1. Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA
2. New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, California 87801, USA
3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
4. Department of Geological Sciences and Engineering, University of Nevada, Reno, Nevada 89557, USA