Tim Holland and Roger Powell received the 2009 Norman L. Bowen Award at the 2009 AGU Fall Meeting, held 14–18 December in San Francisco, Calif. The award recognizes outstanding contributions to volcanology, geochemistry, or petrology.
Tim Holland and Roger Powell receive the 2009 AGU N. L. Bowen Award for an outstanding contribution to petrology and geochemistry—the result of an ongoing collaboration begun in the early 1980s—that has changed the way we carry out quantitative phase equilibria studies. A quantitative understanding of chemical reactions among minerals, fluids, and melts requires accurate representation of their thermodynamic properties, making a compilation of these properties one of the most important data sets in petrology and geochemistry. The Holland and Powell collaboration has produced the most complete data set of thermodynamic properties of end-members of the phases required to perform calculations on the conditions of formation of rocks and their interactions with fluids and melts. The data set is internally consistent, meaning that all of the available information has been appraised and combined statistically (in a least squares sense), yielding uncertainties and correlations. This allows uncertainties on the calculated results to be obtained—an important element of the Holland and Powell approach. However, quantitative phase equilibria studies require more than just a statistical optimization of the thermodynamic properties gleaned from various sources (experimental, calorimetric, etc.), and Holland and Powell have developed formulations for appropriate equations of state, thermodynamic models to treat nonideal mixing properties, ways to estimate thermodynamic properties, and improvements to some classic nonideal formulations to expand their domain of validity. For example, a critical contribution has been estimation of the mixing properties of complex phases such as the chlorites, the amphiboles, and Na-K dominated melts. In turn, this has enabled phase equilibria calculations to be made for a wide range of rock and domain compositions.
Although the responsibilities of Holland and Powell within their collaboration are clearly defined and complementary, the body of work recognized by this award would not have been possible without the collaboration. Their collaboration has produced 35 papers, of which 19 are authored by Holland and Powell or Powell and Holland. Six papers explain the basis for the internally consistent thermodynamic data set, describe methods to use the data set for various calculations, and provide software to enable users to undertake these calculations for particular rock and domain compositions. Additional papers describe the ever more sophisticated activity-composition models. Furthermore, a thermodynamic data set must evolve or its usefulness will diminish. Holland and Powell have been indefatigable over the past quarter century in increasing the number of entries in the data set, refining the quality of the data and the activity-composition models, and improving their software packages, as well as making it all available free via the World Wide Web.
Given the complex nature of phase equilibria calculations, the provision of “industry standard” programs—AX and THERMOCALC—was critical to enabling all of us to undertake these calculations with minimum training. AX is a program that takes mineral analyses and calculates the activities of the mineral end-members useful for thermodynamic computations. THERMOCALC is a thermodynamic calculation software package for addressing mineral equilibria problems that may be used to undertake a wide range of phase diagram calculations, including P–T projections; P–T, P–X, and T–X pseudosections; compatibility diagrams; and µ–µdiagrams. Phase diagram computations for defined bulk and domain compositions made possible by THERMOCALC have enabled researchers throughout the world to make advances in understanding the thermal evolution and the burial/exhumation history of orogenic belts.
The variety of applications of the Holland and Powell “tools” is beyond belief, and the work cited for this award has pervaded our community from low-temperature geochemistry to mineral deposits geology and from high-pressure metamorphic rocks to crustal melting. Please congratulate the 2009 Bowen awardees, Tim Holland and Roger Powell.—Michael Brown, University of Maryland, College Park
I would like to say a big thank you to AGU, in particular to Alex Halliday and the Volcanology, Geochemistry, and Petrology (VGP) group, for the honor of being granted the Bowen Award jointly with Roger Powell. It came as a great surprise (and a delight)—particularly cheering was the mention of it as a “midcareer” recognition! Thank you, Mike, for your kind words on our behalf, in your citation, and particularly for the way you have supported and encouraged us in our work over the years.
I would like to take the opportunity to thank several individuals among many who have been significant in my geological career. It was Steve Richardson, a bright and gifted lecturer at Oxford, who inspired me in metamorphic petrology, particularly that eclogites and Alpine geology could be so fascinating, and who taught me that thermodynamics was a powerful tool in understanding them. Ron Oxburgh showed me that fieldwork was an indispensable part of metamorphic petrology, particularly in making painstaking observations in structural geology. It was in Chicago, as a postdoc with that most superb of all experimental petrologists, Bob Newton, that I learned to trust in thermodynamic calculations after finding, by direct experiment, that they could be relied upon.
But, most important, I owe my biggest debt to Roger Powell, whom I met at a Geological Society meeting in London in the early 1980s and found that we shared a mutual enthusiasm for thermodynamics and petrology. Roger’s abilities as a computer programmer are legendary, and I have learned more than I could acknowledge here from his skills. It has been a real pleasure to work with him over the years, and it is for these, and his role in them, that I am very pleased to accept this Bowen Award for 2009.—Tim Holland, University of Cambridge, Cambridge, UK