1. Institute of Geochemistry and Petrology, Department of Earth Sciences; Swiss Federal Institute of Technology (ETH Zürich); Sonneggstrasse 5 8092 Zürich Switzerland
2. Institute of Geophysics; Swiss Federal Institute of Technology (ETH Zürich) Sonneggstrasse 5; 8092 Zürich Switzerland
3. Department of Earth Sciences; Uppsala University; Villavägen 16 752 36 Uppsala Sweden