2015 James B. Macelwane Medal Winner
Paul Cassak, Bethany List Ehlmann, Colette L. Heald, Matt Jackson, and Kate Maher were awarded the 2015 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2015 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding early career scientist.”
Matt Jackson reinvigorated the type of mantle geochemistry studies pioneered by his Ph.D. adviser Stan Hart through a combination of analytical advances and a focus on -global-scale issues as revealed by extraordinarily fine details of the chemistry of ocean island volcanic rocks.
For his Ph.D., Matt perfected in situ analyses of the strontium isotopic composition of melt inclusions protected within early–crystallizing minerals in oceanic basalts. His results showed beyond doubt that the mantle source of Samoan lavas contains a component of recycled continental crust carried by the deep mantle plume that feeds Samoan hot spot volcanism. Matt, with student Rita Cabral, provided definitive evidence for the presence of recycled sediment in the mantle through their discovery of mass independently fractionated sulfur isotopic composition in basalts from the island of Mangaia. These data confirm a role for recycled sediment but also show that the sediment involved was at Earth’s surface over 2.4 billion years ago. Placing time constraints on the transit time of subducted material through the mantle has been an elusive goal for decades. Matt, working with colleague Rajdeep Dasgupta, showed that mantle compositional variation as reflected in basalt composition is not just expressed in a few obscure trace elements but instead reflects general major element compositional variation in the mantle. As such, the compositional variability has consequences for mantle dynamics because of the contribution of composition to rheology, density, and radiogenic heat production. Matt’s discoveries thus provide a major step forward in the information needed to better understand the forces driving the dynamics of Earth’s interior.
Another of his contributions is a series of papers that attempt to define the characteristics of the hypothetical primitive mantle. Matt first suggested that the high helium-3 mantle source, which most associate with primitive undegassed mantle, has some chemical and isotope characteristics inconsistent with traditional models that invoke chondritic relative abundances of the refractory lithophile elements in the bulk Earth. Matt then matched his model for the “not-so-primitive” primitive mantle to the compositional characteristics of major flood basalt provinces to suggest that the largest volcanic events on Earth sample a mantle reservoir created by differentiation events that accompanied Earth formation.
Matt’s work has dramatically impacted our understanding of the composition of Earth’s interior, the processes accompanying Earth formation that drove initial differentiation, and the longer-term consequences of continent formation and crustal recycling through plate tectonics in creating the Earth we know today.
—Richard Carlson, Carnegie Institution for Science, Washington, D. C.
Thank you, Rick, for your generous citation. And thanks to the cadre of supporters who contributed to my nomination. This really provides an opportunity to thank some of the people who have inspired me over the years.
In my high school days in Montana, Dave Mogk gave me the opportunity to pack his rocks around in the Beartooth Mountains, and I was hooked on geology. Thus primed, I took an introductory geology course from Jeff Park during my freshman year in college. I loved it. Interactions with other folks at Yale—Jay Ague, Karl Turekian, and Brian Skinner—convinced me that I had chosen the right major. Phil Ihinger introduced me to research, and I will forever be thankful for his enthusiasm and the time he invested in shaping my thinking about hot spot volcanoes.
The Woods Hole Oceanographic Institution–Massachusetts Institute of Technology Joint Program was a terrific place to explore hot spot volcanism, so I signed up for 5 years with Stan Hart. I couldn’t have chosen a better adviser and mentor, and he set a wonderful example for how one should mentor students. Nobu Shimizu and Mark Kurz were unofficial thesis advisers and geochemical coconspirators: many ideas were born during conversations in their labs.
A postdoc at Carnegie can only be described as “geochemical paradise.” Rick Carlson was supportive of exploring a lot of neat ideas, and I am lucky to have his mentorship. Rick, Steve Shirey, and Erik Hauri opened up Pandora’s box—unlimited geochemical resources and facilities—and I will always be grateful.
Al Hofmann has been omnipresent in my short career: He’s a gentleman and keeps me on the straight and narrow. Janne Blichert-Toft, Jurek Blusztajn, and Josh Curtice were generous with time and resources when I had no lab, and I am forever indebted.
My graduate and undergraduate students—my academic family—have inspired me to be a better teacher and mentor. In particular, I thank Rita Cabral, Ellie Price, and Drew Reinhard. Your ideas and hard work are the reason I am here today.
My grandfather, a bricklayer and a cowboy, taught me the value of a hard day’s work. I owe a lot to the example he set for me and to the support that I received from my parents, brother, and sister. This medal should really be presented to my wife, Anna, who is infinitely patient and has been my closest friend and my strongest supporter. Thank you, Anna.
—Matt Jackson, University of California, Santa Barbara