Live-blogging is not something I could have managed during GSA, since I’m usually taking notes for myself during the good talks (and trying to catch up with “brilliant thoughts” at other times), but I’m going to try summarizing the ridiculously good session that occurred on the final Wednesday of GSA at the beginning of the month in Denver.
I will note that I did attend other sessions at GSA, but most of the time there were only one or two “amazing” talks (e.g. Jane Selverstone’s talk on the microdiamonds found in the eastern Swiss Alps). The session Wednesday had me writing & thinking the entire time–it was that good.
The session title was “Garnet and Its Use in Unraveling Metamorphic and Tectonic Processes” and was organized by Ethan Baxter, Mark Caddick, and Jay Ague. Talks were held in the morning and the afternoon was dedicated to the poster session in a rapidly emptying hall (last day at GSA generally has attendance issues). The wonderful thing about this session was that it look at a rather variety of ways that garnet could be used within metamorphic rocks and did a great job of bringing people together from different areas of our sub-disciple to talk & think about different ways to look our rocks. And the organizers did a very good job of picking appropriate speakers and ordering the talks, so that there was a flow over the course of the morning.
As stated above, the last day of GSA is frequently a bit sparse attendance-wise. (In 2001 in Boston I had a poster the final morning of GSA and various people appeared with suitcases in tow.) And since the topic wasn’t exactly “sexy” (unless your a metamorphic petrologist!), I personally was thinking the room would be half to quarter empty by the time my own talk occurred at 11.30. Yeah, that was erroneous logic. Turns out the session was full for the entire morning. There were people standing for every talk and new chairs had even appeared during one break. Lots and lots of people were interested in garnet on that day
For me, the greatest benefit of the talks was all of the different moments when I thought to myself, “oh, I need to consider that” or “maybe we should do that with these rocks?” Let me give you a short run-down of the high points (and yes, if you’re not a petrologist, this is probably the time to move on to something else):
- Frank Spear (invited talk) opened the session by asking whether we have to only consider grain boundaries as our effective bulk composition (i.e. what’s actually reacting to form new minerals / grow ones already present), which would lead to some very complicated math… It would also mean that grain size has a direct impact on what kind of garnet zonation patterns are found within rocks. Thought-provoking, but also a bit scary from the re-invention side.
- Thomas Lapen (disclaimer: Lukas Baumgartner is also one of my co-authors as well as Lapen’s) discussed differences in what stage of growth of garnet Sm-Nd vs. Lu-Hf actually records
- Ethan Baxter runs a TIMS lab and his talk gave a good update as to what they could or couldn’t manage to date at this point (garnet can’t be dated in situ like zircon or monazite, you have to actually extract it, which puts limitations on what the resolution of the ages are); for instance, they dated 12 different regions within a 6 cm garnet to get the growth history (episodic not continual)
- Ashley Russell (student of John Valley’s) presented material on using oxygen isotopes within garnet to address the issue of fluid presence / absence during growth within a high pressure / high temperature (HP/HT) region in the Czech Republic
- I was happy to see Greg Dumond’s talk simply because he had complicated pressure-temperature diagrams (which is where mine are headed towards)
- Bill Carlson (also invited talk) returned the session to the theoretical (this is what Spear & Carlson do better than almost anyone else) and discussed why not only large cations, but also small cations, diffuse slower than moderate-sized ions. He ended with a teaser that this may be true for divalent cations (e.g. Mg, Mn2+, Fe2+, Ca), but not for trivalent cations, which he’ll discuss at AGU
- Sumit Chakraborty looked at diffusion rates of elements within garnet comparing the various calibrations that have been made–especially of calcium within garnet–and argued that you need to go with end-members (grossular vs. andratite vs. uvarite) instead of simply Ca vs. Mg vs. Fe. This talk & several others resulted in several serious discussions with members of the audience, but the long & short of the matter is that we need to understand how fast things diffuse & what controls them in order to model the process in real rocks. This theme would also come to the front in Baumgartner’s poster (volumetric differences between garnet end-members) and Caddick’s modeling of diffusion vs. growth and the resultant patterns in garnet (also a poster)
- I’m not reviewing my own talk…
Of the posters, I spent most of my time talking with Mark Caddick and the implications of his model (he has a paper out in November’s issue of the Journal of Petrology if you can 1) get behind the paywall and 2) are interested). Baumgartner’s poster had a rather large crowd in front of it the entire length of the poster session and it was a veritable “who’s who” of metamorphic petrology.
(I want to apologize if I misconstrued anyone’s research–I’m reading my hasty notes in trying to summarize this and may have missed some blatant point or re-interpreted something to suit my own research needs. And if I didn’t cover your talk, it doesn’t mean it didn’t influence me–just means that I had to pick & choose for length.)