Naomi Barshi shares this “deskcrop” Friday fold… Naomi says she found this fold: near the Riffelhorn, Gornergrat, above Zermatt, Switzerland. The sample has befriended my other show-off sample of a mantle xenolith from San Quintin, Baja California. Thanks for sharing, Naomi! The xenolith is a nice bonus!
In keeping with the Arizonarific theme of this week’s posts (thanks to my participation in the 2018 Structural Geology and Tectonics Forum), I thought I would wrap up my ‘geology of the Phoenix area‘ posts with a walk I took on my last day there. This was to what Google Maps calls “Hayden Butte,” but … Read more
I collected only a single rock on my summer travels in France and Italy. (Those of you who know me will realize how extraordinary this low number is!) It’s a flow-banded rhyolite from Vulcano, in the Aeolian Islands north of Sicily a few weeks ago. It contains porphyritic vesicular basalt xenoliths. I featured a similar … Read more
My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths. The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). … Read more
My friend and colleague Lauren Michel, the King Family Fellow at the Perot Museum of Nature and Science in Dallas, Texas, sent me this image from her recent trip to Antarctica: (click to enlarge) This is a beautiful example of a mafic igneous sill, probably of the rock known as “dolerite” (or diabase, to us … Read more
On “Border to Beltway”‘s visit to Kilbourne Hole, after we whet our appetite with Hunt’s Hole, Michael finds a xenobomb. Ernie and Boris look on with envy: A “xenobomb” is a xenolith (in this case, of mantle peridotite), slathered in a coating of lava and tossed out of a volcano in the middle of a … Read more
Kilbourne Hole is the crater of a maar volcano in southern New Mexico, just across the state line from El Paso, Texas. I went there the weekend before last with a team from El Paso Community College, led by Joshua Villalobos. This is the place where xenobombs come from! If you go to the right … Read more
This is my final post on the pre-GSA-Minneapolis structural geology field trip to the Superior Province. The photo above shows a roadcut exposure of boudinage in xenolith-bearing Vermillion Granitic Complex. Here’s another, smaller, more brittle example of boudinage, from another site, the following morning: Gee, it only took me 1.5 years to blog that trip … Read more
On Duck Creek (Ellendale, NC quadrangle), you can see folded xenoliths within the Toluca Granite (383 Ma, 378 Ma, or 368 Ma, depending on which mineral you ask). The granite there contains xenoliths that contain pre-exisiting fabrics and structures, and we stopped at Duck Creek on the pre-GSA-Charlotte field trip I took to the Neoacadian … Read more
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. … Read more
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.
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.
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 … Read more
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 … Read more
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!
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.”
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 … Read more
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 … Read more
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 … Read more