Jon was a Professor of Earth Sciences and Deputy Head of Science Faculty (Research). Jon obtained a BSc Honours degree in Geological Sciences from Durham University in 1981 followed by a PhD from the University of Leeds in 1984. He was appointed to Durham in 2000 and served as Head of Department until 2005. He began his research evaluating the sources and processes which determine the nature of magmatic rocks at arcs. He is recognised for integrating modern geochemical, particularly isotopic, methods with detailed petrology and fieldwork at subduction zones across the world, from the West Indies to Kamchatka, New Zealand and the Andes. More recently he developed techniques for isotopically fingerprinting magmatic components at the scale of individual minerals. His research group now focuses on this approach and leads the world in its application. Jon published more than 100 peer-reviewed articles, edited 2 thematic collections and was lead author of an introductory textbook in Earth Sciences.