1. Geological Survey of Norway, N-7491 Trondheim, Norway
2. Norwegian University of Science and Technology, N-7491, Trondheim, Norway
3. Department of Geosciences, Cambridge University, Downing St, Cambridge CB2 3EQ, UK
4. Bayerisches Geoinstut, Universität Bayreuth, D95440 Bayreuth, Germany
5. Institute of Rock Magnetism, University of Minnesota, Minneapolis, MN 55455, USA