For the past three months, I have almost retraced my footsteps. I started out in January and February at UC Berkeley, where I did my undergrad, and then, last week, I went back to Harvard, where I got my PhD, but this time to give the Agassiz lecture series. I returned to Rice late last Thursday in order to meet up with Dmitri Ionov Friday morning, who was passing through Houston. Dmitri Ionov is one of the world's leading experts on xenoliths, currently at St. Etienee in France. The first time I met Dmitri was back in 1999 during the Goldschmidt conference, which was being held at Harvard. This was also my first Goldschmidt conference, and at the time, I was only 3 years into my PhD. Dmitri crashed at my place and I recall we started talking about potential collaborations. It was at this time I had finally developed Re-Os isotope chemistry and mass spectrometry at Harvard with the help of Qing-zhu Yin and support from Roberta Rudnick and Stein Jacobsen. I had been dating xenoliths mostly from western USA, but after talking to Dmitri, we thought it would be great to measure some xenoliths from Svalbard. I dated 6 xenoliths, but never got around to publishing them after I graduated, and so the data have been sitting in my thesis, forgotten for all these years until Dmitri reminded me of them Friday evening. I have come full circle, in a sense.
One of the things I learned from Dmitri's visit (he also gave an informal talk) is the value of dedicated systematic analysis of xenolith suites. This is something that many of us geochemists don't really do anymore. We tend to focus on some specific isotope system; whatever the flavor of the month seems to be. Instead of fully characterizing our samples - sometimes all we have is a rock powder - we just dive in and measure the isotopic flavor of the month to our hearts' content. I must admit that at times I have been guilty of this, though in my defense, I would say that over the course of many years, I eventually cover all systematics. For example, I come back every year to work on my Sierran xenoliths, with the help of students and post-docts, and over-time, we have developed a very comprehensive set of data. This, however, has taken over 15 years, as I first began working on these rocks as an undergrad at Berkeley with George Brimhall, then as a PhD student with Roberta, and finally as a professor here at Rice. Systematic characterization is tedious and boring, but it is a crucial part of science. One often thinks that great ideas just pop out of people with great minds - the creative genius. However, I think this is rarely the case. Great ideas are borne only when you've done your homework, when you've come to understand your subject to excruciating detail. Because only until you know the current state of your field will you be able to identify a gap in knowledge or an illogical step in the theory. There's no glamor or romance here. It's just hard work in the trenches. But once you've identified a gap, a hole, a problem, and this is something you just can't predict or plan for, you have an idea. If you do the work and persevere, good ideas will naturally come. It rarely works the other way around.
And so, Dmitri presented his work on xenoliths from the Siberian craton. Although he's not finished yet, patterns and interesting observations are already emerging, some of them unexpected, some of them expected, all of them furthering our understanding of cratons. I am sure we will be hearing some very interesting results out of his group in due time.
The second thing I learned while Dmitri was here that people who like xenoliths are probably afflicted with a common disease or genetic disorder. That is, xenoliths are the rara avis of the petrologic world. They're rare, they're exotic. Often times, they are easy to find, if you know where to look. Other times, even if you know where to look, they're quite hard to find, and only those with a good eye can find. I have gone out on a number of xenolith hunting trips and have noticed that some people just have a knack for finding xenoliths. It's something about the subtle shape or color or even texture of a xenolith that may give away its presence. Only those who truly love this pursuit actually find xenoliths consistently.
On Saturday, I took Dmitri out the coastal plain to look at geology, birds, plants, etc. We started off in Galveston, where I showed him the effects of Hurricane Ike and modern beach erosion along the sea-wall. We then headed to the Bolivar Peninsula where we talked about about longshore currents. Just after noon, we stopped at High Island, which sits atop a salt dome, and around its flanks are numerous "donkeys" hard at work sucking oil out of the ground. There weren't many birds around, so we started looking at the plants, and then I learned that Dmitri had an eye for mushrooms. There were mushrooms here, there, everywhere. He said, "hunting mushrooms is like hunting xenoliths". I said, "searching for birds, for me, is like hunting xenoliths". And so we went shrooming, birding, botanicking, and well, foraging. We found a fruiting mulberry tree and then a loquat tree. There's nothing better than just eating fruit directly from the tree.
We ended our day at Anahuac NWR in search of alligators. Dmitri found six of them.
I am now finishing my edits to our long-term climate paper. With a dozen authors, it has been a nightmare trying to accommodate all comments. The worst nightmare is trying to account for all the details so that readers, when the paper is eventually published, don't think we haven't thought deeply about the problem. But if we were to consider every single detail in this paper, which is so broad to begin with, it detracts from the focus of the paper. No reader would be able to get through it. We have to come to some balance, but finding this balance is not easy.
