Mathilde Cannat

The 2020 Stephan Mueller Medal is awarded to Mathilde Cannat for her invaluable contributions to the understanding of the tectonic and magmatic evolution of mid-ocean ridges and the formation of oceanic crust.

Mathilde Cannat is a passionate scientist who has fundamentally changed our concepts of the formation and composition of oceanic crust. Because she investigates the Earth below 2000–4000 metres of seawater, her studies require sophisticated techniques of investigation and inevitably involve close integration of structural geology, geophysics and geochemistry.

Thanks to Cannat’s work, we now know that slow-spreading mid-ocean ridges are radically different from fast-spreading ridges. Fast systems represent the classical view of the mid-oceanic ridge system as a long chain of volcanic edifices. Cannat instead proposed the “smooth seafloor” as a new type of oceanic seafloor that forms in slow systems with minimal melt supply. Her visionary model proposes that at very slow spreading centres mantle-derived peridotite, intruded by numerous gabbroic intrusions, can be tectonically uplifted to the seafloor along detachments faults. Her model was likely responsible for the explosion of geophysical and geological campaigns that led to the discovery of oceanic core complexes.

Extremely detailed in-situ studies of oceanic core complexes by Cannat’s team show the mechanisms of mantle and deep crust exhumation. These studies bridge offshore geology with onshore field studies in ophiolitic units of mountain belts, where the heterogeneities seen on the seafloor and the reworking of mantle and crustal rocks in oceanic sediments have long been reported. Cannat understood long ago the power of comparing ophiolites and the real seafloor. As an expert of the lithosphere and ocean ridges, Mathilde made her first steps by studying ophiolites in the Klamath Mountains in California and the Chenaillet in the western Alps.

Cannat’s work considers dynamics from the scale of the grain to the lithosphere, bridges from ocean depths to onshore outcrops, and combines a wide range of data acquisition techniques. She participated in many cruises and submersible dives, leading an amazing 16 cruises as chief scientist. She recently discovered a new, active low-temperature hydrothermal site (that she called “old city”) within an exhumed mantle domain at the Southwest Indian Ridge. This discovery will undoubtedly launch a new series of both marine geoscience and biology cruises.

Throughout her career, Cannat has organised the scientific community in long-term European research projects and through ocean cruises. She is devoted to sharing knowledge and providing students with the necessary background for becoming mature and independent researchers. For all these reasons, Mathilde Cannat is a worthy recipient of the 2020 Stephan Mueller Medal.