Magmas on the move: in situ 4D experimental investigation into the rheology and mobility of three-phase magmas using ultra fast X-ray tomography

One of the key challenges in understanding the nature of magmatic reservoirs relates to their ultimate destruction: namely what are the mechanisms and processes that enable large volume of generally highly viscous, three phase magmas to become mobile? The controlling mechanical processes operate on the scale of individual crystal-melt-bubble interactions, yet have influence on the entire reservoir system. These processes also control the relative movement of crystals, melts and bubbles, and influence the compositional, mechanical and thermal evolution of the reservoir on all spatial scales. Improved models of reservoir behaviour demand better understanding of these small scale processes. We present the first real time experimental observation of the microstructural evolution of two and three phase suspensions during deformation. We use ultra fast x-ray tomography (TOMCAT beamline, Swiss Light Source) and a custom made "XRheo" in situ rig to study the mobilisation and flow of complex two- and three-phase magmas. We record rheological data and simultaneously observe every individual crystal- melt-bubble interaction within samples of a variety of bubble and crystal contents during the experiment. Using this unique 4D (3D + time) data we are able to develop 3D and 4D maps of both local and sample- scale microstructure, track deformation & strain localisation, and quantify the evolving multi-scale heterogeneous distribution of solid, melt and bubbles through time. From this we develop 4D models of microstructure, deformation mechanisms and rheology that enable us to relate the experimental data to the macroscopic processes we can observe in natural systems, and ultimately improve our understanding of magma reservoir behaviour.