Saturday, September 25, 2010

Deformation in the Desert field trip 2007

Today I read a post by Anne over at Highly Allochthonous on some major flooding she witnessed on her trip to Alice Springs in 2000. This reminded me of my one trip to Alice Springs (it wasn’t flooding when I was there). Since my trip pre-dates my starting this blog, I thought I’d share with you the write-up I did for friends and family.

The below was written on 14 July 2007.

I just returned from the "Deformation in the Desert" Conference, held in Alice Springs, Northern Territory, Australia, sponsored by the Geological Society of Australia Specialist Group in Tectonics and Structural Geology.

The highlight of the conference was the five-day pre-conference field trip (photos below) which looked at the Palaeozoic tectonothermal evolution of the Irindina Province of the eastern Arunta Region. The trip started out in Alice Springs, headed south through the Heavitree Quartzite Gap (the ridge is a wall just south of town, the rocks steeply dipping, with a couple of gaps where the "rivers" cut through--though how you can call a waterless stream course a river, I don't know). From there we took the sealed (read: "paved" if you happen to speak American) road east and thence north into the Strangways and Hearts Range metamorphic complex. As soon as we turned north we were on dirt roads, and stayed on them for most of the rest of the trip.

Each day saw us rise before the sun so as to have breakfast before hitting the road. We stopped at many interesting outcrops, and at each stop the trip leader would show us the map, remind us of the geology at the last stop, tell us about the current stop, and then let us know what the next stop held in store for us. By the end of the trip I had a good understanding of the geology of the region! There were just about 40 people on the trip, including the catering group. They took good care of us, feeding us well (even us fussy eaters with special dietary requirements), and provided "swags" for each of us--a sleeping bag, mattress, pillow and water-proof canvas cover for the lot. We slept each night on the sands of (dry) creek beds, under the stars. There was no rain, nor any clouds (nor would any have been expected), making the camp sites safe enough, though in rainy seasons (once every several years) flash floods would be a problem (see above mentioned post by Anne).

The conference itself was held in Alice Springs and, unlike the conference I attended in Melbourne the year before, had only one track of sessions, so there was never a problem deciding which talk to attend--we simply attended all of them! Most of the talks were interesting, quite a number were very, very well presented, and only one was bad.

Stop 1: Ross River Gorge

Stop 2: Bitter Springs Formation, view to the east

Stop 3 Arumba Sandstone

Stop 3B Ross River syncline

Stop 5 Strangways Metamorphic Complex, with lovely garnets (800C, 6Kbars)

Stop 6: fold in mylonite zone

Stop 7: Argument Gorge, mylonite zone

Stop 7: stretching lineations on mylonite surface (this was the first time I'd seen a good exposure of a mylonite, and suddenly everything I'd been reading about them made so much more sense!

Stop 9: garnet rich boudin (some exceed 1.5 cm)--I liked this stop!

Stop 9, garnet showing sense of shear

Stop 9: mafic layer + garnet sand

Stop 10: near Lizzy creek, view north to the Hearts Range

Stop 11: an old mica mine in a pegmatite dike. Note huge sheets of mica that still litter the ground

Stop 12 Bruna Granitic Gneiss--view to the east

Stop 13: Mt. Ruby garnet zone in amphibolite from the Hearts Range Metaigneous complex

Stop 14: Indiana Granite Hill. We climbed this one.
Us, at the top of Indiana Granite Hill (stop 14)

Stop 16: Huckitta Creek, Intense strain zone
Stop 16: folding
Stop 16: more of the intense strain

Stop 17: Large fold
Stop 17: large deformed pegmatite dike to the right of the above fold. Note boudins in the layers of the fold limb

Stop 19: fold in gneiss
Stop 19: view to the east

Stop 20: Bruna granitic gneiss:
Stop 20 garnet-rich metapelite:

Stop 20: a mylonite zone in gneiss. Note that the mylonite contains garnet, the gneiss does not.
Stop 21: a mica and garnet rich layer in gneiss:
Stop 21: folding in gneiss:

