- Email: [email protected]
Citation for presentation of the 2008 Houtermans Award to Nicolas Dauphas
Available online at www.sciencedirect.com
Geochimica et Cosmochimica Acta 73 (2009) S13 www.elsevier.com/locate/gca
Awards Ceremony Speech
Citation for presentation of the 2008 Houtermans Award to Nicolas Dauphas It is my great pleasure to introduce a good friend and colleague at the University of Chicago – Nicolas Dauphas – as the recipient of the 2008 Houtermans Medal of the European Association for Geochemistry. The Houtermans Medal recognizes exceptional contributions to geochemistry by a young scientist. The description of the medal defines young as being no more than 35 years of age, which Nicolas meets with about 4 years to spare. With regards to the requirement of exceptional contributions to geochemistry, Nicolas meets those criteria by a similarly large margin. He is exceptional, regardless of age, in the range of topics in which he has already made important contributions. These include, to mention just a few, the age of the Milky Way, the injection and homogenization of short-lived radionuclides into the early solar system, discussions for the dual origin of the earth’s atmosphere, the nature of sedimentary protoliths for rocks from Greenland and Canada dated at greater than 3750 Gyrs, and, my favorite, a study of diffusion-driven kinetic isotope effects in Fe and Ni during formation of Widmansta¨tten patterns in iron meteorites. He is outstanding in terms of the clever formulation and thoroughness of his theoretical modeling studies. And with regards the sine qua non of a great geochemist, Nicholas has been developing and applying extraordinarily precise isotopic measurement methods, most notably in the case of iron isotopes, to study both terrestrial and extraterrestrial materials. And despite Nicolas being much taller and thinner than I am, I cannot imagine a more well rounded geochemist. Rather than subject you to a reading of his already extensive CV, I will use one of his recent single-authored papers – Diffusion-driven kinetic isotope fractionation of Fe and Ni during formation of Widmansta¨tten pattern (2007) as illustrative of the degree of innovation, care in execution and significance of his work. The Widmansta¨tten pattern develops in iron meteorites when the high-temperature Fe–Ni phase taenite enters the taenite + kamacite field as the temperature falls below something of the order of 500–800 °C. Starting more than 40 years ago, the texture and Ni concentration profiles of the Widmansta¨tten pattern have been used to infer the cooling rates of particular iron meteorites to constrain the size and thermal evolution of their parent bodies. But this has not been a straightforward exercise because of complications in the low-temperature
doi:10.1016/j.gca.2009.05.046
phase diagram of Fe–Ni alloys plus impurities, the role of nucleation effects, and the difficulty of measuring diffusion rates at the relevant low temperatures of kamacite exsolution. What Nicolas has added to this problem is the recognition that the small but measurable isotopic fractionations of Fe and Ni between taenite and kamacite are associated with diffusion kinetics and thus provide addition constraints on cooling rates that can overcome the uncertainties associated with earlier approaches. He developed his own numerical model for Fe–Ni diffusion during Widmansta¨tten pattern formation and validated the model, first by comparison to analytical solutions to a simplified version of the problem, and then by showing that he could reproduce previously reported numerical results for the time evolution of Fe and Ni profiles. Having demonstrated the validity of his numerical model, he then allowed for kinetic isotope fractionations by specifying the mass-dependence of the mobility of the Fe and Ni isotopes. This allowed him to make a convincing case that the measured differences in the isotopic composition of Fe (+0.1&) and Ni ( 0.4&) between taenite and kamacite from the iron meteorite Toluca was due to diffusion-driven kinetic isotope fractionation, and that the cooling rate at the time kamacite formed must have been of the order of 50 °C/Ma. I chose the Widmansta¨tten pattern paper to make my point because I have special fondness for diffusion-driven kinetic isotope fractionations. But it is just one of many of Nicolas’ papers that I could have used to show the exceptional quality of his contributions. What I find so impressive is that Nicolas has managed, again and again, to bring a new perspective to a longstanding class of problems. He has developed a distinctive style by combining insightful conceptual formulations with sophisticated isotopic measurements, and when appropriate, carefully done numerical modeling. Please join me in welcoming Nicolas Dauphas as the 2008 Houtermann medalist of the European Association for Geochemistry.
