1. a Department of Earth Sciences , University of Bristol , Wills Memorial Building, Queen's Road, Bristol, BS81RJ, UK E-mail:
2. b Department of Geology , University of Leicester , University Road, Leicester, LE1 7RH, UK
3. c Canada ‐ Nunavut Geoscience Office , 626 Tumit Plaza, Suite 202, PO Box 2319, Iqaluit, Nunavut, X0A 0H0, Canada