S-C fabric in meta-ignimbrite

Here’s a sample from my 2004 geology M.S. thesis work in the Sierra Crest Shear Zone of eastern California. The rock is a sheared ignimbrite (ashflow tuff) tuff bearing a porphyritic texture and a nicely-developed “S-C” fabric. With annotations, showing the S- and C-surfaces, and my kinematic interpretation: S-C fabrics develop in transpressional shear zones: [...]

Hol(e)y basalt, Batman!

Today, our theme is vesicles. Here are some images of vesicles in basaltic lava flows in the Owens Valley of California, the same spot where we saw the baked fanglomerate that I showcased a few days back. In this photo (and the zoomed-in detail shot below), you can see a couple of things. One is [...]

Easter egg

Searching through my photo archives this morning for something suitably “Eastery”… something in pastel colors, perhaps? … a petrified lagomorph? … how about an egg, or something egg-shaped? This is as close as I got: This is in the Owens Valley of eastern California, showing a boulder of the Mesozoic Sierra Nevada Batholith bearing a [...]

Baked fanglomerate

A quick post to share a few images of an outcrop I visited last September out in California’s Owens Valley. This is a spot where alluvial fans coming off the eastern Sierra Nevada were overrun by a basaltic lava flow (Jeff, Kim, Fred, and Kurt for scale): The unofficial term for these conglomerates deposited by [...]

Crucifix site 2: Horsts & grabens

So, those sediments we saw yesterday? They’re faulted in the area around the Crucifix Site. As this image shows, the style of faulting is normal faulting: Annotated with some color to jazz things up a bit: In normal faults, the upper block moves downward with respect to the lower block. They are typical of extensional [...]

Crucifix Site 1: Sediments

On the September 2009 GSA field forum in the Owens Valley, the final stop of our first day was to check out the so-called “Crucifix Site,” along Chalk Bluff Road (north of Bishop, California, at the southern margin of the Volcanic Tableland). It’s called the “Crucifix Site” because there is a metal cross erected there: [...]

Plutonic contacts in eastern Sierras

Last September, at the location of the faulted moraine (eastern Sierra Nevada, California), I took some photos of some of the sexier plutonic contacts exposed in big boulders (erratics) of the glacial till composing the moraine. Check them out. What do you see here?

Transtensional quartz vein

On last May’s GSW spring field trip to Chain Bridge Flats, I saw a quartz vein: Surely, upon looking at this photograph, you will be struck by the way the vein is not the same thickness along its length, and parts of it appear to be a white line transitioning into a parallelogram, and back [...]

Dalmatian pluton

Continuing with some photos from eastern California… After checking out the faulted moraine, but before heading up the hill to check out the indurated shear zone (which you can just see in the background of this photo), we stopped to check out this visually-striking outcrop: Look at the glee on the faces of Kurt (green [...]

Mini debris flow

Small-scale debris flows as a muddy slurry flowed over weathered-out chunks of the Bishop Tuff. Probably about two days old. Southern edge of the Volcanic Tableland, last September.