Cees W. Passchier

The 2017 Stephan Mueller Medal is awarded to Cees W. Passchier in recognition of his fundamental contributions to the understanding of deformation in rocks at all scales through innovative tools such as kinematic indicators, microstructural criteria, and vorticity analysis.

Early in his career, Cees Passchier realised the importance of understanding ductile flow in rocks, and made important contributions to the analysis of non-coaxial flow in shear zones, discussing spinning flow regimes, deformation paths in shear zones, the fabric attractor, and vorticity and strain analysis using Mohr diagrams. His deep understanding of microstructures let to his two books on Microtectonics and an Atlas of Mylonitic Microstructures, and formed the basis for the development of kinematic indicators, which have transformed tectonic analyses. His studies of the evolution of different types of porphyroclasts, and porphyroblasts, of flanking structures and boudinage are classics and widely cited. Passchier used elegant physical and numerical modelling techniques, with models guided by sharp intuition and deep understanding of these complex systems. In addition to the development of the (micro-) structural toolbox, Passchier managed to maintain a strong focus on field based research, in complexly deformed metamorphic rocks on all continents, including Antarctica, and in core complexes and extensional tectonics in the Aegean, Turkey, and elsewhere. These papers are beautiful examples of analyses based on solid field observations and careful interpretation. As Chief Editor of the Journal of Structural Geology and president of TecTask he has provided outstanding community service. As a teacher, he inspired generations of young researchers, showing unabating creativity and active involvement. He initiated the Journal of Structural Geology Student Author of the Year Award, motivating and supporting young talent. It is impressive how he combined his research and the tutoring of young scientists with leadership and responsibilities on the highest level in both national and international organisations. Despite his scientific achievements and profound influence on modern structural geology, Passchier has remained a modest person, never putting himself in front, but quietly pursuing scientific advancement. He is the perfect role model for the next generation of geologists with the open, unselfish friendly way of sharing experience and ideas. Passchier is an outstanding scientist who has led and defined our understanding in the field of structural geology and tectonics in the past thirty years.