Magma dynamics in a viscously deforming porous media

June 14, 2011

Time: June 14, 2011
Lecturer: Assistant Professor Marc Hesse
Department of Geological Sciences, The University of Texas in Austin
Venue: Pfaffenwaldring 61, Raum U1.003 (MML), Universität Stuttgart
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Partial melting and subsequent melt-segregation by porous flow leads to large scale planetarydifferentiation, i.e. formation of the layered structure of terrestrial planets: core, mantle and crust.Under typical conditions of melt production in the earth's interior (beneath mid-ocean ridges) the meltpercolates at very low melt fractions (theoretically immediately!), which allows melt extraction byporous flow. The rate at which the melt can be extracted is determined by the rate of compaction of thesolid matrix. The solid deforms by high-temperature creep that can be modeled as a very viscous fluid.This leads to a system of multiphase flow equations, where the melt is governed by Darcy's law and thesolid by Stokes equations. In contrast to classical Darcy-Stokes problems the Darcy and Stokes behaviorare not occurring in separate domains (porous matrix and fracture) but together in a multiphase setting.I will introduce the main concepts of partial melting and melt migration and outline the differentgeological, geochemical and geophysical constraints on the process. Then I will discuss some theoreticalresults and high-resolution numerical simulations for simplified systems of equations. While thesemodels are simple approximations of the true dynamics they reproduce some basic geologicalobservations.Simulation results for melting in a uniformly upwelling mantle. Spontaneous growth of compaction-dissolutionwaves gives rise to channelized melt flow. The evolution of the normalized porosity field is shown in the top rowand the successive depletion of a mineral (opx) that is soluble in the melt is shown in the bottom row. The spatialdimension is in compaction lengths (1-5 km) and the time indicates solid overturns, i.e. time for a solid particle tobe advected through the domain (50,000 yrs).AbstractHesse.pdf
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