Mosaic Canyon, in Death Valley National Park has some beautiful mylonitized marble. Here that marble has been brecciated into fragments by a fault.
Fault pseudotachylyte is formed during an earthquake. The coseismic slip on the fault frictionally heats the surrounding rock and forms a melt. Rapid cooling of the melt forms a glass-like, dark rock, pseudotachylyte. A combination of the dynamic stresses imparted on the wall rock during the earthquake and dynamic pressurization will allow the melt to enter fractures in the wall rock.
In the photo above pseudotachylyte is the thin, black rock. The injection is at a 90 degree angle with the main pseudotachylyte vein.
Well the year is winding down so I thought I would give a little recap of some highlights.
Jess and I are planning our winter Southwest roadtrip I think I’ll have to let her drive a bit. It might get dangerous with me at the wheel. Are you taking a holiday road trip? Don’t forget to bright a geologist. Remember to be the more accurate, it might be necessary to decelerate:
I was conducting what has been called x-mph geology, where x is the miles per hour one is driving; this time I was doing 70-mph geology. Geology at seventy miles per hour (or 70-mph geology) is generally much less detailed and often less accurate than geology at 20 miles per hour (20-mph geology). And it turns out that if you slow down to about 5 mph or less, you can almost complete a rock report on whatever iron-stained jasperoid or copper-stained porphyry you happen to be driving by, and the speed is almost slow enough for the geo-type in the passenger side of the truck to lean out and grab a sample.
Are you looking for that perfect holiday gift for your geologist friend? We’ll maybe a roadside geology guide for that roadtrip route will do the trick. While we’re on the topic of books, two of the best books I read this year are 52 Things You Should Know About Geology and 52 Things You Should Know About Geophysics. These books are collaborative collections of two page essays. The format is a bit “chose you’re own adventure” and encourages skipping around. Both books should be suggested reading for first time grad students and some specific essays should be required reading. Specifically, “Presenting… your career” by Tony Doré, “The trouble with seeing” by Evan Bianco, “Five things I wish I’d known” by Matt Hall, and “Simplify everything” by John Logel are good places to start. I can’t wait to re-read my dog-eared and underlined copies, but first I need to start the latest edition: 52 Things You Should Know About Paleontology. Also, the layout and cover art of these books are elegantly simple and makes an amateur typography nerd smile.
Another book I really enjoyed was The New American Road Trip Mixtape by Brendan Leonard. Brendan writes the blog Semi-Rad and shares stories, satire, and criticism on outdoor adventure culture. Seriously, it’s one of the funniest blogs out there. There’s everything from flowcharts about what to do if there is a cute girl at the climbing gym to love letters to helmets to thoughtful introspection on the meaning of adventure. And don’t forget: GO TO THE MOBILE.
This year I started sharing field photos with the #FridayRocks hashtag. Over the years of doing geology, class field trips, fieldwork, conference field trips, etc. I’ve taken a lot of photos. I’ve been posting the particularly awesome ones. If anyone has photos of rocks they’d like to share, please shoot me an email with the photo and description.
Here are some of the most popular #Friday Rocks:
Soft sediment deformation from Point Lobos, California
Asbestos in Serpentinite and Blueschist
Reactivated Thrust Faults
There’s plenty more! Click here to see the rest.
This weeks photo comes from a spectacular outcrop at Point Lobos, California. If you are there, try to time it with low tide, or you’ll miss this.
Soft sediment deformation occurs in unlithified sediments. Sometimes a trigger such as rapid loading by a mass wasting event or an earthquake is necessary to cause the deformation.
Flame structures (middle right in the photo) form when the overlying sediment (orange) is denser than the underlying sediment (black). This causes the overlying sediment to sink down into the low sediment, which pushes the lower sediment up. The structures formed resemble flames, hence the name.
Also in the photo (near the pointing finger) is a more competent sediment that was normal faulted as the unlithified sediment below it deformed. What other structures do you see in the photo?
Here’s another shot of the flame structures.
I’d packed up all my gear. Ryan had a phone interview at 11, so I said goodbyes to the rafting adventure crew we’d shared the cook shelter with and walked down the bike path to the Squamish Adventure Center for some coffee. When Ryan rocked up, we piled into his Tacoma and drove for Vancouver. The rain had finally shut down climbing at Squamish.
We rolled into Van famished. Ryan knew a sushi spot, so I yelped it and we made our way there. It was a sushi factory. The place was hustling and turning over. We sat down, I didn’t have much time to oogle at the amazing sushi prices before we ordered. Then bam, the sushi was before us and we gorged. I’d never been so full on sushi for so cheap before. As I forced the last bite of raw salmon into my mouth, the bills slammed down on our table. We paid and were kicked out the door to free our table for the next set of mouths.
When I flew into BC a month before, I’d only briefly been in Vancouver. Really just long enough to get on a bus to Horseshoe Bay to meet my old roommate Charlie and get picked up by Ryan to hit Squamish. So I had missed all the pleasures of the city.
The next day Ryan and I walked all over Van. We made our way to Stanley Park so we could jump in the ocean. It wasn’t as cold as I thought it would be for September. We hiked around and then headed into the city. For dinner we found a sushi spot and ordered take out. The weight of the bags they brought out were surprising. For our dining table we found a park bench. Again, so much excellent sushi for so cheap. Seriously, I would move to Vancouver just for the delicious sushi. It really is too good.
I snapped the above photo on our walk back to his truck. No parking ticket made the day end well.
I had to dig this one deep out of my archives, so sorry for the poor image quality.
This is a roadcut in the Marin Headlands, North of San Francisco California. Chert is made of microcrystalline quartz from radiolaria, microscopic protozoa with silicate skeletons. When radiolaria die their skeletons sink to the bottom of the ocean floor. After compaction and diagenesis, chert is made.
The chert in the Marin Headlands is part of an accretionary wedge block and is folded into chevron folds.
Don’t forget to follow Upsection on Instagram to see more rocks!
Do you have pictures of a cool outcrop? Submit them to FridayRocks@upsection.comWahrhaftig, Clyde. “Structure of the Marin Headlands block, California: A progress report.” (1984): 31-50.
This weekend only I’m offering handcarved leather dog collars at a discount for the holidays. Get your best friend something they’ll love for christmas. All collars are treated with neatsfoot oil or mink oil to protect against water. I have a limited number of materials so first come first serve.
Send me your dog’s neck size (remember two fingers should be able to comfortably fit under the collar), dog’s name, and color preference. Email me at firstname.lastname@example.org for more details.
Feel free to leave questions in the comments section. I’ll answer them here.