1. Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA
2. Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan 49931, USA
3. Department of Earth and Planetary Science, University of California, Santa Barbara, California 93106, USA
4. Department of Geosciences, Boise State University, Boise, Idaho 83725, USA