1. Physics of Geological Processes, University of Oslo, Sem Sælands vei 24, NO-0316 Oslo, Norway
2. Center for Advanced Study, Norwegian Academy of Science and Letters, Drammensveien 78, 0271 Oslo, Norway
3. Centre for Geodynamics, Geological Survey of Norway (NGU), Leiv Eirikssons vei 39, 7491 Trondheim, Norway
4. School of Geosciences, University of the Witwatersrand, WITS 2050 Johannesburg, South Africa