An unusual patient: analog magma intrusion-induced host-rock deformation imaged and quantified with dynamic X-ray Computed Tomography
Authors: S. Poppe, E. Holohan, O. Galland, N. Buls, G. Van Gompel, B. Keelson, D. Hollis, A. Nila, J. Brancart and M. Kervyn De Meerendre
Publication Date: Dec. 2018
The use of scaled laboratory modeling to study volcanic deformation processes increasingly involves quantitative image analysis. For granular crustal analogs, deformation is usually monitored at the model surface or along a vertical cross-section at the model side-wall, and only the final deformation state is recorded in model cross-sections. Transparent gelatin as an alternative crustal analog enables an interior view, but it only accommodates idealized elastic deformation. As a result, our understanding of magma propagation modes and the associated inelastic host rock deformation from such models in 4D (i.e. 3D + time) is limited.To surmount this issue, we dynamically image fluid intrusion in a granular crustal analog by using wide beam X-ray Computed Tomography (XCT). We use golden syrup as a magma analog, and granular sand-plaster mixtures at varying mixture ratios as upper crustal rock analogs of varying strengths. We simultaneously visualize the geometric development of the syrup body as well as that of subsurface fractures and surface deformation in the granular analog. We also use Digital Volume Correlation (DVC) to calculate incremental and cumulative 3D volume displacements and 3D strains in the granular host material over time.We image in 4D the development of surface displacement and subsurface strain fields related to the growth of various intrusion geometries laccoliths, cone sheets and dykes -, which form as a function of the strength of the granular host material. Consequently, we show that the combination of XCT and analog modelling provides a novel basis for interpreting geological, geodetic and geophysical data related to volcanic deformation.