The fluid dynamic and thermophysical and constraints on peperite formation, and the vibrational liquefaction model

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University of New Brunswick
Peperite is a textural term to describe a rock formed by the disruption of magma mingling with unconsolidated, typically wet sediments. The current models of peperite formation (magma mingling and breakup driven by sediment fluidization and explosive fuel coolant reactions) do not explain the wide variety of features seen in rocks with peperitic textures. In addition, the peperitic textures catalogued by over 90 authors do not show any evidence of fine scale break up as expected if mingling and explosive fuel-coolant reactions were driving the process. The inherent space problem associated with moderate to large-scale fluidization also cannot be addressed using the current models. The purpose of this thesis was to examine the fluid dynamic and thermophysical constraints on peperite formation. To carry out this goal a series of experiments reproducing peperites in the laboratory setting were performed. Following these experiments a full characterization of the rheological and thermodynamic properties of the melts and the sediments used in the experiments were conducted. Then the processes driving melt breakup (i.e., sediment failure, heat flow and boiling at the sediment interface, and the fluid dynamic breakup of viscous liquids) were examined. The vibrational-liquefaction model proposed in this thesis is the first unified model of peperite formation. It explains both the textural features observed in peperites, and accounts for the disruptions and compaction of sediments without the need for large-scale movement of sediments. The vibrational energy produced by vapour film oscillation and collapse transmits mechanical energy to the surrounding sediments inevitably leading to liquefaction. Liquefaction of the sediments provides magma with the space needed to behave in a ductile or brittle fashion needed for magma breakup to occur without moving large volumes of sediment. The magma can then deform in this zero effective stress as an immiscible fluid, where the dense magma will sink below the less dense liquefied sediments. Numerical simulations of immiscible fluid breakup using openFoam software are then used to show how magma breakup occurs.