1. Department of Earth Sciences, The University of Hong Kong, Hong Kong, P R China, School of Engineering, University of Guelph, Guelph, ON N1G 2W1, Canada, School of Water Resources & Environment, China University of Geosciences, 29 Xueyuan Road, Beijing, China, 100083, Guangdong Geological Survey, 739 East Dongfeng Road, Guangdong, China, 510080, and China Geological Survey, 45 Fuwai Street, Beijing, China, 100037