metamorphic rocks
khannula | July 6, 2009One 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…
khannula | May 30, 2009I made a promise to myself that every month, I would at least look through the abstracts on my RSS feeds and note interesting articles that I wanted to find time to read. So now it's May 30, and I'd better do it before the June issues come out.
So... articles in the May issue of Geology that look interesting:
Extensional tectonics: Extension rates, crustal melting, and core complex dynamics. Metamorphic core complexes are made up of metamorphic and igneous rocks that have been brought nearer to the surface by continental extension. They're characterized by mylonites that separate the hotter,…
khannula | May 20, 2009I have a confession to make. My favorite rocks are flaky. Really flaky.
Phyllites are the metamorphic rock that gets left out of intro geology labs. They're kind of like slates, in that they break into slabs. But they're shiny like schists. The crystals are too small to see with the naked eye - well, except for the big ones, which are about the size of pin-head (at least in my rocks).
They're easy to break with a chisel. They require a lot of squinting and experience to identify their minerals.
And they're gorgeous under a microscope.
I just saw a really neat set of photos of phyllites on…
khannula | April 15, 2009The cores of mountain belts formed by continental collisions often contain metamorphic rocks, formed when sediments were buried in the collision and transformed by heat and pressure.
But the heat and pressure don't happen simultaneously - rocks can be buried (and increase in pressure) much faster than they can heat up. When the rocks are not allowed to heat up significantly, this process can create blueschists, the high pressure/low temperature metamorphic rocks formed in subduction zones. In continental collisions, subduction stops, and the metamorphic rocks sit around at depth, heating up…
khannula | April 13, 2009My reviewers commenters on yesterday's post on chocolate chip cookie deformation had some great points. (Some of them also seem to have been very hungry. For those who want me to experiment more, and to get to analyze the results: looks like I've got something that I can promise once the Donors Choose challenge rolls around.)
Key criticism #1, from DDeden:
First the cookies puffed up, and then they collapsed. While they puffed up, their surface area increased [No, it decreased!], so the cookie crust was pulled apart. When the cookies collapsed, the surface area decreased again [No, it…
khannula | March 4, 2009There has been a lot of cool stuff posted while I was getting this blog set up. From my Google Reader shared items:
Exotic rocks. There's an art exhibit in Oakland, California, that includes metamorphic rocks from Maine. Why? Because the schists sound like xylophone keys when they're struck. I knew there was a reason why I liked hitting metamorphic rocks with my hammer...
Fermi paradox meets the timescale. Why haven't we been visited by intelligent life? Well, if we had been visited by intelligent life sometime during Earth's 4.6-billion-year history, odds are that there wasn't any…