USTL Montpellier, France
Adolphe Nicolas received the Hess Medal at the 2004 Fall Meeting Honors Ceremony on 15 December, in San Francisco, California. The medal is given for outstanding achievements in research in the constitution and evolution of Earth and other planets.
Citation
Adolphe Nicolas is a pioneer in Earth sciences. He has almost created a new field that we can name: the textural geodynamics.
The principle of such study is to observe with a microscope the texture of an ultramafic rock and, combining those observations with field measurement and theoretical considerations about the crystal deformation and rocks plasticity, deduce important information about the dynamics of the mantle.
Originally, he started those studies with the late Dale Jackson from U. S. Geological Survey, which initiated this field on his classical study of the Stillwater Complex ( Montana) and its extraordinary fluid dynamics reconstitution. Adolphe had the chance to work with him, and I remember Dale, who was not overly given to complimenting his colleagues, saying to me, Adolphe is going to be my successor.
He is the best of the new generation of structural geologists of igneous rocks. At that time, Dale was not envisaging his premature death.
Adolphe, in fact, oriented his work in a quite different direction from that followed by Dale. He did not work on molten rock that crystallizes under a fluid dynamics; instead, he worked on solid plastic deformation.
His second collaboration, which has turned very positive, is the association with Jean-Paul Poirier.
In fact, when Adolphe met him, Jean-Paul was a metallurgist expert in plastic deformation of metals. Adolphe convinced him to become a geophysicist, and this conversion was a great benefit for our field.
Together, they worked on several projects and published a classic book, Crystalline Plasticity and Solid State Flow in Metamorphic Rocks (John Wiley). This collaboration gave to Adolphe the theoretical basis that he needed.
This is the genesis. But what is more important is what Adolphe Nicolas has achieved as an original contributor. We can divide his contribution into three important chapters.
The first major contribution is high-temperature peridotites. He studied mainly Lanzo ( Italy) and in less detail Baldissero and Lherz (France). In those studies, made in collaboration with Françoise Boudier, Adolphe has shown how those pieces of mantle have been emplaced in the great tectonics movements of the Alps. But, more important, they deciphered the deformation mechanism. They distinguished the primitive deformation with the pyroxenites layers folded and, to the secondary lineation associated with the tectonics intrusion of the body and with the decompressive melting which generates magmas as gabbros dykes. Those studies were extremely important for us when we developed the marble-cake model for the upper mantle.
The second major contribution of Nicolas’s school was the work done with Anne-Marie Boullier on the xenolith intrusion in kimberlites. They distinguished the texture of the xenoliths coming from the asthenosphere from the one coming from the lithosphere, with the famous pyroxene geotherm and its famous kink.
The third contribution is, of course, his work on the ophiolithes of Oman and the careful study he made about the ultramafics fabrics related to the creation of oceanic crust. This work is itself a monument with implications about the partial melting mechanism, injection of magmas as hydro-fracture to the symmetry of ridge crest to the different regime of oceanic ridges depending of spreading rate.
All of that with careful field work, microscopic observation, and lots of thinking!
Adolphe Nicolas is really a master of modern geoscience in exactly the same spirit of Harry Hess, who started studying serpentine ending to seafloor spreading. Adolphe follows this trend but deciphers the mechanism.
—CLAUDE J. ALLÈGRE, University of Paris, France
Response
Thank you, Claude. Thanks for this flattering citation and for your support through so many years. You have paved the way for my response by evoking the names of outstanding scientists and dear friends who accompanied me during my career. Indeed, my master has been Dale Jackson, who invited me to the USGS in Menlo Park, in 1971, following a memorable trip, the year before, through most western European peridotite massifs. I learned from him what and how to observe in the field. Dale introduced me to microscope textures in the lab; I could start relating field observations with what I knew from solid-state deformation with my background in physics and from illuminating discussions with Harry Green and the David Griggs’ group at UCLA.
Back in France, with Françoise Boudier and Jean-Luc Bouchez, we got acquainted with petrofabric analysis with the Emile Den Tex group in Leyden. Relating textures and fabrics, we discovered the basic principles of kinematic analysis in plastically deformed rocks. Through mapping of the relevant field structures, flow analysis in geological formations became possible. Jean-Luc moved to quartz-bearing crustal rocks, and, with Françoise, we remained in our beloved olivine fabrics and mantle formations. As you mentioned, Claude, my next major encounter has been was Jean-Paul Poirier, who stabilized my shaky knowledge in solid-state deformation and whom, in return, I introduced to field geology. Another important encounter has been with Dave Mainprice, who joined our lab in 1982, opening the new field of petrophysics.
By 1975, we started to apply our structural and kinematic approach to ophiolites, our real interest being in the deep structure and dynamics of oceanic ridges. With dedicated students, our journey led us to map over a dozen ophiolites. In Menlo Park, I had been in the field with Bob Coleman who, through the years, resisted with good humor all our ophiolitic fantasies. In 1979, Bob invited Françoise to Oman. Since then, we have never missed a field season in this marvelous ophiolite. With marine geophysicists who visited it, I think here of Doug Toomey, we have progressed, understanding better now the deep structure and dynamics of fast spreading ridges. Ten years ago, Peter Kelemen was inoculated with the Oman virus. In spite of uneven cooperation, Peter took the initiative of this nomination, finding the words to obtain it. Nice of you, Peter, and thanks.
My last words are to say how proud I am to receive the Hess Medal, sharing Harry Hess’s interest in oceanic ridges and following his approach. Among Hess’s more outstanding contributions, I wish to mention one, which remains central to our lab activity. In 1964, very soon after the discovery of seismic anisotropy in the mantle under oceans, but before any experiment on olivine slip systems and flow in peridotites, he had the right intuition, ascribing anisotropy to olivine-dominated mantle flow. With such a flair, no wonder Harry Hess was able to trace enemy submarines during World War II, finishing with the rank of Rear Admiral!
—ADOLPHE NICOLAS, USTL Montpellier, France