Rock Cycle II: Metamorphic → Igneous
Migmatite is a special rock that is partly metamorphic and partly igneous. Let’s take a look at it in Part 2 of Callan’s “Transitions of the Rock Cycle” series.
igneous
Friday folds: Selkirk Fan
The Friday fold is a selection of five fold photos from the Selkirk Fan in the Omineca Belt of British Columbia, submitted by structural geologist Marek Chichanski of De Anza College (California).
Guest post: Red Rock Canyon
A guest post by Callan’s student Jacob Douma Traveling with Callan Bentley and Pete Berquist through the Canadian Rockies on their Regional Geology Field Course in July 2012, we were exposed to a variety of physiographic features. Among them, was Red Rock Canyon located 16 km from Waterton Townsite within Waterton Lakes National Park, Alberta. … Read more
Thunderbird rhyolite
Have you ever seen a black rhyolite? Neither had geoblogger Callan Bentley – until he went to the Franklin Mountains of West Texas.
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 … Read more
Leopard rock
Callan shares some photos of “leopard rock” (porphyritic mafic dikes) seen along the Beartooth Highway, northeast of Yellowstone National Park.
A clutch of amygdules
Callan presents a collection of well-exposed amygdules, seen along the Dark Hollow Falls trail in Shenandoah National Park, Virginia. These white dots on a green background are the signatures of (1) Iapetan rifting, and (2) Alleghanian metamorphism.
Diabase dike in diabase
Seen in rip-rap on the side of Naked Creek, a week ago yesterday: This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).
Big old vesicles!
Today, for your viewing pleasure, I offer you: A series of big honkin’ gas pockets in a 615 ka basaltic lava flow in the Owens Valley of California. This same lava flow has been featured here before, since it imparted a lovely contact metamorphism to the alluvial fan over which it erupted. These things are … Read more
Deformed pillow basalts from southern Ontario
Have you ever seen Archean pillow basalts? How about Archean pillow basalts that have grown much taller through vertical extrusion along a ductile shear zone? Come to the southern Superior Craton to see more!
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 … Read more
Friday fold: Japanese garden
Richard Littauer, a MSc student in Computational Linguistics at the University of Saarland (on Twitter at @richlitt) sent me today’s Friday fold. It comes from a garden at Nijo Castle in Kyoto, Japan. Definitely some wavy layers there. It’s a lovely specimen that would add gravitas to anyone’s garden. Not sure what it is – … Read more
Red Bluff Granite, and what it intruded into
Returning to his February field trip in west Texas, Callan examines the contact zone where the Red Bluff Granite intruded into a group of surficial rocks, including columnar-jointed basalt.
Scenes from last Sunday: Bishop Tuff and Volcanic Tableland, CA
Sunday was our first full day in the field. Here’s a few looks at my NOVA students doing geology out in eastern California. We spent the day on, and next to, the Volcanic Tableland north of Bishop, a massive stack of ash fall and ignimbrite deposits erupted from Long Valley Caldera 760,000 years ago: the … Read more
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!
New GigaPans: source and sediment
New M.A.G.I.C. GigaPans are shown of two connected Hawaiian samples: one an igneous rock, one a loose beach sand.
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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.”
Contact of the Campus Andesite with host rocks
First thing we saw on the post-InTeGrate field trip to the rocks of El Paso, Texas, was this contact between the aforementioned Campus Andesite, and the Cretaceous sedimentary rocks into which it intruded (contact metamorphosed in the area of this photo): I decided to try switching up my annotation fonts. Whaddya think?
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 … Read more
“Got migmatite?”
Had this brainstorm a few weeks back (or maybe months?). Been meaning to blog it up, but hadn’t gotten the chance to flesh it out. The geologic map of the Commonwealth comes from Chuck Bailey of William & Mary, who gave me permission to use it for this project. Anyhow – do you think there … Read more