Alfred T. Anderson, Jr. received the Bowen Award, presented by the Volcanology, Geochemistry, and Petrology Section at the 2001 Fall Meeting in San Francisco, California, last December.
“I have the honor and great pleasure of giving the citation for the 2001 Bowen Award to Alfred T. Anderson, Jr. Fred Anderson receives this year’s award for pioneering the use of silicate melt inclusions in phenocrysts of volcanic rocks to determine preeruptive volatile concentrations in magmas and for applying melt inclusion analysis to fundamental problems in volcanology, geochemistry, and petrology. A melt inclusion, typically less than 100 microns across, is a glass droplet completely surrounded by its host crystal, which Fred has successfully argued acts as a pressure vessel, preventing degassing of the trapped melt. Knowledge of the volatile content of magmas, mainly water, carbon dioxide, sulfur species, and chlorine, is fundamental to understanding the dynamics of magmas, mechanisms of explosive volcanic eruptions, gas emissions from active volcanoes, volcanic additions to the atmosphere, and magmatic contributions to hydrothermal ore deposits. Because magmas degas as they ascend and erupt, or crystallize at depth, direct knowledge of preeruptive volatile contents long eluded petrologists faced with extracting this information from either rock samples or analyses of volcanic gases.
“Fred’s first paper on dissolved volatiles in melt inclusions was published nearly 30 years ago. There followed several more papers in the early 1970s. In those days, Fred was nearly alone in advocating the importance of measuring dissolved volatile concentrations in melt inclusion glasses. Fred and his student David Harris developed equipment for quantitative extraction and analysis of the gas trapped in single melt inclusions. Published in 1984, their results were the first direct measurements of the preeruptive water and CO2 contents of basaltic and andesitic magmas. A more precise method became available in the early 1980s at Caltech with the use of Fourier transform infrared spectroscopy (FTIR) to determine water and CO2 dissolved in silicate glass. Fred recognized the value of the FTIR method and, with student Chris Skirius, analyzed melt inclusions in quartz phenocrysts from the rhyolitic Bishop Tuff, demonstrating the power of analysis of melt inclusions from stratigraphically controlled samples and sparking a revolution in melt inclusion studies of volcanic rocks. The analytical method perfected by Fred and associates is the industry standard today. Fred’s leadership, however, goes well beyond application of an existing tool to an important problem. His general papers on melt inclusions include how to tease data from seemingly intractable samples by rehomogenizing partially crystalline inclusions, diffusive equilibration of inclusions with melt outside their host crystals, boundary layer enrichment of trace elements during crystallization, and use of hourglass inclusions to understand magma ascent rates. Rigorously placing melt inclusions in a petrographic context has been a characteristic of Fred’s approach, which he has recently extended to zoning in quartz revealed by cathodoluminescence imaging.
“Many of Fred’s discoveries of recorders of igneous processes are the result of his characterization of carefully chosen samples, involving exceedingly tedious preparation and manipulation of tiny things, in order to reveal elusive patterns in nature. He has led the field of melt inclusion research because he has noticed things, measured them, and extracted information about processes others would have missed. A prime example is that of hourglass inclusions, named by Fred, which have leaked bubbly melt to the outside of their host phenocrysts. Rather than ignoring hourglasses as irrelevant to preeruptive conditions, he used them to quantify ascent times of vesiculating magma. The emphasis in analysis of volatiles dissolved in melt inclusions has been on preeruptive concentrations. Fred has taken the subject a step further and, with Paul Wallace, has constrained actual volatile content, the amount of exsolved gas at subsurface conditions. This achievement has a profound impact on determining bulk magma properties that affect eruptive style and that can be related to geophysical data on active magmatic systems.
