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 alluvial fans is “fanglomerate,” and it’s pretty cool to see the contact metamorphism at the top of the fanglomerate. There’s also some weakly-developed columnar jointing in the basalt. Here’s an annotated version, in case the contact wasn’t quite obvious enough:
Here’s a close up (Doug for scale), showing the orange zone of thermal metamorphism at the top of the fanglomerate as the lava flow above baked the hell out of it:
Groovy, eh? Where’s your favorite example of contact metamorphism?
Until I saw this, it was a group of mudstones (Aguja Fm., Terlingua, TX) overlain by some Tertiary volcanics…which bake the muddies from brown to yellow(ish) to the original color of the rock.
But this is very cool. It reminds me of a good cassarole, with a “cooked to a golden brown” top.
That’s a lovely example, but my favorite example of contact metamorphism is going to have to be from a pluton in Vermont… at least until I finish the figures on the paper I’m writing!
the road from tijuana to ensenada in baja california (close to san diego) has a lot of them as well as a very well exposed normal fault.
Was searching for more detail about the fanglomerate/shale/diabase south of Reading, Pennsylvania (home to a variety of minerals not found away from the contact), but this is a great photo.