COMPARING RING FAULT AND CALDERA FORMATION CONDITIONS ON EARTH AND MARS USING FINITE ELEMENT MODELS

Several types of reservoir-derived volcanic features—e.g. circumferential intrusions, radial dike systems, equant calderas, summit eruptions that promote edifice growth—occur persistently on multiple planets/moons and at multiple scales. This suggests (a) that commonly observed patterns of magma reservoir volcanism are not generally dictated by local inhomogeneities, (b) that they instead derive from overarching factors that should be predictable and linked to inflation and/or deflation processes and host rock response, and (c) that numerical modeling of stress conditions adjacent to idealized magma bodies should provide valuable insight into the nature of reservoir rupture and any corresponding magmatic and/or volcanic activity. Calderas, for example, should be more likely to form when volumetric or other adjustments within a magma reservoir prime the surrounding rock for ring faulting; identifying the geological circumstances that promote this priming is thus critical to our understanding of why calderas form. Mohr-Coulomb shear failure leading to ring fault formation will depend, however, upon different factors such as the magnitude of the normal stress—dictated by gravitational loading conditions that differ for each planet/moon—and the aspect ratio of the host rock volume above the reservoir, i.e. upon planet/moon-specific differences in magma reservoir depth. In this presentation, exploring these ideas, I will focus primarily upon sharing modeling-derived insights into why different conditions on Earth and Mars should create fundamentally different expectations for how readily caldera ring faults will form. In addition, as a first order test of these insights, I will compare the model predictions with published observations of the caldera population observed on each of the two planets.