In order to understand the role of an asymmetrically shaped magma chamber on the resurgence-related deformation of a caldera collapsed in a previously deformed crustal sector, a set of analogue models has been carried out. The obtained results have been compared with those of similar experiments, previously performed imposing a symmetrical magma chamber. Two lines of experiments were performed to simulate: a) resurgence in an area with a simple graben-like structure; b) resurgence in a caldera collapsed within the previously generated graben-like structure. On the basis of commonly accepted scaling laws, we used dry-quartz sand to simulate the brittle behaviour of the crust and newtonian siliconee to simulate the ductile behaviour of the intruding magma. An asymmetrical shape of the magma chamber has been simulated moulding handily only the upper surface of the siliconee. The resulting empty space has been then filled with sand. The results of the experiments are similar to those obtained with simmetrically shaped silicone. In the sample with a simple graben-like structure, resurgence occurs through the formation of a discrete number of differentially displaced blocks. The most uplifted portion of the deformed caldera floor is affected by newly formed, high-angle, inward dipping reverse faults. The least uplifted portion of the caldera is affected by normal faults with similar orientation, either newly formed or resulting from reactivation of the pre-existent graben faults. This asymmetric block resurgence has been also observed in the experiments performed with a previous caldera collapse. In this case the caldera collapse-related reverse ring fault is completely erased along the shortened side, and enhances the effect of the extensional faults on the opposite side, facilitating the intrusion of the siliconee. The most uplifted sector, due to an asymmetrically shaped intrusion, is always in correspondence with the thiker overbunden. These results suggest that the stress field induced by resurgence is likely dictated by the geometry of the intruding magma body.
Marotta, E., Acocella, V., DE VITA, S., Funiciello, R., Orsi, G. (2004). The role of magma chamber asymmetrical shape on deformation processes and magma intrusion in analogue models of resurgent calderas..