You are browsing the archive for metamorphism Archives - AGU Blogosphere.
16 April 2021
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.
29 January 2021
I have two Friday folds for you today, both by geovisualizers who contributed to the 2019 Geological Society of America Pardee Symposium on Geoscience Communication in Phoenix, Arizona: The first is a painting by talented geoartist Emma Theresa Jude, showing a fold at Caithness, Scotland. The fold in question can be seen at the site of Figure 5 of this paper. I love Emma’s art. What other lovely folds have you …
24 July 2020
Exploring his new digs in Charlottesville, Callan is introduced to a large exposure of phyllite at a dam’s spillway. The foliation there is folded in many ways. Share in a dozen field photos of the site…
7 February 2020
The Friday fold shows disharmonic crumpling in marbles of the Boyden Cave Root Pendant in California’s Sierra Nevada. The GigaPan image displayed is part of the digital legacy of Ron Schott, who passed away a year and a half ago.
24 January 2020
A roadside boulder in the Bronx shows folded gneissic banding. It’s another guest-submitted Friday fold!
13 December 2019
A pre-Fall Meeting field trip to the coast of northern California yields rare sights of garnet-bearing blueschist, plus eclogite, some pillow basalts, birds, waves, wind, and a lot of rain.
8 November 2019
From a creek bed in northern Colorado, the Friday fold distorts foliation in early Proterozoic quartzofeldspathic gneiss, peppered with small almandine garnets.
9 August 2019
The Friday fold erupted out of a volcano, completing the second part of its two stage cooling history, then later got folded and metamorphosed. It was found atop a high cliff near the northern Newfoundland town of St. Anthony.
3 May 2019
When a dike is subjected to shear, how does it deform? A guest Friday fold from Darrel Cowan of the University of Washington teaches a nice little lesson. Join the field trip in Monarch Canyon of Death Valley National Park…
5 April 2019
The Friday fold is on the north shore of Angel Island, San Francisco Bay, showing blueschist-facies high-contrast metalliferous cherts with folds on many scales.
6 February 2019
We saw last week how glaciation carved out a valley in Scotland called Glen Roy. As the glacier ground into the landscape, it liberated tremendous numbers of sedimentary particles from the bedrock, which is composed of Dalradian metamorphic rocks (mainly porphyroblastic schist in my observation). Then once that now-U-shaped valley had been deglaciated, a new glacier dammed it, making a lake that rose and filled the declivity of Glen Roy, …
2 November 2018
The Friday fold comes to us from Corsica via University of Washington structural geologist Darrel Cowan. It’s a marble that’s been folded *twice!*
26 October 2018
It’s been a very Billy-Goaty week for me. Three times since Sunday afternoon, I’ve taken people to the Billy Goat Trail’s “A” loop in C&O Canal National Historical Park. On Tuesday and Thursday, it was my NOVA Physical Geology students. On Sunday, though, it was just my son and me. Good news! He helped me discover a new fold by exploring some new rock outcrops and climbing on them. He …
22 June 2018
Another guest Friday fold (keep ’em coming, folks!) – This time from Eric Pyle of James Madison University: This is a weathered outcrop of the Connemara Marble in western Ireland, about a meter wide. Thanks for sharing, Eric!
18 May 2018
The Friday fold takes us to the French Mediterranean island of Corsica. Are you ready to dip into the blueschist facies in search of sheath folds?
13 April 2018
The Friday fold is on display in a rock garden outside the Department of Earth and Environmental Sciences at the University of Kentucky.
18 October 2017
The 2017 Virginia Geological Field Conference had a heavy arkose infusion. Meet some of these feldspar-rich Neoproterozoic sediments of the Lynchburg Group.
24 February 2017
For your Friday fold this week, I present to you a 3D model of a sample of kinked schist from Beavertail State Park, Rhode Island. Spin it right round, baby: This is another sample from the structural geology collection of Carol Simpson and Declan De Paor.
17 February 2017
Garnetiferous beds from the aureole of the Leinster Granite east of Baltinglass, County Wicklow, Ireland (Declan De Paor’s senior thesis mapping area, 1973). Manganese-rich metasediments. The prominent ‘elasticas’ or fan folds (folds with a negative inter-limb angle) are superimposed on isoclinal folds: so the brownish layer at top and bottom are the same, though that is not obvious from the image. This is a sample from the structural geology collection …
27 January 2017
The Friday fold can be found along the Fall Zone, where crystalline metaigneous rocks of the Piedmont meet the gently sloping strata of the Atlantic Coastal Plain. Contemplate their high metamorphic grade and their tight folding, and imagine the mighty mountains that once rose on this spot.