All of My Faults Are Stress Related

One of the tricky things to convey about rocks, especially in a lecture or in a textbook, is the way geologists can see such different things at different scales – from thousands of kilometers to a few micrometers – and the way that all those observations fit together to understanding the processes that shape the Earth. Static photos, whether on paper or projected onto a screen or on a computer, don’t convey all the information that one can get from a single outcrop – standing back from it, climbing up close to it, crawling over it with a hand lens. (And that’s leaving out the perspective of putting that outcrop into a regional map, or cutting a thin section and examining it with a microscope or an SEM.)

Which is why gigapans – high resolution panoramas that can be explored at a variety of different scales (like the ones created by Ron Schott and Ian Stimpson) – are so cool. (Ian’s working on a resource that would allow mobility-impaired students to explore an outcrop using gigapans – I can’t wait to see the final product.)

I’ve been admiring Ron and Ian’s work for a while, but last night on Twitter, Ron asked an intriguing question: what about microscopic images that could use a similar treatment – nanogigapans? I work with microscopic textures in deformed metamorphic rocks, and have literally glued photos together to make panoramas of thin section tectures, and YES, I want to play with things like this!


One example: here’s a back-scatter electron image of a metamorphic rock from Vermont. It’s got intriguing metamorphic minerals at a bunch of different scales. For instance, the garnets are big enough to see with a hand lens, though they look a little beat up:

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(Gt = garnet, Bt = biotite, Qtz = quartz, Crd = cordierite)

Between the garnets, though, all sorts of weird things are going on. Zoom in on the edge of one of those garnets, and here’s what you see:

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(Gt = garnet, Crd = cordierite, Si = sillimanite, St = staurolite)

There’s cordierite and some very fine sillimanite in the space between the two sections of garnet, and within them, perfectly shaped micron-scale staurolite crystals. The garnet looks like there’s been new growth on the rim, too (both texturally – those are nice sharp crystal faces – and chemically).

And I have no clue what’s going on. (For people who don’t know those minerals, they are all contain iron, magnesium, aluminum, silicon, and oxygen, and it looks as though some of the minerals have partially reacted to form other ones. But what reaction, exactly, has been captured here? Why did it happen? These are the features that tell stories in metamorphic rocks, but this story has been too cryptic for me so far.) This is a rock that I’ve set aside for nearly a decade. But nano-gigapans could help look at it – if I wanted to make careful observations on an SEM in order to test some ideas about what’s going on, I could use something like that to share my observations with other people. (As it stands, if I had enough time on an SEM, I could make those observations, but I would need to share them with words and a few representative pictures.)

There are other sorts of features that would make great nano-gigapans. Mylonites under an optical microscope. Cataclasites, which have broken grains at all sorts of different scales. Micro-folds, with compositional layering and cleavage. Rocks with multiple foliations. Rocks that were experimentally melted and deformed at the same time. (And those are just structural geology examples. I bet volcanic rocks would look pretty cool, too.)

Anyone else have examples of things they would like to see?

Comments

  1. #1 Lab Lemming
    July 6, 2009

    I think many new SEMs come with auto mapping features, so it should be possible to set up an overnight or afternoon run and have the machine do its deed.

    Of course, the software and stage management needed to retrofit an old instrument all cost $$.

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