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

In the fine-grained Ordovician siliciclastic deposit 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.status: publishe

Large-scale slumping deduced from structural and sedimentary features in the Lower Palaeozoic Anglo-Brabant fold belt, Belgium

Distinguishing slump folds From tectonic folds in poorly exposed areas can be difficult, especially when the scale of the slump folds exceeds outcrop scale. In the southeastern part of the single-phase deformed, Lower Palaeozoic Anglo-Brabant fold belt a comparison of cleavage/fold relationships and stratigraphic polarity shows that a 200 m thick interval of middle Caradoc fine-grained turbidites in the core of a large synform was overturned prior to tectonic deformation. This overturning is attributed to large-scale slumping, which was most likely a result of middle Caradoc seismic activity.status: publishe

Preferred mineral orientation of a chloritoid-bearing slate in relation to its magnetic fabric

A regional analysis of the anisotropy of the magnetic susceptibility on low-grade metamorphic, chloritoid-bearing slates of the Paleozoic in Central Armorica (Brittany, France) revealed very high values for the degree of anisotropy (up to 1.43). Nonetheless, high-field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic. Chloritoid's intrinsic degree of anisotropy of 1.47±0.06, suggests that chloritoid-bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic (s.l.) minerals. To validate this assumption we performed a texture analysis on a representative sample of the chloritoid-bearing slates using hard X-ray synchrotron diffraction. The preferred orientation patterns of both muscovite and chloritoid are extremely strong (~38.6m.r.d. for muscovite, 20.9m.r.d. for chloritoid) and display roughly axial symmetry about the minimum magnetic susceptibility axis, indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid-bearing rocks. However, modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the CPO of chloritoid only partially explains the slate's anisotropy

Preferred mineral orientation of a chloritoid-bearing slate in relation to its magnetic fabric

A regional analysis of the anisotropy of the magnetic susceptibility on low-grade metamorphic, chloritoid-bearing slates of the Paleozoic in Central Armorica (Brittany, France) revealed very high values for the degree of anisotropy (up to 1.43). Nonetheless, high-field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic. Chloritoid's intrinsic degree of anisotropy of 1.47±0.06, suggests that chloritoid-bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic (s.l.) minerals. To validate this assumption we performed a texture analysis on a representative sample of the chloritoid-bearing slates using hard X-ray synchrotron diffraction. The preferred orientation patterns of both muscovite and chloritoid are extremely strong (~38.6m.r.d. for muscovite, 20.9m.r.d. for chloritoid) and display roughly axial symmetry about the minimum magnetic susceptibility axis, indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid-bearing rocks. However, modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the CPO of chloritoid only partially explains the slate's anisotropy

An Introduction to the Geology of Belgium and Luxembourg

peer reviewedBelgium and the Grand-Duchy of Luxembourg show surprising geological diversity over their small combined area of 33,114 km2. Almost all types of sedimentary rocks crop out and are generally preserved along well-described and easily accessible sections or in quarries. Several sections are known worldwide and are visited for stratigraphic or sedimentological purposes. Magmatic rocks are not abundant and metamorphic rocks are restricted to slates. The stratigraphic scale ranges from the Cambrian to the Quaternary, which translates to a half billion years of Earth history. This chapter provides a comprehensive overview of the different stratigraphic units, starting from the oldest and ending with the youngest. Modern stratigraphic schemes highlight formations’ geometries and interrelations. Some of the most remarkable units are further detailed. The two orogenic phases that shaped the Lower Paleozoic inliers and the Devonian-Carboniferous faulted and folded belt, i.e. the Caledonian and Variscan orogeny, are also addressed