1. Univ Angers, Nantes Université, Le Mans Université, CNRS, UMR 6112, Laboratoire de Planétologie et Géosciences F‐49000 Angers France
2. Presently at: Institute of Geology and Mineralogy, Faculty of Mathematics and Natural Sciences University of Cologne Cologne Germany
3. Univ Brest, CNRS, Ifremer, Geo‐Ocean F‐29280 Plouzane France