University of Potsdam, Institut für Geowissenschaften Postfach 60 15 53, Potsdam, D-14415 Germany ; University of Grenoble, LGIT BP 53, Grenoble, F-38045 France
Geological Survey of Canada, 615 Booth Street, Ottawa, ON K1A 0E9 Canada
University of Oslo, Department of Geosciences POB 1047 Blindern, Oslo, N-0316 Norway