“We are recognizing Fred Anderson for his pioneering work on melt inclusions and his leadership in this burgeoning field, particularly in the last decade. I am compelled to note, however, some of Fred’s other major contributions. Early on, he proposed a fundamental subdivision of anorthosites into sodic and calcic varieties, a distinction that is still an issue in anorthosite petrogenesis. In the early 1970s, he was senior author on a seminal paper on oxygen isotopes in co-existing phases in igneous rocks, their significance for geo-thermometry, and fractionation of isotopes during crystallization differentiation. His 1976 paper, ‘Magma mixing: Petrological process and volcanological tool,’ was ahead of the stampede that recognized that this process, neglected for decades, is a widespread and important factor in understanding the diversity of magmas and many petrographic features of igneous rocks. His publications on Kilauea reveal general processes of crystallization, degassing, recharge, and mixing in a basaltic magma reservoir. Revisiting Fred’s papers the other day, I was reminded of some themes that run from the early 1970s to the present and that were not widely embraced when Fred introduced them, but have since become accepted truths, namely, the value of melt inclusions as recorders of magma and volatile history, the high preeruptive concentrations of water in arc magmas, and the near ubiquity of magma mixing.
“Having studied his papers on Fe-Ti oxides when I was a graduate student, I eventually met Fred Anderson in 1979 on an AGU field trip to the Columbia Plateau. He and Dave Harris were in the seat behind mine in an ancient school bus. Memories of conversations with Fred on the bus are still vivid for me, along with the pain of being squished, for hundreds of miles, into a minimally padded bench seat intended for children. Fred’s visionary thinking and broad insight and his free sharing of his ideas with others came out in those conversations. My experience with this generous man has been typical. A friend wrote, ‘his brilliance is accompanied by the complete lack of ego building nonsense. He involves everyone with his thoughts and hides nothing.’ Those of us privileged to receive a detailed letter from Fred on some aspect of igneous rocks all others have overlooked, but that leads to exciting new research directions, will attest to the accuracy of that statement.
At Chicago, Fred is known for his patience with students and his willingness to give of his time. He and his wife, Caroline, for many years have been ‘Resident Masters’ in a large undergraduate dormitory, on 24-hour call for the well-being of over 100 students. His enthusiasm for education extends to giving seminars for teachers in the Chicago area and leading petrologic tours of building stones of downtown Chicago. On top of this, he makes time to be editor of the Journal of Geology.
“In summing up, I will paraphrase some words by a mutual friend. Fred Anderson’s low-key demeanor belies his exceptional scientific acuity and creativity. His published work is characterized by extraordinary originality and insight. Still, his three-decade effort on melt inclusions stands as a single, unified contribution whose importance cuts across disciplinary boundaries and time, and it is for this in particular that he is receiving the Bowen Award. Nature has given us few precious tools with which to look backward through time in the reconstruction of geological processes. A special genius is often required to recognize one of those tools. In the case of melt inclusions as indicators of preeruption volatile contents of magmas, we have Fred Anderson to thank-first for recognizing the potential of melt inclusions to disclose information, and second for having the perseverance and resourcefulness to prove their value.”—Charles R. Bacon, U.S. Geological Survey, Menlo Park, Calif., USA
“Thanks a lot for your generous words, Charlie! I feel very honored to receive the Bowen Award.
“It is indeed a special pleasure for me, a geologist from the University of Chicago, to receive this award. Bowen was a member of our department for part of his career, and his student Julian Goldsmith founded our modernized department and was its chairman when I joined it in 1968.
“For this response, I thought that perhaps you might like to know how I got started on melt inclusions.
“My dissertation under Rob Hargraves at Princeton was a field and mineralogical study of an anorthosite massif in Quebec. It taught me two things: first, that minerals do not a magma make and; second, that mineral separation is tedious and messy. I tried to use mineral compositions to constrain the composition of the melt from which the anorthosite formed. My effort failed. Not because of me, mind you! Nor of Hargraves. It was only that the mineral/melt partition factors were unknown, so knowing the mineral compositions was of little use in reconstructing the magmatic liquid. Anyway, that is how I justified my failure.
