This research was supported by the Agouron Institute, the FRS-FNRS-FWO EOS ET-Home grant 30442502 and the ERC Stg ELiTE FP7/308074. We thank M. Giraldo, M.-C. Sforna, Y. Cornet and S. Smeets (University of Liège) for technical support and the Geological Survey of Canada’s Geomapping for Energy and Minerals Program for fieldwork logistics.

Reviewer information

Nature thanks Linda Graham and the other anonymous reviewer(s) for their contribution to the peer review of this work.