MODE OF INTERNAL DEFORMATION IN SAND WEDGES

Sequential sections of a sand box model are used to quantify displacement along imbricate surfaces and their rotation and volume loss history within an accreting sand wedge. Model results show that both displacement along the imbricate surfaces and compaction of the imbricate sheets decrease with sequential accretion of the wedge. The model wedge propagates episodically along a basal decollement when displacement along the imbricate surfaces decreases dramatically due to their back rotation and steepening. During their back rotation, the model imbricate sheets undergo compaction which resulted in an area loss of 12-13%, while the entire model shows 17% area loss. Back rotation of model imbricate sheets takes place in a domino-type style that is accommodated by ductile deformation of sand layers at deeper levels. Deeply located sand layers undergo 40-50% layer parallel shortening compared to no layer parallel shortening of the shallow located layers within the same imbricate sheet. Model sand wedge does not grow self similarly but rather its length/height ratio increases episodically with deformation.