“My frustrations led me to try and determine the mineral/melt partition factors by analyzing volcanic phenocrysts and their host glass or groundmass. First I turned to oxygen isotopes and spent 2 unforgettable years working in Clayton’s lab at Chicago as a postdoc. Clayton allowed me great freedom, and together with his assistant, Tosh Mayeda, we determined the partitioning of oxygen isotopes between basaltic glass and phenocrysts. My wife reminds me that I had collected these rocks during our honeymoon in Hawaii. Well, I never could get my priorities quite right! Anyway, using my anorthosite mineral separation skills, I laboriously separated the crystals and glass using standard, messy methods. Yes, there was life before the electron probe!
“While at Chicago working with Clayton, I met Ian Carmichael, who had come to visit his fellow countryman, Joe Smith. Joe was developing an electron microprobe, the machine that made my mineral separation skills obsolete. I should have panicked, I think. First, my dissertation goal was a failure; second, the skills that I developed were already obsolete! Well, Buddington had told us that this would happen, so at least I was emotionally prepared.
“Carmichael and I had similar goals. We went on a collecting trip to northern California. In the Medicine Lake Highlands we were nearly killed. It happened on a one-track logging road when I rounded a sharp bend right into the path of a loaded oncoming logging truck. It is a matter of physics that they are incapable of stopping quickly. There was no choice, and I swerved our tiny Volkswagen bug into the forest; Ian’s huge inertia almost flung him out of the car. The dust settled. Somehow the truck had missed us.
“While I was still a postdoc working with Clayton, I went to the Jemez volcanic field, New Mexico. There I met Bob Smith, Roy Bailey, Ray Wilcox, and Herb Shaw. This convinced me to accept a job with the USGS. It was a dream for me to be associated with these people and their colleagues, especially Dave Wones.
“Wones gave me excellent criticism, both severe and friendly, which helped me navigate the Survey internal review process. Some of you can attest to how useful this would be! I also learned a very valuable lesson about experimental lab work. Dave assigned me the task of making wustite. The idea was to pass hot hydrogen gas over finely ground magnetite. After a number of explosions, both Dave and I decided that experimental work was not for me. I appreciated Dave’s magnificent mentoring, and I was devastated when he later died in a car wreck.
“At the Survey, I was assigned an office space in the corner of the lab of Paul Barton. Paul also was very generous in helping me. Ed Roedder was a few steps away. It was impossible not to become interested in inclusions with Roedder close by.
“Thus I began to analyze melt inclusions, especially for their volatile content. With the electron probe I could directly measure both chlorine and sulfur. Water was a guess.
“For my mineral separation work at the Survey, I used facilities at the Navy Yard, where a number of USGS scientists had their offices and labs. There I met Paul Greenland and Dave Gottfried, and we had great fun thinking out loud together. It was a marvelous experience. Gottfried was a walking library, and he told me about Larsen’s work on magma mixing. Sadly, Gottfried had a stroke and died a few years ago. I learned a lot from Dave, and I miss him.
“A pivotal experience occurred after I presented one of my first studies of volatiles in melt inclusions at an AGU meeting in Washington, D.C. After my talk, Pat Hurley came up to me and congratulated me on an important study. He urged me to keep focusing on the volatiles. We had not met previously, but thanks to Gottfried, I knew who he was.
It gave me a great boost to get Hurley’s compliment. From then on, volatiles were the main focus.
“During my 2 years at the USGS I enjoyed a brief stay at the Hawaiian Volcano Observatory. There I worked with Tom Wright and Dick Fiske. They had been struggling with the compositional variations of Kilauean basalts and had decided that magma mixing was part of the story. Magma mixing was not one of Bowen’s favorite petrologic processes, but I had three votes for it: Larsen, Wilcox, and Wright. That was enough for me. I interpreted melt inclusion compositions in terms of magma mixing. This is still going on, perhaps wrongly.
