#structural geology

[camblorite]

Structural geology field trip to Minas Gerais countryside, part 2

More folds and some fractures.

I love every time we have field trips to Minas Gerais, it's such a nice State.

[noosphe-re]

THE USE OF STEREOGRAPHIC PROJECTION IN STRUCTURAL GEOLOGY, F.C. PHILLIPS (Gaston Renard Pty. Ltd.)

[sushi11]

Stuðlagil Canyon, Iceland 🇮🇸 © marcelsiebert

[geotranny]

Folded strata in the Appalachian Basin, located in the Gap Mills region of Southwestern West Virginia. Marcellus Shale formation, somewhere near Waiteville, WV. From my Structural Geo field trip this weekend :)

[mineralsrocksandfossiltalks]

Monday Musings: Mount Everest

The tallest mountain in the world has captured human imagination for centuries. How did something so massive come to be? How can anything possibly live up there? Why are no other mountains as tall as this one? The reasons are found beneath the surface in the geologic structure of the earth.

Mt. Everest is found in the Himalayas right smack in between the Indian Plate and the Eurasian Plate collision zone. India first collided with Eurasia 55 million years ago; long after the extinction of the dinosaurs. India, was a small, very old, strong block f continental lithosphere that had split off of the supercontinent Gondwana about 200 million years ago.

Contrast this with the southern part of Eurasia which was an amalgamation of younger, softer, warmer chunks of lithosphere that had been accreted on by other collisions. So when India joined the fun, it smushed those younger pieces right up like a knife to frosting.

But is that the reason it's the tallest? After all, were't the Alps built in a similar way when Africa collided with Europe? So why aren't they as tall?

It has a little to do with the rate of uplift vs the rate of erosion.

If the rate of erosion is greater than that of uplift, the mountains won't get very tall. If they are the same, you don't get a whole lot of change at all.

Now hang on, the Alps are rising at a rate of 2.5 mm a year with an erosion rate of upo to 1.4 mm a year and the Himalaya are only rising at a rate of 0.5 mm a year and an erosion rate of 2 mm a year. Shouldn't the Alps be taller?

Let's talk a little bit about isostatic rebound. Usually, this is a reference to the removal of weight on the crust as glaciers melt but it can also be used in the case of the removal of rock. Mount Everest is actually growing because of two ancient rivers that combined to become one large river, the Arun.

Large rivers can remove a lot of sediment in a short amount of time. The Arun River runs through some of the steepest terrain in the Himalayas which means it moves a lot of sediment. Mt. Everest is heavy and because of that it sinks into the mantle. The Arun River removes a few loads of sediment over the last 89,000 years or so and moves that weight elsewhere allowing Mount Everest to start bobbing back up.

Isn't geology wild? Tune into tomorrow for some earthshaking trivia! Fossilize you later!

[cordially-stupid]

Hello fellow geology enthusiasts! I've finished my structural class and have now put some of my homework on my redbubble! link is to the socks version >:3 Enjoy!

[grand-arcanist-wynslow]

anyone else up calculating their strike and dip

[bettergeology]

Remarkable rocks of Pine Creek Pass, Sierra Nevada Mountains, California

Pine Creek Pass is a less-used trailhead in the Eastern Sierra of California. It's a steep slog of about 3,500 vertical feet in about 6 miles, ending at just over 11,000 feet. The scenery is remarkable, but so are the rocks.

This an unnamed pinnacle of dark gabbro which has been intruded by younger granite bands. The gray cliff to the right is intruded by the same younger granite bands!

Fractures in the gabbro of the stripy mountain filled with feldspar crystals (formed when liquid). The lighter band is offset slightly by the white vein, which shows lateral movement across that vein when it was forming. These are called en-echelon fractures.

Younger granite intruding (as bands) older granodiorite and a xenolith eclogite inclusion - a chunk of unrelated rock carried by the original melted granodiorite (complex relationships here!).

Granodiorite polished smooth by the abrasive action of glaciers during the last Ice Age (~21,000 years ago in this area).

Outcrop of glacially polished granodiorite.

Glacially polished granodiorite with a thick intrusion (dike) of pink granite that has been offset laterally by a younger and thinner dike of different granite.