Professor Emeritus Adolphe Nicolas

Professor Emeritus Adolphe Nicolas

 

Invited talk: Ophiolite diversity (Oman and North-Mirdita), reflects of fast- and slow-spreading ridges.

 

Professor Emeritus Adolphe Nicolas starting with a basic formation in both Physics and Earth Sciences has always shown interest toward the physical modelling of field data and observations, covering the domains of rock deformation and geodynamics. As early as 1968, his small group was working on the physics of rock deformation, mainly ductile deformation of mantle peridotites.
The discovery in 1971 of the principles of kinematic analysis in plastically deformed rocks led to applications to mantle and crust geodynamics, mechanisms of sea-floor spreading as deduced from structural studies in ophiolites: mantle diapirism, melt extraction, magma chambers structure and dynamics, ridge segmentation and tectonics, very high temperature hydrothermal circulation near oceanic ridges and unconventional model of hydrothermal ridge cooling, origin of chromite deposits and guides for prospection. These results are based on systematic field measurements, mostly obtained and shared with the help of his group.
Professor Adolphe Nicolas has published more than 250 papers, most of them in international journals and 8 monographs, the first in 1976 with J.P. Poirier on crystalline plasticity and the second in 1989 on structural studies in ophiolites and dynamics of oceanic ridges. Two smaller books first appeared in french and have been translated in several languages. The first one deals with the principles of structural geology for a graduate level; the second “les montagnes sous la mer” is a presentation for a wide public of oceanic ridges and ophiolites.
He has made several significant discoveries. The most significant has been to establish the principle of kinematic analysis of plastically deformed rocks. The principle of this analysis was presented in 1971 and 1972 and developed in the 1976 monograph. This discovery has made possible to move from the static and descriptive, at the best mechanistic, structural geology of the early 70s, to a more physical and dynamic approach, a significant contribution to global geodynamics. This discovery that was started within his small group has rapidly diffused and is now "common knowledge". Together with his students, he extended this approach to the study of magmatic bodies (granites, gabbros) developing new kinematic principles and, through the systematic mapping of these geological objects, renewing ideas on their origin and modes of emplacement. All achievements have been based on systematic field measurements, followed by lab analysis and physical modelling.
Being able to distinguish asthenospheric flow structures in peridotite and ophiolite massifs from other deformation structures and to analyze their record of mantle flow, he and his colleagues applied these techniques to the study of rifts and oceanic spreading centers. Based on systematic field measurements, in over 25 massifs in the world, several discoveries have been made which were summarized in a well known 1989 monograph.
Among them, one can cite melt extraction mechanisms below ridges, the discovery of mantle diapirs and the modelling of their activity below ridges, the structures and modelling of magma chambers, the role of spreading rate in ophiolitic and oceanic ridges and the origin of chromite deposits in ophiolites, the complexity of fast oceanic ridges tectonics and the microplate filiation of many ophiolites. Recently, a very high temperature hydrothermal alteration in the Oman ophiolite has been discovered, pointing to seawater penetrating up to 1000°C and down to the Moho below fast spreading ridges. As a result of these 20 years of activity in the field of ophiolites, mainly in Oman, new and premonitory views have been developed on how the oceans spread.
After having served for 4 years as counsellor in charge of Earth, Planetary and Environment Sciences at the French Ministry of Research, he collected a new experience mainly in the latter domain and has written for a wide audience, three comprehensive books on the near future of our Planet and its passengers and the future of energy.