1. Department of Earth and Environmental Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Avenue, Ann Arbor, Michigan 48109-1005, USA
2. Department of Geosciences, University of Texas at Dallas, ROC 21, 800 West Campbell Road, Richardson, Texas 75080-3021, USA
3. Department of Earth and Planetary Sciences, University of New Mexico, Redondo Drive NE, Albuquerque, New Mexico 87106, USA
4. New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA