Part of this research was funded by a grant from the Center of Advanced Studies of the Norwegian Academy of Sciences and by the EU-Network "Precip-Dissolution" contract number HPRN-CT-2000-00058. JA acknowledges funding by the DFG-Graduiertenkolleg "Composition and Evolution of Crust and Mantle". We thank Anders Malthe-Sørenssen for all his help with the discrete particle code, Mark Jessell, Lynn Evans and Paul Bons for their help with "Elle" and Rianne Brunt, Renault Toussaint, Cees Passchier and Bjørn Jamtveit for helpful discussions.