The Peacock Medal, formerly the Past-Presidents' Medal, is awarded to a scientist who has made outstanding contributions to the mineral sciences in Canada. The recipient of the 2014 Peacock Medal is Professor Don Baker of the Department of Earth and Planetary Sciences at McGill University.
Dr Baker is one of the leading experimental igneous petrologists in the world, and has substantially advanced science in his field through the publication of 90 refereed journal articles and other publications that cumulatively have been cited over 2200 times.
Dr Baker first attracted the attention of the igneous petrology community in the 1980s with a series of highly cited experimental studies that investigated the effects of pressure, composition and volatiles on the liquid lines of descent of magmas of mafic to intermediate bulk compositions. In the earliest of these studies, which focused on the volcanic arc environment, he provided the first robust experimental data bearing on the origin and evolution of high alumina basalts at elevated pressures, and showed, contrary to the view prevailing at the time, that these rocks are not necessarily low pressure derivatives of tholeitic magmas. Instead, some may be the products of fractionation of more mafic magmas at substantially higher pressure and, in turn, could have fractionated at lower pressure to form the andesitic lavas, which dominate this environment. In a subsequent paper, he expanded on this work by showing the important role that water plays in determining the path of magma evolution in these systems. Specifically, he demonstrated that, under anhydrous conditions, thermal divides preclude the formation of alkali basalts from tholeiites and andesites from basalts, whereas the presence of small amounts of H2O removes these divides and permits the proposed evolutionary paths. Continuing with this theme, but focusing on the continental rift environment, Don tackled another conventional wisdom, namely that the nepheline-normative trachytes and phonolites, and peralkaline rhyolites, characteristic of this environment, are the products of the fractional crystallization of primitive alkali basalts at mantle depths. In a highly cited paper, he showed, instead, that the genesis of these magmas is better explained by fractionation at shallow depth, where Fe-Ti oxide crystallization is able to drive the alkali basalt magma to high silica concentrations and produce silicic peralkaline magmas.
After working with conventional equilibrium magmatic processes, Dr Baker moved his attention in the late 1980's to non-equilibrium processes, and particularly that of diffusion, understanding of which is essential to interpreting processes such as magma mixing or assimilation. This new direction soon led to several notable successes; including the first experimental demonstration that homogenization of isotopes by diffusion is decoupled from chemical homogenization. This paper was followed by a series of pioneering papers in the early 1990s that elegantly elucidated the role of halogens and water in controlling chemical interdiffusion, showing, for example, that whereas fluorine decreases the activation energy of diffusion, chlorine actually increases it. These papers are the starting point for the work that is currently going on in this active field of research. Recently, Dr Baker has extended his studies of diffusion by combining them with studies of bubble growth in both experimental and natural systems and with numerical models to investigate the effects of diffusion on the compositions of bubbles. This work, impacting as it does on the chemical changes accompanying the exsolution of aqueous fluids from magmas, will find applications in fields as diverse as active volcanology and porphyry/epithermal ore genesis.
Although, as noted above much of his recent research has been concerned with non-equilibrium magmatic processes, Dr Baker has continued to make major contributions to our understanding of equilibrium magmatic processes. This work has focused recently on sulphide silicate equilibria, for which he and his students have produced what may be arguably considered the best empirical model currently available. Finally, we would be remiss to not recognize Dr Baker's work in statistical physics, which includes titles such as The continuum percolation threshold for interpenetrating squares and cubes published in Physical Review E, and Nonlinearlity and multifractality of climate change in the past 420,000 years published in Geophysical Research Letters. These publications speak volumes to the breadth of Dr Baker's interests and his ability to impact not only the relatively large field of igneous petrology and volcanology but also fields well beyond it.
In summary, Don Baker has made seminal contributions to our science and is a very worthy recipient of the 2014 Peacock Medal of the Mineralogical Association of Canada.