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9 April 2012
Pliegue de Viernes? No, pero es una roca ígnea de México
I got an email a few weeks back from Moritz K., a PhD student at the Universidad Nacional Autónoma de México (UNAM) in Querétaro. He wanted to offer up a potential Friday fold. Here’s what he had to say: I wanted to send you a couple of pictures of folds I took in my PhD field area in southern Mexico in a tonalitic/dioritic, strongly banded sequence in the Totoltepec pluton …
1 March 2012
Sea Point Migmatite
Callan visits the Sea Point migmatite, a contact between intrusive granite and older metasedimentary rocks, along the west coast of South Africa near Cape Town. His guide? None other than AGU Blogosphere blogger Evelyn Mervine of Georneys!
18 February 2012
The xenobomb
Callan shows off a new sample from Texas, a peridotite xenolith launched into the air from a maar volcanic eruption, slathered in a layer of basalt. With full intent to coin a neologism, he dubs it a “xenobomb.”
11 February 2012
A campus underlain by porphyritic andesite
The campus of the University of Texas at El Paso is a beautiful place. You can look south into Mexico, a scant half mile away. It’s got rocky hills rising up between buildings and between stadiums (stadia?), and a utterly unique campus architecture based on the Himalayan nation of Bhutan. Here’s a look at the rocks beneath the university… The main rock type is a porphyritic andesite – probably a …
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 …
2 November 2011
The Ottertail Pluton
After the awesome outcrops and pavements of strained metaconglomerates from the Quetico / Wabigoon subprovince boundaries of the Superior Craton, my pre-GSA field trip visited the most charmingly-named magma chamber I’ve ever seen, the cuddly-sounding Ottertail Pluton. This is an Algoman-type pluton which is discordant to tonalite-composition gneisses in the area. As with the Giants Range Batholith that we saw near Virginia, Minnesota, the Ottertail Pluton shows lots of cool …
13 October 2011
Superior Craton trip, stop 1
The first stop on our pre-GSA field trip to the subprovince boundaries of the Superior Craton was a place just north of Virginia, Minnesota, where the Mesabi Iron Ranges are mined (same Proterozoic banded iron formations that were portrayed as the backdrop of the mining activity depicted in the film North Country). The pull-off is locally known (to geologists) as “Confusion Hill,” but marked on the roadside sign as the …
28 September 2011
Roadside wonders of Route 287
Northern Colorado’s route 287 connects Fort Collins, Colorado with Laramie, Wyoming. Along its length, it displays roadcuts into Archean-aged basement complex. Two of these outcrops are featured in this post: one metamorphic (mostly), and a second igneous (mostly), with some intriguing polka-dotted plutons.
29 October 2010
Geology of the Richmond area field trip
On Saturday, after a fruitful 24 hours at the VCCS Science Peer Conference, my colleague Pete Berquist (of Thomas Nelson Community College) and I led a field trip to examine the geology of the Richmond, Virginia, area. We were joined by seven of our VCCS science-teaching colleagues and author Lisa Starr, a speaker at the conference. We started off by driving down to Belle Isle, an island located on the …
13 October 2010
Photos from Virginia Geological Field Conference
For the second year in a row, more exotic travel plans meant that I wasn’t able to attend the superb Virginia Geological Field Conference. I see that they have now posted some photos on the group’s Facebook page, so go check them out to see what we both missed last weekend. Here’s a taste: Sheared meta-conglomerate: Metamorphosed mantle (?) xenoliths:
Callan Bentley is an assistant professor of geology at Northern Virginia Community College in Annandale, Virginia. He is particularly interested in structural geology and the evolution of the Appalachian mountain belt. Callan draws cartoons and writes for EARTH magazine. He lives in Washington, D.C.
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