Frank M. Richter Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA E-mail address: [email protected]
Geochimica et Cosmochimica Acta 73 (2009) S13 www.elsevier.com/locate/gca
Awards Ceremony Speech
Citation for presentation of the 2008 Houtermans Award to Nicolas Dauphas It is my great pleasure to introduce a good friend and colleague at the University of Chicago – Nicolas Dauphas – as the recipient of the 2008 Houtermans Medal of the European Association for Geochemistry. The Houtermans Medal recognizes exceptional contributions to geochemistry by a young scientist. The description of the medal defines young as being no more than 35 years of age, which Nicolas meets with about 4 years to spare. With regards to the requirement of exceptional contributions to geochemistry, Nicolas meets those criteria by a similarly large margin. He is exceptional, regardless of age, in the range of topics in which he has already made important contributions. These include, to mention just a few, the age of the Milky Way, the injection and homogenization of short-lived radionuclides into the early solar system, discussions for the dual origin of the earth’s atmosphere, the nature of sedimentary protoliths for rocks from Greenland and Canada dated at greater than 3750 Gyrs, and, my favorite, a study of diffusion-driven kinetic isotope effects in Fe and Ni during formation of Widmansta¨tten patterns in iron meteorites. He is outstanding in terms of the clever formulation and thoroughness of his theoretical modeling studies. And with regards the sine qua non of a great geochemist, Nicholas has been developing and applying extraordinarily precise isotopic measurement methods, most notably in the case of iron isotopes, to study both terrestrial and extraterrestrial materials. And despite Nicolas being much taller and thinner than I am, I cannot imagine a more well rounded geochemist. Rather than subject you to a reading of his already extensive CV, I will use one of his recent single-authored papers – Diffusion-driven kinetic isotope fractionation of Fe and Ni during formation of Widmansta¨tten pattern (2007) as illustrative of the degree of innovation, care in execution and significance of his work. The Widmansta¨tten pattern develops in iron meteorites when the high-temperature Fe–Ni phase taenite enters the taenite + kamacite field as the temperature falls below something of the order of 500–800 °C. Starting more than 40 years ago, the texture and Ni concentration profiles of the Widmansta¨tten pattern have been used to infer the cooling rates of particular iron meteorites to constrain the size and thermal evolution of their parent bodies. But this has not been a straightforward exercise because of complications in the low-temperature
doi:10.1016/j.gca.2009.05.046
phase diagram of Fe–Ni alloys plus impurities, the role of nucleation effects, and the difficulty of measuring diffusion rates at the relevant low temperatures of kamacite exsolution. What Nicolas has added to this problem is the recognition that the small but measurable isotopic fractionations of Fe and Ni between taenite and kamacite are associated with diffusion kinetics and thus provide addition constraints on cooling rates that can overcome the uncertainties associated with earlier approaches. He developed his own numerical model for Fe–Ni diffusion during Widmansta¨tten pattern formation and validated the model, first by comparison to analytical solutions to a simplified version of the problem, and then by showing that he could reproduce previously reported numerical results for the time evolution of Fe and Ni profiles. Having demonstrated the validity of his numerical model, he then allowed for kinetic isotope fractionations by specifying the mass-dependence of the mobility of the Fe and Ni isotopes. This allowed him to make a convincing case that the measured differences in the isotopic composition of Fe (+0.1&) and Ni ( 0.4&) between taenite and kamacite from the iron meteorite Toluca was due to diffusion-driven kinetic isotope fractionation, and that the cooling rate at the time kamacite formed must have been of the order of 50 °C/Ma. I chose the Widmansta¨tten pattern paper to make my point because I have special fondness for diffusion-driven kinetic isotope fractionations. But it is just one of many of Nicolas’ papers that I could have used to show the exceptional quality of his contributions. What I find so impressive is that Nicolas has managed, again and again, to bring a new perspective to a longstanding class of problems. He has developed a distinctive style by combining insightful conceptual formulations with sophisticated isotopic measurements, and when appropriate, carefully done numerical modeling. Please join me in welcoming Nicolas Dauphas as the 2008 Houtermann medalist of the European Association for Geochemistry.
Frank M. Richter Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA E-mail address: [email protected]