Simulation of crustal melt segregation through cellular automata: Insight on steady and non-steady state effects under deformation

We present a numerical model of melt segregation under variable deformation regimes (pure and/or simple shear) and strain rates. The model is adapted from a cellular automaton. The Lagrangian description requires some initial melt content and obeys two thresholds. One allows melt connection and subsequent melt motion. The other rules melt escape. The geometry of the flow is that of pure and/or simple shear. Deformation is a necessary melt-segregating factor, with contraction being more efficient than simple shear. The ratio of escaping melt to the initial melt content defines the coefficient of melt extraction. It varies linearly with initial melt content, thresholds and deformation, which are tested separately. During each run, transient states of the melt-extraction coefficient were characterized by exponential spikes whose amplitude depends on the initial melt content, thresholds and deformation. Departures in melt extraction from average volume are damped when initial conditions are continuously changed, reflecting a memory effect. We suggest that melt extraction relates to a pinning-depinning process. Melt extraction being discontinuous and irregular with time, we suggest that detailed chemistry does not properly document the melt evolution in source rocks (migmatites).