Estimation of magma depth for resurgent domes: An experimental approach

- Resurgent doming in calderas is a widespread process, generally associated with the rise of new magma.
- Many resurgent domes in nature are elongated and exhibit a graben, or several, at their summit.
- From analogue modelling, we propose a simple geometrical model for the structure of theses grabens.
- Related equations give an estimation of the magma depth for different resurgent domes.

Post-collapse resurgence is a phenomenon affecting many calderas. Attributed to a renewed magma rise, the process is still poorly understood and the associated source parameters remain poorly constrained. A set of experiments has been conducted to gain insight into the structural evolution of caldera resurgent domes. A sand-plaster mixture was chosen as an analogue for the brittle pile of volcanic rocks, and silicone putty simulates the ductile behavior of the intruding magma. Resurgence is driven by the vertical uplift of the silicone, with variable shape and depth. Similarity conditions are achieved through eight dimensionless numbers, which are of the same order of magnitude in both nature and experiments. Results show that extension due to doming is, in many cases, accommodated by one axial graben. Opposite master faults of this graben intersect at depth at the junction with the rising viscous silicone. The simplicity of the geometry of the whole analogue system provides equations which allow the estimation of the silicone depth from surface parameters. These equations are then used in some field examples to assess the magma depth beneath natural resurgent domes.