whole upper crustal Cadomian structures are interpreted as SE verging overbursting prism the sole of which could be the top of the r eflective lower crust.