Abstract

Field studies and geophysical imaging indicate that granitic and non-granitic plutons have both very variable and comparable shapes and sizes. We simulated numerically intrusion of partially molten mantle rocks from a sub-lithospheric magmatic source region (SMSR). Our systematic numerical modelling results show that intrusion typically spans a few hundred kyr spanning three stages: (1) magmatic channel spreading, (2) emplacement and (3) post-intrusive subsidence and cooling. The duration of each of these stages strongly depends on the viscosity of ascending magma. Upward magma transport from sublithospheric depth is driven by the positive buoyancy of the partially-molten rocks with respect to the overriding colder mantle lithosphere. By systematically varying the model parameters we document variations in intrusion dynamics and geometry that range from funnel- and finger-shaped bodies (pipes, dikes) to deep seated balloon-shaped intrusions and flattened shallow magmatic sills. Relatively cold elasto-plastic crust (T <sub>Moho</sub> = 400 degrees C) promotes a strong upward propagation of magma due to the significant decrease of plastic strength of the crust with decreasing confining pressure. Warmer crust (T <sub>Moho</sub> = 600 degrees C) triggers lateral spreading of magma above the Moho.

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