In-situ investigations of grain boundary-fluid inclusion interaction in recrystallizing rock analogues

Investigating the mobility of fluid inclusions and fluid-rock interaction helps characterizing the effect of pore fluid on i) mechanical properties of rocks and ii) transport properties of fluid through rock volume. We present results from deformation and annealing experiments in transmitted light using rock analogues containing a liquid phase. The deformation rig is a high-pressure (up to 30 MPa), high-temperature (up to 200°C) see-through vessel with a controlled pore fluid pressure system. Samples were made of bischofite-brine, camphor-ethanol, and camphor-ethylene mixtures with the solid being polycrystalline with grain sizes ranging from 200 to 600 µm and with varying solubility in the liquid phase. In all systems the liquid phase is predominantly observed in isolated fluid inclusions and fluid pockets along grain boundaries with sizes ranging from 1 to 50 µm. Results show the in-situ pore fluid morphology during grain boundary migration recrystallization with preferential leakage of fluid inclusions along grain boundaries. For grain boundary migration rates ranging from 10-10 to 10-6 ms-1 we observed Zener pinning, drag and drop of fluid inclusions by migrating grain boundaries, but also passage of grain boundaries over fluid inclusions without any noticeable interaction, all being dependent on fluid inclusion size and solubility. Systematic measurements allowed tracing the maximum velocity of dragged fluid inclusions as well as the drag-limiting grain boundary velocity. The effects of these limiting conditions on recrystallized texture and on mobility of isolated fluid inclusions are subject to numerical simulations using the microstructural modeling platform ELLE. Image sequence showing fluid inclusion detaching from migrating grain boundary. Systematic measurements on pore shape evolution through time provide us the base for an empirical solution for pore drag and drop. The dragging time can be described as a function of grain boundary velocity, pore size (mobility) and mass transfer process.