1. Department of Earth and Planetary Sciences Institute of Meteoritics University of New Mexico Albuquerque New Mexico 87106 USA
2. Department of Earth and Atmospheric Sciences University of Alberta Edmonton Alberta T6G 2E3 Canada
3. Department of Earth and Planetary Sciences MacEwan University Edmonton Alberta T5J 4S2 Canada
4. Department of Geoscience University of Nevada, Las Vegas Las Vegas Nevada 89154 USA
5. GSECARS Argonne National Laboratory Lemont Illinois 60439 USA