1. School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada
2. Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta T6G 2E3, Canada
3. Department of Earth Sciences, University of California, Santa Barbara, 1006 Webb Hall, Santa Barbara, California 93106, USA
4. Department of Earth and Environment, Boston University, 685 Commonwealth Avenue, Boston, Massachusetts 02215, USA