You are browsing the archive for November 2011 - Mountain Beltway.
30 November 2011
Continental Drift vs. continental drift
I got this e-mail this morning from a geology colleague. I’ve despecified it and made it gender-neutral: I have a silly question about word usage and I’d love to hear your opinion. Today I overhead [a biologist colleague] talking about continental drift, and I cringed. S/he used it in context with continents moving apart and how that can alter gene populations. I shudder whenever I hear my students use conti …
28 November 2011
Those could be pillows
More pillow-like structures, seen in the Catoctin Formation, on the west side of the Blue Ridge Parkway about ten miles south of Interstate 64. Mini Sharpie for scale – what do you think? They don’t seem to be as strongly fracture-controlled as the Stony Man area “pillows.” But dang, they sure are small… Read the context here, and then asses this new outcrop for likeliness of pillowhood.
25 November 2011
Belated Friday fold: isoclinal Canadian granitoids
Sorry to be late with this – I think that’s the first time I’ve forgotten to post a Friday fold. Blame it on the tryptophan.
22 November 2011
On our way up Compton Peak the other day, my field crew spotted some fibrous growths of ice growing up and out of the ground (perpendicular to the surface of the mountain): (Joe’s hand lens for scale.) The fibrous habit made me think of asbestos, and then I wondered whether the different shapes of ice crystals reflect different mineralogical arrangements of the H and O atoms, and if they are …
21 November 2011
Compton Peak columns
Callan and three students visit a world-class outcrop of columnar jointing in Shenandoah National Park.
18 November 2011
Friday fold: mafic metavolcanics
Okay – in spite of numerous distractions (see every other post so far this week), it’s time to return to the pre-GSA Minneapolis structural geology field trip. Our final stop of the second day in the field was a series of folded up mafic metavolcanics. I’ve got some photographs of them. These mafic volcanics were strained in a relatively incompetent (weak) fashion between two more competent (stiff) gneiss domes in …
17 November 2011
Shear zone in basement complex
Callan visits a new outcrop of highly-sheared rocks in the basement complex of Virginia’s Blue Ridge province.
16 November 2011
Labradorite is mineral du jour
Other members of the geoblogosphere have been posting brief image-heavy missives on labradorite over the past 24 hours. Collectively, they remind me that I’ve got a backlog of photos from the Adirondacks of upstate New York to share. Here are a few scans of cut and polished cobbles of the anorthosite from the Adirondack Massif, including bluish crystals of labradorite. What I find most lovely about these, though, is not …
Vesicle-rich layering in Catoctin Formation
I saw this boulder lining a garden this past weekend down in Nellysford, Virginia, in the scenic valley of the Rockfish River draining the eastern slope of the Blue Ridge. It’s a piece of the Neoproterozoic-aged Catoctin Formation, a series of lava flows and associated rocks that erupted on the breakup of the early supercontinent Rodinia and the subsequent opening of the Iapetus Ocean basin. The white “polka dots” are …
15 November 2011
Happening on campus, right now: