Geologica Belgica

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The Quenast plug: a mega-porphyroclast during the Brabantian Orogeny (Senne valley, Brabant Massif)

(volume 11 (2008) — number 3-4)
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Mots-clés : cleavage, Keywords: Anglo-Brabant Deformation Belt, Nieuwpoort-Asquempont Fault Zone, strain, X-ray pole figure goniometry


ABSTRACT. In the fine-grained Ordovician siliciclastic deposits surrounding the Quenast plug, a variety of structural features demonstrate that the Quenast plug was emplaced prior to the Brabantian deformation event. These features include: a) a large-scale bending of the cleavage, mimicking the shape of the plug; b) a concomitant change in the orientation of the transverse fractures; c) a marked variation in cleavage intensity around the plug, with a high-strain zone along the NE-side of the plug and a low-strain zone along the NW-side of the plug; d) contractional and dilational kink bands. In combination with the ellipsoidal cross-section of the plug, these features indicate that the Quenast plug can be regarded as having acted as a mega-porphyroclast during the Brabantian deformation event.

The different structural features are discussed and related to the geometry and deformation of the Quenast plug. Also the temporal and spatial relationships of the Quenast plug with respect to the Asquempont Detachment System and the Nieuwpoort-Asquempont Fault Zone are discussed. Finally, a preliminary attempt is made at estimating the shortening across the plug. Future work, concentrating on the magnetic fabric within the plug, will shed further light on the behaviour of the plug during the Brabantian deformation event.

To cite this article

Timothy N. DEBACKER & Manuel SINTUBIN, «The Quenast plug: a mega-porphyroclast during the Brabantian Orogeny (Senne valley, Brabant Massif)», Geologica Belgica [En ligne], volume 11 (2008), number 3-4, 199-216 URL :

About: Timothy N. DEBACKER

Research Unit Palaeontology, Geology & Pedology, Universiteit Gent, Krijgslaan 281, S8, B-9000 Gent, E-mail:

About: Manuel SINTUBIN

Geodynamics & Geofluids Research Group, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Leuven, E-mail: