[1] Dipartimento Sci Terra, Pavia, Italy
[2] ETH Zentrum, Dept Earth Sci, Zurich, Switzerland
[3] CNR, IGG, Sezione Pavia, I-27100 Pavia, Italy
[4] Univ Neuchatel, Inst Geol, CH-2000 Neuchatel, Switzerland
[5] Dipartimento Studio Terr & Risorse, Genoa, Italy