1. University of Cape Town, Department of Geological Sciences, Rondebosch 7701, South Africa
2. University of Cincinnati, Department of Geology, 500 Geology Physics Building, Cincinnati, Ohio, USA
3. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
4. School of Earth Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia