1. 1Department of Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa 52242, USA
2. *Now at Clemson University, Clemson, South Carolina 29634, USA
3. 2Yukon Geological Survey, Whitehorse, Yukon Y1A 2C6, Canada
4. 3Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X5, Canada
5. 4Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA