Photograph Of The Month: Boudin Centennial

摘要

This photograph is taken in the Mardasson quarry near Bas-togne, Belgium, the locality where 100 years ago the terms boudin and boudinage were coined. In this outcrop, cuspate-lobate buckling of the interface between metasandstone and metapelite is controlled by the presence of pre-existing layer-perpendicular quartz veins. The buckling does not occur where quartz veins are not present. The quartz veins are confined to the fine-grained micaceous sandstone layers and there is a relationship between vein spacing and layer thickness. The veins result from a hydraulic-fracturing event (Kenis et al., 2002, 2005a). Once formed, the quartz veins acted as rigid plates, stronger than the micaceous sandstones. Subsequent layer-parallel shortening caused cuspate-lobate buckling of both upper and lower interface in between the quartz veins, i.e. the development of mullions. Deformation was by solution-precipitation processes at 350-400℃. The characteristic shape of these mullions allows estimation by geomechanical modelling of the rheological parameters of the rock (Kenis et al., 2004, 2005b).