1. 1Earth and Environmental Science Department, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801, USA
2. 2Department of Geological Sciences, California State University-Fullerton, 800 North State College Boulevard, Fullerton, California 92834, USA
3. 3Geochronology Research Laboratories, New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA
4. 4U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA