Peter Kelemen has integrated geologicobservations with geochemistry, geophysics, thermodynamics and continuum mechanics to reveal unexpected links between the dynamics and evolution of Earth’s crust and upper mantle and unveil a geological solution to carbon sequestration.
Kelemen’s discoveries are sparked by geologic observations. Early on, dunites caught his eye. He saw them as channels through which large volumes of melt had flowed — and reacted. With a quantitative understanding of how they form, he and his colleagues discovered that the formation of melt channels could explain the composition of mid-ocean ridge basalts, the interpretation of U-series disequilibria and strain localization in the mantle. Kelemen’s ideas regarding melt-rock reaction also provided a possible explanation for why the continental crust is andesitic while most primitive melts are basaltic. While melt-rock reaction is a viable hypothesis for the genesis of some continental rock formed at arcs, he realized that the spectrum of crustal formation mechanisms must include those involving primitive basalts. This led him and his colleagues to explore the role of convective instability of lower crust and diapiric upwelling from slabs. His calculations inspired the community to pursue new field work, geochemical analyses and thermodynamic calculations. He took a similar path to invoke a novel model for the formation of oceanic crust at fast spreading centers, inspired by observations of “sill-like” gabbro layers in the Oman ophiolite. He demonstrated that these sills are geochemically isolated, which led to the bold hypothesis that the entire lower crust formed by the injection of sills. Crustal genesis by sill formation remains a leading hypothesis, largely as a result of Kelemen’s innovative work integrating geophysics, thermomechanical models, fabric analyses and cooling rates.
While in Oman, Kelemen became fascinated by remarkable structures in sets of carbonate veins. These observations motivated a multidisciplinary analysis of the carbonation process and an assessment of how much carbon dioxide (CO2) the ophiolite sucks out of the atmosphere today; he realized that with a bit of geoengineering, ophiolite bodies around the world could provide a meaningful CO2 sink.
A hallmark of Kelemen’s work is how he integrates ideas from a broad range of fields, guided by his keen geologic intuition, to relentlessly investigate problems in Earth science. A second hallmark, a willingness to take scientific risks, shows how science can progress in more than incremental steps; as an exemplary recipient of the 2021 Hess Medal, he would make Hess proud.
— Greg Hirth
Brown University
Providence, Rhode Island
— Peter Molnar
University of Colorado Boulder
Boulder, Colorado
Tonight we are here to honor Peter Kelemen, a leader in our field. Peter has led by the single-minded pursuit of a big idea: Virtually everything in VGP is pertinent to or can be explained by reactions between migrating magma and the rocks through which they pass.
I wondered some time ago from where this passion derived. It seems that as a young man, Peter, like many young searchers, went to India and pondered the meaning of life, in Peter's case while doing geological fieldwork. The vision struck while Peter was sitting on an outcrop of mantle peridotite in the Himalayas. There were all these rocks, tens of kilometers thick, with dikes passing through them. How could the magma possibly traverse such long distances without being fundamentally modified by the materials through which they pass? And how could they then not leave a record of their passage?
Armed with this vision, Peter headed to graduate school. Since that time, Peter has investigated melt-rock interaction with amazing breadth and depth, through a combination of careful fieldwork, quantitative chemical modeling, and investigation of the fluid dynamic instabilities associated with migrating magma. He showed us that the ubiquitous "dunite channels" in exposed peridotites were the remnant tracks of migrating magma. This recognition has led to a wide range of subsequent developments in fields that include ophiolite field studies, the fluid dynamics of melt migration, the chemical consequences of melt migration, and U-series disequilibria.
To investigate these problems, Peter was also walking over the ocean crust, and he decided to turn his attention to the physical aspects of its origin by carefully looking at the structures and chemical compositions of the gabbroic layers. This work led to papers that definitively laid to rest competing models for the physical construction of the ocean crust. Through his highly interactive style, Peter has developed far beyond melt-rock interaction. He has related seismic velocity to chemical compositions and identified the physical aspects of delamination of continental lithosphere. He has emerged as a leader of large field programs on land and at sea.
One of the favorite phrases I remember from graduate school is Gil Hanson's comment that "there are no bad problems, only bad scientists." Peter exemplifies the positive aspects of this perspective. It was not necessarily that his vision of mantle-melt interaction was prescient. But Peter pursued this problem with such vigor that he has in many ways redefined our field. It led him to write papers in geophysics, geochemistry, fluid mechanics, seismology, and tectonics, to lead ambitious field programs, to do experiments, and to direct theses in theoretical geodynamics. Out of all these interactions has come a host of scientific advances, new problems to explore beyond melt/rock interaction, and the need for all of us when interpreting our data to consider the consequences of the inevitable reactions that take place during transport.
Friends and colleagues, please welcome Peter Kelemen, a scientist who has redefined the way we think, and one of the most productive and influential contributors to our field in the past five years.
—Charlie Langmuir, Harvard University, Cambridge, Mass.