There was also a mid-conference filed trip--a one day trip to the west of Alice Springs, driving on sealed roads the entire time (in large tourist-style air conditioned busses). The person who sat next to me happened to have been from Tasmania, and graduated years ago from UTAS before moving to the mainland to do geology there. Needless to say we had some very pleasant discussions about the uni we both attended.
The rocks on the mid-confluence trip weren't as pretty (they hadn't been sufficiently deformed to show the pretty folding or nice minerals that we saw on the five day trip), but they were still nice, and we actually saw a few waterholes (one 30 feet deep) which stay wet year-round, despite the fact that the rest of the river course is dry.
Mid conference trip stop 1: looking west at the Arumba Sandstone
Mid-conference trip, stop 2 Elery water hole (and folding of the rocks)

Mid-conference trip Stop 3: anticline in Heavitree quartzite
Mid-conference trip Stop 3 Heavitree quartzite repeated above thrust fault
Mid Conference trip stop 3: Ormiston Gorge (with some nice folding showing)
Mid Conference trip stop 4: Mt. Saunders
Mid conference trip, stop 5: The waterhole at Glen Hellen Gorge

Note: all above photo captions were taken straight from the file names of the photo, I didn't have to look for my field notes from the trip today--I had the sense to give the photos meaningful names, including stop numbers and sometimes even P/T data promptly after taking them.

Sunday, September 19, 2010

word of the day

While reading a journal article* today I encountered a word I’d not noticed before: Aulacogen. The first mention in the article was "Continental extension that fails to lead to ocean opening and subsequently undergoes compression can occur at failed arms of ocean basins (aulacogens) and at intracontinental settings isolated from plate margins".

A quick check shows that there are 220 articles in scopus with that term used. (For comparison—“continental extension” yields 4,780 articles in scopus.) This is a somewhat specialized term, so I don’t feel bad that I missed noticing it (if, indeed, it has even been mentioned in the articles and textbooks I’ve read hitherto). Thus far my research has focused on the results of compression, be it deformation or metamorphism, rather than extension, so there would be no reason for me to think about what happens when extension starts and then stops before an ocean basin forms.

*Cawood, P. A., Kröner, A., Collins, W. J., Kusky, T. M., Mooney, W. D. and Windley, B. F. (2009). Accretionary orogens through Earth history. Geological Society Special Publication: 1-36.

Saturday, September 18, 2010

two days of playing tourist amongst more than a month of travel

When I first scheduled my late summer conference travel schedule it sounded like a good idea to attend first the IMA conference in Budapest, go from there to Vienna for a short-course on the Kinetics of Geological Materials, from there to the European Textile forum, and from there to the Italian SIMP conference. Indeed, I very much enjoyed each of them, in very different ways. However, after 3.5 weeks of non-stop travel and major time commitments happening each day (and, for the last couple of weeks very, very limited internet access), I find that this week has been one of recovery. I’ve accomplished the urgent tasks on my to-do list, but mostly I’m catching up on personal correspondence and basic housekeeping tasks. Now it is time to start blogging once again.
I will start with sharing photos from my weekend as a tourist. Since I had two whole days off between the Budapest conference and the start of the short course in Vienna I decided that it would make more sense to play tourist than to fly home and then head right back out again. Having many fond memories of a salt-mine tour I took with my father when I was a child of five years of age, I decided that I would take the train up to Salzburg and check out the mine again, now that I’m a geologist and will have a better understanding of what I am seeing. However, when I asked my mother she didn’t remember which of mines we went to all those years ago. Since there is more than one to choose from, I made the decision between them the easy way and went with the one recommended by my host—I choose to do CouchSurfing that weekend, so that I’d meet local people rather than staying on my own in a hotel room.
Since the weather in Budapest had been extremely hot and sunny, I was delighted with the cool grey clouds and gentle rain in the Salzburg area. Here is the view from the mine entrance in Hallein:

It was so very wonderful to be surrounded by mountains again—I have missed them so!
The rock in the mine has clearly undergone some deformation looking at the layers on the wall:

Being a tourist mine they have some old-style ore-carts full of rocks ready to haul away:

And a lovely display case of pretty samples from the mine:

Occasionally we could look up into a shaft reaching up to other levels:

They have a large lake in the mine that was used for mining—they put in fresh water, it dissolved salt from the rock, and they extracted and evaporated the brine. This silly statue has a slow, steady, drip of salt brine from the pump, and we were encouraged to taste it if we liked. Yup. Salty.

