NUPUS Seminar presentations

Time: 14th June 2011 at 16:00h
Place: MML (Institut für Wasserbau, Pfaffenwaldring 61)
Presenter:Assistant Professor Marc Hesse
Title: Magma dynamics in a viscously deforming porous media

Partial melting and subsequent melt-segregation by porous flow leads to large scale planetary differentiation, 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 melt percolates at very low melt fractions (theoretically immediately!), which allows melt extraction by porous flow. The rate at which the melt can be extracted is determined by the rate of compaction of the solid 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 the solid by Stokes equations. In contrast to classical Darcy-Stokes problems the Darcy and Stokes behavior are 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 different geological, geochemical and geophysical constraints on the process. Then I will discuss some theoretical results and high-resolution numerical simulations for simplified systems of equations. While these models are simple approximations of the true dynamics they reproduce some basic geological observations. Simulation results for melting in a uniformly upwelling mantle. Spontaneous growth of compaction-dissolution waves gives rise to channelized melt flow. The evolution of the normalized porosity field is shown in the top row and the successive depletion of a mineral (opx) that is soluble in the melt is shown in the bottom row. The spatial dimension is in compaction lengths (1-5 km) and the time indicates solid overturns, i.e. time for a solid particle to be advected through the domain (50,000 yrs).