1Department of Geology, University of Leicester, Leicester, LE1 7RH United Kingdom
2Department of Geology, Trinity College, Dublin 2, Ireland
3U.S. Geological Survey, MS 966, Box 25046, Federal Center, Lakewood, CO 80225, USA
4U.S. Geological Survey, Northern Rocky Mountain Science Center, P.O. Box 173492, Bozeman, MT 59717–3492, USA
5Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
6Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, 510640 Wushan Guangzhou, PR China