Arcuate fold and cleavage patterns in the southeastern part of the Anglo-Brabant Fold Belt (Belgium): tectonic implications

The Brabant Massif (Belgium) is situated at the southeastern extremity of t he Anglo-Brabant Fold Belt, the predominantly concealed eastern branch of t he British-Belgian Caledonides. In contrast to the other parts of this Cale donian slate belt, the deformation history in the Brabant Massif has to dat e never been constrained properly. In this paper a synthesis is presented o f the structural observations in the limited outcrop area of the Brabant Ma ssif, in particular with respect to cleavage and fold trajectories and mutu al cleavage-fold relationships. Arcuate fold and cleavage patterns, as well as the presence of cleavage-transected folds are demonstrated, similar to the other parts of the belt. Moreover, the arcuate trajectories are conside red to reflect the trace of the Caledonian deformation front, once obscured by the Variscan Ardenne Allochthon. Combined with interpretations of the a eromagnetic and Bouguer anomaly maps, an overall kinematic model is propose d for the Acadian deformation event in the Brabant Massif. With the propose d model, calling upon processes of indentation by promontories and lateral escape of lithostructural domains, as well as on the control exerted by rig id granitoid basement blocks, the strong similarities with the other parts of the British-Belgian Caledonides become apparent. By defining an overall shortening direction and proposing a trace for the Caledonian deformation f ront in this southeastern extremity of the Anglo-Brabant Fold Belt, an inte grated tectonic image is obtained for the entire British-Belgian Caledonide s. (C) 1999 Elsevier Science B.V. All rights reserved.