Craig Magee , Domenico Montanari, Giacomo Corti

Host rock deformation in active volcanic settings can signal and be used to constrain magma emplacement. Yet it is difficult to evaluate the accuracy of intrusion parameters derived from inversion of deformation signals because we cannot test estimates by directly accessing the magma body. Physical modelling is thus critical to understanding how intrusion translates into host rock deformation, particularly surface uplift and/or subsidence, because we can use transparent materials or excavate models to view the actual intrusion geometry. However, few physical models have investigated how a heterogeneous, layered host material impacts magma emplacement, despite evidence suggesting the presence of weak layers can control intrusion style and geometry. We conduct several models that simulate emplacement of a felsic magma at ~6 km depth within a granular (sand) host rock; in two of our models we incorporate two, thin, weak microbead layers into the layered host material. We show that intrusion solely within the granular material is primarily accommodated by lateral contraction (compaction and folding) of the host material, resulting in a dyke-like intrusion that erupted. When the microbead layers were present, a cone sheet and saucer-shaped sill preferentially formed, without erupting, accommodated by forced folding. Furthermore, we demonstrate that surface deformation does not simply reflect the complexity of the intrusion geometry or internal host material deformation. Overall, our results indicate that physical models should further explore the role of host material heterogeneity on magma emplacement.