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6 December 2012

More xenoliths from the Boulder Batholith

The week before last, I showed you the Boulder Batholith, as it crops out southeast of Butte, Montana. Today, I’ll share a few more photos of xenoliths (or perhaps microgranular mafic enclaves?) from that same outcrop: Man, I miss that old Swiss Army knife. The damned security actors at Calgary Airport confiscated it last summer. 🙁

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24 November 2012

Rock Cycle III: Igneous → Sedimentary

The Boulder Batholith outside of Butte, Montana, is actively weathering, and shedding off grus. In the third installment of the Transitions of the Rock Cycle series, we watch an igneous rock turn to sediment.

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28 October 2012

Geology and wine in northern Virginia, part I: the Blue Ridge

Callan attends the Geological Society of Washington’s fall field trip, examining the relationship between grape-growing and the underlying geology of two provinces in northern Virginia: the Blue Ridge and the Valley & Ridge. With GSW compatriots, Callan visits Hume Vineyards in the Blue Ridge basement complex and North Mountain Winery in the Shenandoah Valley. This is part I.

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26 June 2012

Leopard rock of the Yaak

After our “pre-honeymoon” sojourn to the Canadian Rockies last summer, Lily and I returned to the U.S. via Porthill, and then drove over to a place I’ve been wanting to visit for a long time: Yaak, Montana. Yaak (or “the Yaak“) is way up in the Kootenai National Forest, in way-way-way-northwesternmost Montana. We camped out nearby, and then in the morning, we rolled into “town,” and had breakfast (“make your …

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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 …

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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!

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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.”

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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 …

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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 …

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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 …

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