“Both the University of Chicago and my colleagues there have been enormously supportive of me, both funding-wise and intellectually. Nowadays people may chuckle when I tell them that my start-up package was a $6K Zeiss microscope. But that was in 1968, and it is still my primary research tool.
“At Chicago, I came to rely increasingly on students, and I want to emphasize their extremely valuable contributions. I will single out just a few. First there were Dave Harris and Emi Ito, with whom I began to explore the evidence of water in magmatic melts revealed by melt inclusions. Harris built a machine that yielded some of the earliest direct determinations of water in melt inclusions.
“Christine Skirius came along at the time Stolper and Newman were developing the spectroscopic method for analyzing water and carbon dioxide in silicate glasses. Chris developed the procedures for applying it to glass inclusions in phenocrysts. This gave us the ability to estimate the depth of origin of melt inclusions and their host crystals to a resolution of about 200 meters. As the Bishop Tuff magma body was at least 3000 meters thick, this is a very helpful resolution in terms of tracking the movement of the crystals in the magma.
“Another Chicago student, Fangqiong Lu, worked with Andy Davis and me to analyze trace elements in melt inclusions using the Chicago ion microprobe. Initially, I tried to discourage Lu from doing some of the work she did, like analyzing phenocrysts, which I thought Hildreth had beaten to death. She went ahead and discovered the reverse zoning of sanidine phenocrysts and inclusions of anomalous magnetites in some quartz phenocrysts. Andy Davis pointed out that the barium and strontium in melt inclusions varied in a way that is incompatible with magma mixing. Our results were so troubling that it took us three rewrites, two rounds of reviews, and almost a decade to get them published. Eventually our interpretation retreated away from magma mixing to a Bowenesque concept of crystallization and sinking of crystals.
“Among the other students who helped me with our Bishop work are five undergraduates: Nate Brown, Dave Lorenz, Paulina Mundkowski, Aaron Borowski, Bret Peppard, and Joe Dufek. Their work was phenomenal and essential.
“I was very lucky to have Paul Wallace come and join me as a postdoc working on the Bishop magma. Paul made a magnificent contribution. I think that the work he did to establish the presence of exsolved gas in preeruptive magma changes our view of rhyolitic magmas fundamentally. Without his help, I know that I would not be standing here today. Paul, thank you very much.
“I want to express a very special thanks to Wes Hildreth. Wes generously shared some samples with us at an early stage. He very importantly and generously continued to keep us abreast of field relations that he and Colin Wilson were developing. Wes often reminded me that our study was limited to only a few samples. This is still true. But he led us to the best samples, and our progress depended on that. Best is better than most. We can argue that later.
“I want to especially thank Charlie Bacon for his continuing encouragement. Charlie went out of his way to mention his interest in my work on several important occasions, and he has been steadfast in his scrutiny of my manuscripts. He always makes me think, a lot!
“Before ending, I want to share a funny story about Paul Wallace and myself. In addition to our joint work on the Bishop Tuff, we also worked on Kilauean basalts. In connection with that we had a collecting trip to Hawaii. When in Hawaii I always take an hour or so to check out the hundreds of Hawaiian shirts in Hilo Hattie’s huge store. Yes, Chicago does have days when Hawaiian shirts are in style!
I got myself a new shirt. I wore it the next day, much to Paul’s amazement and our mutual delight. He had earlier gotten exactly the same shirt for himself! It was then that I realized how much we really do think alike!
“I want to end by thanking my wife, Caroline, and our two children, Eric and Doug. With me they made many spring and summer trips on I-80 to northern California. We got to know practically all the campsites and playgrounds between Chicago and Mount Shasta. We so often ended up in the mountains that my boys identified summer with snow. I had a lot of fun on these field trips, and I am especially glad that my family could be with me then and that my wife is here today.
“I thank you all very much. What a great feeling I have! Thank you again.”—Alfred T. Anderson, University of Chicago, Illinois, USA