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16 April 2021
Friday fold: Colorado cluster
Friday means folds –
This week, we head to the Colorado Rockies for a butterfly-like presentation of a ptygmaticly folded granite dike within biotite schist.
8 November 2019
Friday fold: Rist Canyon cobble
From a creek bed in northern Colorado, the Friday fold distorts foliation in early Proterozoic quartzofeldspathic gneiss, peppered with small almandine garnets.
24 August 2018
Friday fold: Gneiss from Arapaho Pass, Colorado
It’s Friday, and I have another guest Friday fold to share: This one is from my Denver friend Greg Willis, who tells me it’s from near Arapaho Pass, near where we rain-hiked. Ahhhh, yes – a singularly soggy hike up in the Colorado Rockies. I remember it well, and it looks like Greg had better weather on this jaunt! Happy Friday to all!
24 November 2017
Friday fold: Idaho Springs Fm. amphibolite
Here’s a guest Friday fold from reader Carl Brink: Carl tells me that this is: Precambrian Amphibolite schist float boulder from the Idaho Springs Formation in Rist Canyon west of Fort Collins, Colorado. Knife is 2.25 inches long. Thanks for sharing, Carl!
16 September 2016
Friday fold: Centenary migmatite
The Friday fold is a guest submission from Bill Burton, who took the photo of these lovely ptygmatic folds in migmatite in a national park on the 100th anniversary of the founding of the Park Service.
2 September 2015
The Liar’s Club, by Mary Karr
I just finished this excellent memoir by Mary Karr, mostly about her childhood, mostly in east Texas. It’s not explicitly geological but it does feature an oil town economy and a hurricane, as well as some consideration of the Rocky Mountain Front Range in Colorado. I didn’t read it out of any illusions it would be geological, though – I selected it from the library shelf more from a desire …
29 July 2015
Positively-weathering volcanic dike near Granby, Colorado
My friend Barbara am Ende sent along this lovely image of a dike in Colorado: Here’s the site. You can see the dike in Google Earth. Dikes are fractures, filled with molten rock, which then cools and solidifies, sealing the crack shut. In this case, once it got uplifted to Earth’s surface and exposed, the dike rock is tougher (more resistant to weathering) that the older rock it cut across. …
13 February 2015
Friday fold: Ptygmatic Irving Fm., Colorado
Another one from Kim: Kim says: Pygmatic folds in the Precambrian Irving Formation. I think this is 1.7 Ga deformation, late in the Yavapai orogeny, which added various arcs in Colorado to North America. Good place to think about strain ellipses in progressive deformation. Zooming in on the best part, and dialing up the contrast a bit: That’s intense! Seriously strained rocks. What fun!
6 February 2015
Friday fold: Ouray Limestone, Colorado
Kim Hannula shares a fold today: Kim says: The rocks folded here mostly the Devonian Ouray Limestone. There’s a fault through the outcrop, and another fault to the left of the photo. Regionally, the faults are mapped as normal faults, mostly with the east (right in photo) side down. Locally, that’s not what I see in this outcrop, which makes this a funky place to look at a fold with …
26 October 2013
Off to GSA
This morning I’m on a flight to Denver, for the 125th anniversary annual meeting of the Geological Society of America. The annual GSA meeting is a special time of year for me, and for many geology professionals across the country. It’s an intense half-week of talks, sharing, learning, networking, hanging out with old friends, meeting new friends, getting inspired, and hopefully inspiring others. It’s a time to mentor our best …