Xavier Le Pichon
2002 Balzan Prize for Geology
Xavier Le Pichon has made major contributions to the foundation of Plate Tectonics Theory. He was the first to develop a global model based on quantitative analysis. The motions of rigid plates are defined by giving outlines of about a dozen plates, the geographic location of their pole of rotation and the associated angular velocities. The principles of this approach were presented by W.J. Morgan and D.P. McKenzie & R.L. Parker in 1967. Using their methodology, Xavier Le Pichon constructed a global map of the motions related to the six major plates in 1968. This became the basis for a better understanding of the distribution of earthquakes and for the large scale reconstruction of the configuration of continents and ocean basins in the past. His book of 1973 (Plate Tectonics, with Jean Bonnin and Jean Francheteau) became the standard reference work on the Theory of Plate Tectonics for many years.
Xavier Le Pichon later became a leading figure in deep-sea exploration with submersibles. In 1973 he led the French American Midocean Ridge Study (FAMOUS) together with Jim Heirtzler and Bob Ballard. This marked the beginning of a new type of high resolution studies of midoceanic ridges with their hydrothermal sources. From 1979 to 1981 he extended this method of exploration to deep-sea trenches in the Eastern Mediterranean, and to the Pacific trenches off the coast of Japan after 1984. Thus he covered both divergent and convergent plate boundaries and studied geophysical, geological and geochemical processes in these different environments. The role of fluids in these environments is not only important for earthquakes but also for the geochemical balance of the oceans and for the biology of vent communities. Since the late 1990s geodetic methods using satellites have allowed him to shed light on interseismic deformation.
Xavier Le Pichon’s contributions to the concept of “Earth Systems Sciences” have been important for both geologists and the general public. His leading role in the development of marine geology in France and in many international programs, together with his gift of combining mathematics, geophysics and geology have been the basis for his excellent teamwork and guidance of gifted young researchers in the earth sciences.