Alas, my photos from the rat trip across the lake didn’t come out. They do that part accompanied with eerie mood music and a light show. Made for an interesting effect, but felt like a scene from a fantasy movie, and not a real salt mine. This wall is from the far side of the lake:

Without a doubt the highlight of the trip was the slide between levels. This first photo is from the top of the shorter, warm-up slide:

And this photo is from the bottom of the longer slide:

It was so much fun that I climbed the stairs and went down the slide a second time. I can remember a slide from when I was a child, but I sure don’t remember it being this long or this fast. On the other hand, I do remember it as being a long way to fall sidewards if you weren’t wedged in between two grown-ups. This slide doesn’t have a place to fall to the side.

After leaving the mine I decided to walk the 3 km back down the hill to the town, rather than taking a bus, and I’m glad I did—I found a trail so that I didn’t even have to walk along the road.

And finally, the view back up the hill from the town:

I think that my early childhood visit to this mine, and the box of salt rocks that my dad bought me then, was a factor in my growing up to become a geologist. I loved my tour as a child, and found it just as delightful now. There is something comforting about having an entire mountain over my head. In hopes of encouraging the tradition I bought a box of salt rocks to send back to my nieces. This purchase was done with my sister’s encouragement, of course—she was too little to do the mine tour when we were there all those years ago, but she used to enjoy playing with (and licking) my salt-rocks.

Sunday, September 5, 2010

A short course in Vienna

As I type (Saturday morning 4 Sept 2010) this I am sitting on a train, traveling from Vienna to Zurich, where I will change trains for my trip home from my latest adventures. The plan, when I scheduled the travel was to enjoy the mountain views out the window, but the clouds are low, so while I can tell that there are hills out there, I can’t tell if they rise up into mountains. However, as we passed Salzburg I did get glimpses of the peaks as the clouds parted, so the time spent on the train will have been worth it for that view, if no others come along. With luck I will get a chance to post this once I’m home, since I don’t expect to have any internet access at all next week.
After leaving Budapest and the IMA conference I traveled first to Salzburg, where I spent the weekend playing tourist and visiting the salt mine at Hallein (photos from that trip to follow in another post), and then doubled back to Vienna, where I attended a short-course on the Kinetics of Geologic Materials.
The course turned out to be as useful as I’d hoped. I signed up for it in large part because, having had such a long break between taking my last math course and enrolling in my PhD program, I’d found that when reading papers I had a tendency to skip over formulas and jump to the next descriptive part of the text. In an effort to overcome this habit I have checked out text books on the thermodynamics behind the chemical reactions which form minerals, and, to some extent, they helped. However, I still felt like I was missing something in my understanding of the math/formulas that one needs to describe what is happening during mineral-forming reactions, and so this course.
There were more than 25 of us who signed up for the course, traveling there from Italy, Germany, Hungary, the Czech Republic, and more. We range in experience from advance undergraduate geology students to post-doctoral researchers. At the end of our course we shared information on our current research in a poster session ( good percentage of us had attended the IMA conference in Budapest), and our specialties range from experimental studies to traditional petrology—from the crystallization of minerals from a melt, to zoning in metamorphic minerals and a number of points in between. One student is even studying the ability of rocks in Hungary to store man-made CO2.
The lectures started with an introduction to thermodynamics—the study of the relationship to the energy of a system to the equilibrium thereof. The common physical example used to illustrate this point is to stand a rectangular block on its narrow end. So long as it is on a flat surface and nothing happens to it, it will happily stand there all day. However, being taller than it is wide, should anything bump into it the block will fall over and land on its broad side. We describe the block standing on its narrow end as “metastable”, because if energy is added (it gets pushed), it will transform to its more stable state of lying on its broad side. Chemical reactions are much the same. Minerals are each stable in a specific range of conditions (pressure, temperature, and composition of the rock itself), but some chemical reactions take more of a “push” to make them happen than others. In these cases the minerals will often exist in conditions during which they are not expected to exist, in which case, like the block standing on its narrow side, they are metastable.
From this simple example the course built up the mathematical framework of how to describe the energy used to “push” the reactions into happening, and how to use published values for that energy to determine for any conditions what minerals will be expected to be stable in an equilibrium situation. We touched on many related topics related to kinetics, including diffusion (how the elements within the minerals move from one location to another so that the chemical reactions will happen), nucleation (the earliest stages of the growth of a new crystal), and the boundaries between grains and/or phases. For most topics presented we also had exercises to work on during the lab hours—using MATLAB to perform calculations on these processes for model (simplified) systems.
All in all the week was a very valuable experience, but train has reached an area where the mountains are visible, so it is time to shut down the computer and enjoy the view.