In fact, we were thrown into a frenzy this past week because of the response I got in my main talk at Harvard. I gave the Long-term climate talk on Monday of last week. Attendance was large and there were lots of questions in my talk. One professor, in particular, hammered away at me. This was Dan Schrag. I will have to admit that it was difficult for me to keep my composure because Dan just kept coming at me. You will have to ask the audience 1) how I did, 2) whether my message was communicated effectively, and 3) whether they believed anything I had to say. I can't answer any of that for you other than to say that I was still alive and smiling at the end of my talk. In any case, there was one question that caught me off guard. I had presented an equation describing the C budget of exogenic system. This was an equation that I came up with on my own, thinking that the problem wasn't that difficult, so I could figure it out on my own. But one big detail I forgot, which Dan generously pointed out in the middle of my talk, was how the C is partitioned between the atmosphere and ocean. There's nothing worse then getting caught with your pants down, in public. Or at least, that's how I felt at the time. The Harvard crowd is a tough crowd - they make you earn your keep for sure.
Anyway, that night, I emailed all my coauthors, explaining Dan's question. Somehow, we had all overlooked this small, but important point, though I take the blame. Turns out that Tapio Schneider from Caltech, one of my coauthors, happened to be at Harvard at the same time for a workshop on cloud dynamics. He was staying only a few blocks away from me! So we met up late in the night to discuss. We came to the conclusion that we only had to correct the equation with a factor related to the Revelle effect. I continued the discussions with Jerry Dickens, another coauthor, but also my next door neighbor at Rice. In the end, we made the correction to the equation, but it didn't change our analysis. All was fine. Nevertheless, it is better to understand the problems at a deeper level and we thank Dan for pointing this out.
I ended up giving 5 other talks at Harvard. One was a primer for my main talk. The third talk was on continent formation. The fourth was an informal talk on long-term climate change in Charlie Langmuir's class. The fifth was on the redox state of the deep Earth. The last was on the deep sulfur cycle. Except for the main talk, all other talks were chalkboard talks where audience participation was just as important as me presenting. No powerpoint slides. This is how I like to have scientific discussions. Informal and with chalk.
I left Harvard with a great impression of the department. I had discussions with Rick O'Connell, Sujoy Mukhopadhyay, Charlie Langmuir, Stein Jacobsen, Adam Dziewonski, Miaki Ishii, John Shaw, Peter Huybers, Jerry Mitrovica, Shichun Huang, Allison Gale, Muriel Laubier, Steve Turner, David Johnston, Andy Knoll, Francis MacDonald and many students. Miaki also had me over for a very nice dinner with Jim Rice, Renata Dmowska and her students. Everyone seems to be doing such interesting work. Allie sent me back with a porphyritic trachyte and a skarn from crestmore! It was good to see Steve, a former Rice alum, doing well. I also left behind a project on Pb-He with Shichun Huang, which is turning out, as we speak, to be a fascinating project. And on the last day, we heard that Harvard library was having a booksale, and apparently, many of J. B. Thompson's books were on sale, believe it or not, for 1 dollar a piece. I bought as much as I could fit into a big box to carry back on the plane to Houston. The prize for me was Marland Billings's book Structural Geology. It was signed by Billings and dedicated to Thompson himself. I doubt anyone would care about this, but for me, it means a lot and I just couldn't see this book go to waste.
I am now back at Rice, trying to get back into gear. Things have been moving fast, possibly a little too fast for me to keep up with. One of the things that has evolved rapidly is our work on sulfur. Monica reduced her S data on the Franciscan eclogites and lunar soils (the latter is Emanuelle Albalat's project), and one of the things Monica noticed was a good correlation between Fe and S in these retrograded eclogites. There may be a good reason for this, but that's Monica's work, so I won't discuss it here. But because of this, I went back to take a look at whether my S isotopes in the Sierran garnet pyroxenites that I measured in February in Berkeley correlated with Fe. There's of course no logical connection between Monica's eclogites and the Sierran garnet pyroxenites; they are, after all, formed in fundamentally different environments and by different processes. But what the heck, let's just check. Sure enough, there is a striking correlation of S isotopes (del34S) with FeO content! I am not sure what exactly this means, but I suspect it's very important. First of all, the low FeO guys are the most primitive cumulates and also the most deep-seated cumulates. They have mantle-like S isotopic compositions. The high FeO ones are cumulates from more evolved magmas and most likely are mid to lower crustal cumulates. They have quite positive S isotopic compositions, indicating a contribution from crustal sulfate, e.g., oxidized sulfur. And let me tell you one more thing. The high FeO pyroxenites are the cumulates that must form to drive the calc-alkaline differentiation trend in the Sierras. The dots are already connecting in my head.
There are stories to be told in rocks.
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