11 July 2016

Kilometer to millimeter: 4 GigaPans to zoom in on Lewisian gneiss

Posted by Callan Bentley

I’m in the North-West Highlands of Scotland, enjoying spectacular geology and less-than-spectacular weather.

I’ve been fairly productive on the GigaPan front, regardless, nipping outdoors when the weather permits to shoot outcrops and landscapes.

One set I’m particularly pleased with is this suite of four images. They show the Archean-aged Lewisian gneiss, the oldest rock unit in the North-West Highlands, as exposed on a beachside outcrop east of Durness, Sutherland. The largest feature in the first GigaPan is about a kilometer across (entire field of view). Then the second GigaPan is a zoomed-in subset of the first, and the third is a subset of the second, and the fourth is the most zoomed-in of all, a detailed look at a region of the third. The smallest features to be discerned in the last one (mineral grains) are a fraction of millimeter across. Thus, the whole “nested” suite visualizes this place over six orders of magnitude.

In the first, you can see the beach, nearby glacial erratics, as well as some features of coastal geomorphology:
Link GigaPan by Callan Bentley

Now we’re down on the beach, checking out the wall-like sweep of outcrop. Can you find three examples of boudinage?
Link GigaPan by Callan Bentley

Here’s my favorite example of boudinage from the site, located about in the middle of the previous image. Here, you can see it’s a “double” layer of amphibolite that’s been stretched. How would you characterize the boudin ends?
Link GigaPan by Callan Bentley

Finally, we can examine very small scale features associated with the “stern” of the boudin, and the boudin neck in its “wake”. In particular, you can see the “fish mouth” shape to the boudin’s end, and see that it’s “mouth” is full of pegmatite – crystallized evidence of the fluid rich low-pressure zone the formed here when the amphibolite layer separated into chunks.
Link GigaPan by Callan Bentley

Whether you’re more into the geomorphology or the petrology (or the structural geology!), there’s something in this quartet to hold your attention. I hope you enjoy exploring them.