Brittle and ductile deformation around partially melted stepped dykes: insights from analogue modelling

We present the analysis of two analog modelling experiments that studied the processes related to deformation in syntectonic “en echelon” dykes. The analogue materials used are white plasticine for the brittle-ductile host rock, and partially molten chocolate couverture for the melted dykes.The results show the highly heterogeneous distribution of strain around the deforming dykes due to the strong competence contrast between the materials. Dykes stretch and rotate at a higher rate than the host material. The higher strain is concentrated at the tips and the outer margins of the dyke, where shear zones localize. New fractures grow and propagate across dyke overlapping zones. The differences in the initiation and evolution of ductile and brittle structures between the two experiments are related to the initial arrangement of the dyke system (within the shortening or the extensional strain field ). This work gives insight into the relations between structures found in syntectonic dykes and the process and conditions responsible for it developing in nature.