The interplay between tectonism and volcano-tectonism in magma storage and ascent and caldera-resurgence mechanism: insights from analogue models.

In order to understand the role of tectonic and volcano-tectonic pre-existing structures as controlling factors on magma intrusion and caldera resurgence, two lines of experiments were performed to simulate: a) resurgence induced by both symmetrically and asymmetrically shaped magma chambers in an area with a simple graben-like structure; b) resurgence induced by both symmetrically and asymmetrically shaped magma chambers in an area with a caldera collapsed within the previously generated graben-like structure. We used dry sand to simulate the brittle crust and silicone to simulate the intruding magma. Resurgence always occurs through the formation of a discrete number of differentially displaced blocks. In the sample with a simple graben like structure the most uplifted block 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. In the experiments performed with a previous caldera collapse, the 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 silicone. The results of the experiments with an asymmetrically shaped magma chamber are similar to those previously obtained, but the most uplifted sector, in this case, is always in correspondence with the area in which the overburden is thicker. These results suggest that the stress field induced by resurgence is likely dictated by the geometry of the intruding magma body