Posts Tagged ‘garnets’

Hard to believe, but this is my 100th post.   I thought about doing something serious, but honestly, let’s just go with what has been successful for me: garnets throughout my geology career

Garnets in plane light from the Northeast Kingdom of Vermont (BA research):

ERG-25b from the Cow Mountain region of Vermont; garnet inclusions are clearly at an angle to the dominant biotite-muscovite foliation in the rock

Garnet back-scattered electrons (BSE) image from the Connecticut portion of the Bronson HIll terrane (MS research):

BSE image of 99ERG07c

Girl Scouts participating in a Rocks Rock badge workshop (Western Kentucky University, 2002).   We ran the workshop in conjunction with both the Campus Girl Scout troop & the Geology Club the year I taught at Western.

Juniors (4th-5th graders) examining a garnet schist for the rock ID portion of their badge

Wavelength dispersive X-ray spectroscopy (WDS) images from a sample from Payer Land in northeast Greenland (or the PhD project I didn’t end up working on):

WDS mapping of 438965. Garnets are green in the Fe map, blue in the Mg map, and very light in the CP.

In-situ picture of the rocks I did work on for my PhD from Alp de Confin in Switzerland:

bimodal garnet sample that contains kyanite (hard to see without direct sunlight in these samples) from the Adula Nappe

Outcrop photo from a 2007 Vassar field trip to Gore Mt in New York:

amphibole-pyroxene-garnet-plagioclase wall in the upper quarry at the Gore Mt mine

When I taught at the University of Pittsburgh at Johnstown, I started blogging.   At that time I started posting about photomicrographs, including one post about the “jellybean” mylonite from Payer Land.   Hmm, mylonites & garnets together 🙂

Garnet "fish" from the jellybean mylonite.

I started this blog when I moved from UPJ to Gustavus in the summer of 2010.  Over the course of the year, I posted several times during the year about garnets, but the most memorable to me is my summary of the 2010 GSA session in Colorado entitled “Garnet and Its Use in Unraveling Metamorphic and Tectonic Processes”.   Since I didn’t have any pictures to post the first time around, let me just say that garnet research is alive, well, and going in a multitude of directions according to that session.

And last summer I moved back to the Boston area.   Because I’ve only been teaching physical geology & solar system since moving, garnets haven’t come up much in conversation here recently.   In fact, my only garnet-related post was my submission to AW #43 earlier this week.   I obviously need to work on that!

pen & ink drawing of garnet gneiss from Best (1983)

So that’s a 100 posts.   Let’s hope I pick up the pace a bit, add a few more garnets, and hit 200 in less than 18 months 🙂

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I’ve been trying to mix in some culture to my Jterm class on Iceland.   The 2nd Thursday of the class, we watched a few TV shows & an Icelandic movie (all available instantly on Netflix, in case you’re interested):

  • Anthony Bourdain, “No Reservations” Collection 1, Episode 2: Iceland — for some reason they filmed this in Iceland in the winter, so it was an American’s view on non-tourist season Iceland; long & short of it: Icelanders drink quite a bit, like to weight-lift, and eat things that completely grossed out my students
  • “Destination Truth” Season 2, Episode 12: Issie & Icelandic Elves — this was a bit over the top on the “ghost-hunting” side, but gave some decent background on cultural beliefs in Iceland
  • our Icelandic movie (with subtitles) was “Jar City” & is based on the book of the same name by Baltasar Kormakur; long & short of it: Icelanders eat icky things (this was actually worse than Bourdain!), Icelanders seem to know who you’re talking about even if you just use first names, there is an Icelandic genetic database & few enough people live in the country that weird connections can be made, and the Icelandic prison system seems fairly lax

On the third Thursday of the month, we gathered in my house to cook some traditional Icelandic dishes.   There was a strong push due to the TV-watching of the previous week to go vegetarian, so I managed to cobble together a set of non-meat dishes.   The main resource I found was a cooking blog entitled Icelandic cooking, recipes, and food.   What we ended up making:


making the flatbread

Emily rolls out the flatbread

Dustin had the job of pricking all of the flatbread

after a few, Dustin got creative 🙂

the flatbread was cooked in my cast iron pan (no fat / oil / Pam used) instead of directly on the cooktop due to the fact I have an electric stove.   The flatbread was not the most flavorful item, but it did a good job at sopping up the pickled cabbage juice & the soup.

pickled cabbage (front) & boiling the rutabagas (back) on the stove

the only hard part with the “veggies” was figuring out how to chop & peel the rutabaga.

after quartering the cooking & cooled potatoes, Beth & Emily wait for Travis to finish prepping the sugar + butter

waiting for the sugar to brown before adding the butter for the potatoes

Travis stirring the potatoes in to caramelized them... still ended up with clumps of butter-sugar

of the “lunch” portion, the potatoes were probably the best thing.

sitting down to lunch (CW: Beth's hands, Sam, Dustin, Amy, (Travis), Emily)

what the food looked like cooked

after lunch, we made two sets of cookies + rice pudding.   The rice pudding was too bland for the crowd, but Siggi’s cookies were well appreciated.   The snails could have used icing according to my class and then they would have been like cinnamon rolls.

Siggi's cookies - which supposedly will last several months, but were gone by the time the snails came out of the oven

the snails have to go in the fridge for an hour before you can bake them, so we watched part of the NOVA: The Vikings while waiting.

sprawled out in the living room half of my 1st floor - note the grand piano

cinnamon snails (box containing hartshorn showed up after they were in the oven!)

the students were wonderful about cleaning up after the cooking, with Amy taking over the dishwashing corner.

trying to clean up after using a number of my pans & bowls

all of the non-geology students got a huge laugh out of Sam whipping out his handlens to look at my genuine Gore Mt garnet cheeseboard:

Sam proving that he has a future in geology

All in all, it was a good day.   Everyone claimed to be stuffed by the time they tumbled back out into the freezing cold.   Hopefully all the butter gave us a bit of padding to survive the negative temperatures 🙂

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Ann’s Musing on Geology & Other Things is hosting the Accretionary Wedge #29: What geological features about the area you call “home” do you love? and what do you not like? Its a busy time at the end of the semester, but I knew immediately how I would answer this question.

I’ve only recently moved to St. Peter in order to teach for a year at Gustavus College.   Previous to Minnesota, I’ve lived in a variety of places and in my mind they all can be categorized either as “flat” or as “hilly.”   The flat places I’ve landed have all been located on sedimentary rocks & have involved at least a several hour drive to reach a garnet-bearing metamorphic rock.   But some of the hilly places have also been a few hours from garnet-grade rocks.   My ideal “home” would have garnet-bearing rocks either underfoot or within a 30 minute drive and some form of topographic relief greater than a few 100 meters.   Such as:

Alp de Confin--1000 m above the nearest town--with both pelitic & mafic eclogites to ooh & ahh over

However, I currently live on glacial till next to a river valley that cuts down into dolomite & sandstone.   Ok, the erratics have garnet in them occasionally, but that’s not the local bedrock.   Things I can appreciate here, though?   Its not dead flat.   The till has a fairly nice hummocky topography to it.

GoogleMaps terrain map of the area east of St. Peter

I can also get to high grade metamorphic rocks in a few hours, which is almost close enough to drive to during a lab period.   Actually, the gneisses are along the same river that flows through town, so technically I think I could canoe upriver to get to garnets.   Would probably take a while to get there though…

Figure 2 from Schmitz et al. (2006)

I also appreciate the fact that I live within the listening range of Minnesota public radio that has a very diverse & eclectic selection of classical music on their playlist.   But that’s the pianist in me speaking 🙂

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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.)

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