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
It is a pleasure and an honor to receive the 2009 AGU N. L. Bowen Award, jointly with my longtime friend and collaborator, Tim Holland. First, I would like to thank Mike Brown for the kind words in his citation, and also for his strong support of us and our work over many years now.
It is interesting to try and piece together how one comes to be what one is and do what one does. Of course, there have been many small influences as well as a few large ones. In addition to Tim, I would like to single out and thank Steve Richardson and Ian Carmichael, both mentors and exemplars as scientists and people. Steve was my Ph.D. supervisor at Oxford, and Ian was my boss in a year teaching at University of California, Berkeley in my first position out of Oxford. It was Steve who suggested I get involved with equilibrium thermodynamics, seeing that it was the way forward in metamorphic petrology, even though he knew little about how to go about it himself. I had little formal chemistry, but my voyage had started. I had no computer programming skills either, so I taught myself those too.
I would not be standing here were it not for Tim Holland. Neither of us would have dreamt at our first discussions at a meeting in London in the early 1980s that it would lead to such a long-standing, and certainly ongoing, collaboration. He has a great ability to see the big picture in what is needed for furthering understanding of rocks. His skill at bringing together and making consistent the huge volume of disparate thermodynamic data is difficult to comprehend. My peculiar interest has been in writing general software that therefore means that users can do what calculations they want. It is gratifying and humbling to realize that our work has had the impact that it has, and to see the way that it is used to throw light on geological processes. Thank you again for the Bowen Award.—Roger Powell, University of Melbourne, Melbourne, Victoria, Australia