1. Department of Earth Sciences, Aarhus University, C.F. Møllers Allé 4, DK-8000 Aarhus C, Denmark.
2. Corresponding author.
3. Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005 Paris, France.
4. School of Earth Sciences, Stanford University, 397 Panama Mall, Mitchell Building, Suite 101, Stanford, CA 94305-2210, USA.
5. Lancaster University, Bailrigg, Lancaster LA1 4YW, UK.
6. Danish Technical University, Anker Engelunds Vej 1, Bygning 101A 2800 Kgs. Lyngby, Denmark.
7. SkyTEM Surveys, Dyssen 2, DK-8200 Aarhus N, Denmark.
8. Geological Survey of Denmark and Greenland (GEUS), Lyseng Allé 1, 8270 Højbjer, Denmark.