Numerical Modeling of Time-dependent Fluid Dynamics and Differentiation of a Shallow Basaltic Magma Chamber

This contribution presents a numerical model of time-dependent processes and differentiation in a cooling magma chamber obtain the magma and liquid composition and model the distribution minerals and H2O gas bubbles at any moment and place. numerical experiments were mainly carried out simulating 10 of differentiation of a 50 km3 cylindrical stock-like reservoir as of the end-members of a wide spectrum of magma body geometries. detailed space^time distribution of compositional varieties exsolved phases in a chamber of initially superheated basaltic (corresponding to a lava of the HudsonVolcano, Chile) obtained through numerical simulation using the finite-element .The roof of the chamber is located at 2 km depth in a crust a geothermal gradient of 308C/km. The model considers two directions (z and r) and assumes the magma to be an incompressible -Newtonian liquid, following the Navier^Stokes formulation, the density and viscosity depend on the temperature exsolved solid and volatile phase content, but viscosity also on the shear rate. The temperature transfer equation used conduction, convection and latent heat. The setting of the considers that: (1) an extension of 1km into the country rocks the chamber imposed on the heat flow across the margins is ; (2) the reaction rates for phase (solid and gas) exsolution to a Gaussian probability function; (3) the involved , calibrated from MELTS, are olivine, clinopyroxene, magnetite, , orthopyroxene and H2O gas; (4) the velocity of the phase movements with respect to the hosting liquid is given the Stokes’ velocity; (5) the sizes of crystals and bubbles in the vary in space and time up to a maximum given by the modal size observed in the Hudson Volcano. Our results indicate the convection dynamics of the reservoir are characterized by distinct flows of decreasing velocity with time: convective cells, and layer flows along the walls. The along-wall magma , which persists during most of the 10 kyr of magma cooling, contributes the thermal insulation of the chamber interior, giving to a nearly permanent coexistence of liquids of contrasting composition. strong compositional stratification is generated in the half of the chamber, with a downward-increasing thickness of . Such stratification is mainly the result of continuous upward and storage on top of the sidewall residual melts. The lower of the chamber exhibits an independent convective pattern dominated ascending plumes. A less pronounced stratification is generated as a consequence of mixing between the residual liquid in ascending plumes and the surrounding melt. Crystal accumulations olivine, clinopyroxene and magnetite at the bottom generate significant volume of ultrabasic magma at the end of 10 kyr. plagioclase-rich solidification front along the walls is formed the last stages of crystallization, when the along-wall flow diminishes in velocity. An application of the numerical to a cylindrical sill-like chamber is presented to emphasize role of the aspect ratio in the magma fluid dynamics, compositional and exsolved phase distribution. The stock-like favors the formation of steep compositional gradients and 2O gas concentration at the roof. Concentration of the exsolved along the margins is favored in a sill-like chamber. From the results, it is possible to infer that stock-like chambers be more eruptible and would exhibit a wider compositional of eruptive materials than sill-like chambers. Because and liquid dispersion follow different patterns in a convective , the record of crystal^liquid equilibrium would be an .