Structural analysis of the adjacent Acadian and Variscan fold belts in Belgium and northern France from geophysical and geological evidence

Abstract

Two Palaeozoic fold belts are juxtaposed in Belgium and northern France. The northern belt of the Brabant Massif, traditionally considered a part of the European Caledonides, was folded during the Acadian orogeny in the early Devonian. Although it is largely concealed, gravity and magnetic maps give a general picture of the existing structures. A curved gravity trend is interpreted as an arc-shaped succession of granitic batholiths. Structures north and south of this arc are completely different. The northern subdomain, containing magnetic lower Cambrian metasediments, shows multiple thrust faults towards the south over the granites, whereas the southern subdomain, without magnetic rocks, is moulded around the granitic core. The southern Variscan belt is characterized in general by thrusting with a north, NW and NE vergence. During the Variscan orogeny the Brabant Massif acted as an obstacle to the general transport of the Ardennes Massif to the N–NW. The oblique convergence with the Brabant Massif caused differential displacement towards the northwest, the western areas having travelled farther, as seen from a pattern of WNW-oriented strike-slip faults.